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New Discoveries and Opportunities from Two-Dimensional Materials

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† Department of Physics, University of Wisconsin−Madison, Madison, Wisconsin 53711, United States
‡ Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States
Cite this: ACS Photonics 2017, 4, 3, 407–411
Publication Date (Web):March 15, 2017
https://doi.org/10.1021/acsphotonics.7b00194

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Since the isolation of graphene in 2004, work on atomically thin two-dimensional (2D) materials has progressed rapidly across a diversity of scientific and engineering subfields. The types of 2D materials available has been ever-growing and now include insulators (e.g., hexagonal boron nitride), semiconductors (e.g., transition metal dichalcogenides, TMDs), and additional semimetals (e.g., black phosphorus). From these new materials, a wide array of optical, mechanical, chemical, and electric phenomena has been realized in 2D crystals produced using top-down exfoliation or bottom-up synthesis (e.g., by chemical vapor deposition, CVD). As 2D material science has become a mature field in-and-of itself, several key advantages have emerged that can be leveraged for new experimentation and device creation. These advantages include the amenability of 2D materials toward top-down and bottom-up lithography methods; their pliability and ability to be mechanically strained to create new structure–property–function relationships; and their unique chemistry, with large surface areas that lead to properties that are highly environmentally dependent.

In this virtual issue (http://pubs.acs.org/page/vi/2Dmaterials.html), we have compiled a collection of articles from Nano Letters, ACS Photonics, ACS Nano, and Chemistry of Materials that highlight some unique properties of 2D materials including their flexibility toward new synthesis methods and doping techniques, their compatibility with scanned probe measurement techniques, the electronic and optoelectronic properties of their p–n junctions, and their potentially useful optical properties. These articles summarize studies by ACS authors that display the manner in which 2D systems are being grown, modeled, measured, and used in new ways that are made possible by their atomic thinness and particular electronic structures and that could potentially be transformative in creating new areas of research.

From a perspective of offering new measurement opportunities, 2D materials provide a unique platform for scanned probe measurements such as scanning tunneling microscopy (STM) as well as scanned gate techniques, and several key papers in this area have recently appeared in Nano Letters. Unlike conventional three-dimensional (3D) materials or interfacial GaAs−GaAlAs 2D systems, 2D materials—in which the surface is the bulk—are entirely accessible to such probes, and, since there are no bulk states, the information provided by scanned probe methods can potentially provide complete characterization of the environmentally dependent structural, electronic, and defect properties. Furthermore, these measurements can be conducted while the sample is being gated in situ, thus providing unprecedented information on how quasiparticle behavior changes with carrier density and how the local electronic structure changes under transport conditions.

The first gate-dependent measurements of few-layer MoS2 came from exfoliated samples, which provided a direct measurement of the MoS2 band gap and the carrier density dependent Fermi level, as well as a direct measurement of deep intergap states that were found in thicker samples. (1) More recently, metal–organic chemical vapor deposition (MOCVD) bilayer and monolayer MoS2 grown on SiO2 were measured under STM with in situ gating. This new growth technique enabled larger samples with more contact area and less surface contamination, and those measurements could directly extract the gate-dependent conduction band edge position as well as the gap energy; these data could then be compared to photoluminescence data to determine the exciton binding energy. (2) Local measurements of the grain boundaries in those samples, meanwhile, probed the angle dependence of their atomic structure and found that all angles were electronically inert in MOCVD-grown samples. (2) By comparison, STM measurements of CVD-transferred WSe2 samples on graphite revealed deep intergap states that formed along the grain boundaries with different periodicities, revealing different edge chemistries in comparison to MOCVD samples. (3) Monolayer MoS2 crystals grown via CVD on graphite substrates, meanwhile, have enabled direct STM measurements of metallic edge states, which were shown to locally pin the Fermi level and to create lateral band bending near the crystal edge with a 5 nm depletion width. (4)

Scanned probe methods can also be used to modify or induce local properties in 2D materials, both reversibly and irreversibly. For example, for graphene samples exfoliated onto boron nitride, an STM tip has been shown to ionize defects in the h-BN and create local, 50 nm scale doped regions in the graphene, with a polarity that can be controlled via the applied backgate voltage. These doping patterns can control the macroscopic transport properties of the device and, remarkably, can also be “erased” via optical exposure or by using another controlled gate pulse, which effectively deionizes the h-BN dopants. (5) A charged tip can also be used as a local gate, which impedes electron flow and can be used to directly probe the motion of quasiparticles in 2D materials. This phenomenon was shown most dramatically for h-BN/graphene/h-BN samples in a Hall bar geometry, where an applied field from a scanned probe tip could locally block the cyclotron motion in high magnetic fields and, thus, provide an effective image of the cyclotron orbits by preventing transport from one electrode to another. (6) Finally, scanned probe methods have also been used to extract the local optical properties of 2D materials. For MoS2 samples grown on a Au(111) surface, STM methods have been used to find freestanding monolayer patches, which luminesce upon electron injection from the STM tip. (7)

Just as 2D crystals provide new opportunities for measurement, several key papers in Nano Letters have shown they can also be stacked, integrated, and layered to create both lateral and vertical p–n junctions with atomic precision. Such junctions are often not restricted by lattice matching criterion, and the constituent 2D materials can be gated over wide ranges, switching between p- and n-type behavior and displaying an array of band alignments within the same device. This variation has led to an assortment of interesting electronic and optoelectronic effects to be realized. For example, MoS2/WSe2 stacks have been shown to display a lateral, type II band alignment (8, 9) whereby an electrostatic backgate can be used to switch the WSe2 from p-type to n-type, which creates a gate-dependent p–n junction between the two layers. For the appropriate backgate voltages, this junction can be operated as a photovoltaic device, with maximum external quantum efficiencies in the range 1.5–12%, depending on the device geometry and contacts. Similar effects can be realized by integrating 2D materials with other semiconducting systems, such as organic semiconductors, which further broaden the range of band alignments that can be realized. For example, by evaporating pentacene onto MoS2, a type II device was created that displays full antiambipolar behavior with either material switching from intrinsic to doped, which enables current through the p–n junction to be highly gate-dependent. (10) Such devices can also be structured to act as optical emitters that display strong, gate-dependent electroluminescence to create dynamic light-emitting diode (LED) devices. In even basic geometries, electroluminescence has been observed from carriers moving across a MoS2/WSe2 junction and recombining. (8) However, the effect can be maximized and optimized through fabrication of unique tunneling devices, as was shown with WSe2 monolayers sandwiched between thin h-BN sheets, with transparent graphene electrodes on either side. (11) When the correct bias was applied across those devices, electrons (holes) could tunnel into the conduction (valence) band of the WSe2 and recombine, emitting light in the process at frequencies that are representative of the unique, tightly bound exciton states that have been shown to exist in 2D crystals. Unlike typical LEDs, this process actually becomes more efficient at high temperature due to the spin−orbit splitting of the WSe2 bands, which creates a low-energy dark exciton state in WSe2. Interestingly, some of the observed emission features in such devices are due to defects in the WSe2, which localize the excitons and create sharp, energetically shifted emission peaks. With careful control of device geometry and biasing, these defects have been shown to act as single-photon sources that can be electrically controlled and that display fine spectral signatures that are representative of quantum mechanically derived energy splittings. (12) These quantized phenomena can also be observed directly in the electrical tunneling signal of stacked 2D materials. For example, a simple Au/h-BN/Au tunneling device has been shown to display Coloumb blockade type effects, indicative of a defect-mediated transport process whereby the discrete charging of defects leads to steps in the I–V curve of the device. (13)

The atomic thinness of 2D materials also enables a wide array of interesting and useful optical properties beyond those observed via electroluminescence, and several of these phenomena have recently been reported in ACS Photonics and Nano Letters. Perhaps best known are the highly confined optical modes that can be supported in extremely thin materials, including both plasmonic and polaritonic waves. In the case of graphene, the plasmonic modes have wavelengths that can be more that 102 smaller than free space, a factor that—along with oscillator strength—has been shown to display a strong carrier dependence. These effects enable graphene plasmons to be extremely sensitive to their environment and also to potentially be useful for optoelectronic applications. In his ACS Photonics review (14) Garcia de Abajo discusses the fundamental physics that make these effects possible and describes many of the challenges the field must address to increase the wavelength range and efficiencies at which graphene plasmonic devices can operate. Most notably, he highlights the possibility of observing quantum effects in extremely small graphene devices that could be created via bottom-up molecular techniques or through the use of advanced fabrication methods. The extreme confinement of polariton modes in h-BN, meanwhile, has been displayed experimentally through a scattering near-field scanning optical microscope measurement, which showed dramatic focusing effects in a naturally occurring h-BN wedge. (15)

In addition to supporting novel and tunable optical modes in the near field, 2D materials offer opportunities to manipulate light via their strong excitonic effects and interband and intraband absorption processes. These effects offer new opportunities to create media with dynamic optical properties, and the inherently small optical cross sections due to atomic thinness can often be overcome by the ability to incorporate 2D materials into light-trapping structures, which can greatly enhance the strength of light–matter interactions. For example, excitons in TMDs have strong binding energies and spectral signatures that are highly dependent on their environment, local structure, and layer thickness. One recent study showing these behaviors was performed on ReS2, a highly anisotropic TMD: reflection and photoluminescence measurements of varying sample thicknesses showed excitonic features that shifted several hundred meV as the sample thickness was decreased from 7 layers to 1 layer. The samples also displayed strongly polarized emission, which varied between exciton states and was representative of the local atomic structure of the ReS2. (16) In another study, in order to enhance the effective optical cross section of excitons in WS2, gold plasmonic antennas were placed on the surface, and when the antenna frequency was closely matched to the exciton energy, it enhanced both the emission and absorption efficiency of the TMD, leading to a 10× increase in photoemission intensity. (17) An alternative method to enhance absorption in 2D materials is to couple them to the guided modes photonic crystal structures. This technique was recently demonstrated theoretically for the case of MoS2 on a 100 nm thick photonic crystal with a gold backreflector, where calculations showed nearly total absorption at certain resonant frequencies and more than 50% absorption averaged above the MoS2 band gap, raising hope for the possibility of creating a highly efficient—and extremely lightweight—TMD-based solar cell. (18)

In the case of graphene, it is the inter- and intraband absorption processes that provide outstanding opportunities for index tunabilitiy, and several key experiments have recently demonstrated that through clever chemistry and engineering these effects can be leveraged to create useful optoelectronic devices. For example, multilayer graphene placed on a flexible paper substrate soaked in ionic liquid displayed a significant change in transmittance when an electric potential was applied, which led to ion intercalation of the graphene and subsequent blocking of interband transitions. (19) The effect is fully reversible, with a time scale of ∼1 s, and a flexible, room-temperature device was demonstrated that behaved similarly to an e-ink or liquid crystal display (LCD). In addition, the interband transitions in monolayer graphene are a powerful way to tune the optical resonances of nearby metal plasmonic structures that are engineered to have resonant modes in the mid-IR. This method was used to create a perfect absorber device at 7 μm, with 1 μm of bandwidth tunability that could operate at 20 GHz. (20) A similar device was used to demonstrate dynamic phase tunability, where the phase of a 7.7 μm reflected beam could be varied by 55° at speeds that could potentially reach tens of GHz. (21) The bandwidth and resolution advantages of such devices over conventional LCD or microelectromechanical systems technology present a significant opportunity for the creation of a spatial light modulator or holographic display based on 2D materials that could outperform current devices. Finally, graphene has recently been incorporated into sensing devices that take advantage of in-plane potential gradients to collect excited carriers with high efficiency and speed. In one such device, large-area CVD graphene was draped over a silicon waveguide tuned to the 1550 nm C-band. The waveguide was constructed such that there was significant spatial overlap between the waveguide mode and the graphene, and optical signal pulses could be detected by collecting excited electrons in the graphene at a nearby electrode. By using this scheme, 50 Gbit/s data rates could be detected, and the device demonstrated −3 dBm of bandwidth at 40 GHz. (22) Another graphene-based detector was tuned to operate at 2 THz by placing the graphene inside a metallic bowtie antenna composed of metals with different work functions. This placement created a sloped potential landscape, which led to a strong photovoltaic effect in the graphene and a sensor responsivity of 34 μA/W. (23) As demonstrated in these works, the ability to create highly efficient optoelectronic devices from the visible to the THz is a key advantage of graphene.

In recent months and years, ACS journals have shown us considerable advancements in the processing of well-known 2D materials and the synthesis of new ones. Advancement in the chemical vapor deposition of MoS2 enabled the growth of large-area monolayers with control over the lattice orientations of grains. This control was achieved by epitaxial growth on a sapphire substrate. MoS2 crystals were mostly limited to orientations of 0° and ±60°, and electrical resistance was negligibly low at the boundaries between these oriented grains. The mobilities of a single-crystal-length (4 μm) device and an 80-μm-long device were not discernibly different, and the films could readily be transferred to other substrates by etching the sapphire. The uncompromised electrical and photovoltaic performance of this film over such large areas may make it suitable for application in electronics and photovoltaics. (24) Similarly, large oriented films of MoO3 have also been reported, by epitaxial growth on mica. Despite existing as few-layer crystals, the MoO3 is found to have a monolayer-like band structure by density functional theory (DFT). MoO3 crystals of up to a millimeter can be grown by remarkably simple means: rather than using a conventional CVD chamber, the film is prepared in open air by using a hot plate to sublime molybdenum foil onto a mica target. The oriented crystals can be transferred to other substrates and are an effective photodetector material. (25)

Recent work in the synthesis of graphene nanoribbons highlights the potential of surface-assisted molecular assembly strategies. Atomically precise chiral graphene ribbons could be formed by polymerization of an anthracene-based molecule adsorbed to a copper surface. The strategic placement of bromine atoms on the molecule blocked off undesired connection geometries, ensuring the desired edge structure was maintained, and when kinks in the wires did occur, π-conjugation was uninterrupted through the kink. By these means, graphene nanoribbons could be grown between prepatterned electrodes. (26) Another unusual graphene geometry was seen during the van der Waals epitaxy synthesis of graphene on a boron nitride monolayer. The nonepitaxial interaction between h-BN and its nickel substrate can be so weak that the graphene layer can grow on the underside of the h-BN, sandwiched between the h-BN and the substrate. This may prove an effective way to create precise stacks of differing 2D materials. Similarly a second h-BN layer can be grown on the bottom of the first. (27)

Recent characterization studies of substrate-bound 2D materials have revealed properties that may be useful for patterning. Both ReS2 and sulfur-deficient MoS2 were observed to offer tunable atomic-scale electron transport paths. In the case of ReS2, the diamond-shaped chain-like structural motif known to be present on the sheet surface was found to be directly correlated to electronic mobility, with transport favored along the length of the chains. Furthermore, the strain induced by electron beam irradiation could be used to alter the directions of the diamond-shaped chains, thereby patterning conductive pathways into the sheet. (28) Meanwhile, periodic buckled stripes were seen in MoS2 on Au(111), owing to the slight lattice mismatch. The strain in the sheet induces a shift in the band energies, effectively creating a periodic doping of the MoS2 sheet. (29) Separately, aberration-corrected transmission electron microscopy has also shown that sulfur vacancies in monolayer MoS2 tend to arrange themselves into line defects as a way of mitigating accumulated strain energy. By DFT these line defects are predicted to be metallic, and this finding suggests that focused irradiation of the nanosheet could be used to pattern atomic wires into the otherwise semiconducting sheet. (30) Another use for irradiation may be to weld nanoscopic components together. The use of electron beam irradiation to create defects at a graphene–metal junction was shown to improve electrical contact at the junction, evidently by helping the system overcome the barrier to helpful atomic rearrangements. (31)

Meanwhile, exfoliation continues to attract intense research interest as a scalable synthesis strategy for 2D materials. Phosphorene, first isolated in 2014 by mechanical exfoliation, has recently been synthesized at a much larger scale by liquid exfoliation. A combination of shear mixing and sonication in a water- and oxygen-free environment led to the successful exfoliation in N-methyl-2-pyrrolidone at up to a 6 g scale. Centrifugal size separation enabled the isolation of different products ranging from nanometers-wide monolayers to micrometer-wide multilayers, and band absorption experiments reveal that the band gap of this semiconducting 2D material is markedly dependent on the number of layers in the particle, ranging continuously from the monolayer value of 1.8 eV to the bulk value of 0.3 eV. (32) Tin sulfur selenide and gallium sulfide were recently added to the list of materials that can be exfoliated to form liquid dispersions of atom-thin sheets. SnS2–xSex sheets can be synthesized over the full range of possible compositions and exfoliated by sonication in ethanol. The resulting semiconducting sheets are a single-unit-cell thick and micrometers in area; when assembled into chemiresistor gas sensors, the exfoliated sheets responded rapidly to analytes, owing to their large surface area. (33) GaS exfoliation did not proceed so easily, and the optimized GaS sheets were multilayered with a sheet size of less than one micrometer. Analysis of the exfoliated sheets’ stability in various solvents enabled an estimate of the sheets’ solubility parameter and pointed to ideal solvents for exfoliation. GaS sheets were applied as hydrogen evolution catalysts, where once again the best performance was shown by the smallest, thinnest sheets with the most active sites. (34) As in years before, graphene has been the subject of numerous exfoliation studies. By use of a new combination of chemical exfoliants, a dispersion of graphene platelets was obtained in quantitative yield. The micrometers-wide platelets were 20–100 atomic layers thick, but the interlayer registry between them was broken. (35) Meanwhile, a stable aqueous dispersion of graphene sheets could be generated in good yield using graphene quantum dots (GQDs) as a dispersing agent. Graphene quantum dots are surfactants in a sense, since their oxidized regions stabilize them in water, while their graphitic regions interact favorably with graphene. Addition of a small amount of GQDs enabled an outsize amount of graphene to be exfoliated into 2–3 layer sheets at high yield. After the graphene sheets were processed into films, the stabilizing particles could be removed by washing. (36) Also recently demonstrated was an alternative synthesis strategy for GQDs. A monolayer GQD sample was prepared in high yield by cage-opening of fullerene molecules. As might be expected, the GQDs obtained this way are especially monodisperse and strongly fluorescent. (37)

A unique subset of 2D materials named “MXenes” can be made by selectively etching layered carbides or carbonitrides, followed by exfoliation. Recently two new groups of 2D double transition metal carbides have been experimentally verified: M′2M″C2 and M′2M″2C3, where M′ and M″ represent two different transition metals (e.g., Mo or Cr and Ti). In such double transition metal MXenes, the inner M″ atoms stabilize the backbone lattice and the outer M′ atoms control the surface chemical properties. This discovery suggests that the scope of MXene materials can be greatly broadened. (38) Graphene quantum dots were observed to buckle into chiral configurations when they were decorated with chiral moieties around their perimeter. However, GQDs of different chirality displayed different biotoxicity, and molecular dynamics simulations suggest that this differing biotoxicity may be caused by a difference in the GQDs’ ability to enter the lipid bilayer membrane. (39) Beyond buckling, 2D nanosheets have continued to find use in larger 3D architectures. Graphene oxide (GO) sheets, for instance, were assembled into highly porous spherical particles by a process akin to deep-frying. The fluffy, low-density particle preserved the high surface area of the 2D nanosheets and buffered against the mechanical expansion of encapsulated silicon particles, enabling the material to function effectively in a battery electrode application. (40) Meanwhile, a family of 2D material composites was synthesized by using GO as the oxidant in the synthesis of conducting polymers. Graphene oxide was reduced in the process, yielding rGO flakes coated with globules of conducting polymer. Although the composites were not shown to be conductive or responsive, the ease of synthesis and versatility toward several conducting polymers may yet make this an attractive strategy for future work. (41)

The articles featured in this virtual issue represent large subfields of 2D material science that are uniquely possible in 2D systems and provide broad opportunities for device applications. On the other hand, since a diverse array of well-studied 2D materials are already available, we are now much better prepared to pursue a new research direction using bottom-up assembly to create bulk-sized, engineering materials based on 2D building blocks. Compared to nanostructures with other shapes, 2D sheets have a unique advantage to address the stability and scalability challenges for creating such new bulk nanostructured materials with emerging material properties or scalable materials performances. (42) We look forward to further developments in 2D material research, as new chemistry, physics, and device integration methods continue to be discovered by ACS authors.

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  • Corresponding Author
    • Victor W. Brar,  Department of Physics, University of Wisconsin−Madison, Madison, Wisconsin 53711, United States
  • Authors
    • Andrew R. Koltonow,  Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States
    • Jiaxing Huang,  Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, United States,  Orcidhttp://orcid.org/0000-0001-9176-8901
  • Notes
    Views expressed in this editorial are those of the authors and not necessarily the views of the ACS.

Acknowledgment

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J.H. thanks the support of the Office of Naval Research (ONRN000141310556). V.W.B. thanks the support of the Wisconsin Alumni Research Foundation.

References

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This article references 42 other publications.

  1. 1
    Lu, C.-P.; Li, G.; Mao, J.; Wang, L.-M; Andrei, E. Y. Bandgap, Mid-Gap States, and Gating Effects in MoS2 Nano Lett. 2014, 14, 4628– 4633 DOI: 10.1021/nl501659n
    Google Scholar
    1
    Bandgap, Mid-Gap States, and Gating Effects in MoS2
    Lu, Chih-Pin; Li, Guohong; Mao, Jinhai; Wang, Li-Min; Andrei, Eva Y.
    Nano Letters (2014), 14 (8), 4628-4633CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    The discovery of graphene has put the spotlight on other layered materials including transition metal dichalcogenites (TMD) as building blocks for novel heterostructures assembled from stacked at. layers. Molybdenum disulfide, MoS2, a semiconductor in the TMD family, with its remarkable thermal and chem. stability and high mobility, has emerged as a promising candidate for postsilicon applications such as switching, photonics, and flexible electronics. Because these rely on controlling the position of the Fermi energy (EF), it is crucial to understand its dependence on doping and gating. To elucidate these questions we carried out gated scanning tunneling microscopy (STM) and spectroscopy (STS) measurements and compared them with transport measurements in a field effect transistor (FET) device configuration. This made it possible to measure the bandgap and the position of EF in MoS2 and to track its evolution with gate voltage. For bulk samples, the measured bandgap (∼1.3 eV) is comparable to the value obtained by photoluminescence, and the position of EF (∼0.35 eV) below the conduction band, is consistent with N-doping reported in this material. We show that the N-doping in bulk samples can be attributed to S vacancies. In contrast, the significantly higher N-doping obsd. in thin MoS2 films deposited on SiO2 is dominated by charge traps at the sample-substrate interface.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhtFWgsbvM&md5=0b9bc1bc4293e117f6193ccba0cc9243
  2. 2
    Zhou, X.; Kang, K.l; Xie, S.; Dadgar, A.; Monahan, N. R.; Zhu, X.-Y.; Park, J.; Pasupathy, A. N. Atomic-Scale Spectroscopy of Gated Monolayer MoS2 Nano Lett. 2016, 16, 3148– 3154 DOI: 10.1021/acs.nanolett.6b00473
    Google Scholar
    2
    Atomic-Scale Spectroscopy of Gated Monolayer MoS2
    Zhou, Xiaodong; Kang, Kibum; Xie, Saien; Dadgar, Ali; Monahan, Nicholas R.; Zhu, X.-Y.; Park, Jiwoong; Pasupathy, Abhay N.
    Nano Letters (2016), 16 (5), 3148-3154CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    The electronic properties of semiconducting monolayer transition-metal dichalcogenides can be tuned by electrostatic gate potentials. Here we report gate-tunable imaging and spectroscopy of monolayer MoS2 by at.-resoln. scanning tunneling microscopy/spectroscopy (STM/STS). Our measurements are performed on large-area samples grown by metal-org. chem. vapor deposition (MOCVD) techniques on a silicon oxide substrate. Topog. measurements of defect d. indicate a sample quality comparable to single-crystal MoS2. From gate voltage dependent spectroscopic measurements, we det. that in-gap states exist in or near the MoS2 film at a d. of 1.3 × 1012 eV-1 cm-2. By combining the single-particle band gap measured by STS with optical measurements, we est. an exciton binding energy of 230 meV on this substrate, in qual. agreement with numerical simulation. Grain boundaries are obsd. in these polycryst. samples, which are seen to not have strong electronic signatures in STM imaging.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XlvV2it78%253D&md5=b8be0242ee5f5fbef493b1f69330cfc0
  3. 3
    Huang, Y.; Ding, Z.; Zhang, W.; Chang, Y.-H.; Shi, Y.; Li, L.-J.; Song, Z.; Zheng, Y. J.; Chi, D.; Quek, S. Y. Gap States at Low-Angle Grain Boundaries in Monolayer Tungsten Diselenide Nano Lett. 2016, 16, 3682– 3688 DOI: 10.1021/acs.nanolett.6b00888
    Google Scholar
    3
    Gap States at Low-Angle Grain Boundaries in Monolayer Tungsten Diselenide
    Huang, Yu Li; Ding, Zijing; Zhang, Wenjing; Chang, Yung-Huang; Shi, Yumeng; Li, Lain-Jong; Song, Zhibo; Zheng, Yu Jie; Chi, Dongzhi; Quek, Su Ying; Wee, Andrew T. S.
    Nano Letters (2016), 16 (6), 3682-3688CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Two-dimensional (2D) transition metal dichalcogenides (TMDs) have revealed many novel properties of interest to future device applications. In particular, the presence of grain boundaries (GBs) can significantly influence the material properties of 2D TMDs. However, direct characterization of the electronic properties of the GB defects at the at. scale remains extremely challenging. In this study, scanning tunneling microscopy and spectroscopy is employed to investigate the at. and electronic structure of low-angle GBs of monolayer tungsten diselenide (WSe2) with misorientation angles of 3-6°. Butterfly features are obsd. along the GBs, with the periodicity depending on the misorientation angle. D. functional theory calcns. show that these butterfly features correspond to gap states that arise in tetragonal dislocation cores and extend to distorted six-membered rings around the dislocation core. Understanding the nature of GB defects and their influence on transport and other device properties highlights the importance of defect engineering in future 2D device fabrication.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XntFCjsLg%253D&md5=eaf34700a6f9ca8f1424328c84915008
  4. 4
    Zhang, C.; Johnson, A.; Hsu, C.-L.; Li, L.-J.; Shih, C.-K. Direct Imaging of Band Profile in Single Layer MoS2 on Graphite: Quasiparticle Energy Gap, Metallic Edge States, and Edge Band Bending Nano Lett. 2014, 14, 2443– 2447 DOI: 10.1021/nl501133c
    Google Scholar
    4
    Direct Imaging of Band Profile in Single Layer MoS2 on Graphite: Quasiparticle Energy Gap, Metallic Edge States, and Edge Band Bending
    Zhang, Chendong; Johnson, Amber; Hsu, Chang-Lung; Li, Lain-Jong; Shih, Chih-Kang
    Nano Letters (2014), 14 (5), 2443-2447CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Using scanning tunneling microscopy and spectroscopy, we probe the electronic structures of single layer MoS2 on graphite. The apparent quasiparticle energy gap of single layer MoS2 is measured to be 2.15 ± 0.06 eV at 77 K, albeit a higher second conduction band threshold at 0.2 eV above the apparent conduction band min. is also obsd. Combining it with photoluminescence studies, we deduce an exciton binding energy of 0.22 ± 0.1 eV (or 0.42 eV if the second threshold is use), a value that is lower than current theor. predictions. Consistent with theor. predictions, we directly observe metallic edge states of single layer MoS2. In the bulk region of MoS2, the Fermi level is located at 1.8 eV above the valence band max., possibly due to the formation of a graphite/MoS2 heterojunction. At the edge, however, we observe an upward band bending of 0.6 eV within a short depletion length of about 5 nm, analogous to the phenomena of Fermi level pinning of a 3D semiconductor by metallic surface states.
    >> More from SciFinder ®
    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXnt1amu7c%253D&md5=75f218d8d1d54e2ce9584865ca5f27e8
  5. 5
    Velasco, J., Jr.; Ju, L.; Wong, D.; Kahn, S.; Lee, J.; Tsai, H.-Z.; Germany, C.; Wickenburg, S.; Lu, J.; Taniguchi, T. Nanoscale control of rewriteable doping patterns in pristine graphene/boron nitride heterostructures Nano Lett. 2016, 16, 1620– 1625 DOI: 10.1021/acs.nanolett.5b04441
    Google Scholar
    5
    Nanoscale Control of Rewriteable Doping Patterns in Pristine Graphene/Boron Nitride Heterostructures
    Velasco, Jairo; Ju, Long; Wong, Dillon; Kahn, Salman; Lee, Juwon; Tsai, Hsin-Zon; Germany, Chad; Wickenburg, Sebastian; Lu, Jiong; Taniguchi, Takashi; Watanabe, Kenji; Zettl, Alex; Wang, Feng; Crommie, Michael F.
    Nano Letters (2016), 16 (3), 1620-1625CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Nanoscale control of charge doping in two-dimensional (2D) materials permits the realization of electronic analogs of optical phenomena, relativistic physics at low energies, and technol. promising nanoelectronics. Electrostatic gating and chem. doping are the two most common methods to achieve local control of such doping. However, these approaches suffer from complicated fabrication processes that introduce contamination, change material properties irreversibly, and lack flexible pattern control. Here the authors demonstrate a clean, simple, and reversible technique that permits writing, reading, and erasing of doping patterns for 2-dimensional materials at the nanometer scale. The authors accomplish this by employing a graphene/B nitride heterostructure that is equipped with a bottom gate electrode. By using electron transport and scanning tunneling microscopy (STM), spatial control of charge doping can be realized with the application of either light or STM tip voltage excitations in conjunction with a gate elec. field. The authors' straightforward and novel technique provides a new path toward on-demand graphene p-n junctions and ultrathin memory devices.
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  6. 6
    Bhandari, S.; Lee, G.-H.; Klales, A.; Watanabe, K.; Taniguchi, T.; Heller, E.; Kim, P.; Westervelt, R. M. Imaging Cyclotron Orbits of Electrons in Graphene Nano Lett. 2016, 16, 1690– 1694 DOI: 10.1021/acs.nanolett.5b04609
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    6
    Imaging Cyclotron Orbits of Electrons in Graphene
    Bhandari, Sagar; Lee, Gil-Ho; Klales, Anna; Watanabe, Kenji; Taniguchi, Takashi; Heller, Eric; Kim, Philip; Westervelt, Robert M.
    Nano Letters (2016), 16 (3), 1690-1694CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Electrons in graphene can travel for several microns without scattering at low temps., and their motion becomes ballistic, following classical trajectories. When a magnetic field B is applied perpendicular to the plane, electrons follow cyclotron orbits. Magnetic focusing occurs when electrons injected from one narrow contact focus onto a second contact located an integer no. of cyclotron diams. away. By tuning the magnetic field B and electron d. n in the graphene layer, we observe magnetic focusing peaks. We use a cooled scanning gate microscope to image cyclotron trajectories in graphene at 4.2 K. The tip creates a local change in d. that casts a shadow by deflecting electrons flowing nearby; an image of flow can be obtained by measuring the transmission between contacts as the tip is raster scanned across the sample. On the first magnetic focusing peak, we image a cyclotron orbit that extends from one contact to the other. In addn., we study the geometry of orbits deflected into the second point contact by the tip.
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  7. 7
    Krane, N.; Lotze, C.; Läger, J. M.; Reecht, G.; Franke, K. J. Electronic Structure and Luminescence of Quasi-Freestanding MoS2 Nanopatches on Au(111) Nano Lett. 2016, 16, 5163– 5168 DOI: 10.1021/acs.nanolett.6b02101
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    7
    Electronic Structure and Luminescence of Quasi-Freestanding MoS2 Nanopatches on Au(111)
    Krane, Nils; Lotze, Christian; Laeger, Julia M.; Reecht, Gael; Franke, Katharina J.
    Nano Letters (2016), 16 (8), 5163-5168CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Monolayers of transition metal dichalcogenides are interesting materials for optoelectronic devices due to their direct electronic band gaps in the visible spectral range. Here, we grow single layers of MoS2 on Au(111) and find that nanometer-sized patches exhibit an electronic structure similar to their freestanding analog. We ascribe the electronic decoupling from the Au substrate to the incorporation of vacancy islands underneath the intact MoS2 layer. Excitation of the patches by electrons from the tip of a scanning tunneling microscope leads to luminescence of the MoS2 junction and reflects the one-electron band structure of the quasi-freestanding layer.
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  8. 8
    Cheng, R.; Li, D.; Zhou, H.; Wang, C.; Yin, A.; Jiang, S.; Liu, Y.; Chen, Y.; Huang, Y.; Duan, X. Electroluminescence and Photocurrent Generation from Atomically Sharp WSe2/MoS2 Heterojunction p–n Diodes Nano Lett. 2014, 14, 5590– 5597 DOI: 10.1021/nl502075n
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    8
    Electroluminescence and Photocurrent Generation from Atomically Sharp WSe2/MoS2 Heterojunction p-n Diodes
    Cheng, Rui; Li, Dehui; Zhou, Hailong; Wang, Chen; Yin, Anxiang; Jiang, Shan; Liu, Yuan; Chen, Yu; Huang, Yu; Duan, Xiangfeng
    Nano Letters (2014), 14 (10), 5590-5597CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    The p-n diodes represent the most fundamental device building blocks for diverse optoelectronic functions, but are difficult to achieve in atomically thin transition metal dichalcogenides (TMDs) due to the challenges in selectively doping them into p- or n-type semiconductors. An atomically thin and sharp heterojunction p-n diode can be created by vertically stacking p-type monolayer W diselenide (WSe2) and n-type few-layer Mo disulfide (MoS2). Elec. measurements of the vertically staked WSe2/MoS2 heterojunctions reveal excellent current rectification behavior with an ideality factor of 1.2. Photocurrent mapping shows rapid photoresponse over the entire overlapping region with a highest external quantum efficiency up to 12%. Electroluminescence studies show prominent band edge excitonic emission and strikingly enhanced hot-electron luminescence. A systematic study shows distinct layer-no. dependent emission characteristics and reveals important insight about the origin of hot-electron luminescence and the nature of electron-orbital interaction in TMDs. Probably these atomically thin heterojunction p-n diodes represent an interesting system for probing the fundamental electrooptical properties in TMDs and can open up a new pathway to novel optoelectronic devices such as atomically thin photodetectors, photovoltaics, as well as spin- and valley-polarized light emitting diodes, on-chip lasers.
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  9. 9
    Furchi, M. M.; Pospischil, A.; Libisch, F.; Burgdörfer, J.; Mueller, T. Photovoltaic Effect in an Electrically Tunable van der Waals Heterojunction Nano Lett. 2014, 14, 4785– 4791 DOI: 10.1021/nl501962c
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    9
    Photovoltaic Effect in an Electrically Tunable van der Waals Heterojunction
    Furchi, Marco M.; Pospischil, Andreas; Libisch, Florian; Burgdoerfer, Joachim; Mueller, Thomas
    Nano Letters (2014), 14 (8), 4785-4791CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Semiconductor heterostructures form the cornerstone of many electronic and optoelectronic devices and are traditionally fabricated using epitaxial growth techniques. More recently, heterostructures have also been obtained by vertical stacking of two-dimensional crystals, such as graphene and related two-dimensional materials. These layered designer materials are held together by van der Waals forces and contain atomically sharp interfaces. Here, we report on a type-II van der Waals heterojunction made of molybdenum disulfide and tungsten diselenide monolayers. The junction is elec. tunable, and under appropriate gate bias an atomically thin diode is realized. Upon optical illumination, charge transfer occurs across the planar interface and the device exhibits a photovoltaic effect. Advances in large-scale prodn. of two-dimensional crystals could thus lead to a new photovoltaic solar technol.
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  10. 10
    Jariwala, D.; Howell, S. L.; Chen, K.-S.; Kang, J.; Sangwan, V. K.; Filippone, S. A.; Turrisi, R.; Marks, T. J.; Lauhon, L. J.; Hersam, M. C. Hybrid, Gate-Tunable, van der Waals p–n Heterojunctions from Pentacene and MoS2 Nano Lett. 2015, 16, 497– 503 DOI: 10.1021/acs.nanolett.5b04141
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    There is no corresponding record for this reference.
  11. 11
    Withers, F.; Del Pozo-Zamudio, O.; Schwarz, S.; Dufferwiel, S.; Walker, P. M.; Godde, T.; Rooney, A. P.; Gholinia, A.; Woods, C. R.; Blake, P. WSe2 Light-Emitting Tunneling Transistors with Enhanced Brightness at Room Temperature Nano Lett. 2015, 15, 8223– 8228 DOI: 10.1021/acs.nanolett.5b03740
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    11
    WSe2 Light-Emitting Tunneling Transistors with Enhanced Brightness at Room Temperature
    Withers, F.; Del Pozo-Zamudio, O.; Schwarz, S.; Dufferwiel, S.; Walker, P. M.; Godde, T.; Rooney, A. P.; Gholinia, A.; Woods, C. R.; Blake, P.; Haigh, S. J.; Watanabe, K.; Taniguchi, T.; Aleiner, I. L.; Geim, A. K.; Fal'ko, V. I.; Tartakovskii, A. I.; Novoselov, K. S.
    Nano Letters (2015), 15 (12), 8223-8228CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Monolayers of molybdenum and tungsten dichalcogenides are direct bandgap semiconductors, which makes them promising for optoelectronic applications. In particular, van der Waals heterostructures consisting of monolayers of MoS2 sandwiched between atomically thin hexagonal boron nitride (hBN) and graphene electrodes allows one to obtain light emitting quantum wells (LEQWs) with low-temp. external quantum efficiency (EQE) of 1%. However, the EQE of MoS2- and MoSe2-based LEQWs shows behavior common for many other materials: it decreases fast from cryogenic conditions to room temp., undermining their practical applications. Here the authors compare MoSe2 and WSe2 LEQWs. The EQE of WSe2 devices grows with temp., with room temp. EQE reaching 5%, which is 250× more than the previous best performance of MoS2 and MoSe2 quantum wells in ambient conditions. The authors attribute such different temp. dependences to the inverted sign of spin-orbit splitting of conduction band states in tungsten and molybdenum dichalcogenides, which makes the lowest-energy exciton in WSe2 dark.
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  12. 12
    Clark, G.; Schaibley, J. R.; Ross, J.; Taniguchi, T.; Watanabe, K.; Hendrickson, J. R.; Mou, S.; Yao, W.; Xu, X. Single Defect Light Emitting Diode in a van der Waals Heterostructure Nano Lett. 2016, 16, 3944– 3948 DOI: 10.1021/acs.nanolett.6b01580
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  13. 13
    Chandni, U.; Watanabe, K.; Taniguchi, T.; Eisenstein, J. P. Evidence for Defect-Mediated Tunneling in Hexagonal Boron Nitride-Based Junctions Nano Lett. 2015, 15, 7329– 7333 DOI: 10.1021/acs.nanolett.5b02625
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    13
    Evidence for defect-mediated tunneling in hexagonal boron nitride-based junctions
    Chandni, U.; Watanabe, K.; Taniguchi, T.; Eisenstein, J. P.
    Nano Letters (2015), 15 (11), 7329-7333CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    We investigate electron tunneling through atomically thin layers of hexagonal boron nitride (hBN). Metal (Cr/Au) and semimetal (graphite) counter-electrodes are employed. While the direct tunneling resistance increases nearly exponentially with barrier thickness as expected, the thicker junctions also exhibit clear signatures of Coulomb blockade, including strong suppression of the tunnel current around zero bias and step-like features in the current at larger biases. The voltage sepn. of these steps suggests that single-electron charging of nanometer-scale defects in the hBN barrier layer are responsible for these signatures. We find that annealing the metal-hBN-metal junctions removes these defects and the Coulomb blockade signatures in the tunneling current.
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  14. 14
    Garcia de Abajo, F. J. Graphene Plasmonics: Challenges and Opportunities ACS Photonics 2014, 1, 135– 152 DOI: 10.1021/ph400147y
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    14
    Graphene Plasmonics: Challenges and Opportunities
    Garcia de Abajo, F. Javier
    ACS Photonics (2014), 1 (3), 135-152CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
    A review. Graphene plasmons are rapidly emerging as a viable tool for fast elec. manipulation of light. The prospects for applications to electrooptical modulation, optical sensing, quantum plasmonics, light harvesting, spectral photometry, and tunable lighting at the nanoscale are further stimulated by the relatively low level of losses and high degree of spatial confinement that characterize these excitations compared with conventional plasmonic materials, alongside the large nonlinear response of graphene. The authors start with a general description of the plasmonic behavior of extended graphene, followed by anal. methods that lead to reasonably accurate ests. of both the plasmon energies and the strengths of coupling to external light in graphene nanostructures, including graphene ribbons. Although graphene plasmons have so far been obsd. at mid-IR and longer wavelengths, there are several possible strategies to extend them toward the visible and near-IR, including a redn. in the size of the graphene structures and an increase in the level of doping. Specifically, plasmons in narrow ribbons and mol.-size graphene structures are discussed. The authors further formulate prescriptions based on geometry to increase the level of electrostatic doping without causing elec. breakdown. Results are also presented for plasmons in highly-doped single-wall C nanotubes, which exhibit similar characteristics as narrow ribbons and show a relatively small dependence on the chirality of the tubes. The authors further discuss perfect light absorption by a single-atom C layer, which the authors illustrate by studying arrays of ribbons using fully anal. expressions. Finally, the authors explore the possibility of exploiting optically pumped transient plasmons in graphene, whereby the optically heated graphene valence band can sustain collective plasmon oscillations similar to those of highly doped graphene, and well-defined during the picosecond time window over which the electron is at an elevated temp. In brief, a no. of exciting possibilities to extend graphene plasmons toward the visible and near-IR spectral regions and toward the ultrafast time domain, thus configuring a vast range of possibilities for fundamental studies and technol. applications are discussed.
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  15. 15
    Nikitin, A. Y.; Yoxall, E.; Schnell, M.; Vélez, S.; Dolado, I.; Alonso-GOnzalez, P.; Casanova, F.; Hueso, L. E.; Hillenbrand, R. Nanofocusing of Hyperbolic Phonon-Polaritons in a Tapered Boron Nitride Slab ACS Photonics 2016, 3, 924– 929 DOI: 10.1021/acsphotonics.6b00186
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  16. 16
    Aslan, O. B.; Chenet, D. A.; van der Zande, A. M.; Hone, J. C.; Heinz, T. F. Linearly Polarized Excitons in Single-and Few-Layer ReS2 Crystals ACS Photonics 2015, 3, 96– 101 DOI: 10.1021/acsphotonics.5b00486
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  17. 17
    Kern, J.; Trügler, A.; Niehaus, I.; Ewering, J.; Schmidt, R.; Schneider, R.; Najmaei, S.; George, A.; Zhang, J.; Lou, J. Nanoantenna-Enhanced Light–Matter Interaction in Atomically Thin WS2 ACS Photonics 2015, 2, 1260– 1265 DOI: 10.1021/acsphotonics.5b00123
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    17
    Nanoantenna-Enhanced Light-Matter Interaction in Atomically Thin WS2
    Kern, Johannes; Truegler, Andreas; Niehues, Iris; Ewering, Johannes; Schmidt, Robert; Schneider, Robert; Najmaei, Sina; George, Antony; Zhang, Jing; Lou, Jun; Hohenester, Ulrich; Michaelis de Vasconcellos, Steffen; Bratschitsch, Rudolf
    ACS Photonics (2015), 2 (9), 1260-1265CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
    Atomically thin transition metal dichalcogenides (TMDCs) are an emerging class of 2-dimensional semiconductors. Recently, the 1st optoelectronic devices featuring photodetection as well as electroluminescence were demonstrated using monolayer TMDCs as active material. However, the light-matter coupling for atomically thin TMDCs is limited by their small absorption length and low photoluminescence quantum yield. Here, the authors significantly increase the light-matter interaction in monolayer W disulfide (WS2) by coupling the atomically thin semiconductor to a plasmonic nanoantenna. Due to the plasmon resonance of the nanoantenna, strongly enhanced optical near-fields are generated within the WS2 monolayer. The authors observe an increase in photoluminescence intensity by >1 order of magnitude, resulting from a combined absorption and emission enhancement of the exciton in the WS2 monolayer. The polarization characteristics of the coupled system are governed by the nanoantenna. The robust nanoantenna-monolayer hybrid paves the way for efficient photodetectors, solar cells, and light-emitting devices based on 2-dimensional materials.
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  18. 18
    Piper, J. R.; Fan, S. Total Absorption in a Graphene Monolayer in the Optical Regime by Critical Coupling with a Photonic Crystal Guided Resonance ACS Photonics 2014, 1, 347– 353 DOI: 10.1021/ph400090p
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    18
    Total Absorption in a Graphene Monolayer in the Optical Regime by Critical Coupling with a Photonic Crystal Guided Resonance
    Piper, Jessica R.; Fan, Shanhui
    ACS Photonics (2014), 1 (4), 347-353CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
    The total absorption in graphene in the near-IR and visible wavelength ranges was numerically demonstrated by crit. coupling with guided resonances of a photonic crystal slab. In this wavelength range, there is no plasmonic response in undoped graphene, so the crit. coupling is entirely controlled by the properties of the photonic crystal resonance. The general theory and conditions for absorption enhancement and crit. coupling in a thin film and give design rules for a totally absorbing system are discussed. The authors present examples in the near-IR and visible, using both a lossless metallic mirror and a realistic multilayer dielec. mirror.
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  19. 19
    Polat, E. O.; Uzlu, H. B.; Balci, O.; Kakenov, N.; Kovalska, E.; Kocabas, C. Graphene-Enabled Optoelectronics on Paper ACS Photonics 2016, 3, 964– 971 DOI: 10.1021/acsphotonics.6b00017
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    19
    Graphene-Enabled Optoelectronics on Paper
    Polat, Emre O.; Uzlu, Hasan Burkay; Balci, Osman; Kakenov, Nurbek; Kovalska, Evgeniya; Kocabas, Coskun
    ACS Photonics (2016), 3 (6), 964-971CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
    The realization of optoelectronic devices on paper has been an outstanding challenge due to the large surface roughness and incompatible nature of paper with optical materials. Here, we demonstrate a new class of optoelectronic devices on a piece of printing paper using graphene as an elec. reconfigurable optical medium. Our approach relies on electro-modulation of optical properties of multilayer graphene on paper via blocking the interband electronic transitions. The paper based devices yield high optical contrast in the visible spectrum with a fast response. Pattering graphene into multiple pixels, folding paper into three-dimensional shapes or printing colored ink on paper substrates enable us to demonstrate novel optoelectronic devices which cannot be realized with wafer-based techniques.
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  20. 20
    Yao, Y.; Shankar, R.; Kats, M. A.; Song, Y.; Kong, J.; Loncar, M.; Capasso, F. Electrically Tunable Metasurface Perfect Absorbers for Ultrathin Mid-Infrared Optical Modulators Nano Lett. 2014, 14, 6526– 6532 DOI: 10.1021/nl503104n
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    20
    Electrically Tunable Metasurface Perfect Absorbers for Ultrathin Mid-Infrared Optical Modulators
    Yao, Yu; Shankar, Raji; Kats, Mikhail A.; Song, Yi; Kong, Jing; Loncar, Marko; Capasso, Federico
    Nano Letters (2014), 14 (11), 6526-6532CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Dynamically reconfigurable metasurfaces open up unprecedented opportunities in applications such as high capacity communications, dynamic beam shaping, hyperspectral imaging, and adaptive optics. The realization of high performance metasurface-based devices remains a great challenge due to very limited tuning ranges and modulation depths. A widely tunable metasurface composed of optical antennas on graphene can be incorporated into a subwavelength-thick optical cavity to create an elec. tunable perfect absorber. By switching the absorber in and out of the crit. coupling condition via the gate voltage applied on graphene, a modulation depth of up to 100% can be achieved. Ultrathin (thickness < λ0/10) high speed (up to 20 GHz) optical modulators were demonstrated over a broad wavelength range (5-7 μm). The operating wavelength can be scaled from the near-IR to the terahertz by simply tailoring the metasurface and cavity dimensions.
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  21. 21
    Dabidian, N.; Dutta-Gupta, S.; Kholmanov, I.; Lai, K.; Lu, F.; Lee, J.; Jin, M.; Trendafilov, S.; Khanikaev, A.; Fallahazad, B. Experimental Demonstration of Phase Modulation and Motion Sensing Using Graphene-Integrated Metasurfaces Nano Lett. 2016, 16, 3607– 3615 DOI: 10.1021/acs.nanolett.6b00732
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    21
    Experimental Demonstration of Phase Modulation and Motion Sensing Using Graphene-Integrated Metasurfaces
    Dabidian, Nima; Dutta-Gupta, Shourya; Kholmanov, Iskandar; Lai, Kueifu; Lu, Feng; Lee, Jongwon; Jin, Mingzhou; Trendafilov, Simeon; Khanikaev, Alexander; Fallahazad, Babak; Tutuc, Emanuel; Belkin, Mikhail A.; Shvets, Gennady
    Nano Letters (2016), 16 (6), 3607-3615CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Strong interaction of graphene with light accounts for 1 of its most remarkable properties: the ability to absorb 2.3% of the incident light's energy within a single at. layer. Free carrier injection via field-effect gating can dramatically vary the optical properties of graphene, thereby enabling fast graphene-based modulators of the light intensity. The very thinness of graphene makes it difficult to modulate the other fundamental property of the light wave: its optical phase. Considerable phase control can be achieved by integrating a single-layer graphene (SLG) with a resonant plasmonic metasurface that contains nanoscale gaps. By concg. the light intensity inside of the nanogaps, the metasurface dramatically increases the coupling of light to the SLG and enables control of the phase of the reflected mid-IR light by ≤55° via field-effect gating. Graphene-based phase modulators that maintain the amplitude of the reflected light essentially const. over most of the phase tuning range are exptl. demonstrated. Rapid nonmech. phase modulation enables a new exptl. technique, graphene-based laser interferometry, which was used to demonstrate motion detection with nanoscale precision. By the judicious choice of a strongly anisotropic metasurface the graphene-controlled phase shift of light can be rendered polarization-dependent. Using the exptl. measured phases for the 2 orthogonal polarizations, the polarization state of the reflected light can be by modulated by carrier injection into the SLG. These results pave the way for novel high-speed graphene-based optical devices and sensors such as polarimeters, ellipsometers, and frequency modulators.
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  22. 22
    Schall, D.; Neumaier, D.; Mohsin, M.; Chmielak, B.; Bolten, J.; Porschatis, C.; Prinzen, A.; Matheisen, C.; Kuebart, W.; Junginger, B. 50 GBit/s Photodetectors Based on Wafer-Scale Graphene for Integrated Silicon Photonic Communication Systems ACS Photonics 2014, 1, 781– 784 DOI: 10.1021/ph5001605
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    22
    50 GBit/s photodetectors based on wafer-scale graphene for integrated silicon photonic communication systems
    Schall, Daniel; Neumaier, Daniel; Mohsin, Muhammad; Chmielak, Bartos; Bolten, Jens; Porschatis, Caroline; Prinzen, Andreas; Matheisen, Christopher; Kuebart, Wolfgang; Junginger, Bernhard; Templ, Wolfgang; Giesecke, Anna Lena; Kurz, Heinrich
    ACS Photonics (2014), 1 (9), 781-784CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
    Optical data links are the backbone of today's telecommunication infrastructure. The integration of electronic and optic components on one chip is one of the most attractive routes to further increase the system performance. Here, the authors present the fabrication of photodetectors based on CVD-grown graphene on silicon photonic waveguides. The devices operate bias-free in the C-band at 1550 nm and show an extrinsic -3 dB bandwidth of 41 GHz. The authors demonstrate that these detectors work at data rates up to 50 GBit/s with excellent signal integrity.
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  23. 23
    Degl’Innocenti, R.; Xiao, L.; Jessop, D. S.; Kindress, S. J.; Ren, Y.; Lin, H.; Zeitler, J. A.; Alexander-Webber, J. A.; Joyce, H. J.; Braeuninger-Weimer, P. Fast Room-Temperature Detection of Terahertz Quantum Cascade Lasers with Graphene-Loaded Bow-Tie Plasmonic Antenna Arrays ACS Photonics 2016, 3, 1747– 1753 DOI: 10.1021/acsphotonics.6b00405
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    23
    Fast Room-Temperature Detection of Terahertz Quantum Cascade Lasers with Graphene-Loaded Bow-Tie Plasmonic Antenna Arrays
    Degl'Innocenti, Riccardo; Xiao, Long; Jessop, David S.; Kindness, Stephen J.; Ren, Yuan; Lin, Hungyen; Zeitler, J. Axel; Alexander-Webber, Jack A.; Joyce, Hannah J.; Braeuninger-Weimer, Philipp; Hofmann, Stephan; Beere, Harvey E.; Ritchie, David A.
    ACS Photonics (2016), 3 (10), 1747-1753CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
    We present a fast room-temp. terahertz detector based on interdigitated bow-tie antennas contacting graphene. Highly efficient photodetection was achieved by using two metals with different work functions as the arms of a bow-tie antenna contacting graphene. Arrays of the bow-ties were fabricated in order to enhance the responsivity and coupling of the incoming light to the detector, realizing an efficient imaging system. The device has been characterized and tested with a terahertz quantum cascade laser emitting in single frequency around 2 THz, yielding a responsivity of ∼34 μA/W and a noise-equiv. power of ∼1.5 × 10-7 W/Hz1/2.
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  24. 24
    Dumcenco, D.; Ovchinnikov, D.; Marinov, K.; Lazić, P.; Gibertini, M.; Marzari, N.; Lopez Sanchez, P.; Kung, Y.-C.; Krasnozhon, D.; Chen, W.-W. Large-Area Epitaxial Mono Layer MoS2 ACS Nano 2015, 9, 4611– 4620 DOI: 10.1021/acsnano.5b01281
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  25. 25
    Molina-Mendoza, A. J.; Lado, J. L.; Island, J. O.; Niño, M. A.; Aballe, L.; Foerster, M.; Bruno, F. Y.; López-Moreno, A.; Vaquero-Garzon, L.; van der Zant, H. S. J Centimeter-Scale Synthesis of Ultrathin Layered MoO3 by van der Waals Epitaxy Chem. Mater. 2016, 28, 4042– 4051 DOI: 10.1021/acs.chemmater.6b01505
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    25
    Centimeter-Scale Synthesis of Ultrathin Layered MoO3 by van der Waals Epitaxy
    Molina-Mendoza, Aday J.; Lado, Jose L.; Island, Joshua O.; Nino, Miguel Angel; Aballe, Lucia; Foerster, Michael; Bruno, Flavio Y.; Lopez-Moreno, Alejandro; Vaquero-Garzon, Luis; van der Zant, Herre S. J.; Rubio-Bollinger, Gabino; Agrait, Nicolas; Perez, Emilio M.; Fernandez-Rossier, Joaquin; Castellanos-Gomez, Andres
    Chemistry of Materials (2016), 28 (11), 4042-4051CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    We report on the large-scale synthesis of highly oriented ultrathin MoO3 layers using a simple and low-cost atm. pressure, van der Waals epitaxy growth on muscovite mica substrates. By this method, we are able to synthesize high quality centimeter-scale MoO3 crystals with thicknesses ranging from 1.4 nm (two layers) up to a few nanometers. The crystals can be easily transferred to an arbitrary substrate (such as SiO2) by a deterministic transfer method and be extensively characterized to demonstrate the high quality of the resulting crystal. We also study the electronic band structure of the material by d. functional calcns. Interestingly, the calcns. demonstrate that bulk MoO3 has a rather weak electronic interlayer interaction, and thus, it presents a monolayer-like band structure. Finally, we demonstrate the potential of this synthesis method for optoelectronic applications by fabricating large-area field-effect devices (10 μm × 110 μm in lateral dimensions) and find responsivities of 30 mA W-1 for a laser power d. of 13 mW cm-2 in the UV region of the spectrum and also as an electron acceptor in a MoS2-based field-effect transistor.
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  26. 26
    Han, P.; Akagi, K.; Canova, F. F.; Shimizu, R.; Oguchi, H.; Shiraki, S.; Weiss, P. S.; Asao, N.; Hitosugi, T. Self-Assembly Strategy for Fabricating Connected Graphene Nanoribbons ACS Nano 2015, 9, 12035– 12044 DOI: 10.1021/acsnano.5b04879
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    26
    Self-Assembly Strategy for Fabricating Connected Graphene Nanoribbons
    Han, Patrick; Akagi, Kazuto; Federici Canova, Filippo; Shimizu, Ryota; Oguchi, Hiroyuki; Shiraki, Susumu; Weiss, Paul S.; Asao, Naoki; Hitosugi, Taro
    ACS Nano (2015), 9 (12), 12035-12044CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    We use self-assembly to fabricate and to connect precise graphene nanoribbons end to end. Combining scanning tunneling microscopy, Raman spectroscopy, and d. functional theory, we characterize the chem. and electronic aspects of the interconnections between ribbons. We demonstrate how the substrate effects of our self-assembly can be exploited to fabricate graphene structures connected to desired electrodes.
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  27. 27
    Yang, Y.; Fu, Q.; Li, H.; Wei, M.; Xiao, J.; Wei, W.; Bao, X. Creating a Nanospace under an h-BN Cover for Adlayer Growth on Nickel(111) ACS Nano 2015, 9, 11589– 11598 DOI: 10.1021/acsnano.5b05509
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    27
    Creating a Nanospace under an h-BN Cover for Adlayer Growth on Nickel(111)
    Yang, Yang; Fu, Qiang; Li, Haobo; Wei, Mingming; Xiao, Jianping; Wei, Wei; Bao, Xinhe
    ACS Nano (2015), 9 (12), 11589-11598CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Heterostructures of two-dimensional (2D) at. crystals have attracted increasing attention, while fabrication of the 2D stacking structures remains a challenge. In this work, we present a route toward formation of 2D heterostructures via confined growth of a 2D adlayer underneath the other 2D overlayer. Taking a hexagonal boron nitride (h-BN) monolayer on Ni(111) as a model system, both epitaxial and nonepitaxial h-BN islands have been identified on the Ni surface. Surface science studies combined with d. functional theory calcns. reveal that the nonepitaxial h-BN islands interact weakly with the Ni(111) surface, which creates a 2D nanospace underneath the h-BN islands. An addnl. h-BN or graphene layer can be grown in the space between the nonepitaxial h-BN islands and Ni(111) surface, forming h-BN/h-BN bilayer structures and h-BN/graphene heterostructures. These results suggest that confined growth under 2D covers may provide an effective route to obtain stacks of 2D at. crystals.
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  28. 28
    Lin, Y.-C.; Komsa, H.-P.; Yeh, C.-H.; Björkman, T.; Liang, Z.-Y.; Ho, C.-H.; Huang, Y.-S.; Chio, P.-W.; Krasheninnikov, A. V.; Suenaga, K. Single-Layer ReS2: Two-Dimensional Semiconductor with Tunable In-Plane Anisotropy ACS Nano 2015, 9, 11249– 11257 DOI: 10.1021/acsnano.5b04851
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    28
    Single-Layer ReS2: Two-Dimensional Semiconductor with Tunable In-Plane Anisotropy
    Lin, Yung-Chang; Komsa, Hannu-Pekka; Yeh, Chao-Hui; Bjorkman, Torbjorn; Liang, Zheng-Yong; Ho, Ching-Hwa; Huang, Ying-Sheng; Chiu, Po-Wen; Krasheninnikov, Arkady V.; Suenaga, Kazu
    ACS Nano (2015), 9 (11), 11249-11257CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Rhenium disulfide (ReS2) and diselenide (ReSe2), the group 7 transition metal dichalcogenides (TMDs), are known to have a layered at. structure showing an in-plane motif of diamond-shaped-chains (DS-chains) arranged in parallel. Using a combination of TEM and transport measurements, the authors demonstrate here the direct correlation of electron transport anisotropy in single-layered ReS2 with the at. orientation of the DS-chains, as also supported by the authors' d. functional theory calcns. Further the direction of conducting channels in ReS2 and ReSe2 can be controlled by electron beam irradn. at elevated temps. and follows the strain induced to the sample. Also, high chalcogen deficiency can induce a structural transformation to a nonstoichiometric phase, which is again strongly direction-dependent. This tunable in-plane transport behavior opens up great avenues for creating nanoelectronic circuits in 2-dimensional materials.
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  29. 29
    Zhou, X.; Shi, J.; Qi, Y.; Liu, M.; Ma, D.; Zhang, Y.; Ji, Q.; Zhang, Z.; Li, C.; Liu, Z. Periodic Modulation of the Doping Level in Striped MoS2 Superstructures ACS Nano 2016, 10, 3461– 3468 DOI: 10.1021/acsnano.5b07545
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    29
    Periodic Modulation of the Doping Level in Striped MoS2 Superstructures
    Zhou, Xiebo; Shi, Jianping; Qi, Yue; Liu, Mengxi; Ma, Donglin; Zhang, Yu; Ji, Qingqing; Zhang, Zhepeng; Li, Cong; Liu, Zhongfan; Zhang, Yanfeng
    ACS Nano (2016), 10 (3), 3461-3468CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Although the recently discovered monolayer transition metal dichalcogenides exhibit novel electronic and optical properties, fundamental phys. issues such as the quasiparticle bandgap tunability and the substrate effects remain undefined. Herein, we present the report of a quasi-one-dimensional periodically striped superstructure for monolayer MoS2 on Au(100). The formation of the unique striped superstructure is found to be mainly modulated by the symmetry difference between MoS2 and Au(100) and their lattice mismatch. More intriguingly, we find that the monolayer MoS2 is heavily n-doped on the Au(100) facet with a bandgap of 1.3 eV, and the Fermi level is upshifted by ∼0.10 eV on the ridge (∼0.2 eV below the conduction band) in contrast to the valley regions (∼0.3 eV below the conduction band) of the striped patterns after high-temp. sample annealing process. This tunable doping effect is considered to be caused by the different defect densities over the ridge/valley regions of the superstructure. Addnl., an obvious bandgap redn. is obsd. in the vicinity of the domain boundary for monolayer MoS2 on Au(100). This work should therefore inspire intensive explorations of adlayer-substrate interactions, the defects, and their effects on band-structure engineering of monolayer MoS2.
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  30. 30
    Wang, S. S.; Lee, G. D.; Lee, S.; Yoon, E.; Warner, J. H. Detailed Atomic Reconstruction of Extended Line Defects in Monolayer MoS2 ACS Nano 2016, 10, 5419– 5430 DOI: 10.1021/acsnano.6b01673
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    30
    Detailed Atomic Reconstruction of Extended Line Defects in Monolayer MoS2
    Wang, Shanshan; Lee, Gun-Do; Lee, Sungwoo; Yoon, Euijoon; Warner, Jamie H.
    ACS Nano (2016), 10 (5), 5419-5430CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    We study the detailed bond reconstructions that occur in S vacancies within monolayer MoS2 using a combination of aberration-cor. transmission electron microscopy, d. functional theory (DFT), and multislice image simulations. Removal of a single S atom causes little perturbation to the surrounding MoS2 lattice, whereas the loss of two S atoms from the same at. column causes a measurable local contraction. Aggregation of S vacancies into linear line defects along the zigzag direction results in larger lattice compression that is more pronounced as the length of the line defect increases. For the case of two rows of S line vacancies, we find two different types of S atom reconstructions with different amts. of lattice compression. Increasing the width of line defects leads to nanoscale regions of reconstructed MoS2 that are shown by DFT to behave as metallic channels. These results provide important insights into how defect structures could be used for creating metallic tracks within semiconducting monolayer MoS2 films for future applications in electronics and optoelectronics.
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  31. 31
    Kim, S.; Russell, M.; Kulkarni, D. D.; Henry, M.; Kim, S.; Naik, R. R.; Voevodin, A. A.; Jang, S. S.; Tsukruk, V. V.; Fedorov, A. G. Activating ″Invisible″ Glue: Using Electron Beam for Enhancement of Interfacial Properties of Graphene-Metal Contact ACS Nano 2016, 10, 1042– 1049 DOI: 10.1021/acsnano.5b06342
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  32. 32
    Woomer, A. H.; Farnsworth, T. W.; Hu, J.; Wells, R. A.; Donley, C. L.; Warren, S. C. Phosphorene: Synthesis, Scale-Up, and Quantitative Optical Spectroscopy ACS Nano 2015, 9, 8869– 8884 DOI: 10.1021/acsnano.5b02599
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    32
    Phosphorene: Synthesis, Scale-Up, and Quantitative Optical Spectroscopy
    Woomer, Adam H.; Farnsworth, Tyler W.; Hu, Jun; Wells, Rebekah A.; Donley, Carrie L.; Warren, Scott C.
    ACS Nano (2015), 9 (9), 8869-8884CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Phosphorene, a 2-dimensional (2D) monolayer of black P, has attracted considerable theor. interest, although the exptl. realization of monolayer, bilayer, and few-layer flakes was a significant challenge. Conditions for liq. exfoliation to achieve the 1st large-scale prodn. of monolayer, bilayer, and few-layer P, was systematically surveyed with exfoliation demonstrated at the 10 g scale. A rapid approach for quantifying the thickness of 2D P is described, and monolayer and few-layer flakes produced by the approach are cryst. and unoxidized, while air exposure leads to rapid oxidn. and the prodn. of acid. With large quantities of 2D P now available, the 1st quant. measurements of the material's absorption edge, which is nearly identical to the material's band gap under the exptl. conditions, was performed as a function of flake thickness. The interpretation of the absorbance spectrum relies on an anal. method introduced allowing the accurate detn. of the absorption edge in polydisperse samples of quantum-confined semiconductors. Using this method, the band gap of black P increased from 0.33 ± 0.02 eV in bulk to 1.88 ± 0.24 eV in bilayers, a range that is larger than that of any other 2D material. A higher-energy optical transition (VB-1 to CB) was quantified, which changes from 2.0 eV in bulk to 3.23 eV in bilayers. Several methods are described for producing and analyzing 2D P while also yielding a class of 2D materials with unprecedented optoelectronic properties.
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  33. 33
    Yang, Z. H.; Liang, H.; Wang, X.; Ma, X.; Zhang, T.; Yang, Y.; Xie, L.; Chen, D.; Long, Y.; Chen, J. Atom-Thin SnS2-xSex with Adjustable Compositions by Direct Liquid Exfoliation from Single Crystals ACS Nano 2016, 10, 755– 762 DOI: 10.1021/acsnano.5b05823
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  34. 34
    Harvey, A.; Backes, C.; Gholamvand, Z.; Hanlon, D.; McAteer, D.; Nerl, H. C.; McGuire, E.; Seral-Ascaso, A.; Ramasse, Q. M.; McEvoy, N. Preparation of Gallium Sulfide Nanosheets by Liquid Exfoliation and Their Application As Hydrogen Evolution Catalysts Chem. Mater. 2015, 27, 3483– 3493 DOI: 10.1021/acs.chemmater.5b00910
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    34
    Preparation of Gallium Sulfide Nanosheets by Liquid Exfoliation and Their Application As Hydrogen Evolution Catalysts
    Harvey, Andrew; Backes, Claudia; Gholamvand, Zahra; Hanlon, Damien; McAteer, David; Nerl, Hannah C.; McGuire, Eva; Seral-Ascaso, Andres; Ramasse, Quentin M.; McEvoy, Niall; Winters, Sinead; Berner, Nina C.; McCloskey, David; Donegan, John F.; Duesberg, Georg S.; Nicolosi, Valeria; Coleman, Jonathan N.
    Chemistry of Materials (2015), 27 (9), 3483-3493CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Large quantities of gallium sulfide (GaS) nanosheets have been produced by liq. exfoliation of layered GaS powder. The exfoliation was achieved by sonication of the powder in suitable solvents. The variation of dispersed concn. with solvent was consistent with classical soln. thermodn. and showed successful solvents to be those with Hildebrand soly. parameters close to 21.5 MPa1/2. In this way, nanosheets could be produced at concns. of up to ∼0.2 mg/mL with lateral sizes and thicknesses of 50-1000 nm and 3-80 layers, resp. The nanosheets appeared to be relatively defect-free although oxygen was obsd. in the vicinity of the edges. Using controlled centrifugation techniques, it was possible to prep. dispersions contg. size-selected nanosheets. Spectroscopic measurements showed the optical properties of the dispersions to vary strongly with nanosheet size, allowing the elucidation of spectroscopic metrics for in situ estn. of nanosheet size and thickness. These techniques allow the prodn. of nanosheets with controlled sizes, which will be important for certain applications. Films of GaS nanosheets of three different sizes were prepd. for use as hydrogen evolution electrocatalysts. A clear correlation between performance and size was found, showing small nanosheets to be more effective. This is consistent with the catalytically active sites residing on the nanosheet edges.
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  35. 35
    Dimiev, A. M.; Ceriotti, G.; Metzger, A.; Kim, N. D.; Tour, J. M. Chemical Mass Production of Graphene Nanoplatelets in Similar to 100% Yield ACS Nano 2016, 10, 274– 279 DOI: 10.1021/acsnano.5b06840
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    There is no corresponding record for this reference.
  36. 36
    He, P.; Sun, J.; Tian, S.; Yang, S.; Ding, S.; Ding, G.; Xie, X.; Jiang, M. Processable Aqueous Dispersions of Graphene Stabilized by Graphene Quantum Dots Chem. Mater. 2015, 27, 218– 226 DOI: 10.1021/cm503782p
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    36
    Processable Aqueous Dispersions of Graphene Stabilized by Graphene Quantum Dots
    He, Peng; Sun, Jing; Tian, Suyun; Yang, Siwei; Ding, Shengju; Ding, Guqiao; Xie, Xiaoming; Jiang, Mianheng
    Chemistry of Materials (2015), 27 (1), 218-226CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    Dispersing graphene in various solvents is one of the key technologies toward the practical applications of graphene. Herein, using graphene quantum dots (GQDs) as stabilizer, aq. dispersions of graphene with good stability were demonstrated by directly dispersing commercialized graphene powder into water. Amazingly, 100 mg of graphene powder could be stabilized by an av. of merely 7.8 mg GQDs to form aq. dispersions with a max. concn. of up to 0.4 mg/mL and stability at least 3 mo. The introduction of a small amt. of GQDs also allowed for the fabrication of water-redispersible graphene slurry and powder, which would largely facilitate the transportation and applications of graphene. The mechanism of the GQDs stabilized graphene in water was proposed and exptl. verified through UV-visible spectroscopy and zeta potential measurements. Moreover, flexible graphene papers directly assembled from the water-dispersible graphene exhibited controllable thickness, good cond., and acceptable strength. With properties not compromised by GQDs, water-dispersible graphene is expected to be widely applicable in elec. and electrochem. device fields.
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  37. 37
    Chua, C. K.; Sofer, Z.; Šimek, P.; Jankovský, O.; Klímová, K.; Bakardjieva, S.; Kučková, S. H.; Pumera, M. Synthesis of Strongly Fluorescent Graphene Quantum Dots by Cage-Opening Buckminsterfullerene ACS Nano 2015, 9, 2548– 2555 DOI: 10.1021/nn505639q
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    37
    Synthesis of Strongly Fluorescent Graphene Quantum Dots by Cage-Opening Buckminsterfullerene
    Chua, Chun Kiang; Sofer, Zdenek; Simek, Petr; Jankovsky, Ondrej; Klimova, Katerina; Bakardjieva, Snejana; Hrdlickova Kuckova, Stepanka; Pumera, Martin
    ACS Nano (2015), 9 (3), 2548-2555CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Graphene quantum dots is a class of graphene nanomaterials with exceptional luminescence properties. Precise dimension control of graphene quantum dots produced by chem. synthesis methods is currently difficult to achieve and usually provides a range of sizes from 3 to 25 nm. Fullerene C60 is used as starting material, due to its well-defined dimension, to produce very small graphene quantum dots (∼2-3 nm). Treatment of fullerene C60 with a mixt. of strong acid and chem. oxidant induced the oxidn., cage-opening, and fragmentation processes of fullerene C60. The synthesized quantum dots were characterized and supported by LDI-TOF MS, TEM, XRD, XPS, AFM, STM, FTIR, DLS, Raman spectroscopy, and luminescence analyses. The quantum dots remained fully dispersed in aq. suspension and exhibited strong luminescence properties, with the highest intensity at 460 nm under a 340. nm excitation wavelength. Further chem. treatments with hydrazine hydrate and hydroxylamine resulted in red- and blue-shift of the luminescence, resp.
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  38. 38
    Anasori, B.; Xie, Y.; Beidaghi, M.; Lu, J.; Hosler, B. C.; Hultman, L.; Kent, P. R. C.; Gogotsi, Y.; Barsoum, M. W. Two-Dimensional, Ordered, Double Transition Metals Carbides (MXenes) ACS Nano 2015, 9, 9507– 9516 DOI: 10.1021/acsnano.5b03591
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    38
    Two-Dimensional, Ordered, Double Transition Metals Carbides (MXenes)
    Anasori, Babak; Xie, Yu; Beidaghi, Majid; Lu, Jun; Hosler, Brian C.; Hultman, Lars; Kent, Paul R. C.; Gogotsi, Yury; Barsoum, Michel W.
    ACS Nano (2015), 9 (10), 9507-9516CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    The higher the chem. diversity and structural complexity of two-dimensional (2D) materials, the higher the likelihood they possess unique and useful properties. Herein, d. functional theory (DFT) was used to predict the existence of two new families of 2-dimensional ordered, carbides (MXenes), M'2M''C2 and M'2M''2C3, where M' and M'' are two different early transition metals. In these solids, M' layers sandwich M'' carbide layers. By synthesizing Mo2TiC2Tx, Mo2Ti2C3Tx, and Cr2TiC2Tx (T is a surface termination), the authors validated the DFT predictions. Since the Mo and Cr atoms are on the outside, they control the 2-dimensional flakes' chem. and electrochem. properties. The latter was proven by showing quite different electrochem. behavior of Mo2TiC2Tx and Ti3C2Tx. This work further expands the family of 2-dimensional materials, offering addnl. choices of structures, chemistries, and ultimately useful properties.
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  39. 39
    Suzuki, N.; Wang, Y.; Elvati, P.; Qu, Z.-B.; Kim, K.; Jiang, S.; Baumeister, E.; Lee, J.; Yeom, B.; Bahng, J. H. Chiral Graphene Quantum Dots ACS Nano 2016, 10, 1744– 1755 DOI: 10.1021/acsnano.5b06369
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    39
    Chiral Graphene Quantum Dots
    Suzuki, Nozomu; Wang, Yichun; Elvati, Paolo; Qu, Zhi-Bei; Kim, Kyoungwon; Jiang, Shuang; Baumeister, Elizabeth; Lee, Jaewook; Yeom, Bongjun; Bahng, Joong Hwan; Lee, Jaebeom; Violi, Angela; Kotov, Nicholas A.
    ACS Nano (2016), 10 (2), 1744-1755CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Covalent attachment of L/D-cysteine moieties to the edges of graphene quantum dots (GQDs) leads to their helical buckling due to chiral interactions at the crowded edges. CD spectra of the GQDs revealed bands at ∼210-220 and 250-265 nm that changed their signs for different chirality of the cysteine edge ligands. The high-energy chiroptical peaks at 210-220 nm correspond to the hybridized MOs involving the chiral center of amino acids and atoms of graphene edges. Diverse exptl. and modeling data, including d. functional theory calcns. of CD spectra with probabilistic distribution of GQD isomers, indicate that the band at 250-265 nm originates from the 3-dimensional twisting of the graphene sheet and can be attributed to the chiral excitonic transitions. The pos. and neg. low-energy CD bands correspond to the left and right helicity of GQDs, resp. Exposure of liver HepG2 cells to L/D-GQDs reveals their general biocompatibility and a noticeable difference in the toxicity of the stereoisomers. Mol. dynamics simulations demonstrated that D-GQDs have a stronger tendency to accumulate within the cellular membrane than L-GQDs. Emergence of nanoscale chirality in GQDs decorated with biomols. is expected to be a general stereochem. phenomenon for flexible sheets of nanomaterials.
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  40. 40
    Park, S. H.; Kim, H.-K.; Yoon, S.-B.; Lee, C.-W.; Ahn, D.; Lee, S.-I.; Roh, K. C.; Kim, K.-B. Spray-Assisted Deep-Frying Process for the In Situ Spherical Assembly of Graphene for Energy-Storage Devices Chem. Mater. 2015, 27, 457– 465 DOI: 10.1021/cm5034244
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    40
    Spray-Assisted Deep-Frying Process for the In Situ Spherical Assembly of Graphene for Energy-Storage Devices
    Park, Sang-Hoon; Kim, Hyun-Kyung; Yoon, Seung-Beom; Lee, Chang-Wook; Ahn, Dongjoon; Lee, Sang-Ick; Roh, Kwang Chul; Kim, Kwang-Bum
    Chemistry of Materials (2015), 27 (2), 457-465CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
    To take full advantage of graphene in macroscale devices, it is important to integrate two-dimensional graphene nanosheets into a micro/macrosized structure that can fully utilize graphene's nanoscale characteristics. To this end, a novel spray-assisted self-assembly process is developed to create a spherically integrated graphene microstructure (graphene microsphere) using a high-temp. org. solvent in a manner reminiscent of deep-frying. This graphene microsphere improves the electrochem. performance of supercapacitors, in contrast to nonassembled graphene, which is attributed to its structural and pore characteristics. Furthermore, this synthesis method can also produce an effective graphene-based hybrid microsphere structure, in which Si nanoparticles are efficiently entrapped by graphene nanosheets during the assembly process. When used in a Li-ion battery, this material can provide a more suitable framework to buffer the considerable vol. change that occurs in Si during electrochem. lithiation/delithiation, thereby improving cycling performance. This simple and versatile self-assembly method is therefore directly relevant to the future design and development of practical graphene-based electrode materials for various energy-storage devices.
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  41. 41
    Kim, M.; Lee, C.; Seo, Y. D.; Cho, S.; Kim, J.; Lee, G.; Kim, Y. K.; Jang, J. Fabrication of Various Conducting Polymers Using Graphene Oxide as a Chemical Oxidant Chem. Mater. 2015, 27, 6238– 6248 DOI: 10.1021/acs.chemmater.5b01408
    Google Scholar
    There is no corresponding record for this reference.
  42. 42
    Luo, J.; Gao, J.; Wang, A.; Huang, J. Bulk Nanostructured Materials Based on Two-Dimensional Building Blocks: A Roadmap ACS Nano 2015, 9, 9432– 9436 DOI: 10.1021/acsnano.5b05259
    Google Scholar
    42
    Bulk Nanostructured Materials Based on Two-Dimensional Building Blocks: A Roadmap
    Luo, Jiayan; Gao, Jun; Wang, Aoxuan; Huang, Jiaxing
    ACS Nano (2015), 9 (10), 9432-9436CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    The family of two-dimensional (2D) materials, in particular MXenes, can now be greatly expanded based on a new "double metal" strategy as reported by Anasori, Xie, and Beidaghi et al. in this issue of ACS Nano. Now that a diverse array of well-defined nanoscale building blocks, esp. the 2D systems, has become available, we are better prepd. to think about scaling up nanomaterials in the broader context of materials science and engineering. In this Perspective, we construct a roadmap for assembling nanoscale building blocks into bulk nanostructured materials, and define some of the crit. challenges and goals. Two-dimensional sheets are uniquely well-suited in this roadmap for constructing dense, bulk-sized samples with scalable material performance or interesting emergent properties.
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    This article references 42 other publications.

    1. 1
      Lu, C.-P.; Li, G.; Mao, J.; Wang, L.-M; Andrei, E. Y. Bandgap, Mid-Gap States, and Gating Effects in MoS2 Nano Lett. 2014, 14, 4628– 4633 DOI: 10.1021/nl501659n
      1
      Bandgap, Mid-Gap States, and Gating Effects in MoS2
      Lu, Chih-Pin; Li, Guohong; Mao, Jinhai; Wang, Li-Min; Andrei, Eva Y.
      Nano Letters (2014), 14 (8), 4628-4633CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      The discovery of graphene has put the spotlight on other layered materials including transition metal dichalcogenites (TMD) as building blocks for novel heterostructures assembled from stacked at. layers. Molybdenum disulfide, MoS2, a semiconductor in the TMD family, with its remarkable thermal and chem. stability and high mobility, has emerged as a promising candidate for postsilicon applications such as switching, photonics, and flexible electronics. Because these rely on controlling the position of the Fermi energy (EF), it is crucial to understand its dependence on doping and gating. To elucidate these questions we carried out gated scanning tunneling microscopy (STM) and spectroscopy (STS) measurements and compared them with transport measurements in a field effect transistor (FET) device configuration. This made it possible to measure the bandgap and the position of EF in MoS2 and to track its evolution with gate voltage. For bulk samples, the measured bandgap (∼1.3 eV) is comparable to the value obtained by photoluminescence, and the position of EF (∼0.35 eV) below the conduction band, is consistent with N-doping reported in this material. We show that the N-doping in bulk samples can be attributed to S vacancies. In contrast, the significantly higher N-doping obsd. in thin MoS2 films deposited on SiO2 is dominated by charge traps at the sample-substrate interface.
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    2. 2
      Zhou, X.; Kang, K.l; Xie, S.; Dadgar, A.; Monahan, N. R.; Zhu, X.-Y.; Park, J.; Pasupathy, A. N. Atomic-Scale Spectroscopy of Gated Monolayer MoS2 Nano Lett. 2016, 16, 3148– 3154 DOI: 10.1021/acs.nanolett.6b00473
      2
      Atomic-Scale Spectroscopy of Gated Monolayer MoS2
      Zhou, Xiaodong; Kang, Kibum; Xie, Saien; Dadgar, Ali; Monahan, Nicholas R.; Zhu, X.-Y.; Park, Jiwoong; Pasupathy, Abhay N.
      Nano Letters (2016), 16 (5), 3148-3154CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      The electronic properties of semiconducting monolayer transition-metal dichalcogenides can be tuned by electrostatic gate potentials. Here we report gate-tunable imaging and spectroscopy of monolayer MoS2 by at.-resoln. scanning tunneling microscopy/spectroscopy (STM/STS). Our measurements are performed on large-area samples grown by metal-org. chem. vapor deposition (MOCVD) techniques on a silicon oxide substrate. Topog. measurements of defect d. indicate a sample quality comparable to single-crystal MoS2. From gate voltage dependent spectroscopic measurements, we det. that in-gap states exist in or near the MoS2 film at a d. of 1.3 × 1012 eV-1 cm-2. By combining the single-particle band gap measured by STS with optical measurements, we est. an exciton binding energy of 230 meV on this substrate, in qual. agreement with numerical simulation. Grain boundaries are obsd. in these polycryst. samples, which are seen to not have strong electronic signatures in STM imaging.
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    3. 3
      Huang, Y.; Ding, Z.; Zhang, W.; Chang, Y.-H.; Shi, Y.; Li, L.-J.; Song, Z.; Zheng, Y. J.; Chi, D.; Quek, S. Y. Gap States at Low-Angle Grain Boundaries in Monolayer Tungsten Diselenide Nano Lett. 2016, 16, 3682– 3688 DOI: 10.1021/acs.nanolett.6b00888
      3
      Gap States at Low-Angle Grain Boundaries in Monolayer Tungsten Diselenide
      Huang, Yu Li; Ding, Zijing; Zhang, Wenjing; Chang, Yung-Huang; Shi, Yumeng; Li, Lain-Jong; Song, Zhibo; Zheng, Yu Jie; Chi, Dongzhi; Quek, Su Ying; Wee, Andrew T. S.
      Nano Letters (2016), 16 (6), 3682-3688CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Two-dimensional (2D) transition metal dichalcogenides (TMDs) have revealed many novel properties of interest to future device applications. In particular, the presence of grain boundaries (GBs) can significantly influence the material properties of 2D TMDs. However, direct characterization of the electronic properties of the GB defects at the at. scale remains extremely challenging. In this study, scanning tunneling microscopy and spectroscopy is employed to investigate the at. and electronic structure of low-angle GBs of monolayer tungsten diselenide (WSe2) with misorientation angles of 3-6°. Butterfly features are obsd. along the GBs, with the periodicity depending on the misorientation angle. D. functional theory calcns. show that these butterfly features correspond to gap states that arise in tetragonal dislocation cores and extend to distorted six-membered rings around the dislocation core. Understanding the nature of GB defects and their influence on transport and other device properties highlights the importance of defect engineering in future 2D device fabrication.
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    4. 4
      Zhang, C.; Johnson, A.; Hsu, C.-L.; Li, L.-J.; Shih, C.-K. Direct Imaging of Band Profile in Single Layer MoS2 on Graphite: Quasiparticle Energy Gap, Metallic Edge States, and Edge Band Bending Nano Lett. 2014, 14, 2443– 2447 DOI: 10.1021/nl501133c
      4
      Direct Imaging of Band Profile in Single Layer MoS2 on Graphite: Quasiparticle Energy Gap, Metallic Edge States, and Edge Band Bending
      Zhang, Chendong; Johnson, Amber; Hsu, Chang-Lung; Li, Lain-Jong; Shih, Chih-Kang
      Nano Letters (2014), 14 (5), 2443-2447CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Using scanning tunneling microscopy and spectroscopy, we probe the electronic structures of single layer MoS2 on graphite. The apparent quasiparticle energy gap of single layer MoS2 is measured to be 2.15 ± 0.06 eV at 77 K, albeit a higher second conduction band threshold at 0.2 eV above the apparent conduction band min. is also obsd. Combining it with photoluminescence studies, we deduce an exciton binding energy of 0.22 ± 0.1 eV (or 0.42 eV if the second threshold is use), a value that is lower than current theor. predictions. Consistent with theor. predictions, we directly observe metallic edge states of single layer MoS2. In the bulk region of MoS2, the Fermi level is located at 1.8 eV above the valence band max., possibly due to the formation of a graphite/MoS2 heterojunction. At the edge, however, we observe an upward band bending of 0.6 eV within a short depletion length of about 5 nm, analogous to the phenomena of Fermi level pinning of a 3D semiconductor by metallic surface states.
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    5. 5
      Velasco, J., Jr.; Ju, L.; Wong, D.; Kahn, S.; Lee, J.; Tsai, H.-Z.; Germany, C.; Wickenburg, S.; Lu, J.; Taniguchi, T. Nanoscale control of rewriteable doping patterns in pristine graphene/boron nitride heterostructures Nano Lett. 2016, 16, 1620– 1625 DOI: 10.1021/acs.nanolett.5b04441
      5
      Nanoscale Control of Rewriteable Doping Patterns in Pristine Graphene/Boron Nitride Heterostructures
      Velasco, Jairo; Ju, Long; Wong, Dillon; Kahn, Salman; Lee, Juwon; Tsai, Hsin-Zon; Germany, Chad; Wickenburg, Sebastian; Lu, Jiong; Taniguchi, Takashi; Watanabe, Kenji; Zettl, Alex; Wang, Feng; Crommie, Michael F.
      Nano Letters (2016), 16 (3), 1620-1625CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Nanoscale control of charge doping in two-dimensional (2D) materials permits the realization of electronic analogs of optical phenomena, relativistic physics at low energies, and technol. promising nanoelectronics. Electrostatic gating and chem. doping are the two most common methods to achieve local control of such doping. However, these approaches suffer from complicated fabrication processes that introduce contamination, change material properties irreversibly, and lack flexible pattern control. Here the authors demonstrate a clean, simple, and reversible technique that permits writing, reading, and erasing of doping patterns for 2-dimensional materials at the nanometer scale. The authors accomplish this by employing a graphene/B nitride heterostructure that is equipped with a bottom gate electrode. By using electron transport and scanning tunneling microscopy (STM), spatial control of charge doping can be realized with the application of either light or STM tip voltage excitations in conjunction with a gate elec. field. The authors' straightforward and novel technique provides a new path toward on-demand graphene p-n junctions and ultrathin memory devices.
      >> More from SciFinder ®
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    6. 6
      Bhandari, S.; Lee, G.-H.; Klales, A.; Watanabe, K.; Taniguchi, T.; Heller, E.; Kim, P.; Westervelt, R. M. Imaging Cyclotron Orbits of Electrons in Graphene Nano Lett. 2016, 16, 1690– 1694 DOI: 10.1021/acs.nanolett.5b04609
      6
      Imaging Cyclotron Orbits of Electrons in Graphene
      Bhandari, Sagar; Lee, Gil-Ho; Klales, Anna; Watanabe, Kenji; Taniguchi, Takashi; Heller, Eric; Kim, Philip; Westervelt, Robert M.
      Nano Letters (2016), 16 (3), 1690-1694CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Electrons in graphene can travel for several microns without scattering at low temps., and their motion becomes ballistic, following classical trajectories. When a magnetic field B is applied perpendicular to the plane, electrons follow cyclotron orbits. Magnetic focusing occurs when electrons injected from one narrow contact focus onto a second contact located an integer no. of cyclotron diams. away. By tuning the magnetic field B and electron d. n in the graphene layer, we observe magnetic focusing peaks. We use a cooled scanning gate microscope to image cyclotron trajectories in graphene at 4.2 K. The tip creates a local change in d. that casts a shadow by deflecting electrons flowing nearby; an image of flow can be obtained by measuring the transmission between contacts as the tip is raster scanned across the sample. On the first magnetic focusing peak, we image a cyclotron orbit that extends from one contact to the other. In addn., we study the geometry of orbits deflected into the second point contact by the tip.
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    7. 7
      Krane, N.; Lotze, C.; Läger, J. M.; Reecht, G.; Franke, K. J. Electronic Structure and Luminescence of Quasi-Freestanding MoS2 Nanopatches on Au(111) Nano Lett. 2016, 16, 5163– 5168 DOI: 10.1021/acs.nanolett.6b02101
      7
      Electronic Structure and Luminescence of Quasi-Freestanding MoS2 Nanopatches on Au(111)
      Krane, Nils; Lotze, Christian; Laeger, Julia M.; Reecht, Gael; Franke, Katharina J.
      Nano Letters (2016), 16 (8), 5163-5168CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Monolayers of transition metal dichalcogenides are interesting materials for optoelectronic devices due to their direct electronic band gaps in the visible spectral range. Here, we grow single layers of MoS2 on Au(111) and find that nanometer-sized patches exhibit an electronic structure similar to their freestanding analog. We ascribe the electronic decoupling from the Au substrate to the incorporation of vacancy islands underneath the intact MoS2 layer. Excitation of the patches by electrons from the tip of a scanning tunneling microscope leads to luminescence of the MoS2 junction and reflects the one-electron band structure of the quasi-freestanding layer.
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    8. 8
      Cheng, R.; Li, D.; Zhou, H.; Wang, C.; Yin, A.; Jiang, S.; Liu, Y.; Chen, Y.; Huang, Y.; Duan, X. Electroluminescence and Photocurrent Generation from Atomically Sharp WSe2/MoS2 Heterojunction p–n Diodes Nano Lett. 2014, 14, 5590– 5597 DOI: 10.1021/nl502075n
      8
      Electroluminescence and Photocurrent Generation from Atomically Sharp WSe2/MoS2 Heterojunction p-n Diodes
      Cheng, Rui; Li, Dehui; Zhou, Hailong; Wang, Chen; Yin, Anxiang; Jiang, Shan; Liu, Yuan; Chen, Yu; Huang, Yu; Duan, Xiangfeng
      Nano Letters (2014), 14 (10), 5590-5597CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      The p-n diodes represent the most fundamental device building blocks for diverse optoelectronic functions, but are difficult to achieve in atomically thin transition metal dichalcogenides (TMDs) due to the challenges in selectively doping them into p- or n-type semiconductors. An atomically thin and sharp heterojunction p-n diode can be created by vertically stacking p-type monolayer W diselenide (WSe2) and n-type few-layer Mo disulfide (MoS2). Elec. measurements of the vertically staked WSe2/MoS2 heterojunctions reveal excellent current rectification behavior with an ideality factor of 1.2. Photocurrent mapping shows rapid photoresponse over the entire overlapping region with a highest external quantum efficiency up to 12%. Electroluminescence studies show prominent band edge excitonic emission and strikingly enhanced hot-electron luminescence. A systematic study shows distinct layer-no. dependent emission characteristics and reveals important insight about the origin of hot-electron luminescence and the nature of electron-orbital interaction in TMDs. Probably these atomically thin heterojunction p-n diodes represent an interesting system for probing the fundamental electrooptical properties in TMDs and can open up a new pathway to novel optoelectronic devices such as atomically thin photodetectors, photovoltaics, as well as spin- and valley-polarized light emitting diodes, on-chip lasers.
      >> More from SciFinder ®
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    9. 9
      Furchi, M. M.; Pospischil, A.; Libisch, F.; Burgdörfer, J.; Mueller, T. Photovoltaic Effect in an Electrically Tunable van der Waals Heterojunction Nano Lett. 2014, 14, 4785– 4791 DOI: 10.1021/nl501962c
      9
      Photovoltaic Effect in an Electrically Tunable van der Waals Heterojunction
      Furchi, Marco M.; Pospischil, Andreas; Libisch, Florian; Burgdoerfer, Joachim; Mueller, Thomas
      Nano Letters (2014), 14 (8), 4785-4791CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Semiconductor heterostructures form the cornerstone of many electronic and optoelectronic devices and are traditionally fabricated using epitaxial growth techniques. More recently, heterostructures have also been obtained by vertical stacking of two-dimensional crystals, such as graphene and related two-dimensional materials. These layered designer materials are held together by van der Waals forces and contain atomically sharp interfaces. Here, we report on a type-II van der Waals heterojunction made of molybdenum disulfide and tungsten diselenide monolayers. The junction is elec. tunable, and under appropriate gate bias an atomically thin diode is realized. Upon optical illumination, charge transfer occurs across the planar interface and the device exhibits a photovoltaic effect. Advances in large-scale prodn. of two-dimensional crystals could thus lead to a new photovoltaic solar technol.
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    10. 10
      Jariwala, D.; Howell, S. L.; Chen, K.-S.; Kang, J.; Sangwan, V. K.; Filippone, S. A.; Turrisi, R.; Marks, T. J.; Lauhon, L. J.; Hersam, M. C. Hybrid, Gate-Tunable, van der Waals p–n Heterojunctions from Pentacene and MoS2 Nano Lett. 2015, 16, 497– 503 DOI: 10.1021/acs.nanolett.5b04141
      There is no corresponding record for this reference.
    11. 11
      Withers, F.; Del Pozo-Zamudio, O.; Schwarz, S.; Dufferwiel, S.; Walker, P. M.; Godde, T.; Rooney, A. P.; Gholinia, A.; Woods, C. R.; Blake, P. WSe2 Light-Emitting Tunneling Transistors with Enhanced Brightness at Room Temperature Nano Lett. 2015, 15, 8223– 8228 DOI: 10.1021/acs.nanolett.5b03740
      11
      WSe2 Light-Emitting Tunneling Transistors with Enhanced Brightness at Room Temperature
      Withers, F.; Del Pozo-Zamudio, O.; Schwarz, S.; Dufferwiel, S.; Walker, P. M.; Godde, T.; Rooney, A. P.; Gholinia, A.; Woods, C. R.; Blake, P.; Haigh, S. J.; Watanabe, K.; Taniguchi, T.; Aleiner, I. L.; Geim, A. K.; Fal'ko, V. I.; Tartakovskii, A. I.; Novoselov, K. S.
      Nano Letters (2015), 15 (12), 8223-8228CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Monolayers of molybdenum and tungsten dichalcogenides are direct bandgap semiconductors, which makes them promising for optoelectronic applications. In particular, van der Waals heterostructures consisting of monolayers of MoS2 sandwiched between atomically thin hexagonal boron nitride (hBN) and graphene electrodes allows one to obtain light emitting quantum wells (LEQWs) with low-temp. external quantum efficiency (EQE) of 1%. However, the EQE of MoS2- and MoSe2-based LEQWs shows behavior common for many other materials: it decreases fast from cryogenic conditions to room temp., undermining their practical applications. Here the authors compare MoSe2 and WSe2 LEQWs. The EQE of WSe2 devices grows with temp., with room temp. EQE reaching 5%, which is 250× more than the previous best performance of MoS2 and MoSe2 quantum wells in ambient conditions. The authors attribute such different temp. dependences to the inverted sign of spin-orbit splitting of conduction band states in tungsten and molybdenum dichalcogenides, which makes the lowest-energy exciton in WSe2 dark.
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    12. 12
      Clark, G.; Schaibley, J. R.; Ross, J.; Taniguchi, T.; Watanabe, K.; Hendrickson, J. R.; Mou, S.; Yao, W.; Xu, X. Single Defect Light Emitting Diode in a van der Waals Heterostructure Nano Lett. 2016, 16, 3944– 3948 DOI: 10.1021/acs.nanolett.6b01580
      There is no corresponding record for this reference.
    13. 13
      Chandni, U.; Watanabe, K.; Taniguchi, T.; Eisenstein, J. P. Evidence for Defect-Mediated Tunneling in Hexagonal Boron Nitride-Based Junctions Nano Lett. 2015, 15, 7329– 7333 DOI: 10.1021/acs.nanolett.5b02625
      13
      Evidence for defect-mediated tunneling in hexagonal boron nitride-based junctions
      Chandni, U.; Watanabe, K.; Taniguchi, T.; Eisenstein, J. P.
      Nano Letters (2015), 15 (11), 7329-7333CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      We investigate electron tunneling through atomically thin layers of hexagonal boron nitride (hBN). Metal (Cr/Au) and semimetal (graphite) counter-electrodes are employed. While the direct tunneling resistance increases nearly exponentially with barrier thickness as expected, the thicker junctions also exhibit clear signatures of Coulomb blockade, including strong suppression of the tunnel current around zero bias and step-like features in the current at larger biases. The voltage sepn. of these steps suggests that single-electron charging of nanometer-scale defects in the hBN barrier layer are responsible for these signatures. We find that annealing the metal-hBN-metal junctions removes these defects and the Coulomb blockade signatures in the tunneling current.
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    14. 14
      Garcia de Abajo, F. J. Graphene Plasmonics: Challenges and Opportunities ACS Photonics 2014, 1, 135– 152 DOI: 10.1021/ph400147y
      14
      Graphene Plasmonics: Challenges and Opportunities
      Garcia de Abajo, F. Javier
      ACS Photonics (2014), 1 (3), 135-152CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
      A review. Graphene plasmons are rapidly emerging as a viable tool for fast elec. manipulation of light. The prospects for applications to electrooptical modulation, optical sensing, quantum plasmonics, light harvesting, spectral photometry, and tunable lighting at the nanoscale are further stimulated by the relatively low level of losses and high degree of spatial confinement that characterize these excitations compared with conventional plasmonic materials, alongside the large nonlinear response of graphene. The authors start with a general description of the plasmonic behavior of extended graphene, followed by anal. methods that lead to reasonably accurate ests. of both the plasmon energies and the strengths of coupling to external light in graphene nanostructures, including graphene ribbons. Although graphene plasmons have so far been obsd. at mid-IR and longer wavelengths, there are several possible strategies to extend them toward the visible and near-IR, including a redn. in the size of the graphene structures and an increase in the level of doping. Specifically, plasmons in narrow ribbons and mol.-size graphene structures are discussed. The authors further formulate prescriptions based on geometry to increase the level of electrostatic doping without causing elec. breakdown. Results are also presented for plasmons in highly-doped single-wall C nanotubes, which exhibit similar characteristics as narrow ribbons and show a relatively small dependence on the chirality of the tubes. The authors further discuss perfect light absorption by a single-atom C layer, which the authors illustrate by studying arrays of ribbons using fully anal. expressions. Finally, the authors explore the possibility of exploiting optically pumped transient plasmons in graphene, whereby the optically heated graphene valence band can sustain collective plasmon oscillations similar to those of highly doped graphene, and well-defined during the picosecond time window over which the electron is at an elevated temp. In brief, a no. of exciting possibilities to extend graphene plasmons toward the visible and near-IR spectral regions and toward the ultrafast time domain, thus configuring a vast range of possibilities for fundamental studies and technol. applications are discussed.
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    15. 15
      Nikitin, A. Y.; Yoxall, E.; Schnell, M.; Vélez, S.; Dolado, I.; Alonso-GOnzalez, P.; Casanova, F.; Hueso, L. E.; Hillenbrand, R. Nanofocusing of Hyperbolic Phonon-Polaritons in a Tapered Boron Nitride Slab ACS Photonics 2016, 3, 924– 929 DOI: 10.1021/acsphotonics.6b00186
      There is no corresponding record for this reference.
    16. 16
      Aslan, O. B.; Chenet, D. A.; van der Zande, A. M.; Hone, J. C.; Heinz, T. F. Linearly Polarized Excitons in Single-and Few-Layer ReS2 Crystals ACS Photonics 2015, 3, 96– 101 DOI: 10.1021/acsphotonics.5b00486
      There is no corresponding record for this reference.
    17. 17
      Kern, J.; Trügler, A.; Niehaus, I.; Ewering, J.; Schmidt, R.; Schneider, R.; Najmaei, S.; George, A.; Zhang, J.; Lou, J. Nanoantenna-Enhanced Light–Matter Interaction in Atomically Thin WS2 ACS Photonics 2015, 2, 1260– 1265 DOI: 10.1021/acsphotonics.5b00123
      17
      Nanoantenna-Enhanced Light-Matter Interaction in Atomically Thin WS2
      Kern, Johannes; Truegler, Andreas; Niehues, Iris; Ewering, Johannes; Schmidt, Robert; Schneider, Robert; Najmaei, Sina; George, Antony; Zhang, Jing; Lou, Jun; Hohenester, Ulrich; Michaelis de Vasconcellos, Steffen; Bratschitsch, Rudolf
      ACS Photonics (2015), 2 (9), 1260-1265CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
      Atomically thin transition metal dichalcogenides (TMDCs) are an emerging class of 2-dimensional semiconductors. Recently, the 1st optoelectronic devices featuring photodetection as well as electroluminescence were demonstrated using monolayer TMDCs as active material. However, the light-matter coupling for atomically thin TMDCs is limited by their small absorption length and low photoluminescence quantum yield. Here, the authors significantly increase the light-matter interaction in monolayer W disulfide (WS2) by coupling the atomically thin semiconductor to a plasmonic nanoantenna. Due to the plasmon resonance of the nanoantenna, strongly enhanced optical near-fields are generated within the WS2 monolayer. The authors observe an increase in photoluminescence intensity by >1 order of magnitude, resulting from a combined absorption and emission enhancement of the exciton in the WS2 monolayer. The polarization characteristics of the coupled system are governed by the nanoantenna. The robust nanoantenna-monolayer hybrid paves the way for efficient photodetectors, solar cells, and light-emitting devices based on 2-dimensional materials.
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    18. 18
      Piper, J. R.; Fan, S. Total Absorption in a Graphene Monolayer in the Optical Regime by Critical Coupling with a Photonic Crystal Guided Resonance ACS Photonics 2014, 1, 347– 353 DOI: 10.1021/ph400090p
      18
      Total Absorption in a Graphene Monolayer in the Optical Regime by Critical Coupling with a Photonic Crystal Guided Resonance
      Piper, Jessica R.; Fan, Shanhui
      ACS Photonics (2014), 1 (4), 347-353CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
      The total absorption in graphene in the near-IR and visible wavelength ranges was numerically demonstrated by crit. coupling with guided resonances of a photonic crystal slab. In this wavelength range, there is no plasmonic response in undoped graphene, so the crit. coupling is entirely controlled by the properties of the photonic crystal resonance. The general theory and conditions for absorption enhancement and crit. coupling in a thin film and give design rules for a totally absorbing system are discussed. The authors present examples in the near-IR and visible, using both a lossless metallic mirror and a realistic multilayer dielec. mirror.
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    19. 19
      Polat, E. O.; Uzlu, H. B.; Balci, O.; Kakenov, N.; Kovalska, E.; Kocabas, C. Graphene-Enabled Optoelectronics on Paper ACS Photonics 2016, 3, 964– 971 DOI: 10.1021/acsphotonics.6b00017
      19
      Graphene-Enabled Optoelectronics on Paper
      Polat, Emre O.; Uzlu, Hasan Burkay; Balci, Osman; Kakenov, Nurbek; Kovalska, Evgeniya; Kocabas, Coskun
      ACS Photonics (2016), 3 (6), 964-971CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
      The realization of optoelectronic devices on paper has been an outstanding challenge due to the large surface roughness and incompatible nature of paper with optical materials. Here, we demonstrate a new class of optoelectronic devices on a piece of printing paper using graphene as an elec. reconfigurable optical medium. Our approach relies on electro-modulation of optical properties of multilayer graphene on paper via blocking the interband electronic transitions. The paper based devices yield high optical contrast in the visible spectrum with a fast response. Pattering graphene into multiple pixels, folding paper into three-dimensional shapes or printing colored ink on paper substrates enable us to demonstrate novel optoelectronic devices which cannot be realized with wafer-based techniques.
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    20. 20
      Yao, Y.; Shankar, R.; Kats, M. A.; Song, Y.; Kong, J.; Loncar, M.; Capasso, F. Electrically Tunable Metasurface Perfect Absorbers for Ultrathin Mid-Infrared Optical Modulators Nano Lett. 2014, 14, 6526– 6532 DOI: 10.1021/nl503104n
      20
      Electrically Tunable Metasurface Perfect Absorbers for Ultrathin Mid-Infrared Optical Modulators
      Yao, Yu; Shankar, Raji; Kats, Mikhail A.; Song, Yi; Kong, Jing; Loncar, Marko; Capasso, Federico
      Nano Letters (2014), 14 (11), 6526-6532CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Dynamically reconfigurable metasurfaces open up unprecedented opportunities in applications such as high capacity communications, dynamic beam shaping, hyperspectral imaging, and adaptive optics. The realization of high performance metasurface-based devices remains a great challenge due to very limited tuning ranges and modulation depths. A widely tunable metasurface composed of optical antennas on graphene can be incorporated into a subwavelength-thick optical cavity to create an elec. tunable perfect absorber. By switching the absorber in and out of the crit. coupling condition via the gate voltage applied on graphene, a modulation depth of up to 100% can be achieved. Ultrathin (thickness < λ0/10) high speed (up to 20 GHz) optical modulators were demonstrated over a broad wavelength range (5-7 μm). The operating wavelength can be scaled from the near-IR to the terahertz by simply tailoring the metasurface and cavity dimensions.
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    21. 21
      Dabidian, N.; Dutta-Gupta, S.; Kholmanov, I.; Lai, K.; Lu, F.; Lee, J.; Jin, M.; Trendafilov, S.; Khanikaev, A.; Fallahazad, B. Experimental Demonstration of Phase Modulation and Motion Sensing Using Graphene-Integrated Metasurfaces Nano Lett. 2016, 16, 3607– 3615 DOI: 10.1021/acs.nanolett.6b00732
      21
      Experimental Demonstration of Phase Modulation and Motion Sensing Using Graphene-Integrated Metasurfaces
      Dabidian, Nima; Dutta-Gupta, Shourya; Kholmanov, Iskandar; Lai, Kueifu; Lu, Feng; Lee, Jongwon; Jin, Mingzhou; Trendafilov, Simeon; Khanikaev, Alexander; Fallahazad, Babak; Tutuc, Emanuel; Belkin, Mikhail A.; Shvets, Gennady
      Nano Letters (2016), 16 (6), 3607-3615CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Strong interaction of graphene with light accounts for 1 of its most remarkable properties: the ability to absorb 2.3% of the incident light's energy within a single at. layer. Free carrier injection via field-effect gating can dramatically vary the optical properties of graphene, thereby enabling fast graphene-based modulators of the light intensity. The very thinness of graphene makes it difficult to modulate the other fundamental property of the light wave: its optical phase. Considerable phase control can be achieved by integrating a single-layer graphene (SLG) with a resonant plasmonic metasurface that contains nanoscale gaps. By concg. the light intensity inside of the nanogaps, the metasurface dramatically increases the coupling of light to the SLG and enables control of the phase of the reflected mid-IR light by ≤55° via field-effect gating. Graphene-based phase modulators that maintain the amplitude of the reflected light essentially const. over most of the phase tuning range are exptl. demonstrated. Rapid nonmech. phase modulation enables a new exptl. technique, graphene-based laser interferometry, which was used to demonstrate motion detection with nanoscale precision. By the judicious choice of a strongly anisotropic metasurface the graphene-controlled phase shift of light can be rendered polarization-dependent. Using the exptl. measured phases for the 2 orthogonal polarizations, the polarization state of the reflected light can be by modulated by carrier injection into the SLG. These results pave the way for novel high-speed graphene-based optical devices and sensors such as polarimeters, ellipsometers, and frequency modulators.
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    22. 22
      Schall, D.; Neumaier, D.; Mohsin, M.; Chmielak, B.; Bolten, J.; Porschatis, C.; Prinzen, A.; Matheisen, C.; Kuebart, W.; Junginger, B. 50 GBit/s Photodetectors Based on Wafer-Scale Graphene for Integrated Silicon Photonic Communication Systems ACS Photonics 2014, 1, 781– 784 DOI: 10.1021/ph5001605
      22
      50 GBit/s photodetectors based on wafer-scale graphene for integrated silicon photonic communication systems
      Schall, Daniel; Neumaier, Daniel; Mohsin, Muhammad; Chmielak, Bartos; Bolten, Jens; Porschatis, Caroline; Prinzen, Andreas; Matheisen, Christopher; Kuebart, Wolfgang; Junginger, Bernhard; Templ, Wolfgang; Giesecke, Anna Lena; Kurz, Heinrich
      ACS Photonics (2014), 1 (9), 781-784CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
      Optical data links are the backbone of today's telecommunication infrastructure. The integration of electronic and optic components on one chip is one of the most attractive routes to further increase the system performance. Here, the authors present the fabrication of photodetectors based on CVD-grown graphene on silicon photonic waveguides. The devices operate bias-free in the C-band at 1550 nm and show an extrinsic -3 dB bandwidth of 41 GHz. The authors demonstrate that these detectors work at data rates up to 50 GBit/s with excellent signal integrity.
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    23. 23
      Degl’Innocenti, R.; Xiao, L.; Jessop, D. S.; Kindress, S. J.; Ren, Y.; Lin, H.; Zeitler, J. A.; Alexander-Webber, J. A.; Joyce, H. J.; Braeuninger-Weimer, P. Fast Room-Temperature Detection of Terahertz Quantum Cascade Lasers with Graphene-Loaded Bow-Tie Plasmonic Antenna Arrays ACS Photonics 2016, 3, 1747– 1753 DOI: 10.1021/acsphotonics.6b00405
      23
      Fast Room-Temperature Detection of Terahertz Quantum Cascade Lasers with Graphene-Loaded Bow-Tie Plasmonic Antenna Arrays
      Degl'Innocenti, Riccardo; Xiao, Long; Jessop, David S.; Kindness, Stephen J.; Ren, Yuan; Lin, Hungyen; Zeitler, J. Axel; Alexander-Webber, Jack A.; Joyce, Hannah J.; Braeuninger-Weimer, Philipp; Hofmann, Stephan; Beere, Harvey E.; Ritchie, David A.
      ACS Photonics (2016), 3 (10), 1747-1753CODEN: APCHD5; ISSN:2330-4022. (American Chemical Society)
      We present a fast room-temp. terahertz detector based on interdigitated bow-tie antennas contacting graphene. Highly efficient photodetection was achieved by using two metals with different work functions as the arms of a bow-tie antenna contacting graphene. Arrays of the bow-ties were fabricated in order to enhance the responsivity and coupling of the incoming light to the detector, realizing an efficient imaging system. The device has been characterized and tested with a terahertz quantum cascade laser emitting in single frequency around 2 THz, yielding a responsivity of ∼34 μA/W and a noise-equiv. power of ∼1.5 × 10-7 W/Hz1/2.
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    24. 24
      Dumcenco, D.; Ovchinnikov, D.; Marinov, K.; Lazić, P.; Gibertini, M.; Marzari, N.; Lopez Sanchez, P.; Kung, Y.-C.; Krasnozhon, D.; Chen, W.-W. Large-Area Epitaxial Mono Layer MoS2 ACS Nano 2015, 9, 4611– 4620 DOI: 10.1021/acsnano.5b01281
      There is no corresponding record for this reference.
    25. 25
      Molina-Mendoza, A. J.; Lado, J. L.; Island, J. O.; Niño, M. A.; Aballe, L.; Foerster, M.; Bruno, F. Y.; López-Moreno, A.; Vaquero-Garzon, L.; van der Zant, H. S. J Centimeter-Scale Synthesis of Ultrathin Layered MoO3 by van der Waals Epitaxy Chem. Mater. 2016, 28, 4042– 4051 DOI: 10.1021/acs.chemmater.6b01505
      25
      Centimeter-Scale Synthesis of Ultrathin Layered MoO3 by van der Waals Epitaxy
      Molina-Mendoza, Aday J.; Lado, Jose L.; Island, Joshua O.; Nino, Miguel Angel; Aballe, Lucia; Foerster, Michael; Bruno, Flavio Y.; Lopez-Moreno, Alejandro; Vaquero-Garzon, Luis; van der Zant, Herre S. J.; Rubio-Bollinger, Gabino; Agrait, Nicolas; Perez, Emilio M.; Fernandez-Rossier, Joaquin; Castellanos-Gomez, Andres
      Chemistry of Materials (2016), 28 (11), 4042-4051CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      We report on the large-scale synthesis of highly oriented ultrathin MoO3 layers using a simple and low-cost atm. pressure, van der Waals epitaxy growth on muscovite mica substrates. By this method, we are able to synthesize high quality centimeter-scale MoO3 crystals with thicknesses ranging from 1.4 nm (two layers) up to a few nanometers. The crystals can be easily transferred to an arbitrary substrate (such as SiO2) by a deterministic transfer method and be extensively characterized to demonstrate the high quality of the resulting crystal. We also study the electronic band structure of the material by d. functional calcns. Interestingly, the calcns. demonstrate that bulk MoO3 has a rather weak electronic interlayer interaction, and thus, it presents a monolayer-like band structure. Finally, we demonstrate the potential of this synthesis method for optoelectronic applications by fabricating large-area field-effect devices (10 μm × 110 μm in lateral dimensions) and find responsivities of 30 mA W-1 for a laser power d. of 13 mW cm-2 in the UV region of the spectrum and also as an electron acceptor in a MoS2-based field-effect transistor.
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    26. 26
      Han, P.; Akagi, K.; Canova, F. F.; Shimizu, R.; Oguchi, H.; Shiraki, S.; Weiss, P. S.; Asao, N.; Hitosugi, T. Self-Assembly Strategy for Fabricating Connected Graphene Nanoribbons ACS Nano 2015, 9, 12035– 12044 DOI: 10.1021/acsnano.5b04879
      26
      Self-Assembly Strategy for Fabricating Connected Graphene Nanoribbons
      Han, Patrick; Akagi, Kazuto; Federici Canova, Filippo; Shimizu, Ryota; Oguchi, Hiroyuki; Shiraki, Susumu; Weiss, Paul S.; Asao, Naoki; Hitosugi, Taro
      ACS Nano (2015), 9 (12), 12035-12044CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      We use self-assembly to fabricate and to connect precise graphene nanoribbons end to end. Combining scanning tunneling microscopy, Raman spectroscopy, and d. functional theory, we characterize the chem. and electronic aspects of the interconnections between ribbons. We demonstrate how the substrate effects of our self-assembly can be exploited to fabricate graphene structures connected to desired electrodes.
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    27. 27
      Yang, Y.; Fu, Q.; Li, H.; Wei, M.; Xiao, J.; Wei, W.; Bao, X. Creating a Nanospace under an h-BN Cover for Adlayer Growth on Nickel(111) ACS Nano 2015, 9, 11589– 11598 DOI: 10.1021/acsnano.5b05509
      27
      Creating a Nanospace under an h-BN Cover for Adlayer Growth on Nickel(111)
      Yang, Yang; Fu, Qiang; Li, Haobo; Wei, Mingming; Xiao, Jianping; Wei, Wei; Bao, Xinhe
      ACS Nano (2015), 9 (12), 11589-11598CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Heterostructures of two-dimensional (2D) at. crystals have attracted increasing attention, while fabrication of the 2D stacking structures remains a challenge. In this work, we present a route toward formation of 2D heterostructures via confined growth of a 2D adlayer underneath the other 2D overlayer. Taking a hexagonal boron nitride (h-BN) monolayer on Ni(111) as a model system, both epitaxial and nonepitaxial h-BN islands have been identified on the Ni surface. Surface science studies combined with d. functional theory calcns. reveal that the nonepitaxial h-BN islands interact weakly with the Ni(111) surface, which creates a 2D nanospace underneath the h-BN islands. An addnl. h-BN or graphene layer can be grown in the space between the nonepitaxial h-BN islands and Ni(111) surface, forming h-BN/h-BN bilayer structures and h-BN/graphene heterostructures. These results suggest that confined growth under 2D covers may provide an effective route to obtain stacks of 2D at. crystals.
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    28. 28
      Lin, Y.-C.; Komsa, H.-P.; Yeh, C.-H.; Björkman, T.; Liang, Z.-Y.; Ho, C.-H.; Huang, Y.-S.; Chio, P.-W.; Krasheninnikov, A. V.; Suenaga, K. Single-Layer ReS2: Two-Dimensional Semiconductor with Tunable In-Plane Anisotropy ACS Nano 2015, 9, 11249– 11257 DOI: 10.1021/acsnano.5b04851
      28
      Single-Layer ReS2: Two-Dimensional Semiconductor with Tunable In-Plane Anisotropy
      Lin, Yung-Chang; Komsa, Hannu-Pekka; Yeh, Chao-Hui; Bjorkman, Torbjorn; Liang, Zheng-Yong; Ho, Ching-Hwa; Huang, Ying-Sheng; Chiu, Po-Wen; Krasheninnikov, Arkady V.; Suenaga, Kazu
      ACS Nano (2015), 9 (11), 11249-11257CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Rhenium disulfide (ReS2) and diselenide (ReSe2), the group 7 transition metal dichalcogenides (TMDs), are known to have a layered at. structure showing an in-plane motif of diamond-shaped-chains (DS-chains) arranged in parallel. Using a combination of TEM and transport measurements, the authors demonstrate here the direct correlation of electron transport anisotropy in single-layered ReS2 with the at. orientation of the DS-chains, as also supported by the authors' d. functional theory calcns. Further the direction of conducting channels in ReS2 and ReSe2 can be controlled by electron beam irradn. at elevated temps. and follows the strain induced to the sample. Also, high chalcogen deficiency can induce a structural transformation to a nonstoichiometric phase, which is again strongly direction-dependent. This tunable in-plane transport behavior opens up great avenues for creating nanoelectronic circuits in 2-dimensional materials.
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    29. 29
      Zhou, X.; Shi, J.; Qi, Y.; Liu, M.; Ma, D.; Zhang, Y.; Ji, Q.; Zhang, Z.; Li, C.; Liu, Z. Periodic Modulation of the Doping Level in Striped MoS2 Superstructures ACS Nano 2016, 10, 3461– 3468 DOI: 10.1021/acsnano.5b07545
      29
      Periodic Modulation of the Doping Level in Striped MoS2 Superstructures
      Zhou, Xiebo; Shi, Jianping; Qi, Yue; Liu, Mengxi; Ma, Donglin; Zhang, Yu; Ji, Qingqing; Zhang, Zhepeng; Li, Cong; Liu, Zhongfan; Zhang, Yanfeng
      ACS Nano (2016), 10 (3), 3461-3468CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Although the recently discovered monolayer transition metal dichalcogenides exhibit novel electronic and optical properties, fundamental phys. issues such as the quasiparticle bandgap tunability and the substrate effects remain undefined. Herein, we present the report of a quasi-one-dimensional periodically striped superstructure for monolayer MoS2 on Au(100). The formation of the unique striped superstructure is found to be mainly modulated by the symmetry difference between MoS2 and Au(100) and their lattice mismatch. More intriguingly, we find that the monolayer MoS2 is heavily n-doped on the Au(100) facet with a bandgap of 1.3 eV, and the Fermi level is upshifted by ∼0.10 eV on the ridge (∼0.2 eV below the conduction band) in contrast to the valley regions (∼0.3 eV below the conduction band) of the striped patterns after high-temp. sample annealing process. This tunable doping effect is considered to be caused by the different defect densities over the ridge/valley regions of the superstructure. Addnl., an obvious bandgap redn. is obsd. in the vicinity of the domain boundary for monolayer MoS2 on Au(100). This work should therefore inspire intensive explorations of adlayer-substrate interactions, the defects, and their effects on band-structure engineering of monolayer MoS2.
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    30. 30
      Wang, S. S.; Lee, G. D.; Lee, S.; Yoon, E.; Warner, J. H. Detailed Atomic Reconstruction of Extended Line Defects in Monolayer MoS2 ACS Nano 2016, 10, 5419– 5430 DOI: 10.1021/acsnano.6b01673
      30
      Detailed Atomic Reconstruction of Extended Line Defects in Monolayer MoS2
      Wang, Shanshan; Lee, Gun-Do; Lee, Sungwoo; Yoon, Euijoon; Warner, Jamie H.
      ACS Nano (2016), 10 (5), 5419-5430CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      We study the detailed bond reconstructions that occur in S vacancies within monolayer MoS2 using a combination of aberration-cor. transmission electron microscopy, d. functional theory (DFT), and multislice image simulations. Removal of a single S atom causes little perturbation to the surrounding MoS2 lattice, whereas the loss of two S atoms from the same at. column causes a measurable local contraction. Aggregation of S vacancies into linear line defects along the zigzag direction results in larger lattice compression that is more pronounced as the length of the line defect increases. For the case of two rows of S line vacancies, we find two different types of S atom reconstructions with different amts. of lattice compression. Increasing the width of line defects leads to nanoscale regions of reconstructed MoS2 that are shown by DFT to behave as metallic channels. These results provide important insights into how defect structures could be used for creating metallic tracks within semiconducting monolayer MoS2 films for future applications in electronics and optoelectronics.
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    31. 31
      Kim, S.; Russell, M.; Kulkarni, D. D.; Henry, M.; Kim, S.; Naik, R. R.; Voevodin, A. A.; Jang, S. S.; Tsukruk, V. V.; Fedorov, A. G. Activating ″Invisible″ Glue: Using Electron Beam for Enhancement of Interfacial Properties of Graphene-Metal Contact ACS Nano 2016, 10, 1042– 1049 DOI: 10.1021/acsnano.5b06342
      There is no corresponding record for this reference.
    32. 32
      Woomer, A. H.; Farnsworth, T. W.; Hu, J.; Wells, R. A.; Donley, C. L.; Warren, S. C. Phosphorene: Synthesis, Scale-Up, and Quantitative Optical Spectroscopy ACS Nano 2015, 9, 8869– 8884 DOI: 10.1021/acsnano.5b02599
      32
      Phosphorene: Synthesis, Scale-Up, and Quantitative Optical Spectroscopy
      Woomer, Adam H.; Farnsworth, Tyler W.; Hu, Jun; Wells, Rebekah A.; Donley, Carrie L.; Warren, Scott C.
      ACS Nano (2015), 9 (9), 8869-8884CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Phosphorene, a 2-dimensional (2D) monolayer of black P, has attracted considerable theor. interest, although the exptl. realization of monolayer, bilayer, and few-layer flakes was a significant challenge. Conditions for liq. exfoliation to achieve the 1st large-scale prodn. of monolayer, bilayer, and few-layer P, was systematically surveyed with exfoliation demonstrated at the 10 g scale. A rapid approach for quantifying the thickness of 2D P is described, and monolayer and few-layer flakes produced by the approach are cryst. and unoxidized, while air exposure leads to rapid oxidn. and the prodn. of acid. With large quantities of 2D P now available, the 1st quant. measurements of the material's absorption edge, which is nearly identical to the material's band gap under the exptl. conditions, was performed as a function of flake thickness. The interpretation of the absorbance spectrum relies on an anal. method introduced allowing the accurate detn. of the absorption edge in polydisperse samples of quantum-confined semiconductors. Using this method, the band gap of black P increased from 0.33 ± 0.02 eV in bulk to 1.88 ± 0.24 eV in bilayers, a range that is larger than that of any other 2D material. A higher-energy optical transition (VB-1 to CB) was quantified, which changes from 2.0 eV in bulk to 3.23 eV in bilayers. Several methods are described for producing and analyzing 2D P while also yielding a class of 2D materials with unprecedented optoelectronic properties.
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    33. 33
      Yang, Z. H.; Liang, H.; Wang, X.; Ma, X.; Zhang, T.; Yang, Y.; Xie, L.; Chen, D.; Long, Y.; Chen, J. Atom-Thin SnS2-xSex with Adjustable Compositions by Direct Liquid Exfoliation from Single Crystals ACS Nano 2016, 10, 755– 762 DOI: 10.1021/acsnano.5b05823
      There is no corresponding record for this reference.
    34. 34
      Harvey, A.; Backes, C.; Gholamvand, Z.; Hanlon, D.; McAteer, D.; Nerl, H. C.; McGuire, E.; Seral-Ascaso, A.; Ramasse, Q. M.; McEvoy, N. Preparation of Gallium Sulfide Nanosheets by Liquid Exfoliation and Their Application As Hydrogen Evolution Catalysts Chem. Mater. 2015, 27, 3483– 3493 DOI: 10.1021/acs.chemmater.5b00910
      34
      Preparation of Gallium Sulfide Nanosheets by Liquid Exfoliation and Their Application As Hydrogen Evolution Catalysts
      Harvey, Andrew; Backes, Claudia; Gholamvand, Zahra; Hanlon, Damien; McAteer, David; Nerl, Hannah C.; McGuire, Eva; Seral-Ascaso, Andres; Ramasse, Quentin M.; McEvoy, Niall; Winters, Sinead; Berner, Nina C.; McCloskey, David; Donegan, John F.; Duesberg, Georg S.; Nicolosi, Valeria; Coleman, Jonathan N.
      Chemistry of Materials (2015), 27 (9), 3483-3493CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Large quantities of gallium sulfide (GaS) nanosheets have been produced by liq. exfoliation of layered GaS powder. The exfoliation was achieved by sonication of the powder in suitable solvents. The variation of dispersed concn. with solvent was consistent with classical soln. thermodn. and showed successful solvents to be those with Hildebrand soly. parameters close to 21.5 MPa1/2. In this way, nanosheets could be produced at concns. of up to ∼0.2 mg/mL with lateral sizes and thicknesses of 50-1000 nm and 3-80 layers, resp. The nanosheets appeared to be relatively defect-free although oxygen was obsd. in the vicinity of the edges. Using controlled centrifugation techniques, it was possible to prep. dispersions contg. size-selected nanosheets. Spectroscopic measurements showed the optical properties of the dispersions to vary strongly with nanosheet size, allowing the elucidation of spectroscopic metrics for in situ estn. of nanosheet size and thickness. These techniques allow the prodn. of nanosheets with controlled sizes, which will be important for certain applications. Films of GaS nanosheets of three different sizes were prepd. for use as hydrogen evolution electrocatalysts. A clear correlation between performance and size was found, showing small nanosheets to be more effective. This is consistent with the catalytically active sites residing on the nanosheet edges.
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    35. 35
      Dimiev, A. M.; Ceriotti, G.; Metzger, A.; Kim, N. D.; Tour, J. M. Chemical Mass Production of Graphene Nanoplatelets in Similar to 100% Yield ACS Nano 2016, 10, 274– 279 DOI: 10.1021/acsnano.5b06840
      There is no corresponding record for this reference.
    36. 36
      He, P.; Sun, J.; Tian, S.; Yang, S.; Ding, S.; Ding, G.; Xie, X.; Jiang, M. Processable Aqueous Dispersions of Graphene Stabilized by Graphene Quantum Dots Chem. Mater. 2015, 27, 218– 226 DOI: 10.1021/cm503782p
      36
      Processable Aqueous Dispersions of Graphene Stabilized by Graphene Quantum Dots
      He, Peng; Sun, Jing; Tian, Suyun; Yang, Siwei; Ding, Shengju; Ding, Guqiao; Xie, Xiaoming; Jiang, Mianheng
      Chemistry of Materials (2015), 27 (1), 218-226CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      Dispersing graphene in various solvents is one of the key technologies toward the practical applications of graphene. Herein, using graphene quantum dots (GQDs) as stabilizer, aq. dispersions of graphene with good stability were demonstrated by directly dispersing commercialized graphene powder into water. Amazingly, 100 mg of graphene powder could be stabilized by an av. of merely 7.8 mg GQDs to form aq. dispersions with a max. concn. of up to 0.4 mg/mL and stability at least 3 mo. The introduction of a small amt. of GQDs also allowed for the fabrication of water-redispersible graphene slurry and powder, which would largely facilitate the transportation and applications of graphene. The mechanism of the GQDs stabilized graphene in water was proposed and exptl. verified through UV-visible spectroscopy and zeta potential measurements. Moreover, flexible graphene papers directly assembled from the water-dispersible graphene exhibited controllable thickness, good cond., and acceptable strength. With properties not compromised by GQDs, water-dispersible graphene is expected to be widely applicable in elec. and electrochem. device fields.
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    37. 37
      Chua, C. K.; Sofer, Z.; Šimek, P.; Jankovský, O.; Klímová, K.; Bakardjieva, S.; Kučková, S. H.; Pumera, M. Synthesis of Strongly Fluorescent Graphene Quantum Dots by Cage-Opening Buckminsterfullerene ACS Nano 2015, 9, 2548– 2555 DOI: 10.1021/nn505639q
      37
      Synthesis of Strongly Fluorescent Graphene Quantum Dots by Cage-Opening Buckminsterfullerene
      Chua, Chun Kiang; Sofer, Zdenek; Simek, Petr; Jankovsky, Ondrej; Klimova, Katerina; Bakardjieva, Snejana; Hrdlickova Kuckova, Stepanka; Pumera, Martin
      ACS Nano (2015), 9 (3), 2548-2555CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Graphene quantum dots is a class of graphene nanomaterials with exceptional luminescence properties. Precise dimension control of graphene quantum dots produced by chem. synthesis methods is currently difficult to achieve and usually provides a range of sizes from 3 to 25 nm. Fullerene C60 is used as starting material, due to its well-defined dimension, to produce very small graphene quantum dots (∼2-3 nm). Treatment of fullerene C60 with a mixt. of strong acid and chem. oxidant induced the oxidn., cage-opening, and fragmentation processes of fullerene C60. The synthesized quantum dots were characterized and supported by LDI-TOF MS, TEM, XRD, XPS, AFM, STM, FTIR, DLS, Raman spectroscopy, and luminescence analyses. The quantum dots remained fully dispersed in aq. suspension and exhibited strong luminescence properties, with the highest intensity at 460 nm under a 340. nm excitation wavelength. Further chem. treatments with hydrazine hydrate and hydroxylamine resulted in red- and blue-shift of the luminescence, resp.
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    38. 38
      Anasori, B.; Xie, Y.; Beidaghi, M.; Lu, J.; Hosler, B. C.; Hultman, L.; Kent, P. R. C.; Gogotsi, Y.; Barsoum, M. W. Two-Dimensional, Ordered, Double Transition Metals Carbides (MXenes) ACS Nano 2015, 9, 9507– 9516 DOI: 10.1021/acsnano.5b03591
      38
      Two-Dimensional, Ordered, Double Transition Metals Carbides (MXenes)
      Anasori, Babak; Xie, Yu; Beidaghi, Majid; Lu, Jun; Hosler, Brian C.; Hultman, Lars; Kent, Paul R. C.; Gogotsi, Yury; Barsoum, Michel W.
      ACS Nano (2015), 9 (10), 9507-9516CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      The higher the chem. diversity and structural complexity of two-dimensional (2D) materials, the higher the likelihood they possess unique and useful properties. Herein, d. functional theory (DFT) was used to predict the existence of two new families of 2-dimensional ordered, carbides (MXenes), M'2M''C2 and M'2M''2C3, where M' and M'' are two different early transition metals. In these solids, M' layers sandwich M'' carbide layers. By synthesizing Mo2TiC2Tx, Mo2Ti2C3Tx, and Cr2TiC2Tx (T is a surface termination), the authors validated the DFT predictions. Since the Mo and Cr atoms are on the outside, they control the 2-dimensional flakes' chem. and electrochem. properties. The latter was proven by showing quite different electrochem. behavior of Mo2TiC2Tx and Ti3C2Tx. This work further expands the family of 2-dimensional materials, offering addnl. choices of structures, chemistries, and ultimately useful properties.
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    39. 39
      Suzuki, N.; Wang, Y.; Elvati, P.; Qu, Z.-B.; Kim, K.; Jiang, S.; Baumeister, E.; Lee, J.; Yeom, B.; Bahng, J. H. Chiral Graphene Quantum Dots ACS Nano 2016, 10, 1744– 1755 DOI: 10.1021/acsnano.5b06369
      39
      Chiral Graphene Quantum Dots
      Suzuki, Nozomu; Wang, Yichun; Elvati, Paolo; Qu, Zhi-Bei; Kim, Kyoungwon; Jiang, Shuang; Baumeister, Elizabeth; Lee, Jaewook; Yeom, Bongjun; Bahng, Joong Hwan; Lee, Jaebeom; Violi, Angela; Kotov, Nicholas A.
      ACS Nano (2016), 10 (2), 1744-1755CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Covalent attachment of L/D-cysteine moieties to the edges of graphene quantum dots (GQDs) leads to their helical buckling due to chiral interactions at the crowded edges. CD spectra of the GQDs revealed bands at ∼210-220 and 250-265 nm that changed their signs for different chirality of the cysteine edge ligands. The high-energy chiroptical peaks at 210-220 nm correspond to the hybridized MOs involving the chiral center of amino acids and atoms of graphene edges. Diverse exptl. and modeling data, including d. functional theory calcns. of CD spectra with probabilistic distribution of GQD isomers, indicate that the band at 250-265 nm originates from the 3-dimensional twisting of the graphene sheet and can be attributed to the chiral excitonic transitions. The pos. and neg. low-energy CD bands correspond to the left and right helicity of GQDs, resp. Exposure of liver HepG2 cells to L/D-GQDs reveals their general biocompatibility and a noticeable difference in the toxicity of the stereoisomers. Mol. dynamics simulations demonstrated that D-GQDs have a stronger tendency to accumulate within the cellular membrane than L-GQDs. Emergence of nanoscale chirality in GQDs decorated with biomols. is expected to be a general stereochem. phenomenon for flexible sheets of nanomaterials.
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    40. 40
      Park, S. H.; Kim, H.-K.; Yoon, S.-B.; Lee, C.-W.; Ahn, D.; Lee, S.-I.; Roh, K. C.; Kim, K.-B. Spray-Assisted Deep-Frying Process for the In Situ Spherical Assembly of Graphene for Energy-Storage Devices Chem. Mater. 2015, 27, 457– 465 DOI: 10.1021/cm5034244
      40
      Spray-Assisted Deep-Frying Process for the In Situ Spherical Assembly of Graphene for Energy-Storage Devices
      Park, Sang-Hoon; Kim, Hyun-Kyung; Yoon, Seung-Beom; Lee, Chang-Wook; Ahn, Dongjoon; Lee, Sang-Ick; Roh, Kwang Chul; Kim, Kwang-Bum
      Chemistry of Materials (2015), 27 (2), 457-465CODEN: CMATEX; ISSN:0897-4756. (American Chemical Society)
      To take full advantage of graphene in macroscale devices, it is important to integrate two-dimensional graphene nanosheets into a micro/macrosized structure that can fully utilize graphene's nanoscale characteristics. To this end, a novel spray-assisted self-assembly process is developed to create a spherically integrated graphene microstructure (graphene microsphere) using a high-temp. org. solvent in a manner reminiscent of deep-frying. This graphene microsphere improves the electrochem. performance of supercapacitors, in contrast to nonassembled graphene, which is attributed to its structural and pore characteristics. Furthermore, this synthesis method can also produce an effective graphene-based hybrid microsphere structure, in which Si nanoparticles are efficiently entrapped by graphene nanosheets during the assembly process. When used in a Li-ion battery, this material can provide a more suitable framework to buffer the considerable vol. change that occurs in Si during electrochem. lithiation/delithiation, thereby improving cycling performance. This simple and versatile self-assembly method is therefore directly relevant to the future design and development of practical graphene-based electrode materials for various energy-storage devices.
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    41. 41
      Kim, M.; Lee, C.; Seo, Y. D.; Cho, S.; Kim, J.; Lee, G.; Kim, Y. K.; Jang, J. Fabrication of Various Conducting Polymers Using Graphene Oxide as a Chemical Oxidant Chem. Mater. 2015, 27, 6238– 6248 DOI: 10.1021/acs.chemmater.5b01408
      There is no corresponding record for this reference.
    42. 42
      Luo, J.; Gao, J.; Wang, A.; Huang, J. Bulk Nanostructured Materials Based on Two-Dimensional Building Blocks: A Roadmap ACS Nano 2015, 9, 9432– 9436 DOI: 10.1021/acsnano.5b05259
      42
      Bulk Nanostructured Materials Based on Two-Dimensional Building Blocks: A Roadmap
      Luo, Jiayan; Gao, Jun; Wang, Aoxuan; Huang, Jiaxing
      ACS Nano (2015), 9 (10), 9432-9436CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      The family of two-dimensional (2D) materials, in particular MXenes, can now be greatly expanded based on a new "double metal" strategy as reported by Anasori, Xie, and Beidaghi et al. in this issue of ACS Nano. Now that a diverse array of well-defined nanoscale building blocks, esp. the 2D systems, has become available, we are better prepd. to think about scaling up nanomaterials in the broader context of materials science and engineering. In this Perspective, we construct a roadmap for assembling nanoscale building blocks into bulk nanostructured materials, and define some of the crit. challenges and goals. Two-dimensional sheets are uniquely well-suited in this roadmap for constructing dense, bulk-sized samples with scalable material performance or interesting emergent properties.
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