The study of first-order structural transformations has been of great interest to scientists in many disciplines. Expectations from phase-transition theory are that the system fluctuates between two equilibrium structures near the... more
The study of first-order structural transformations has been of great interest to scientists in many disciplines. Expectations from phase-transition theory are that the system fluctuates between two equilibrium structures near the transition point and that the region of transition broadens in small crystals. We report the direct observation of structural fluctuations within a single nanocrystal using transmission electron microscopy. We observed trajectories of structural transformations in individual nanocrystals with atomic resolution, which reveal details of the fluctuation dynamics, including nucleation, phase propagation, and pinning of structural domains by defects. Such observations provide crucial insight for the understanding of microscopic pathways of phase transitions.
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Chemistry, Science, Transmission Electron Microscopy, Medicine, Multidisciplinary, and 11 morePhase transition, First-Order Logic, Nanorod, Structural Transformation, Fluctuations, First Order Logic, Crystal Defects, Surface Energy, Music Information Dynamics, Atomic Resolution, and Fast Fourier Transforms
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This paper describes an approach to retrieve the three-dimensional atomic structure of a nanocrystalline particle from the reconstructed electron exit wave function in a single projection direction. The method employs wave propagation to... more
This paper describes an approach to retrieve the three-dimensional atomic structure of a nanocrystalline particle from the reconstructed electron exit wave function in a single projection direction. The method employs wave propagation to determine the local exit surface of each atomic column together with its mass. The exit wave in between colums is used as internal calibration so as to remove the background noise and improve the precision to the level of single atom sensitivity. The validity of the approach is tested with exit wave functions of a gold wedge reconstructed from simulated images containing different levels of noise.
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The Transmission Electron Aberration-corrected Microscope (TEAM) project was initiated by the US Department of Energy as a collaborative effort to redesign the electron microscope around aberration-corrected optics [1], and is aimed at... more
The Transmission Electron Aberration-corrected Microscope (TEAM) project was initiated by the US Department of Energy as a collaborative effort to redesign the electron microscope around aberration-corrected optics [1], and is aimed at achieving 50 pm resolution. But the ability to resolve deep sub-Ångstrom spacing entails a number of unresolved questions that can now be addressed. Among them is an ongoing debate about the physical meaning of resolution. Traditional strategies include the recording of Young’s fringes, the detection of image Fourier components from STEM images, the demonstration of a suitable peak separation in periodic lattices or signal width measurements from images of single atoms, to name a few. The drawback is that seemingly conflicting results are produced [e.g. 2]. Further, these methods define resolution through a selectable object, unlike light microscopy where resolution is instrument-defined. Two limitations of this approach are electron channeling [3, 4] and elastic scattering at single crystals [5]. The TEAM Project adopted a pragmatic view of information transfer below 50 pm: detecting Young’s fringes in TEM and (660) image Fourier components from gold (111) STEM images at 48 pm. Recently the TEAM 0.5 prototype microscope achieved this goal [1].
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ABSTRACTNovel Fe2O3 nanowires have been successfully synthesized by a simple oxidation process of pure iron. The microstructure of the Fe2O3 nanowires have been systematically investigated by means of X-ray diffraction, scanning electron... more
ABSTRACTNovel Fe2O3 nanowires have been successfully synthesized by a simple oxidation process of pure iron. The microstructure of the Fe2O3 nanowires have been systematically investigated by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM). The investigated materials are found to be stoichiometric rhombohedral α-Fe2O3 with typical diameters of 20–80 nm and lengths up to 20 μm. In addition to known single crystal Fe2O3 nanowires, a great amount of novel bicrystalline nanowires were found with ellipsoidal heads. Investigations indicate that most of the bicrystalline nanowires are twins and their orientation relationship is obtained to be (−1, 1, 10)M//(−1, 1, 10)T, [110]M//[-1-10]T. High resolution TEM with numerical reconstruction of the electron exit wave was used to investigated the atomic structure of the micro-twins. Their growth mechanism is briefly discussed on the basis of solid phase growth process.
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This contribution reviews the current status of sub Ångstrom electron microscopy. High Resolution Transmission Electron Microscopy (HRTEM) and Scanning Transmission Electron Microscopy (STEM) are considered and compared for imaging... more
This contribution reviews the current status of sub Ångstrom electron microscopy. High Resolution Transmission Electron Microscopy (HRTEM) and Scanning Transmission Electron Microscopy (STEM) are considered and compared for imaging applications. While both techniques provide comparable sub Ångstrom resolution around 0.8Å noise levels and chemical discrimination are dissimilar, which result in complementary characteristics for the detection of different elements. In particular, the ability to detect single atoms benefits greatly from the ongoing resolution enhancement and corrections of lens aberrations. As a result it is feasible aiming at single atom analyses in three dimensions.
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ABSTRACTGaN films were grown on sapphire substrates at temperatures below 725 °C utilizing a Constricted Glow Discharge plasma source. A three dimensional growth mode is observed at such low growth temperatures resulting in films that are... more
ABSTRACTGaN films were grown on sapphire substrates at temperatures below 725 °C utilizing a Constricted Glow Discharge plasma source. A three dimensional growth mode is observed at such low growth temperatures resulting in films that are composed of individual but oriented grains. The strain that originates from the growth on the lattice mismatched substrate with a different thermal expansion coefficient is utilized to influence the thin film growth. The strain can be largely altered by the growth of suitable buffer layers. Thereby, optical and structural film properties can be engineered. It is argued that the surface diffusion of Ga ad-atoms is affected by engineering the strain. Alternatively, surface diffusion can be influenced by surfactants. It is demonstrated that the use of bismuth as a surfactant allows to modify the surface morphology of the GaN films that reflects the size of the grains in the films. The results suggest that a substantial increase of the oriented grain s...
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The functional properties of transition metal dichalcogenides (TMDs) may be promoted by the inclusion of other elements. Here, we studied the local stoichiometry of single cobalt promoter atoms in an industrial-style MoS2-based... more
The functional properties of transition metal dichalcogenides (TMDs) may be promoted by the inclusion of other elements. Here, we studied the local stoichiometry of single cobalt promoter atoms in an industrial-style MoS2-based hydrotreating catalyst. Aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy show that the Co atoms occupy sites at the (-100) S edge terminations of the graphite-supported MoS2 nanocrystals in the catalyst. Specifically, each Co atom has four neighboring S atoms that are arranged in a reconstructed geometry, which reflects an equilibrium state. The structure agrees with complementary studies of catalysts that were prepared under vastly different conditions and on other supports. In contrast, a small amount of residual Fe in the graphite is found to compete for the S edge sites, so that promotion by Co is strongly sensitive to the purity of the raw materials. The present single-atom-sensitive analytical method t...
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The use of bright field TEM for tomography in physical sciences is often hampered by Bragg contributions. In Figure 1 it is illustrated that the morphology of Pt nanoparticles (5-7 nm) is well reconstructed, but artificial cavities are... more
The use of bright field TEM for tomography in physical sciences is often hampered by Bragg contributions. In Figure 1 it is illustrated that the morphology of Pt nanoparticles (5-7 nm) is well reconstructed, but artificial cavities are observed inside the 3D reconstructions of the ...
ABSTRACTIn this study we examine the immediate interface between matrix grains and the amorphous intergranular film in a Si3N4 ceramic doped with rare-earth oxides La2O3, Sm2O3, Er2O3, Yb2O3 and Lu2O3, extracting unique structural and... more
ABSTRACTIn this study we examine the immediate interface between matrix grains and the amorphous intergranular film in a Si3N4 ceramic doped with rare-earth oxides La2O3, Sm2O3, Er2O3, Yb2O3 and Lu2O3, extracting unique structural and atomic bonding information. In particular, we relate the structure of the interface to the ionic size and electronic structure of the rare-earth elements and the presence of oxygen in the intergranular film. We relate these results to the measured fracture toughness.
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Although the physics of materials at surfaces and edges has been extensively studied, the movement of individual atoms at an isolated edge has not been directly observed in real time. With a transmission electron aberration–corrected... more
Although the physics of materials at surfaces and edges has been extensively studied, the movement of individual atoms at an isolated edge has not been directly observed in real time. With a transmission electron aberration–corrected microscope capable of simultaneous atomic spatial resolution and 1-second temporal resolution, we produced movies of the dynamics of carbon atoms at the edge of a hole in a suspended, single atomic layer of graphene. The rearrangement of bonds and beam-induced ejection of carbon atoms are recorded as the hole grows. We investigated the mechanism of edge reconstruction and demonstrated the stability of the “zigzag” edge configuration. This study of an ideal low-dimensional interface, a hole in graphene, exhibits the complex behavior of atoms at a boundary.
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Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007
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Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.
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Transmission electron microscopy (TEM) analysis showed that the grain-boundary thin layer is a kind of Nd-rich phase. The high-resolution micrographs of the grain-boundary thin layer were obtained. The lattice constant c of the matrix... more
Transmission electron microscopy (TEM) analysis showed that the grain-boundary thin layer is a kind of Nd-rich phase. The high-resolution micrographs of the grain-boundary thin layer were obtained. The lattice constant c of the matrix phase is measured as 12.2 A˚. The grain-boundary thin layer is coherent with the matrix.
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Engineering, Materials Engineering, Physics, Condensed Matter Physics, Materials Science, and 13 moreApplied Physics, Transmission Electron Microscopy, Mathematical Sciences, High Resolution Transmission Electron Microscopy, Physical sciences, Magnetic Properties, Iron, High Resolution, Grain Boundary, Microstructures, Biochemistry and cell biology, Electron Microscope, and Thin Layer
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ABSTRACT S2-basierte Nanokatalysatoren werden zur Hydrodesulfurierung in Ölraffinerien eingesetzt. In der Zuschrift auf S. 10 335 ff. präsentieren S. Helveg et al. einzelatomempfindliche Transmissionselektronenmikroskopieaufnahmen... more
ABSTRACT S2-basierte Nanokatalysatoren werden zur Hydrodesulfurierung in Ölraffinerien eingesetzt. In der Zuschrift auf S. 10 335 ff. präsentieren S. Helveg et al. einzelatomempfindliche Transmissionselektronenmikroskopieaufnahmen industriell hergestellter Nanokatalysatoren. Die beobachteten katalytisch wichtigen Kantenabschlüsse stimmen mit Voraussagen aus Modellstudien überein. Bild: P. Møller und S. Nygaard, Haldor Topsøe A/S.
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... Atomic-Scale Edge Structures on Industrial-Style MoS 2 Nanocatalysts †. Lars P. Hansen 1 ,; Quentin M. Ramasse 2 ,; Christian Kisielowski 3 ,; Michael Brorson 1 ,; Erik Johnson 4 ,; Henrik Topsøe 1 ,; Stig Helveg 1,*. ... Moses, JK... more
... Atomic-Scale Edge Structures on Industrial-Style MoS 2 Nanocatalysts †. Lars P. Hansen 1 ,; Quentin M. Ramasse 2 ,; Christian Kisielowski 3 ,; Michael Brorson 1 ,; Erik Johnson 4 ,; Henrik Topsøe 1 ,; Stig Helveg 1,*. ... Moses, JK Nørskov, H. Topsøe, Catal. Today 2008, 130, 86–96 ...
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Materials Science, Graphene, Crystallization, Scanning Transmission Electron Microscopy, Nanotechnology, and 15 moreMedicine, Multidisciplinary, Graphite, Nanostructures, Grain, Grain Boundary, Polycrystalline, Particle Size, Length scale, Molecular Conformation, Materials Testing, Graphene Sheets, Crystallite, Direct Mapping, and dark field microscopy
ABSTRACTFePt nanoparticles are promising materials for high-density magnetic data storage media [1] and bio-medical applications such as drug-targeting and hyperthermia [2]. To understand their magnetic properties [3] it is essential to... more
ABSTRACTFePt nanoparticles are promising materials for high-density magnetic data storage media [1] and bio-medical applications such as drug-targeting and hyperthermia [2]. To understand their magnetic properties [3] it is essential to get insights into the lattice structure of isolated nanoparticles which influence the magnetic behavior.Typically, lattice fringes are observed with high-resolution transmission electron microscopy (HR-TEM). In this case delocalization effects disturb imaging of the lattice structure in particular if 2 to 6 nm small nanoparticles are involved. Therefore, FePt nanocrystals were investigated by reconstructing amplitude and phase of the scattered electron wave from a focal series of HRTEM images, which can produce delocalization free and direct images of the crystal structure [4]. The formation of 5-fold twinned structures of 3 to 7 nm face-centered cubic FePt nanocrystals is investigated that were grown from a colloidal solution [1]. The results are co...
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High resolution electron microscopes with field emission sources opened the possibility to investigate solids on a 100 pm range. Either electron holograpy can be applied or an information limit that may even extend into a region below 100... more
High resolution electron microscopes with field emission sources opened the possibility to investigate solids on a 100 pm range. Either electron holograpy can be applied or an information limit that may even extend into a region below 100 pm can be exploited to reach this goal [1]. However, lens aberrations such as the three-fold astigmatism often complicate an image interpretation in the 100 pm range or even make it impossible [2]. On the other hand, there is growing need to understand physical processes at a mono-atomic level in order to further develop artificially structured materials such as nano-crystals, ceramic coatings or semiconductors. Commonly, such materials contain light elements like C, N, or O with bond lengths that are shorter than a typical 180 pm point resolution of a high resolution, electron microscope. The carbon-carbon distance of 150 pm is the shortest bond length value in crystalline solids. Moreover, any projection of a diamond lattice along a low index zon...
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Recent progress in High Resolution Transmission Electron Microscopy makes it possible to investigate crystalline materials by phase contrast microscopy with a resolution close to the 80 pm information limit of a 300 kV field emission... more
Recent progress in High Resolution Transmission Electron Microscopy makes it possible to investigate crystalline materials by phase contrast microscopy with a resolution close to the 80 pm information limit of a 300 kV field emission microscope'"". A reconstruction of the electron exit wave from a focal series of lattice images converts the recorded information into interpretable resolution. The present contribution illustrates some recent applications of this technique to interfaces.Fig. 1 shows a reconstructed electron exit wave of a heterophase interface between GaN and sapphire. The experiment takes advantage of three factors: First, we resolved the GaN lattice in projection, which requires at least 0.15 nm resolution. The projection eliminates the stacking fault contrast that usually obscures lattice images in the commonly recorded projection. Thus, image interpretation is drastically simplified. Second, all atom columns at the interface and in the sapphire are re...
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It is now established that the 3D structure of homogeneous nanocrystals can be recovered from in-line hologram of single projections. The method builds on a quantitative contrast interpretation of electron exit wave functions. Since... more
It is now established that the 3D structure of homogeneous nanocrystals can be recovered from in-line hologram of single projections. The method builds on a quantitative contrast interpretation of electron exit wave functions. Since simulated exit wave functions of single and bilayers of graphene reveal the atomic structure of carbon-based materials with sufficient resolution, we explore theoretically how the approach can be expanded beyond periodic carbon-based materials to include non-periodic molecular structures. We show here theoretically that the 3D atomic structure of randomly oriented oleic acid molecules can be recovered from a single projection.
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Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.
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Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.
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ABSTRACTBulk single crystals of 4H-SiC have been deformed in compression in the temperature range 550–1300°C, whereas a GaN thin film grown on a (0001) sapphire substrate was deformed by Vickers indentation in the temperature range... more
ABSTRACTBulk single crystals of 4H-SiC have been deformed in compression in the temperature range 550–1300°C, whereas a GaN thin film grown on a (0001) sapphire substrate was deformed by Vickers indentation in the temperature range 25–800°C. The TEM observations of the deformed crystals indicate that deformation-induced dislocations in 4H-SiC all lie on the (0001) basal plane but depending on the deformation temperature, are one of two types. The dislocations induced by deformation at temperatures above ∼1 100°C are complete, with a Burgers vector, b, of but are all dissociated into two partials bounding a ribbon of stacking fault. On the other 3 hand, the dislocations induced by deformation in the temperature range 550<T<∼ 1100°C were predominantly single leading partials each dragging a stacking fault behind them. From the width of dissociated dislocations in the high-temperature deformed crystals, the stacking fault energy of 4H-SiC has been estimated to be 14.7±2.5 mJ/m2. ...
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ABSTRACTThe microstructural evolution and structural characteristics and transitions in the thin grain-boundary oxide films in a silicon nitride ceramic, specifically between two adjacent grains and not the triple junctions, are... more
ABSTRACTThe microstructural evolution and structural characteristics and transitions in the thin grain-boundary oxide films in a silicon nitride ceramic, specifically between two adjacent grains and not the triple junctions, are investigated to find their effect on the macroscopic fracture properties. It is found that by heat treating a model Si3N4-2wt% Y2O3 ceramic for ∼200 hr at 1400°C in air, the fracture toughness can be increased by ∼100%, coincident with a change in fracture mechanism from transgranular to intergranular. Structural phase transformations occur in the thin grain boundaries during oxidation that are revealed by XRD, EDX, Raman and EELS analyses. They affect the local bonding of atoms. It is concluded that only specific crystal “building blocks”, i.e., tetrahedra, are transformed along the grain boundary and the resulting difference in the atomic structure of the oxide interface is seen directly to alter the macroscopic fracture behavior.
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This study analyzes the impact of most common impurities and dopants on the c lattice parameter for thin films of Gallium Nitride (GaN) deposited on basal plane sapphire. Both Mg (∼1017 cm-3) and Zn (∼3 × 1020 cm-3) doping were found to... more
This study analyzes the impact of most common impurities and dopants on the c lattice parameter for thin films of Gallium Nitride (GaN) deposited on basal plane sapphire. Both Mg (∼1017 cm-3) and Zn (∼3 × 1020 cm-3) doping were found to expand the c lattice parameter as much as +0.38% and +0.62%, respectively. On the contrary, Oxygen up to concentrations 9 1021 cm-3 is shown to replace N in GaN thin films reducing the c parameter only by a small amount. Incorporation of Si leads to a large decrease of the c parameter which can not be attributed to the different size of Ga and Si atom. It is suggested that doping alters the film stoichiometry by a predicted Fermi level dependence of defect formation energies. The impact of stoichiometry on c lattice parameter and the effect of hydrostatic strain on resistivity in undoped and doped GaN is discussed.
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... D. Lubyshev, WK Liu, TR Stewart, AB Cornfeld, XM Fang, X. Xu, P. Specht, C. Kisielowski, M. Naidenkova, MS Goorsky, CS Whelan, WE Hoke, PF ... extended to an In(Ga)AlAs quaternary M-buffer scheme where the Ga mole fraction was chosen... more
... D. Lubyshev, WK Liu, TR Stewart, AB Cornfeld, XM Fang, X. Xu, P. Specht, C. Kisielowski, M. Naidenkova, MS Goorsky, CS Whelan, WE Hoke, PF ... extended to an In(Ga)AlAs quaternary M-buffer scheme where the Ga mole fraction was chosen to be low enough to keep the M ...
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ABSTRACTWe investigate here for the first time GaN and AIGaN films by using x-ray photoemission spectromicroscopy. As compared to conventional x-ray photoemission spectroscopy (XPS), spectromicroscopy can provide spatially resolved... more
ABSTRACTWe investigate here for the first time GaN and AIGaN films by using x-ray photoemission spectromicroscopy. As compared to conventional x-ray photoemission spectroscopy (XPS), spectromicroscopy can provide spatially resolved information on the chemical composition of the sample surface. The experimental results where obtained by using MAXIMUM, a scanning photoemission microscope installed on 12.0 undulator beamline at the Advanced Light Source (ALS), Berkelely, allowing for a spatial resolution of 100 nm. We investigate here GaN and AlGaN thin films grown on sapphire substrate by metalorganic chemical vapor deposition (MOCVD). The results clearly indicate the great potential of spectromicroscopy in investigating chemical inhomogeneity, inpurities and localization in GaN and AlGaN thin films.
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This volume of Micron highlights a cross section of presentaions from the Symposium on “Electron Microscopy of Materials”, hich was held during the XXII International Materials Congress in ancun, Mexico, August 11–15, 2013. Similar to... more
This volume of Micron highlights a cross section of presentaions from the Symposium on “Electron Microscopy of Materials”, hich was held during the XXII International Materials Congress in ancun, Mexico, August 11–15, 2013. Similar to previous symposia n 2006 and 2011 it focuses on the advancement and applicaion of leading-edge, aberration-corrected transmission electron icroscopy. These meetings were held during a time period of round breaking innovations that were driven by projects such s TEAM (http://ncem.lbl.gov/TEAM-project/index.html), CREST http://www.jst.go.jp/kisoken/crest/), SALVE (http://www.salveroject.de) or others, which enabled the detection of single atoms cross the Periodic Table of Elements at deep sub-Ångstrom resoution with electron beams of variable voltages between 15 kV and 00 kV. In the wake of these projects it became clear that such equipent operates now at the edge of physical limits to resolution that s set as much by technology as it is set by beam-sample interctions. A majority of current, advanced applications decode the lectronic and atomic structure of materials together with their hemical composition at a resolution of one Ångstrom or less. Scintifically, they provide astounding insight into the static structure f matter as long as irradiation effects are negligible or suitably ontrolled. Some of them are documented in this contribution. Nevrtheless, any argument in favor of resolution improvement can o longer serve as the only driving force to further improve on icroscope performance. Alternatives are sought and they are extraordinary rich. Most utstanding are concepts and applications that capture the time volution of materials or reveal dynamic processes and functionlity at the atomic scale. They include the exciting perspective o directly observe chemical reactions at a relevant temperature nd pressure, or the long-sought ability to recover the threeimensional structure of matter at atomic resolutions from a single r only a few projections. In any such advanced applications, he control of beam–sample interactions is mandatory to undertand the reversible or irreversible nature of the observed sample
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The recent development of atomic resolution, low dose-rate electron microscopy allows investigating 2D materials as well as catalytic nano particles without compromising their structural integrity. For graphene and a variety of... more
The recent development of atomic resolution, low dose-rate electron microscopy allows investigating 2D materials as well as catalytic nano particles without compromising their structural integrity. For graphene and a variety of nanoparticle compositions, it is shown that a critical dose rate exists of <100 e(-)/Å(2) s at 80 keV of electron acceleration that allows maintaining the genuine object structures including their surfaces and edges even if particles are only 3 nm large or smaller. Moreover, it is demonstrated that electron beam-induced phonon excitation from outside the field of view contributes to a contrast degradation in recorded images. These degradation effects can be eliminated by delivering electrons onto the imaged area, only, by using a Nilsonian illumination scheme in combination with a suitable aperture at the electron gun/monochromator assembly.
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Publisher Summary This chapter describes the defect processes in semiconductors studied at the atomic level by transmission electron microscopy. The semiconductor industry roadmap for the next decade calls for the fabrication of chips... more
Publisher Summary This chapter describes the defect processes in semiconductors studied at the atomic level by transmission electron microscopy. The semiconductor industry roadmap for the next decade calls for the fabrication of chips consisting of up to 50 billion transistors, each being 200 atoms long and 50 atoms deep. This degree of manufacturability requires unprecedented control of a variety of defect-mediated processes in near-surface regions with microscopic lateral dimensions. To predict and control diffusion behavior or interfacial roughness on such length scales, characterization techniques offering resolution and sensitivity are indispensable for process development and optimization. Many characterization techniques have been developed, each with its specific strengths and limitations. Each method can be classified by its spatial resolution, sensitivity, statistical reliability, and ease of use. Recently, high-resolution transmission electron microscopy (HRTEM) entered the quantitative era. Different approaches for quantitative evaluation of HRTEM lattice images have been developed for specific problem classes.