The present work describes the preparation and the investigation of the room temperature electrical and optical properties of a series of liquid nanocomposites (lnC) prepared with different concentrations of multiwalled carbon nanotubes... more
The present work describes the preparation and the investigation of the room temperature electrical and optical properties of a series of liquid nanocomposites (lnC) prepared with different concentrations of multiwalled carbon nanotubes (MWCNT) in a variety of liquid matrices: glycerin, Vaseline, glucose, propylene glycol and silicone oil (SIO). Special attention is deserved to the SIO matrix, owing to its convenient electrical properties for our purposes. We verified that a small percent fraction of MWCNT dispersed along the SIO matrix is capable of improving the electrical conductivity of the matrix by orders of magnitude, indicating that the MWCNT strongly participates in the electrical conduction mechanism. Also, the application of an external electric field to this lnC resulted in large changes in the optical transmittance, that were interpreted as a consequence of the fieldinduced MWCNT alignment into the liquid matrix. The characteristics of such a new category of nanocomposite in the liquid state suggest further studies.
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At the beginning of 2020, the COVID-19 pandemic surprised the world, affecting activities that promote attendance, including abruptly impacting the education area. Educational institutions, from preschool to university, were required to... more
At the beginning of 2020, the COVID-19 pandemic surprised the world, affecting activities that promote attendance, including abruptly impacting the education area. Educational institutions, from preschool to university, were required to adopt alternative teaching methods to continue their activities. Distance learning has been adopted by educators to address this unprecedented challenge. Our University, more specifically the Department of Physics, reacted to the problem in an ambitious and creative way, taking advantage of it as an opportunity to put into practice methodologies related to the teaching of disciplines that were only practiced in person, such as the discipline of Experimental Physics. This study aims to describe the implementation of the discipline of Experimental Physics I at our University, promoted remotely by professors of the Department of Physics. We verified: (i) that the choice of the best technologies as a tool for teaching is fundamental for the better dissem...
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Abstract We report on the optical properties of Syngonanthus nitens, the golden grass, which is used to produce golden handicraft articles. The dry stems of the plant were analyzed with scanning electron microscopy, X-ray photoelectron... more
Abstract We report on the optical properties of Syngonanthus nitens, the golden grass, which is used to produce golden handicraft articles. The dry stems of the plant were analyzed with scanning electron microscopy, X-ray photoelectron spectroscopy, fluorescence microscopy; angle resolved optical reflectance and absorption/emission spectroscopy. The extract of the stems composed by 8 glucopyranosylflavones was also optically characterized. Electronic and geometric properties of the flavonoids were studied using ab initio and semi-empirical quantum mechanical calculations. The experimental and theoretical results explain the characteristic golden color of S. nitens dried stems.
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Since the number of antibiotic-resistant bacterial infections is growing and cases are getting worse every year, the search for new alternative bactericidal wound dressing treatments is becoming crucial. Within this context, the use of... more
Since the number of antibiotic-resistant bacterial infections is growing and cases are getting worse every year, the search for new alternative bactericidal wound dressing treatments is becoming crucial. Within this context, the use of polysaccharides from plants and seeds in innovative biopolymer technologies is of key importance. In this work, bio-nano-composite guar gum/polyvinyl alcohol (PVOH) membranes loaded with aluminum-doped zinc oxide nanoparticles were produced via electrospinning. Citric acid was added to the mixture to increase spinnability. However, depending on the pH, zinc oxide nanoparticles are partially dissociated, decreasing their bactericidal efficiency. Thus, a second successful alkaline thermo-chemical regrowth step was added to the process to treat the obtained fibers. This alkaline thermo-chemical treatment reconstituted both the nanoparticles and their bactericidal properties. The Staphylococcus aureus antibacterial assay results show that the membranes ob...
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Abstract$$\hbox {CeO}_2$$CeO2 films were fabricated by combining both a modified spray pyrolysis and the vapour transport deposition techniques. Two different precursors, cerium chloride and cerium acetate, were explored. In our approach,... more
Abstract$$\hbox {CeO}_2$$CeO2 films were fabricated by combining both a modified spray pyrolysis and the vapour transport deposition techniques. Two different precursors, cerium chloride and cerium acetate, were explored. In our approach, the pyrolytic process was not concomitant with the spray deposition and the introduction of the vapour transport condition has showed to improve both the morphological and optical quality of the films. Samples obtained from cerium chloride show a porous morphology, usual for polycrystalline $$\hbox {CeO}_2$$CeO2 layers, and a homogeneous light emission. When using vapour transport during thermal treatment, we achieved an enhanced luminescence, blue shifted to 3.08 eV and with negligible presence of defect bands. Films obtained from cerium acetate present similar crystalline properties, and a more defined light emission line shape, also peaked at 3.08 eV but with even lower contribution from known green–red defect bands. These results show that the proposed combined technique leads to $$\hbox {CeO}_2$$CeO2 films with homogeneous, enhanced optical properties.
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Chemical Engineering, Materials Science, Organic Chemistry, Nanoparticle, Cell Adhesion, and 15 moreMedicine, Electricity, Biocompatibility, Cell line, Mice, Animals, Membrane, Polyvinyl alcohol, Food Sciences, Materials Testing, Hydrogen-Ion Concentration, Carbohydrate Polymers, Magnetite Nanoparticles, Guar Gum, and Mannans
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Physics, Condensed Matter Physics, Materials Science, Surfaces and Interfaces, Nanocrystalline Material, and 11 moreMagnetism, Thin Film, Physical sciences, Magnetic Properties, Electronic Structure, CHEMICAL SCIENCES, Learning Theory and Modeling, Cerium, Magnetization, Local Density Approximation, and Ferromagnetism
A new nanocomposite was synthesized by reacting the layered double hydroxide Al0.33Mg0.67(OH)2(C12H25SO4)0.33·0.64H2O with poly(ethylene oxide). The composite was characterized with X-ray powder diffraction, thermal analysis (simultaneous... more
A new nanocomposite was synthesized by reacting the layered double hydroxide Al0.33Mg0.67(OH)2(C12H25SO4)0.33·0.64H2O with poly(ethylene oxide). The composite was characterized with X-ray powder diffraction, thermal analysis (simultaneous thermogravimetric analysis/differential scanning calorimetry), Fourier transform infrared spectroscopy, photoelectron spectroscopy, and electron diffraction. The nanocomposite has the layered structure of the double hydroxide simultaneously intercalated with dodecyl sulfate anions and poly(ethylene oxide) molecules. The characterization indicates a nanocomposite with a well-ordered structure.
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In this paper we report on the structural, morphological and magnetic properties of semiconducting GaSe epilayers, grown by molecular beam epitaxy, doped to different iron contents (ranging from 1 to 22 at.% Fe). Our results indicate that... more
In this paper we report on the structural, morphological and magnetic properties of semiconducting GaSe epilayers, grown by molecular beam epitaxy, doped to different iron contents (ranging from 1 to 22 at.% Fe). Our results indicate that iron forms metallic Fe nanoparticles with diameters ranging from 1 to 20 nm embedded in the crystalline GaSe matrix. The Fe incorporation proceeds
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The magnetic behaviour of Fe/Cu multilayers produced by electron-beam evaporation has been investigated in the range 5 to 400 K and in magnetic fields up to 1 kOe using SQUID magnetometry. The multilayers exhibit an irreversible behaviour... more
The magnetic behaviour of Fe/Cu multilayers produced by electron-beam evaporation has been investigated in the range 5 to 400 K and in magnetic fields up to 1 kOe using SQUID magnetometry. The multilayers exhibit an irreversible behaviour below a characteristic temperature 0953-8984/11/1/005/img9. Low-field DC magnetic moment measurements on samples cooled in zero field revealed the usual signature of a spin-glass state. Time relaxation of the remanence and frequency-shift of the peak of the imaginary part of the AC magnetic moment were also observed. The irreversibility line was fitted to a de Almeida-Thouless line with a crossover critical exponent 0953-8984/11/1/005/img10. We have interpreted these results as being due to the presence of some interdiffusion between Fe and Cu at the interfaces. The surprisingly high characteristic irreversibility temperatures indicate that diffused Fe atoms aggregate in clusters at the interfaces.
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The Fe/Cu superlattices were grown on HF-cleaned Si(111) wafers at room temperature by electron beam evaporation in ultravacuum. X-ray diffraction and transmission electron microscopy indicate that epitaxial Fe/Cu superlattices are... more
The Fe/Cu superlattices were grown on HF-cleaned Si(111) wafers at room temperature by electron beam evaporation in ultravacuum. X-ray diffraction and transmission electron microscopy indicate that epitaxial Fe/Cu superlattices are obtained for Cu layers thinner than 24 Å. This epitaxial growth is crucially dependent on which element is deposited first on the Si(111) surface. All superlattices show typically ferromagnetic hysteresis
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ABSTRACT The growth process as well as optical and magnetic properties of the ZnSe-Fe and ZnSe-Co granular films deposited electrochemically have been investigated. We demonstrate that the ferromagnetic nanoscaled particles with... more
ABSTRACT The growth process as well as optical and magnetic properties of the ZnSe-Fe and ZnSe-Co granular films deposited electrochemically have been investigated. We demonstrate that the ferromagnetic nanoscaled particles with multidomain structure are embedded in a ZnSe matrix with a polycrystalline structure exhibiting semiconductor behavior at room temperature. (C) 2003 The Electrochemical Society.
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Engineering, Chemistry, Materials Chemistry, Content Analysis, Materials, and 15 moreTransmission Electron Microscopy, Medicine, Infrared spectroscopy, Silica, Physical sciences, Chemical Analysis, CHEMICAL SCIENCES, Thermal Analysis, X ray diffraction, Fourier transform infrared spectroscopy, Thermal Decomposition, Colloid, Experimental Data, Kaolinite, and Total Organic Matter
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... Phase identification and crystallographic orientation were accomplished with selected area electron diffraction (SAED) in transmission electron microscopy (TEM), x-ray diffraction (XRD) in the θ2θ geometry ... 6, 305 (1971); A.... more
... Phase identification and crystallographic orientation were accomplished with selected area electron diffraction (SAED) in transmission electron microscopy (TEM), x-ray diffraction (XRD) in the θ2θ geometry ... 6, 305 (1971); A. Chevy, thesis, Université Paris VI, Paris, France, 1981 ...
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ABSTRACT ZnSe-Fe and ZnSe-Co granular films have been successfully obtained by electrodeposition under potentiostatic conditions. Cyclic voltammograms of the solutions containing all precursors of the systems are consistent with anomalous... more
ABSTRACT ZnSe-Fe and ZnSe-Co granular films have been successfully obtained by electrodeposition under potentiostatic conditions. Cyclic voltammograms of the solutions containing all precursors of the systems are consistent with anomalous codeposition of the zinc and iron-group metals. Electron microscopy analyses reveal a network of Fe and Co particles dispersed in polycrystalline ZnSe without evidence of intermediate compound formation.
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Engineering, Materials Science, Thermodynamics, Technology, Nanoparticle, and 12 morePHOTOELECTRON SPECTROSCOPY, Nanoparticles, Transmission Electron Microscopy, Medicine, Band Gap, Vanadium oxide, CHEMICAL SCIENCES, X ray diffraction, Particle Size, Cysteine, X Ray Photoelectron Spectroscopy, and Nanoscience and nanotechnology
In this paper we report on the giant magnetoresistance effect and oscillatory exchange coupling in electrodeposited Co87Fe13/Cu compositionally modulated alloys. The alloys are compositionally modulated over nanometre length scales with... more
In this paper we report on the giant magnetoresistance effect and oscillatory exchange coupling in electrodeposited Co87Fe13/Cu compositionally modulated alloys. The alloys are compositionally modulated over nanometre length scales with ferromagnetic Co87Fe13 (Cu) alloy layers and non-magnetic Cu layers. Co87Fe13/Cu multilayered thin films were electrodeposited from a single sulfate plating solution containing all metallic ions of interest under computer-controlled potentiostat
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We have grown MnAs layers on GaAs(111)B by molecular beam epitaxy and studied their surface and epilayer morphology and its interconnection with magnetic properties. The influence of growth variables such as the As/Mn flux ratio and... more
We have grown MnAs layers on GaAs(111)B by molecular beam epitaxy and studied their surface and epilayer morphology and its interconnection with magnetic properties. The influence of growth variables such as the As/Mn flux ratio and substrate temperature on the properties of the epilayer was studied. These parameters were found to drastically modify the epilayer's characteristics, including its structural quality, and also strongly alter its magnetic properties. A more in-depth knowledge of how these parameters affect epilayers would be extremely useful in tailoring epilayers with specific desirable properties.
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Abstract Dolomitic rocks from the Rio Bonito Quarry, located in the Agua Clara Formation, record multistage dolomitization processes linked with porosity development in the southern Brazilian Shield. Dolomitic marble and breccia samples... more
Abstract Dolomitic rocks from the Rio Bonito Quarry, located in the Agua Clara Formation, record multistage dolomitization processes linked with porosity development in the southern Brazilian Shield. Dolomitic marble and breccia samples from this unit contain three textural types of dolomite that either are fabric destructive or void-filling phases. To study the role of dissolution in the porosity development in these dolomite types - from sedimentary to metamorphic domains - we combine petrographic methods, cathodoluminescence, Raman spectroscopy, micro-computed tomography, stable isotopes of carbon and oxygen, and fluid inclusion analysis. The protoliths of the dolomitic rocks of Rio Bonito Quarry are assumed as Mesoproterozoic (ca. 1.5 Ga) marls presenting shallow shelf to deep water lithofacies. The first dolomitization stage, forming a nonmimic replacement of the primary carbonate (Dol1) is fabric destructive and related to a burial setting (δ18O: -12.42 to - 9.68‰; δ13C: -2.29–0.40‰). The development of bedding-parallel stylolites of low amplitude led to increasing of porosity (up to 0.2%) and promoted the fluid circulation. During the Neoproterozoic Brasiliano tectonic events (ca. 650-550 Ma), the metamorphism of marls into dolomitic marble is intimately connected to the development of second replacement dolomite (Dol2). Penecontemporaneous brecciation is assumed as triggering factor to the fluid change, where Dol2 is akin to dolomites from MVT-deposits (δ18O: -19.12 to −12.03‰; δ13C: -0.07 to −2.17‰), and the total porosity is enhanced to 2%. The ubiquitous tectonic stress boosted the hydraulic fracturing, providing conditions to saddle dolomite (Dol3) precipitation, occurring as a replacement and void-filling phase. Lower isotopic values of Dol3 (δ18O: -14.93 to −10.77‰; δ13C: -3.36 to −1.89‰) suggest disequilibrium between the host-rock and the dolomitization fluid, while the porosity is augmented to 9%. The subsequent dedolomitization, generating void-filling calcite, is associated to meteoric phreatic input (δ18O: -8.31 to −5.56‰; δ13C: -5.59 to −2.56‰), similarly to the development of calcretes; therefore, diminishing the porosity towards 4%. Microthermometric data shows different signatures in the dolomitization fluid, which started at 100–150 °C and moderate-salinity (3–4 wt% eq.NaCl) in a burial setting, reaching up to 270 °C and low-salinity (0-2 wt% eq.NaCl) as a response to a shifting tectonic environment or fluid mixing. Additionally, the temperature shift between the host rock (120–130 °C) and the different dolomitization stages (from 140-150° to 210–270 °C), above 10 °C offset, point to a hydrothermal setting.
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Gold nanorods (AuNRs) are suitable for constructing self-assembled structures for the development of biosensing devices and are usually obtained in the presence of cetyltrimethylammonium bromide (CTAB). Here, a sulfated chitosan (ChiS)... more
Gold nanorods (AuNRs) are suitable for constructing self-assembled structures for the development of biosensing devices and are usually obtained in the presence of cetyltrimethylammonium bromide (CTAB). Here, a sulfated chitosan (ChiS) and gum arabic (GA) were employed to encapsulate CTAB/AuNRs with the purpose of studying the interactions of the polysaccharides with CTAB, which is cytotoxic and is responsible for the instability of nanoparticles in buffer solutions. The presence of a variety of functional groups such as the sulfate groups in ChiS and the carboxylic groups in GA, led to efficient interactions with CTAB/AuNRs as evidenced through UV-vis and FTIR spectroscopies. Electron microscopies (HR-SEM and TEM) revealed that nanoparticle clusters were formed in the GA-AuNRs sample, whereas individual AuNRs, surrounded by a dense layer of polysaccharides, were observed in the ChiS-AuNRs sample. Therefore, the presented work contributes to the understanding of the driving forces that control the surface interactions of the studied materials, providing useful information in the building-up of gold self-assembled nanostructures.
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Micro-Raman spectroscopy has been carried out on hybrid systems consisting of magnetic Fe and Co nanoclusters immersed in a semiconductor ZnSe host. The experimental results clearly reveal surface-enhanced Raman scattering for the ZnSe... more
Micro-Raman spectroscopy has been carried out on hybrid systems consisting of magnetic Fe and Co nanoclusters immersed in a semiconductor ZnSe host. The experimental results clearly reveal surface-enhanced Raman scattering for the ZnSe matrix phonon modes. The intensity enhancement correlates with the Fe content and sample morphology. Enhancement factors of up to about one order were achieved, as compared to the pure ZnSe sample.
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The structural and magnetic properties of MnAs epilayers grown on GaAs(111)B have been investigated by x-ray diffraction and magnetometry. The strain evolution of the epilayer was followed during the phase transition by x-ray diffraction.... more
The structural and magnetic properties of MnAs epilayers grown on GaAs(111)B have been investigated by x-ray diffraction and magnetometry. The strain evolution of the epilayer was followed during the phase transition by x-ray diffraction. The results show a high fraction of the alpha ferromagnetic phase at room temperature and an elevated value of the structural phase transition temperature. The system
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ZnSe–Co granular films have been electrodeposited under potentiostatic condition on polished stainless steel substrates. X-ray diffraction and transmission electron microscopy measurements indicate the formation of polycrystalline... more
ZnSe–Co granular films have been electrodeposited under potentiostatic condition on polished stainless steel substrates. X-ray diffraction and transmission electron microscopy measurements indicate the formation of polycrystalline granular films with Co particles dispersed in an ZnSe matrix without evidence of intermediate compound formation. Magnetic measurements reveal low values of coercive field and remanence, indicating that the overall magnetic response of the
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Heterogeneous (Co0.87Fe0.13)xCu1−x alloys were electrodeposited with various additives from a single sulfate plating solution under potentiostatic conditions on Cu substrates. The alloys are polycrystalline with a predominant... more
Heterogeneous (Co0.87Fe0.13)xCu1−x alloys were electrodeposited with various additives from a single sulfate plating solution under potentiostatic conditions on Cu substrates. The alloys are polycrystalline with a predominant face-centered cubic structure and for x<0.45 consist of small ferromagnetic particles in a Cu matrix. The order induced by discontinuous multilayered structures affects magnetoresistance significantly.
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We report on the surface morphology, crystalline, and electronic properties of Fe thin films potentiostatically eletrodeposited on hydrogen-terminated Si(lll) substrates. Spontaneous reaction between Fe deposits and hydrogen-terminated Si... more
We report on the surface morphology, crystalline, and electronic properties of Fe thin films potentiostatically eletrodeposited on hydrogen-terminated Si(lll) substrates. Spontaneous reaction between Fe deposits and hydrogen-terminated Si surfaces have been observed at room temperature with formation of polycrystalline silicides Fe 2 Si and Fe 5 Si 3 , together with metallic Fe having a body-centered cubic structure. X-ray photoemission spectroscopy and X-ray diffraction measurements have been performed to investigate the thermal stability between Fe and Si under high-vacuum thermal treatments up to 300°C.
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ABSTRACT