The Experts below are selected from a list of 32571 Experts worldwide ranked by ideXlab platform
Nigel D Browning - One of the best experts on this subject based on the ideXlab platform.
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the impact of surface and retardation losses on Valence Electron energy loss spectroscopy
Ultramicroscopy, 2008Co-Authors: Rolf Erni, Nigel D BrowningAbstract:Abstract The inelastic scattering of fast Electrons transmitting thin foils of silicon (Si), silicon nitride (Si 3 N 4 ), gallium arsenide (GaAs), gallium nitride (GaN) and cadmium selenide (CdSe) was analyzed using dielectric theory. In particular, the impact of surface and bulk retardation losses on Valence Electron energy-loss spectroscopy (VEELS) was studied as a function of the foil thickness. It is shown that for the materials analyzed, surface and retardation losses can cause a systematic, thickness-dependent modulation of the dielectric volume losses, which can hamper the determination of the bulk dielectric data as well as the identification of band-gap and interband transition energies by VEELS. For Si and GaAs, where the dielectric function is strongly peaked with high absolute values, retardation losses lead to additional intensity maxima in the spectrum. For thin films of these materials (below ∼100 nm), the additional intensity maxima are related to retardation effects due to the finite size of the sample leading to the excitation of guided light modes. For thicker films, exceeding about 200 nm, the intensity maxima are caused by bulk retardation losses, i.e., Cerenkov losses. Although thickness-dependent modulations were observed for Si 3 N 4 , GaN and CdSe, the form of the dielectric functions and their lower maxima, means that for TEM samples
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quantification of the size dependent energy gap of individual cdse quantum dots by Valence Electron energy loss spectroscopy
Ultramicroscopy, 2007Co-Authors: Rolf Erni, Nigel D BrowningAbstract:Valence Electron energy-loss spectroscopy (VEELS) performed in a monochromated scanning transmission Electron microscope was used to measure the energy gaps of individual quantum dots (QDs). The gap energies of a series of CdSe QDs measured by VEELS reveal the expected quantum confinement effect; the gap energy increases with decreasing particle size. However, the values derived from these first VEELS measurements of single QDs are larger than the values commonly measured by optical spectroscopy. As standard optical methods lack the spatial resolution to probe individual nanoparticles, the particle-size distribution influences the optical response. It is suggested that the impact of the particle-size distribution accounts for the discrepancy between the energy-gap values derived from VEELS of single QDs and from optical methods of ensembles of QDs.
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Valence Electron energy loss spectroscopy in monochromated scanning transmission Electron microscopy
Ultramicroscopy, 2005Co-Authors: Rolf Erni, Nigel D BrowningAbstract:Abstract With the development of monochromators for (scanning) transmission Electron microscopes, Valence Electron energy-loss spectroscopy (VEELS) is developing into a unique technique to study the band structure and optical properties of nanoscale materials. This article discusses practical aspects of spatially resolved VEELS performed in scanning transmission mode and the alignments necessary to achieve the current optimum performance of ∼0.15 eV energy resolution with an Electron probe size of ∼1 nm. In particular, a collection of basic concepts concerning the acquisition process, the optimization of the energy resolution, the spatial resolution and the data processing are provided. A brief study of planar defects in a Y 1 Ba 2 Cu 3 O 7− δ high-temperature superconductor illustrates these concepts and shows what kind of information can be accessed by VEELS.
Ken Kurosaki - One of the best experts on this subject based on the ideXlab platform.
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tuning Valence Electron concentration in the mo13ge23 ru2ge3 pseudobinary system for enhancement of the thermoelectric properties
Journal of Applied Physics, 2019Co-Authors: Takayuki Sasaki, Shimpei Kuwahara, Yuji Ohishi, Hiroaki Muta, Ken KurosakiAbstract:Nowotny Chimney-Ladder (NCL) compounds are attracting increased attention as good thermoelectric (TE) materials. Although the TE properties of Si-based NCL compounds such as higher manganese silicides are well investigated, those of Ge-based ones are scarcely studied. Here, we demonstrate that a series of the Ge-based NCL compounds in the Mo13Ge23-Ru2Ge3 pseudobinary system, i.e., Mo1-xRuxGe1.769, shows quite low lattice thermal conductivity as well as good electrical properties like a material called phonon-glass Electron-crystal and thus it shows good TE properties. By tuning the Valence Electron concentration, the TE properties are optimized and the maximum zT, called materials dimensionless figure of merit, reaches 0.23 for x = 0.6 in Mo1-xRuxGe1.769, which is approximately 15 times higher than that of x = 0 in Mo1-xRuxGe1.769, i.e., Mo13Ge23.Nowotny Chimney-Ladder (NCL) compounds are attracting increased attention as good thermoelectric (TE) materials. Although the TE properties of Si-based NCL compounds such as higher manganese silicides are well investigated, those of Ge-based ones are scarcely studied. Here, we demonstrate that a series of the Ge-based NCL compounds in the Mo13Ge23-Ru2Ge3 pseudobinary system, i.e., Mo1-xRuxGe1.769, shows quite low lattice thermal conductivity as well as good electrical properties like a material called phonon-glass Electron-crystal and thus it shows good TE properties. By tuning the Valence Electron concentration, the TE properties are optimized and the maximum zT, called materials dimensionless figure of merit, reaches 0.23 for x = 0.6 in Mo1-xRuxGe1.769, which is approximately 15 times higher than that of x = 0 in Mo1-xRuxGe1.769, i.e., Mo13Ge23.
Zhilin Liu - One of the best experts on this subject based on the ideXlab platform.
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analysis of the effect of alloy elements on martensitic transformation in titanium alloy with the use of Valence Electron structure parameters
Materials Chemistry and Physics, 2011Co-Authors: Cheng Lin, Guili Yin, Yongqing Zhao, Zhilin LiuAbstract:Abstract Because martensitic transformation in titanium alloy significantly affects properties and applications of the alloys, the analysis of the effect of alloy elements on martensitic transformation becomes primarily important. Through using the Valence Electron structure parameters calculated by the empirical Electron theory (EET) of solids and molecules, our analysis results reveal that the addition of alloy elements (such as Zr, Nb, W, Mo, V) has the beneficial effect on the formation of orthorhombic martensite α″ as well as the addition of alloy elements (e.g., Al, Fe, Cr, Sn) has advantage to the formation of hcp-structured martensite α′. Our analysis results not only present the understanding about the effect of alloy elements on martensitic transformation at the Electron structure level, but also provide a theoretical basis for the chemical composition design of titanium alloys.
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statistical values of Valence Electron structure parameters applied to research on phase transition temperature and eutectoid reaction of titanium alloy
Science China-technological Sciences, 2008Co-Authors: Cheng Lin, Zhilin LiuAbstract:Based on the empirical Electron theory of solids and molecules (EET), the statistical values of Valence Electron structure parameters Sn A and SE A which can characterize the properties of alloy phases are calculated, and influences of alloying elements (e.g., V, Nb, Mo, Hf, Zr, Fe, Mn, Co, Cr, Si, and so on) on the phase transition temperature and eutectoid reaction of titanium alloy are discussed with the statistical values of Valence Electron structure parameters. The research results agree well with real situations.
Rolf Erni - One of the best experts on this subject based on the ideXlab platform.
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the impact of surface and retardation losses on Valence Electron energy loss spectroscopy
Ultramicroscopy, 2008Co-Authors: Rolf Erni, Nigel D BrowningAbstract:Abstract The inelastic scattering of fast Electrons transmitting thin foils of silicon (Si), silicon nitride (Si 3 N 4 ), gallium arsenide (GaAs), gallium nitride (GaN) and cadmium selenide (CdSe) was analyzed using dielectric theory. In particular, the impact of surface and bulk retardation losses on Valence Electron energy-loss spectroscopy (VEELS) was studied as a function of the foil thickness. It is shown that for the materials analyzed, surface and retardation losses can cause a systematic, thickness-dependent modulation of the dielectric volume losses, which can hamper the determination of the bulk dielectric data as well as the identification of band-gap and interband transition energies by VEELS. For Si and GaAs, where the dielectric function is strongly peaked with high absolute values, retardation losses lead to additional intensity maxima in the spectrum. For thin films of these materials (below ∼100 nm), the additional intensity maxima are related to retardation effects due to the finite size of the sample leading to the excitation of guided light modes. For thicker films, exceeding about 200 nm, the intensity maxima are caused by bulk retardation losses, i.e., Cerenkov losses. Although thickness-dependent modulations were observed for Si 3 N 4 , GaN and CdSe, the form of the dielectric functions and their lower maxima, means that for TEM samples
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quantification of the size dependent energy gap of individual cdse quantum dots by Valence Electron energy loss spectroscopy
Ultramicroscopy, 2007Co-Authors: Rolf Erni, Nigel D BrowningAbstract:Valence Electron energy-loss spectroscopy (VEELS) performed in a monochromated scanning transmission Electron microscope was used to measure the energy gaps of individual quantum dots (QDs). The gap energies of a series of CdSe QDs measured by VEELS reveal the expected quantum confinement effect; the gap energy increases with decreasing particle size. However, the values derived from these first VEELS measurements of single QDs are larger than the values commonly measured by optical spectroscopy. As standard optical methods lack the spatial resolution to probe individual nanoparticles, the particle-size distribution influences the optical response. It is suggested that the impact of the particle-size distribution accounts for the discrepancy between the energy-gap values derived from VEELS of single QDs and from optical methods of ensembles of QDs.
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Valence Electron energy loss spectroscopy in monochromated scanning transmission Electron microscopy
Ultramicroscopy, 2005Co-Authors: Rolf Erni, Nigel D BrowningAbstract:Abstract With the development of monochromators for (scanning) transmission Electron microscopes, Valence Electron energy-loss spectroscopy (VEELS) is developing into a unique technique to study the band structure and optical properties of nanoscale materials. This article discusses practical aspects of spatially resolved VEELS performed in scanning transmission mode and the alignments necessary to achieve the current optimum performance of ∼0.15 eV energy resolution with an Electron probe size of ∼1 nm. In particular, a collection of basic concepts concerning the acquisition process, the optimization of the energy resolution, the spatial resolution and the data processing are provided. A brief study of planar defects in a Y 1 Ba 2 Cu 3 O 7− δ high-temperature superconductor illustrates these concepts and shows what kind of information can be accessed by VEELS.
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band transitions in wurtzite gan and inn determined by Valence Electron energy loss spectroscopy
Solid State Communications, 2005Co-Authors: Rolf Erni, P Specht, R Armitage, E R Weber, Christian KisielowskiAbstract:Abstract Valence Electron energy loss spectroscopy (VEELS) was applied to determine band transitions in wurtzite InN, deposited by molecular beam epitaxy on (0001) sapphire substrates or GaN buffer layers. The GaN buffer layer was used as VEELS reference. At room temperature a band transition for wurtzite InN was found at (1.7±0.2 eV) and for wurtzite GaN at (3.3±0.2 eV) that are ascribed to the fundamental bandgap. Additional band transitions could be identified at higher and lower energy losses. The latter may be related to transitions involving defect bands. In InN, neither oxygen related crystal phases nor indium metal clusters were observed in the areas of the epilayers investigated by VEELS. Consequently, the obtained results mainly describe the properties of the InN host crystal.
Gordon J. Miller - One of the best experts on this subject based on the ideXlab platform.
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influence of Valence Electron concentration on laves phases structures and phase stability of pseudo binary mgzn2 xpdx
ChemInform, 2015Co-Authors: Srinivasa Thimmaiah, Gordon J. MillerAbstract:The series of title compounds (0.15 ≤ x ≤ 1.0) is synthesized from the elements (Ta tubes, Ar, 750 °C, 18 h, followed by annealing at 400 °C for 5 d, 90—95% yields) and characterized by single crystal XRD and TB-LMTO-ASA Electronic structure calculations to analyze the effect of Valence Electron concentration on MgZn2.
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ordered baal4 type variants in the baauxsn4 x system a unified view on their phase stabilities versus Valence Electron counts
Inorganic Chemistry, 2014Co-Authors: Qisheng Lin, Gordon J. Miller, John D CorbettAbstract:Three ordered structures of the tetragonal BaAl4 type were identified in the Ba–Au–Sn system, from which a unified view of the interplay between the Valence Electron counts (VECs) and phase stabilities of these three types of derivatives can be developed. The BaNiSn3 (I4mm), ThCr2Si2 (I4/mmm), and CaBe2Ge2 (P4/nmm) type BaAuxSn4–x phases occurred respectively at x = 0.78(1)–1, 1.38(1)–1.47(1), and 1.52(1)–2.17(1), consistent with theoretical atomic “coloring” analyses that reveal an optimal VEC of ∼14 for the ThCr2Si2 type but larger and smaller values respectively for the BaNiSn3- and CaBe2Ge2-type structures.
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Gd5Si4−xPx: Targeted Structural Changes through Increase in Valence Electron Count
Journal of the American Chemical Society, 2009Co-Authors: Volodymyr Svitlyk, Gordon J. Miller, Yurij MozharivskyjAbstract:Phase transformations in the Gd5Si4-xPx system (0 ≤ x ≤ 2), studied through X-ray diffraction techniques, reveal an intimate coupling between the crystal structure and Valence Electron count. An increase in the Valence Electron count through P substitution results in breaking the interslab T−T dimers (dT−T = 3.74 A; T is a mixture of Si and P) and shear movement of the ∝2[Gd5T4] slabs in Gd5Si2.75P1.25. The Gd5Si2.75P1.25 phase extends the existence of the orthorhombic Sm5Ge4-type structures to the Valence Electron count larger than 31 e−/formula unit. Tight-binding linear-muffin-tin-orbital calculations trace the origin of the T−T dimer cleavage in Gd5Si2.75P1.25 to a larger population of antibonding states within the dimers.
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gd5si4 xpx targeted structural changes through increase in Valence Electron count
Journal of the American Chemical Society, 2009Co-Authors: Volodymyr Svitlyk, Gordon J. Miller, Yurij MozharivskyjAbstract:Phase transformations in the Gd5Si4-xPx system (0 ≤ x ≤ 2), studied through X-ray diffraction techniques, reveal an intimate coupling between the crystal structure and Valence Electron count. An increase in the Valence Electron count through P substitution results in breaking the interslab T−T dimers (dT−T = 3.74 A; T is a mixture of Si and P) and shear movement of the ∝2[Gd5T4] slabs in Gd5Si2.75P1.25. The Gd5Si2.75P1.25 phase extends the existence of the orthorhombic Sm5Ge4-type structures to the Valence Electron count larger than 31 e−/formula unit. Tight-binding linear-muffin-tin-orbital calculations trace the origin of the T−T dimer cleavage in Gd5Si2.75P1.25 to a larger population of antibonding states within the dimers.