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Phenomenological description of strain relief in step-graded metamorphic buffer layers based on In x Al1 ? x As ternary solutions
摘要： Spatial distributions of the residual elastic strains in layers of step-graded metamorphic buffers of two different designs, grown via molecular beam epitaxy on the basis of InxAl1 ? xAs ternary solutions, are obtained by means of reciprocal space mapping. It is shown that with allowance for work hardening, which affects strain relief in buffer layers and increases the strain in dislocation-free layers, the mechanism of strain relief in the final buffer steps, and the residual elastic strain in a buffer dislocation-free layer, are governed by the same phenomenological law as in a single-layer heterostructure.
关键词： InxAl1 ? xAs ternary solutions,step-graded metamorphic buffer layers,strain relief,reciprocal space mapping,molecular beam epitaxy
更新于2025-09-11 14:15:04
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Photoemission and Soft X-ray Absorption Spectroscopy Study of Gd-substituted Thermoelectric and Topological Bi2Te3
摘要： The electronic structures of Gd-substituted Bi2?xGdxTe3 single crystals have been investigated by employing synchrotron-radiation spectroscopies, such as soft X-ray absorption spectroscopy (XAS), soft X-ray magnetic circular dichroism (XMCD), photoemission spectroscopy (PES), and scanning photoelectron microscopy (SPEM). SPEM measurements confirm that Gd ions are substituted homogeneously in Bi2?xGdxTe3 crystals. The measured Gd 3d XAS and XMCD spectra provide evidence that the substituted Gd ions are trivalent and magnetic. The hν-dependence of the valence-band (VB) PES spectra are described well by the hν-dependent contributions of the Te 5p and Bi 6p states. A good agreement is found between the measured VB PES spectra of Bi2?xGdxTe3 and the calculated partial densities of states, revealing that the Te 5p states will play an important role in determining the thermoelectric and topological properties of Bi2?xGdxTe3.
关键词： Gd-substituted Bi2Te3,XAS,thermoelectric,topological,XMCD,PES,SPEM
更新于2025-09-10 09:29:36
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Local, electronic and surface structure of multi–component Fe–doped CdTe(S) systems
摘要： Local structural and electronic properties around Fe in multi–component Cd0.99Fe0.01Te0.97S0.03 system were studied by means of X–ray absorption fine structure (XAFS). Composition of non–polar (110) surfaces of Cd0.97Fe0.03Te and Cd0.99Fe0.01Te0.97S0.03 systems and mechanism of their oxidation in ambient conditions were studied by Atomic Force Microscopy (AFM) and X–ray Photoelectron Spectroscopy (XPS). It has been found that Fe preferentially substitutes Cd, but due to much smaller covalent radius and preferences for paring with S, it causes local distortion of the host CdTe lattice. The distortion is confined to the Fe–immediate surrounding and the second and third coordination shell atoms are (inside experimental uncertainties) placed at distances expected in CdTe. Although local structure around Fe is well defined in the bulk of both samples, their near–surface region is completely depleted from Fe, and in case of Cd0.99Fe0.01Te0.97S0.03 somewhat enriched in S. Special attention is, therefore, paid to characterization of the near–surface region and evaluation of its composition and structure. To that end we have introduced a general standard–free algorithm for XPS data analysis of the two–layer surface structure (bulk, oxide layer, and the impurity layer). Results of the in–depth composition analysis revealed that despite different bulk composition and impurity layer thickness, underneath the topmost impurity layer lays approximately one monolayer of CdTeO3 which passivates the surface.
关键词： XAS,XPS,II–VI semiconductors,iron impurity,oxidation
更新于2025-09-09 09:28:46
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Chemical Speciation and Mapping of the Si in Si Doped LFP Ingot with Synchrotron Radiation Technique
摘要： Development of LiFePO4 cathode material with high cycle life through Si doping (substituting Si at P sites of LiFePO4) has shown that small changes to the structure of LiFePO4 can significantly affect the performance of Li ion batteries. However, determining the nature of elemental doping and their effects on the electronic and atomic structure of LiFePO4 remains challenging. Here we present X-ray absorption spectroscopy and X-ray fluorescence mapping as ideal characterization methods for understanding the effect of Si doped LiFePO4 prepared using a melt-synthesis process. X-ray absorption spectra of silicon doped LiFePO4 indicate subtle changes in the local structure surrounding the dopants compared to SiO2 and amorphous glass phases formed as impurities in Si containing un-doped samples. The study of Fe and P K-edges X-ray absorption spectra illustrates the effect of Si in the LiFePO4 structure in doped and impurity containing samples. Utilizing X-ray absorption spectroscopy, in conjunction with X-ray fluorescence mapping, has enabled a better overview of the non-uniform nature of prepared ingot samples. These results highlight the power of X-ray absorption spectroscopy as a tool for better understanding the structure of modified LiFePO4 and subsequently designing materials for Li ion batteries. This article is protected by copyright. All rights reserved
关键词： Li ion battery,XRF mapping,XAS,silicon doping,LiFePO4
更新于2025-09-04 15:30:14
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Accurate Fe3+/Fe ratio from XAS spectra at the Fe K-edge
摘要： A new approach to extract accurate information on the Fe oxidation state has been tested on three different Fe-rich amphiboles annealed at 194 °C and 520 °C. The method is based on the analysis of the pre-edge structure of the X-ray absorption spectra at the Fe-K edge. The pre-edge band is deconvolved into four Gaussian components where the integrated intensities of the pairs of lower- and higher-energy bands are related to the ferrous to ferric ion ratio. These Fe3+/Fetot ratios have been compared with those obtained with independent techniques (X-ray diffraction and Mossbauer spectroscopy) on the same samples. The experimental data allowed establishing a calibration curve that is in good agreement with a recent statistical analysis based on spectroscopic data for the same type of minerals. The method could be extended to the analysis of other complex systems containing both Fe3+ and Fe2+ in octahedral coordination or to study the dynamics of iron under non-ambient conditions.
关键词： XAS spectra,oxidation state,amphiboles,Fe3+/Fetot ratio,Fe K-edge
更新于2025-09-04 15:30:14
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The Effect of Charge Transport Mechanisms on the Efficiency of AlxGa1 – xAs/GaAs Photodiodes
摘要： Photovoltaic characteristics of heterostructure AlxGa1 – xAs/GaAs p–i–n photodiodes fabricated by molecular-beam epitaxy have been studied. Efficiencies of 50% were reached in conversion of monochromatic light in the photovoltaic mode at power density of up to 200 W/cm2 at a wavelength λ = 830 nm. A relationship was demonstrated between the “saturation currents” for the diffusion-related charge-transport mechanism (Shockley) in p–i–n photodiodes, calculated from dark current–voltage characteristics, and the experimental values of efficiency. As the “saturation current” of the diffusion-related charge-transport mechanism increases by an order of magnitude, a relative decrease in the efficiency from the maximum value by more than 10% is observed under excitation by constant or pulsed monochromatic light.
关键词： efficiency,charge transport mechanisms,molecular-beam epitaxy,photodiodes,AlxGa1 – xAs/GaAs
更新于2025-09-04 15:30:14
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Band Gap Width Control by Cu Intercalation into ZrSe <sub/>2</sub>
摘要： The CuxZrSe2 intercalation single crystals have been synthesized and studied in a concentration range of x = 0 – 0.3, in which the semiconductor-metal transition was observed. The evolution of the electronic structure of CuxZrSe2 as a function of the copper content has been studied experimentally using the XPS and XAS methods. The obtained results indicate the gradual shift of the Fermi level with increasing copper content, which does not allow the metal-insulator transition to be associated with charge transfer to the conduction band. This transition is associated with the formation of the covalent bond between copper and the nearest selenium atoms and of the p-d hybridized states inside the Zr 4d/Se 4p band gap. First-principle calculations were performed in order to obtain a theoretical description of the density of states near the Fermi level and confirm this conclusion.
关键词： first-principle calculations,covalent bond,Fermi level,CuxZrSe2,semiconductor-metal transition,XPS,XAS,p-d hybridized states,intercalation,electronic structure
更新于2025-09-04 15:30:14