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Elastic and optoelectronic properties of CaTa2O6 compounds: Cubic and orthorhombic phases
摘要： Using first principles density functional theory (DFT) simulations, the structural, electronic, optical and elastic properties of CaTa2O6 oxide for cubic and orthorhombic phases are studied by highly accurate (FP-LAPW) method within the GGA + U approximation. The calculated lattice parameters are consistent with available experimental data. The electronic band structure calculations have shown that the band gaps in CaTa2O6 are equal to 3.08 eV and 4.40 eV for the cubic and orthorhombic structures, respectively. For both the phases the main optical properties, e.g., absorption coefficient, dielectric constant, energy loss function, and reflectivity, refractive index, and extinction coefficient are calculated and discussed in detail in the spectral range 0-14 eV. Cubic and orthorhombic phases exhibit significantly different optical characteristics. The electronic bonding characters of CaTa2O6 with different symmetries are explored via charge density distribution mapping. Strong covalent bonding character dominates in both the phases of CaTa2O6. Elastic properties of CaTa2O6 for cubic and orthorhombic phases are also investigated. The stress strain method is used for the determination of elastic constants in both the phases. The bulk modulus, shear modulus, Young’s modulus, along with the important elastic anisotropy factors and Poisson’s ratio are studied in detail.
关键词： First principles density functional theory,GGA+U approximation,FP-LAPW method,Optical constants,Electronic band structure,electro technical materials
更新于2025-09-23 15:22:29
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Electronic structure and photoluminescence of Dy3+ single-doped and Dy3+/Tm3+ co-doped NaBi(WO4)2 phosphors
摘要： A single-phase white light emitting NaBi(WO4)2:Dy3+, Tm3+ phosphor has been successfully prepared by conventional high-temperature solid-state method. First-principles calculations were used to investigate the electronic structures of NaBi(WO4)2. The calculation results show that NaBi(WO4)2 has an indirect band gap with 3.02 eV. The crystal structure and PL properties of the obtained phosphor are characterized by SEM, powder X-ray and photoluminescence spectra, respectively. The results demonstrate that all as-prepared crystalline in a tetragonal crystal system with a space group of I4ˉ. PL results confirmed that the obtained phosphors can be efficiently excited by 365 nm and generated white light emission. Then the energy transfer between Dy3+ and Tm3+ in the host NaBi(WO4)2 was investigated. Finally, the chromaticity coordinates of preferred NaBi0.91-x(WO4)2:0.09Dy3+, 0.11 Tm3+ (0.3319, 0.3395) were close to the standard white light point (0.333, 0.333). All these results reveal that NaBi(WO4)2:Dy3+/Tm3+ was a potential single phase white light-emitting phosphor candidate for NUV-based w-LEDs.
关键词： White emission,Luminescence properties,Electronic structure,NaBi(WO4)2:Dy3+/Tm3+
更新于2025-09-23 15:22:29
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Infrared Spectroscopy on Electronic Structures of Platinum-group Metal Pernitrides MN2 (M = Ru, Rh, Ir, and Pt)
摘要： The electronic structures of platinum-group metal pernitrides MN2 (M = Ru, Rh, Ir, and Pt) were investigated via synchrotron radiation infrared spectroscopy and first-principles calculations. Measured reflectance spectra of marcasite-type RuN2 and RhN2 showed Drude-like responses, approaching 1 as the photon energy was decreased, whereas reflectance of arsenopyrite-type IrN2 and pyrite-type PtN2 became ~0.3 in the low photon energy region with a few features. These findings agreed well with the predictions of the metallic nature of marcasite-type RuN2 and RhN2 and the semiconducting properties of arsenopyrite-type IrN2 and pyrite-type PtN2, respectively. The measured reflectance spectra were also reasonably consistent with the calculated optical responses. The band gaps of IrN2 and PtN2 were estimated to be 0.8 and 2.1 eV, respectively, via first-principles calculation with a modified Becke–Johnson (MBJ) potential for the exchange potential.
关键词： first-principles calculation,platinum-group metal pernitride,infrared reflectance spectra,valence band electronic structure
更新于2025-09-23 15:22:29
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Electronic structure and hydrogen evolution reaction in layered ReS<sub>2</sub> regulated by alkali-metal atom intercalation
摘要： Recently, the atom intercalation method has been developed and applied into two-dimensional (2D) materials to regulate their pristine physical property. However, as an important application in hydrogen evolution reaction (HER), the influence of alkali-metal-intercalated technology upon 2D material's electronic structure and catalytic activity should be investigated systematically. In this work, layered ReS2 crystals with a charge decoupling are chosen as a model to explore changes in electronic structure and Gibbs free energies induced by alkali-metal intercalated compounds and external strain. The calculated results disclose that the structural transformation induced by intercalated alkali atom and external strain not only leads to decrease in band gap of ReS2 but also make Gibbs free energy of adsorbed hydrogen close to zero. Our calculations provide an insight to improve HER performance by a simple alkali-metal-intercalated technology.
关键词： hydrogen evolution reaction,electronic structure,alkali-metal-intercalated technology
更新于2025-09-23 15:22:29
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Hybrids made of defective nanodiamonds interacting with DNA nucleobases
摘要： The characteristics of hybrids made of a defective nanodiamond and a biomolecule unit are investigated in this work. Focus is given on the interaction between the nanodiamond and a DNA nucleobase. The latter is placed close to the former in two different arrangements, realizing different bonding types. The nanodiamond includes a negatively charged nitrogen-vacancy center and is hydrogen terminated. Using quantum-mechanical calculations, we could elucidate the structural and electronic properties of such hybrids. Our study clearly identifies the importance of the relative orientation of the two components, the nanodiamond and the nucleobase, in the complex in controlling the electronic properties of the resulting hybrid. The position of the defect at the center or closer to its interface with the nucleobase further controls the electronic orbitals around the defect center, hence its optical activity. In the end, we discuss the relevance of our work in biosensing.
关键词： electronic structure,defects,DFT,DNA,nanodiamond
更新于2025-09-23 15:22:29
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Optical absorption via intersubband transition of electrons in GaAs/Al <sub/>x</sub> Ga <sub/>1?x</sub> As multi-quantum wells in an electric field
摘要： Based on the effective mass approximation, the Schr?dinger equation and Poisson equation in GaAs/AlxGa1?xAs multi-quantum wells (MQWs) are self-consistently solved to obtain the wave functions and energy levels of electrons in the conduction band for the ground first excited state by considering a lateral electric field (LEF). Then, the effects of size, ternary mixed crystal, doping concentration, and temperature on linear and nonlinear intersubband optical absorption coefficients (IOACs), and refractive index changes (RICs) due to the transition between ground states and the first excited states of electrons are discussed based on Fermi’s golden rule. The results show that, under a fixed LEF, with increase of Al composition and doping concentration, the IOACs produce a red shift. With increases of both widths of the wells and barriers IOACs appear as blue shifts and their amplitudes increase, but the barrier width change is much more important to affect nonlinear IOACs, whereas increasing the temperature results in a blue shift first and then a red shift of IOACs. When the other parameters are fixed but there is an increase in the LEF, IOACs occur with a blue shift, and the RICs have similar properties.
关键词： multi-quantum wells,optical absorption of electronic intersubband transition,refractive index changes,lateral electric field
更新于2025-09-23 15:22:29
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[IEEE 2018 International Flexible Electronics Technology Conference (IFETC) - Ottawa, ON, Canada (2018.8.7-2018.8.9)] 2018 International Flexible Electronics Technology Conference (IFETC) - Stretchable Optical and Electronic Fibers via Thermal Drawing
摘要： Stretchable optical and electronic fibers constitute increasingly important building blocks for a myriad of emerging applications, such as smart textile, robotics, or medical implants. Yet, it remains challenging to fabricate efficient and advanced soft fiber-base devices in a simple and scalable way. Conventional fiber manufacturing methods, such as wet and dry spinning, or extrusion, are not well adapted to fabricate multi-material functional fibers. The thermal drawing technique on the other hand is an emerging powerful platform to fabricate multi-material fibers with complex architectures and functionalities. Thus far however, this fabrication approach has been restricted to rigid thermoplastic or glass fibers. In this contribution we will show how we could revisit the selection criteria for cladding materials compatible with the thermal drawing process. In particular, thanks to a deeper rheological characterization, we could identify thermoplastic elastomers that could be drawn from a solid preform at high viscosity. Subsequently, we will demonstrate that thermoplastics, metals, and conductive polymer composites could be co-drawn with prescribed architectures within thermoplastic elastomer cladding. This allowed us to successfully fabricate stretchable optical and electronic fibers that are used as precise and robust pressure and strain sensors, as well as soft and stretchable waveguides as we will show via concrete examples, the ability to thermally draw soft multi-material fibers open new opportunities not only for exploring new academic research directions, but also in industrializing fiber-based flexible and stretchable devices for applications in sensing, health care, robotics and smart textiles.
关键词： fibers,electronic,thermoplastic,stretchable,optical
更新于2025-09-23 15:22:29
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Recent Advancement of Semiconductor Materials and Devices
摘要： 本論文では, 主に GaAs および GaAs 系混晶半導体の MBE 成長とそのデバイス応用について取り上げたが, その他にも窒化物半導体, 酸化物半導体, II-VI 族半導体といった多くの半導体の成長や, 量子細線, 量子ドットのような量子井戸以上に複雑な構造の製作にも MBE 法は活用されている. 基礎研究から実用化まで, 半導体デバイスの開発において MBE 法が成し遂げてきた功績は極めて大きい. 今後も素子構造の製作, 新規半導体材料の成長, 結晶欠陥の制御など様々な要求のある結晶成長時に MBE 法は活用され続けるであろう.
关键词： Compound semiconductors,Optical and electronic devices,Molecular beam epitaxy
更新于2025-09-23 15:22:29
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Charge Transfer Tuned by the Surrounding Dielectrics in TiO2-Ag Composite Arrays
摘要： TiO2/Ag bilayer ?lms sputtered onto a 2D polystyrene (PS) bead array in a magnetron sputtering system were found to form a nanocap-shaped nanostructure composed of a TiO2-Ag composite on each PS bead, in which the Ag nanoparticles were trapped partially or fully in the TiO2 matrix, depending on the TiO2 thickness. X-ray Photoelectron Spectroscopy (XPS) results showed the opposite shifts of binding energy for Ti 2p and Ag 3d, indicating the transfer of electrons from metallic Ag to TiO2 owing to the Ag-O-TiO2 composite formation. UV-Vis absorption spectra showed the blue shifts of the surface plasma resonance peaks, and the maximum absorption peak intensity was obtained for TiO2 at 30 nm. The surface-enhanced Raman scattering (SERS) peak intensity ?rst increased and then decreased when the TiO2 thickness changed. The observations of SERS, XPS, and UV-Vis absorption spectra were explained by the dependency of the charge-transfer process on TiO2 thickness, which was ascribed to the changing dielectric properties in the metal/semiconductor system.
关键词： electronic transfer,TiO2-Ag composites,surrounding dielectrics
更新于2025-09-23 15:22:29
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The utility of an omni-directional photoelectronic sensor device to measure meso-scale variability in aeolian sediment transport activity
摘要： Electronic sensors (i.e., acoustic, piezoelectric, and photoelectric) have been utilized extensively and effectively in recent years for measuring aeolian transport intensity. The bulk of these studies, however, position the devices in stationary, fixed orientation during field experiments. These practices work fine for shorter, micro-scale field studies; yet, during longer experiments lasting months or even years, a fixed directional orientation is unrealistic due to shifts in wind direction. This issue has ultimately limited the use of electronic sensors for meso-scale aeolian research. In light of this constraint, this paper presents a device to measure aeolian transport activity across a 360-degree azimuthal range. The Rotating Wenglor Device (RWD) was deployed on Santa Rosa Island, Florida for a three-month field study. The data reveal that the prevailing transport activity did not align with the dominant wind direction. The implications of this finding can be further elucidated when analyzing our data using the Fryberger drift potential model. Our findings indicate that the traditional Fryberger method, constructed using our wind data, produced a resultant transport drift towards the northwest; however, the RWD illustrated a resultant transport direction towards the northeast and at a rate three times slower. These finding highlights a major benefit of the RWD as it would produce a more accurate measure of meso-scale transport activity and therefore dune development than models derived strictly from meteorological station data, such as the Fryberger method. An additional advantage of the RWD is that the device operates unattended for extended periods, yet can provide high-resolution data regarding micro-scale transport dynamics.
关键词： Sediment transport,Omni-directional,Electronic sensors,Meso-scale,Instrumentation,Wenglor
更新于2025-09-23 15:22:29