Infrared optical properties and crystal structure of Cu2GeS3

Infrared reflectivity and transmission spectra of Cu₂GeS₃ are measured at room temperature in the wavenumber range from 180 to 4000 cm⁻¹. From an analysis of the spectra the parameters of the fundamental infrared active lattice modes and of the two-phonon combination modes are determined. From a comparison of the experimental data with group theoretical predictions for the structure models proposed for Cu₂GeS₃ in the literature it is concluded that Cu₂GeS₃ crystallizes in a monoclinic lattice.     

GeS/MoS2异质结电子结构及光学性能的第一性原理研究

以MoS₂、GeS为代表的二维层状材料在光学、电学等方面表现出优异的物理性能。如何将两者的优良性能结合,同时获得具有新的协同功能的复合材料对电子器件的发展和应用具有重要意义。本文采用密度泛函理论的第一性原理计算方法,对GeS/MoS₂异质结的电子结构及光学性质进行了系统研究,并探索了界面间距、应变和电场对异质结电子结构和光学性能的影响。研究结果表明,GeS/MoS₂异质结是Ⅱ型能带排列,该能带排列有利于光生电子-空穴对的分离。进一步研究发现,通过应变和电场等手段可以实现对GeS/MoS₂异质结能带排列及光吸收系数的有效调控。该研究结果表明GeS/MoS₂异质结在光催化、光电器件等领域具有潜在的应用,为设计与制备GeS/MoS₂相关的光电器件提供了理论指导。     

Optical absorption in vitreous GeSb2Se4

Optical absorption of vitreous GeSb₂Se₄ was studied in spectral region 0.7–25 μm. At low absorption levels near the edge the absorption coefficient K depends exponentially on energy. At high absorption levels the quadratical energy dependence of K is observed. In the present work we determined the optical energy gap E^opt_g = 1.29 eV and discussed the temperature dependence of the absorption coefficient. Measured reflectivity curves were used to estimate the value of the refractive index of GeSb₂Se₄ ($\text{n = 3.13–3.56}\text{at}\text{h}\text{?}\text{ω = 1.00–1.70}\text{eV}$). Vitreous GeSb₂Se₄ is also transparent in the spectral interval 2–15.7 μm.     

Influence of doping on physical properties of vitreous As2Se3

The influence of impurities added in different chemical forms on the physical properties of vitreous As₂Se₃ is investigated. The impurities used can substantially change the electrical (U, Ga, and Cu), dielectric (U, Tl, Ge, and Cu), thermo-physical (O, Ge, and Tl), or mechanical (B, Hg, In) properties of the glass. Doping with small amounts of oxygen results in a distinct decrease of T_g. The most electrically effective impurity is U – at 0.2 mol%; it decreases the conductivity by 10⁻³ times and the permittivity by 25%. For electrical applications, Ti seems to be a suitable scavenger; it binds oxygen effectively but influences the electrical conductivity only slightly.     

Optical properties of flash-evaporated CuInTe2 thin films

Optical absorption spectra of flash-evaporated polycrystalline thin films of CuInTe₂ are measured in the photon energy range from 0.5 to 3.0 eV. A gap energy in the range from 0.96 to 0.99 eV and a spin-orbit splitting of the valence band of 0.61 ± 0.03 eV are derived from the spectra. It is found that the spectra are considerably influenced by grain boundary effects.     

Thermal properties of vitreous silica with He impurities

The specific heat and thermal conductivity of vitreous silica (Suprasil W) doped with He at 420°C and 200 bar has been measured at low temperatures (0.5 K to 8 K). While with respect to an undoped sample the specific heat shows an excess contribution which varies as T^1.7, no effect of doping on the thermal conductivity is observed. This shows that the coupling to phonons of the excitations introduced by He doping is weak compared to that of intrinsic low energy excitations common to glasses. The excess specific heat can be attributed to excitations of He atoms in cavities.     

Crystallization effects in annealed thin GeS2 films photodiffused with Ag

We have investigated the diffusion products occurring after photodiffusion of Ag in GeS₂ films at room temperature and after annealing up to 430 °C. Quantitative data regarding the host film composition and the amount of diffused silver has been gathered using Rutherford backscattering spectrometry. The structure of the glassy host and the changes appearing after silver photodiffusion and annealing are characterized using Raman spectroscopy. The crystalline diffusion products are depicted and their size calculated using X-ray diffraction. We have found that silver reacts with the host to form Ag₂S and Ag₂GeS₃ and this leads to formation of Ge-rich backbone and overall nanostructured heterogeneous medium. Annealing at temperatures close to the glass transition temperature affects the backbone and brings about the appearance of a new diffusion product – Ag₈GeS₆.     

Optical properties of 2‐aminopyridinium nitrato silver

Crystals of 2‐aminopyridinium nitrato silver have been synthesized by slow evaporation method. Grown crystals have been subjected to FTIR, Single crystal X‐Ray diffraction and UV‐Visible studies in order to investigate the structural and optical properties of the crystal. The FTIR spectrum reveals the presence of the functional group that corresponds to both 2‐aminopyridine and silver nitrate, suggesting the formation of the compound, 2‐aminopyridinium nitrato silver. From XRD it is observed that the crystal crystallizes in the structure of monoclinic with the space group of P2₁/c. The optical transmittance spectrum shows the maximum transparency of about 95% in the visible region is in consistent with the wide band gap, estimated as 4.738 eV. The optical constants n and k has also been determined from the transmittance data. The static dielectric constant is found to be 0.851. The wide band gap and the less dielectric constant suggest the suitability of this compound material for photoconductive applications. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties of selenite glasses

The aim of this work is to obtain multicomponent selenite glasses containing other non-traditional glass formers such as V₂O₅, TeO₂ and MoO₃ and to verify their optical properties in the visible spectral region. Glasses containing MoO₃ and TeO₂ are transparent in the visible range and near IR region from 400 to 2300 nm. Transparent coloured glasses were obtained due to the electron transfer charge processes. Using IR spectroscopy it was determined the main building units of the amorphous network. It was found the presence of TeO₄, SeO₃ and MoO₄ units.     

Optical properties of chalcogenide glasses

Over the past two decades chalcogenide glasses have been researched in order to assess their suitability as passive bulk optical component materials for 3–5μm and 8–12μm infrared applications. This research has led to a greater understanding of the physical properties of these materials, and the present paper concentrates on the optical properties and applications of these bulk chalcogenide glasses. The various factors influencing the intrinsic and extrinsic optical loss mechanisms in materials are discussed, numerical data on the basic optical properties of chalcogenide glasses is presented and applications are discussed.     

Optical properties of ZnO nanotubes

Tubular ZnO nanostructures have been obtained via a hydrothermal method at low temperature (90 °C) without any catalysts or templates. The XRD measurement reveals that the tubes are single crystals with hexagonal wurtzite structure. SEM shows that the diameters of ZnO nanotubes ranged from 400 to 550 nm. The Raman and PL spectra indicate that oxygen vacancies or Zn interstitials are responsible for the green emission in the ZnO nanotubes. A possible growth mechanism on the formation of crystalline ZnO nanotubes has been presented. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties of amorphous semiconductors

The density of states and the dielectric constant of electrons in crystalline solids can be discussed easily by using the band structure scheme. This is due to the fact that a crystal is defined by both a short range order and a long range order of atoms. If the long range order is relaxed this procedure no longer works and one has to calculate the measurable quantities directly, which involves some configurational averaging process.     

Luminescence behaviors of the Eu2+ ions in the GeS2-Ga2S3-CsCl chalcohalide glasses

In the paper, we report the luminescence behaviors of Eu²⁺-doped chalcohalide glasses. Composition of glass matrix is 37.5GeS₂-22.5Ga₂S₃-40CsCl (mol%) with the concentration of Eu²⁺ in the range of 0.1–0.25 (mol%). The optimal Eu²⁺ doping concentration was 0.15 mol% at which the glass exhibited an enhanced emission peaking at 434 nm with a full width at half maximum (FWHM) about 80 nm with the excitation at 395 nm.     

Origin of Rayleigh scattering and anomaly of elastic properties in vitreous and molten GeO2

Vitreous (v) and molten (m) GeO₂ were studied by Rayleigh and Mandel’shtam–Brillouin scattering spectroscopy and high-temperature acoustics. Original measurement apparatus and procedure were used that included Bayseian deconvolution of light scattering spectra of vGeO₂ and a specially designed high-temperature (up to 1500 °C) acoustic interferometer to measure temperature and frequency dependence of ultrasonic (US) velocity and attenuation in mGeO₂. Landau–Placzek ratios for vGeO₂ were found optically (from the light scattering spectrum) and acoustically (through the Schroeder’s formalism). Dispersion of optical and other physical parameters of vGeO₂ found by many authors is explained by the existence of small amount of GeO in the samples. It means that properties of vGeO₂ are under the influence of redox synthesis conditions controlling the GeO₂ ↔ GeO and coordination [GeO₄] ↔ [GeO₆] equilibrium in vGeO₂. Measurements of temperature dependencies of longitudinal ultrasonic velocities in mGeO₂ and in the PbO–GeO₂ glass melts as a function of PbO concentration shows existence of ‘water-like anomaly’ in mGeO₂ and in liquid germanates with the rich content of GeO₂ where equilibrium sound velocity increases with the temperature.     

Crystal structure and specific features of formation of vibrational spectra of Pb2GeS4

The structure of Pb₂GeS₄ single crystals is confirmed and the polarized Raman spectra of these crystals are recorded. The vibrational spectra was considered in terms of analysis of intramolecular vibrations of [GeS₄] tetrahedral formations, the main structural elements of this compound.     

Silver sulfide based glasses: (II). Electrochemical properties of GeS2Ag2SAgl glasses: transference number measurement and redox stability range

The transference numbers of the species responsible for current transport, in GeS₂Ag₂SAgI glasses, have been determined. Tubandt's method shows that the transference number of the Ag cation is equal to 1 (to within 2%). By electrochemical semipermeability flux measurement, the electronic transference number was estimate to be less than 10^?8, and by tringular voltammetry, the transference number of the iodide anion at approximately 10^?5. Triangular voltammetry can also be used to measure the redox stability range, which is about 3 V for current densities of 0.1 mA/cm². This high value is due to the low mobility of the anions below the glass transition temperature.     

Controlled crystallization of GeS2–Sb2S3–CsCl glass for fabricating infrared transmitting glass-ceramics

The crystallization of selected glasses from the GeS₂–Sb₂S₃–CsCl ternary system has been studied under non-isothermal condition. The nucleation and crystal growth mechanisms have been investigated and proved to be dependant on the glass composition. It has been found that the 80GeS₂–10Sb₂S₃–10CsCl is a good candidate for controlled crystallization. The best nucleation temperature and time have been determined. Crystals of about 20–30 nm have been uniformly generated in the glass and the obtained glass-ceramics have the same transmission in the mid and far infrared transmission.