Radiation-Induced Coordination Topological Defects in Chalcogenide Glasses

The radiation-induced (γ-quanta of ⁶⁰Co source) coordination topological defect formation in chalcogenide glasses of quasi-binary AS₂S₃—GeS₂ system is studied using experimental techniques of IR Fourier spectroscopy and positron annihilation lifetime measurements. The new model of open-volume microvoids connected with negatively charged under-coordinated defects is developed at the basis of the obtained results.     

PAL spectroscopy as experimental probe for extended free-volume defects in inorganic glasses and ceramics

Extended free-volume defects trapping positrons are studied in inorganic glasses and functional ceramics using positron annihilation lifetime spectroscopy. Obtained results are treated in terms of general macroscopic approach grounded on physical–chemical properties of the tested materials which depend on the value of free volume content. At the example of chalcogenide glasses of ternary Ge–Sb–S system and spinel-type mixed transition-metal manganite Cu_0.4Co_0.4Ni_0.4Mn_1.8O₄ and magnesium aluminate MgAl₂O₄ ceramics, it is shown that strict correlation exists between numerical values of free volumes of potential positron traps and lifetime parameters determined within two-state positron trapping model.     

Variable angle spectroscopic ellipsometry and its applications in determining optical constants of chalcogenide glasses in infrared

The principle of variable angle spectroscopic ellipsometry(VASE) and the data analysis models, as well as the applications of VASE in the characterization of chalcogenide bulk glasses and thin films are reviewed. By going through the literature and summarizing the application scopes of various analysis models, it is found that a combination of various models, rather than any single data analysis model, is ideal to characterize the optical constants of the chalcogenide bulk glasses and thin films over a wider wavelength range. While the reliable optical data in the mid-and far-infrared region are limited, the VASE is flexible and reliable to solve the issues, making it promising to characterize the optical properties of chalcogenide glasses.     

Pressure dependence of the thermal conductivity of glasses

The volume (pressure) dependence of the thermal conductivity for a number of glasses has been evaluated. The calculation is based on a simple model, assuming the thermal conductivity of the glass to be equal to the minimum of the thermal conductivity, and treating the acoustical phonons by a continuum Debye model, and the optical phonons by an Einstein type model. For SiO₂ based glasses, the logarithmic volume derivative of the thermal conductivity turns out to be small, with both positive and negative values occurring, while for the chalcogenide glass As₂S₃ this quantity is appreciably larger and positive.     

Superionic and ion-conducting chalcogenide glasses: Transport regimes and structural features

Chalcogenide glasses are essentially known as amorphous semiconductors with interesting electronic and optical properties. In contrast to vitreous oxide systems which belong mostly to ionic insulators and/or conductors, the ion transport is not common for chalcogenide glasses and was observed for the first time in the seventies. Nevertheless, a higher polarisability of sulphur, selenium or tellurium compared to oxygen and respectively a higher ionic mobility and diffusivity, makes appropriate chalcogenide glassy systems favourable candidates for both fundamental research and practical applications in the field of solid-state ionics. The observed drastically different ion transport regimes that are closely related to the mobile cation distribution in the structure of silver and copper chalcogenide and chalcohalide glasses will be discussed in the present contribution which represents a compilation of recent results obtained by the author.     

On the super-linear frequency dependent conductivity of amorphous semiconductors

A super-linear frequency dependent conductivity has been observed experimentally in several amorphous semiconductors. An explanation for this behaviour is proposed, in particular for the case of chalcogenide glasses, where it is shown to be a consequence of a particular spatial probability distribution for charged centres. The fundamental mechanism for a.c. conduction in chalcogenide glasses is the same as that proposed previously; namely, the simultaneous hopping of two electrons over the barrier separating two oppositely charged centres, the barrier height being correlated with the intersite separation via the Coulomb interaction. It is demonstrated that this phenomenon should be most marked in those glasses having a large band-gap.     

Photoinduced stable second-harmonic generation in chalcogenide glasses

We report on photoinduced second-harmonic generation (SHG) in chalcogenide glasses. Fundamental and second-harmonic waves from a nanosecond pulsed Nd:YAG laser were used to induce second-order nonlinearity in chalcogenide glasses. The magnitude of SHG in 20G?20A?60S glass was 10(4) larger than that of tellurite glass with a composition of 15Nb(2)O (5) 85TeO(2) (mol.%). Moreover, no apparent decay of photoinduced SHG in 20G?20A?60S glass was observed after optical poling at room temperature. We suggest that the large and stable value of chi((2)) is due to the induced defect structures and large chi((3)) of the chalcogenide glasses.     

Concentration dependence of radiation-induced changes in the optical properties of Ge<Subscript>x</Subscript>As<Subscript>40−<Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>60</Subscript> films

Radiation-induced changes in the optical properties of chalcogenide glasses in the Ge-As-S system are investigated as a function of the concentration. Theoretical calculations are performed with due regard for possible constraints on the range of variation in the number of homobonds and heterobonds upon their switching in the structural network of chalcogenide glasses. The experimental data are obtained upon irradiation of Ge_xAs_40?xS₆₀ thin films with fast electrons (6 MeV). The possible mechanism of structural transformations responsible for the specific features in the concentration dependence of the change in the band gap of chalcogenide glasses is discussed.     

Numerical investigation of taper parameters for high Q infiltrated nanobeam slot microcavities

Photonic nanobeam microcavities are devices for applications where strong light–matter-interaction is needed. They are characterized by a strong field enhancement in a small volume, which can be used for nonlinear optical applications. To enhance such effects, a solid microcavity can be replaced by a slot, that can be infiltrated with a material of choice (e.g. chalcogenide glasses or nonlinear polymers). Here, the parameters needed to create high quality nanobeam slot microcavities are numerically investigated. Design rules for the minimization of scattering losses and thus the enhancement of the Q factor are reviewed and discussed.     

非晶态半导体的缺陷态化学键的量子化学研究

用量子化学的半经验自洽场分子轨道方法CNDO/2研究硫属玻璃中的各种缺陷态,包括带正电荷、负电荷和中性的三配位硫原子簇的化学键。从原子簇能量、原子净电荷、键级函数(双原子能量)等方面作了比较,取得了与Kastner相一致的结果,验证了K-A-F的换价对(VAP)理论。探讨了孤对电子对于缺陷态化学键的影响,证实了孤对电子在硫属玻璃中的重要作用。 关键词：     

Time dependence of the polarization of the luminescence in chalcogenide glasses

Time dependence of the polarization of the luminescence with polarized exciting light and its temperature dependence were observed in chalcogenide glasses. The experimental data can be analyzed with a model based on localized excitons in a fluctuating potential due to random structure of the glasses.     

Self-organization and the physics of glassy networks

Network glasses are the physical prototype for many self-organized systems, ranging from proteins to computer science. Conventional theories of gases, liquids and crystals do not account for the strongly material-selective character of the glass-forming tendency, the phase diagrams of glasses or their optimizable properties. A new topological theory, only 25 years old, has succeeded where conventional theories have failed. It shows that (probably all slowly quenched) glasses, including network glasses, are the result of the combined effects of a few simple mechanisms. These glass-forming mechanisms are topological in nature and have already been identified for several important glasses, including chalcogenide alloys, silicates (window glass and computer chips) and proteins.     

Broadband Infrared Luminescence from Bismuth-Doped GeS2--Ga2S3 Chalcogenide Glasses

Near-infrared luminescence is observed from bismuth-doped GeS2-Ga2Sa chalcogenide glasses excited by an 808 nm laser diode. The emission peak with a maximum at about 1260 nm is observed in 80GeS2-2OGa2 Sa：O.fBi glass and it shifts toward the long wavelength with the addition of Bi gradually. The full width of half maximum （FWHM） is about 200 nm. The broadband infrared luminescence of Bi-doped GeS2-Ga2Sa chalcogenide glasses may be predominantly originated from the low valence state of Bi, such as Bi＋. Raman scattering is also conducted to claxify the structure of glasses. These Bi-doped GeS2 Ga2Sa chalcogenide glasses can be applied potentially in novel broadband optical fibre amplifiers and broadly tunable laser in optical communication system.     

Hot-embossing fabrication of chalcogenide glasses rib waveguide for mid-infrared molecular sensing

Chalcogenide glasses have shown promise in fabricating mid infrared(MIR) photonic sensing devices due to their excellent optical properties in MIR. In addition, the glass transition temperature of chalcogenide glasses are generally low,making them ideal to create the high-throughput patterns of micro-scale structures based on hot embossing that is alternative to the standard lithographic technology. In this paper, we outline the research progress in the chalcogenide waveguide based on the hot embossing method, and discuss the problems remaining to be solved and the possible solutions.     

Recent advancement in metal containing multicomponent chalcogenide glasses

Amorphous semiconductors or chalcogenide glasses are the key materials in modern optoelectronics to make comfortable life of our society. Understanding of physical properties (like microstructure, thermal, optical, electrical) of these materials is important for their different uses. Predominant study of physical properties of the metal containing multicomponent chalcogenide glasses have attracted much attention, due to their interesting variable features and wide range of structural network modifications. Structural modifications in these materials are usually described with respect to the values of structural units (or average coordination number). In significance to this, the present work demonstrates the chronological development in the field of chalcogenide glasses along with scanning electron microscopy (SEM) morphologies. Optical, electrical and thermal correlative properties of recent developed Se_93?xZn₂Te₅In_x (0 ?? x ?? 10) metallic multicomponent chalcogenide glasses are discussed. Variation in SEM morphology, refractive index (n), extinction coefficient (K), optical energy band gap (E_g), electrical conductivity (??_av), crystallization activation energy (E_c) and glass forming ability (GFA) with structural units of Se-Zn-Te-In glasses have been demonstrated in this study. Subjected materials thermal, optical and electrical parameters have been achieved higher and lower in a respective manner at the threshold structural unit value ??r??.     

Chalcogenide glasses as a medium for controlling ultrashort IR pulses: Part I

Chalcogenide glasses are ideal materials for developing fiber lasers and amplifiers, remote sensors, high-speed switches, and other devices that operate in the IR range of 1–10 μm. The nonlinear refractive index of chalcogenide glasses may exceed that of quartz glass by a factor of 100–1200 or even more. The data on the dispersion properties of some chalcogenide glass compositions in the IR range are presented. The possibility of forming waveguide structures with specified dispersion properties (in particular with a fixed wavelength at which the group velocity dispersion is zero) from these glasses is numerically investigated. It is shown by the example of completely glassy periodic waveguide structures with planar geometry that the use of photonic band gap modes makes it possible the change the position of zero dispersion in a wide wavelength range. In the calculations the contrast of waveguide structures was varied using parameters of glasses of different composition.     

Middle-infrared chalcogenide glass fibers with losses lower than 100 db km−1

Optical losses and mechanical strength of chalcogenide glass fibers prepared by crucible technique are reported. Mechanisms of optical losses in the high-transparancy region of chalcogenide glasses are discussed.     

Wide-angle stop-gap chalcogenide photonic crystals generated by direct multiple-line laser writing

We present the fabrication and the angle-resolved optical characterizations of three-dimensional chalcogenide photonic crystals with a wide-angle stop gap. Multiple-line scanning provides an effective remedy to the elongation of the focal spot in the z direction during direct laser writing fabrication in high refractive index and highly nonlinear chalcogenide glasses. The aspect ratio of the rods is reduced from 4.46 to 1.53, thus allowing the successful fabrication of three-dimensional chalcogenide photonic crystals with a face-centered cubic symmetry and quasi-circular rods. Suppression of the angle-resolved transmission spectra is observed at a wide range of incident angles.     

129I-Mössbauer spectroscopic study of iodide-containing chalcogenide glasses

¹²⁹I-Mössbauer spectroscopy was used to study the short-range order in I-containing chalcogenide glasses. It was found that AsXI glasses, where X=S or Se, are molecular solids composed from molecular units of arsenic iodide and arsenic chalcogenide. The local environment of iodide ions in ternary superionic conducting glasses AgI?Ag₂S?As₂S₃ is similar to that in the crystalline superionic conductor Ag₃SI and differs distinctly from iodide local order in binary vitreous alloys AgI?As₂S₃ and crystalline AgI.¹²⁹I-Mössbauer spectra of all glasses were fitted satisfactory, when a distribution of the electric-quadrupole coupling constant is taken into account.     

Freely adjusted properties in Ge–S based chalcogenide glasses with iodine incorporation

In this study, we examined the function of halogen iodine acting as a glass network modifier in green chalcogenide glasses based on the Ge–S system. We obtained a series of Ge–S–I glasses and determined their glass-forming region. We then recorded the physical, thermal, and optical properties and studied the effect of halogen iodine on Ge–S–I glasses. Results show that these glasses have relatively wide optical transmission window for infrared (IR) applications. The softening temperature of Ge–S–I glasses varies from 210.54 °C to 321.63 °C, this temperature fits well with some kinds of high-temperature polymers, such as PES and PEI, the polymers serve as protective layers with high strength and flexibility, thus simplifying the fabrication processes of IR chalcogenide glass fiber. Finally, we performed a purification process to eliminate impurities and to improve optical spectra.