A model of photostructural changes in chalcogenide vitreous semiconductors: 1. Theoretical considerations

Light-induced processes in chalcogenide vitreous semiconductors are considered in the framework of a configurational model of two stable states (ground and metastable) of atomic units with optical and thermal transitions between these states. Probabilities of these transitions as functions of photon energy and temperature are calculated. an expression for the metastable state population kinetics is given.     

Nuclear magnetic resonance in water solutions of inorganic salts in vitreous and liquid states

Peculiarities of the behavior of water solutions of inorganic salts at temperatures of ～(120–150) K are examined. At these temperatures the solutions are in the vitreous state. At higher temperatures (up to 240 K) the solutions may be in metastable liquid, crystalline, or usual liquid states.     

A new model for the structure of chalcogenide glasses: The closed cluster model

A new model is proposed for the structure of low atomic coordination chalcogenide glasses. The closed clusters model is based on the various types of clusters, packed by van der Waals forces in a molecular-type packing. Arguments are given to support the new model, taken as example the typical chalcogenide glass As₂S₃.     

Characteristics of structure formation in zinc and cadmium chalcogenide films deposited on nonorienting substrates

The phase composition, texture quality, size of coherent scattering domains, microstrain level, and concentration of stacking faults in zinc and cadmium chalcogenide (ZnS, ZnSe, ZnTe, CdSe, CdTe) films deposited by close-spaced vacuum sublimation method on nonorienting substrates have been investigated. The analysis was performed by X-ray diffraction. The substructural characteristics were determined from the physical broadening of diffraction lines using the Hall method and threefold convolution. The dependence of the structural properties of chalcogenide films on the deposition conditions are characterized.     

Synthesis and structure of new systems containing pyramidalized double bonds

Syn- andanti-isomers of substituted tetracyclo[6.2.2.2^3.6.1^2.7]tetradeca-2(7)-ene have been synthesized. In thesyn-isomers steric interactions between cyclopropane hydrogen atoms lead to a pyramidalization of the C(sp²) atoms of the central double bond. The parameters from three crystal structures are compared with geometry optimized structures using PCWIN, MM3, and MOPAC. Plots of X-ray distances versus theoretically optimized distances give correlation coefficients between 0.91 and 0.97. Analysis of the discrepancies suggest modifications in some molecular mechanics parameters are needed to model the solid state structures.     

Selective wet-etching and characterization of chalcogenide thin films in inorganic alkaline solutions

This paper deals with sensitivity of chalcogenide based photoresists in inorganic alkaline solutions. The thin films of As₃₃S₆₇, As₃₃S₅₀Se₁₇, As₃₃S_33.5Se_33.5, As₃₃S₁₇Se₅₀, and As₃₃Se₆₇ were studied. The selective wet-etching was carried out using NaOH, Na₂S and (NH₄)₂S alkaline solutions. The different sensitivity according to sample composition and used etching solution were found. Chalcogenide films as a potential photoresists could be classified either as ‘high-contrast’ or ‘low-contrast’ depending on the sample compositions, type of etchant and its concentration or on incident light energy.     

Investigation of inorganic network formation in photopatternable hybrid sol-gel films by Si liquid NMR

Liquid ²⁹Si NMR spectroscopy was used to investigate the sol-gel process of methacryloxypropyltrimethoxysilane. This hybrid precursor was involved in the realization of optical elements in laminated crack-free thick films (up to 100 μm), through spatially controlled photopolymerization. Understanding the formation of the inorganic network was of first importance to insure the creation of crack-free photopatterned thick films in a laminated configuration. Material preparation required evaporation of the volatile solvents released during the sol-gel process and limitation of the condensation degree. Both conditions were achieved by a drying process at room temperature. The structure and the composition of the sols were investigated and compared to non-dried sols. Evolution of inorganic species distribution was also studied under increasing aging time or storage temperature. NMR peak fitting of T1 species gave fruitful information on the sol structure evolution during the sol-gel process. It pointed out the presence of a large variety of oligomers in the sol. The study also allowed the identification of more constraint cyclic species in dried sols stored at room temperature. Their amount significantly decreased when increasing the storage temperature and was attributed to ring opening of cyclic species. Consequently, the structure of the dried sol will depend both of the aging time and of the storage temperature. All these results have to be taken into account when the degree of condensation has to be limited to achieved photopatternable hybrid layers for specific optical applications.     

Glass formation and properties of chalcogenide systems XXVI: Permittivity and the structure of glasses AsxSe1−x and GexSe1−x

Correlation between the real part of the dielectric constant and the structure of glasses in the system As_xSe_1?x and Ge_xSe_1?x is reported. The mole polarization is calculated using the Sellmeyer approximation neglecting the Lorentz field. The vibrationally caused part of the permittivity which is obtained by subtraction of the mole refraction reflects ordered states in the investigated series. Besides the known crystalline compounds As₂Se₃ and As₄Se₄ the formation of the vitreous AsSe₃ and As₃Se₂ from the liquid state has to be supposed. In the system Ge_xSe_1?x the formation of the compounds GeSe₂ and Ge₂Se₃ is completed by GeSe₄ which as Ge₂Se₃ obviously only exists in the non-crystalline state. GeTe₄ has been reported as a metastable crystalline phase. The temperature dependence of ?_r of vitreous As₂Se₃ is tentatively interpreted in terms of the dipole orientation caused by conversion of the charge in valence alternation pairs.     

Emission and local structure of rare-earth ions in chalcogenide glasses

Local structures of rare-earth ions in Ge–Ga–S–CsBr glasses were investigated to understand the structural origin on the emission property enhancement. The frequency of the phonon vibration controlling the multiphonon relaxation was changed to 245 cm⁻¹ due to the formation of Ga–Br bonds with CsBr addition to sulfide glasses. Formation of this new chemical bond was also confirmed from the phonon side band spectra of Eu³⁺ ions. Analyses of the EXASF spectra proved that Tm³⁺ ions were surrounded by approximately seven S ions in Ge_0.25Ga_0.10S_0.65 glass but were coordinated by ∼6 Br ions in the glass with 10 mol% of CsBr.     

The relationship between statistical aspects of switching and the structure of chalcogenide glasses

Variation in the switching parameters, threshold voltage and delay time, has been observed for devices based on bulk chalcogenide glass. Experimental analysis revealed that the variation has two main components: (1) slow semi-reversible ageing taking place throughout the life of the device, (2) fast fluctuations occurring from operation to operation. It was further shown that the latter variation is not random but that correlation exists between sequential switching operations. A semi-quantitative theoretical model is presented to explain the observed phenomena in terms of microstructural changes in the glass during switching.     

Glass formation regions and chemical durability of some ZnCl2-based halide systems

This paper describes the glass formation behavior and chemical durability of some ZnCl₂-based halide glasses. Different corrosion mechanisms are discussed with respect to oxide glass and halide glass.     

The effect of charged additives on the conductivity and the thermopower in liquid selenium

The simultaneous measurements of conductivoty σ and thermopower S for liquid Se and its dilute mixtures containing Na, Tl and Cl have been performed in the temperature and pressure range up to 1500°C and 2200 bar. The addition of Na, Tl and Cl give rise to a substantial increase in σ at low temperatures. The value of S of liquid Se is large positive at low temperature. The sign of S is changed to be negative by addition of Na and Tl. By the addition of Cl the sign of S remains positive and the value increases. The effect of charged additives on the transport properties of liquid Se is discussed in connection with the change of the bonding configuration.     

The radial distribution function and structure factor of liquid and amorphous gallium as described by the quasi-crystalline model

The far RDF oscillations and the main peak of the structure factor for liquid and amorphous gallium are described in terms of the quasi-crystalline model representing spatial correlations in liquids on the basis of a smeared crystal lattice. The initial lattice is a modified BCC lattice for liquid gallium and β-Ga structure for the amorphous state. The liquid gallium structure is inferred to be closely packed atoms complicated by their covalent coupling. Amorphous gallium has a microcrystalline structure with islets formed in a similar way as for β-Ga crystals.     

Solid-state studies. Part XXIV: Raman spectral consequences of disorder in the structure of phase II of ammonium nitrate

The Raman spectra of a wide variety of isotopomeric polycrystalline samples of phase II of ammonium nitrate are explained on a model in which the disorder within the lattice is incorporated within factor-group correlations. This model also provides an explanation for the single crystal Raman data.     

Strain of interatomic bonds and multiple-well potential in crystals with perovskite structure

A method for determining the strain characteristics of interatomic bonds in crystals of ABX₃ compounds with perovskite structure is developed. The bond strain energy ΔU _s is estimated. This energy is responsible for the formation of ordered lattice distortions related to the rotation of octahedra and/or the cooperative displacement of cations. It is shown that ΔU _s correlates with the characteristics of ordered distortions and the temperature of the phase transition of compounds to the cubic structure. It is ascertained that the interatomicinteraction potential in crystals with strained bonds is a local multiple-well potential, the form of which depends on the nature of interacting atoms. It is shown that the occurrence of the ferroelectric state in the noted crystals may be due to the presence of bond strains and the anisotropy of the covalent component of the cation-anion interaction.     

The role of hydrodynamics and supersaturation in the formation of liquid inclusions in KDP

The formation of liquid inclusions in large potassium dihydrogen phosphate crystals is a result of depletion in stable eddies formed at the rear (downstream) faces. A large concentration jump can be expected at the point where the “exhausted” fluid meets the fresh liquid. The response of a step train on a jump in supersaturation has been investigated by means of computer simulations. The results are in good agreement with the experiments.     

The charge transfer and ion formation in liquid Li–Tl alloys

The ⁷Li NMR Knight shift, K, and the spin-lattice relaxation time, T₁, were measured for liquid Li–Tl alloys. The K decreases rapidly with the addition of Tl up to 20 at.% Tl. In the concentration from 20 to 50 at.% Tl, the K decreases only slightly and the K of 50 at.% Tl is 60% of K for the pure liquid Li. Such a decrease of K is considered as an indication for the strong charge transfer from Li to Tl. These tendencies are similar to those from previous studies for liquid Li–Ga and Li–In alloys. However, beyond 50 at.% Tl, the K increases and reaches to an almost constant value (70% of K for the pure liquid Li). Such a back donation of charge is absent for liquid Li–Ga and Li–In alloys. It is considered that the tendency of the formation of ionic structural unit for liquid Li–Tl alloys is slightly weaker compared with the cases of liquid Li–Ga and Li–In alloys. The T₁ is also discussed with the relation to the Knight shift and the electronic properties.     

The structure of liquid lead: EXAFS and MD studies

Accurate L-edge EXAFS (Extended X-ray Absorption Fine Structure) measurements of liquid Pb have been collected and analyzed using an advanced data-analysis technique (GNXAS) based on exact spherical wave multiple-scattering calculation of the absorption cross-section. Structural models obtained using molecular-dynamics (MD) simulations with an empirical and an embedded-atom potential, as well as structural data on liquid lead obtained from neutron and X-ray diffraction by other authors, have been put to a test using our new experimental results. The empirical two body potential, originally designed for the liquid state, reproduces quite accurately our experimental results. At the same time, the embedded atom potential, originally designed for the solid state, has turned out to inappropriately reproduce the first-neighbor g(r) peak. A comparison with previous XD and ND studies has shown that EXAFS analysis can improve our knowledge of the first-neighbor distribution. Previous observations of an apparent reduction in the coordination number in liquid Pb detected by EXAFS are briefly discussed.