A photoelectric study on the interface between metallic silver and vitreous As2S3

The electrostatic potential at the AgAs₂S₃ interface was investigated. In the dark, cells of a structure, Ag/As₂S₃/Al behaved like and an electrochemical battery. When light fell onto the cells, short-circuit currents were observed, but their appearancesvaried much, depending on the excitation wavelength and the material of the illuminated electrode. At wavelengths longer than the absorption edge of As₂S₃ glass, photocurrents were characteristic of the polarization current and little influenced by the external field. A model for explaining these findings was proposed on an assumption of an interface reaation between silver and vitreous As₂S₃ in the dark. The interfacial reaction was supposed to accompany a charge separation leading to formation of a potential barrier at the interface.     

On the photodissolution kinetics of silver in glassy As2S3

The kinetics of the photodissolution of Ag into glassy As₂S₃ films and its dependence on temperature have been studied by monitoring the changes that occur both in their transmission spectra and transmission of weakly absorbed broadband light. It was shown that besides of a low induction period, the photodissolution kinetics consists of two linear steps with different activation energies, followed by a parabolic tail. The transitions between photodissolution steps was found to be not monotonous and explained in terms of Elliott’s model, which asserts a simultaneous ionic and electronic charge transport controlled by chalcogenide properties, illumination and temperature. The evidence is given that the islanding of Ag layer in the course of photoreaction, results in an inversion of maxima and minima of transmission spectra. It is suggested that the islanding of Ag layer is not a consequence of a non-uniform dissolution but arises itself at critical thickness, at which Ag forms a continuous film.     

Raman spectrum of vitreous As2S3

The spontaneous Stokes and anti-Stokes Raman spectrum of vitreous As₂S₃ is reported. The spectrum was recorded with both HeNe and Ar ion laser excitation lines in the transmission and reflection modes respectively. Spectra were recorded at various temperatures between 20°K and 465°K, the softening temperature of As₂S₃ glass. It is shown conclusively that the quasicontinous scattering observed at low wave number shifts (< 100 cm⁻¹) is real in agreement with the theory of Shuker and Gammon and not an arbitrary background as previously reported. An approximate density of vibrational states is deduced from the polarized Raman spectra.     

Local structure and vibrational spectra of vAs2O3

We discuss the atomic displacements of the optically active vibrational modes of vitreous (v-)As₂O₃ through comparisons of the infrared (ir) and Raman response with the corresponding spectra of the two crystalline polymorphs, claudetite, a layer crystal similar to orpiment, and arsenolite, a molecular crystal based on the As₄O₆ molecule. We conclude from these comparisons that the structure of the glass is composed of $\text{AsO}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ pyramidal units that are corner connected to form a continuous random network. The character of the strong ir and polarized Raman modes in the vitreous form, suggests that the interconnection of these pyramidal units cannot be described by a random distribution of dihedral angles, but rather has peaks at angles characteristic of the different ordering in two-dimensional macromolecular layer basis of claudetite, and the As₄O₆ molecule. The comparisons are extended to v-As₂S₃ and vAs₂Se₃ where we conclude the dihedral angle distributions characteristic of an As₄O₆-like local geometry are less prevalent.     

Vibrational properties of As2S3 glass

Vibrational densities of states and infrared and Raman spectra have been calculated for a structural model of As₂S₃ glass. The calculations are based on simple semi-empirical forms for interatomic potentials, electric dipole moment and Raman polarizability. The bands of the calculated spectra agree well with those of the observed infrared and Raman spectra of As₂S₃ glass in intensity and position, although a small concentration of the wrong SS bonds remains in the structural model and causes an additional peak in the higher frequency region. The calculated depolarization ratio of the Raman spectra is consistent with the observed one.     

Bulk and impurity infrared absorption in 0.5 As2Se30.5 GeSe2 glass

A study of infrared absorption in the 250–4000 cm^?1 region has been carried out for 0.5 As₂Se₃0.5 GeSe₂ glasses quantitatively doped with oxide impurity. The frequencies of the intrinsic 2- and 3-phonon absorption bands at 490 and 690 cm^?1 correspond well to those predicted from combinations of the high frequency bands in the first order IR and Raman spectra of As₂Se₃ and GeSe₂ glasses.Glasses doped with As₂O₃ exhibit the same oxide impurity absorptionbands as those doped with GeO₂. Unlike As₂Se₃ glass, at impurity concentrations up to 1000 ppm As₂O₃, 0.5 As₂Se₃0.5 GeSe₂ glass exhibits only one major oxide impurity species, characterized by absorption bands at 780 and 1260 cm^?1 and due to oxygen bonded to network Ge. The observation of a much weaker network AsO vibration band at 670 cm^?1 confirms that oxygen bonds preferentially to Ge in this glass. The same minor oxide species appears to determine excess IR absorption at the CO₂ laser wavelength of 10.6 μm in both As₂Se₃ and 0.5 As₂Se₃ 0.5 GeSe₂ glasses. The frequencies and intensities of absorption bands due to hydrogen impurities are also quite comparable for these two materials.     

Ac conductivity of Ag-doped bulk,glassy As2S3

Measurements of the electrical conductivity of Ag-doped bulk As₂S₃ glasses have been made as functions of temperature, pressure, frequency and Ag doping level. A Debye-like loss peak was observed near 10⁴ Hz. The frequency of the loss peak is dependent on temperature, pressure and doping level, but these dependences are different from those of the dc conductivity. The ac loss is attributed to the Maxwell-Wagner losses characteristic of inhomogeneous materials. The materials are presumed to be inhomogeneous mixtures of As₂S₃ and Ag₂S. We have also searched unsuccessfully for ac conductance in several bulk chalcogenide glasses.     

X-ray photoelectron spectroscopic studies on Se/As2S3 and Sb/As2S3 nanomultilayered film

Photoinduced diffusion in Se/As₂S₃ and Sb/As₂S₃ nanomultilayered thin films are studied by X-ray photoelectron spectroscopy (XPS). The XPS measurements show the atomic movements during photoinduced diffusion in Se/As₂S₃ and Sb/As₂S₃ nanomultilayered film. The analysis of experimental data describes the nature of light induced changes in different structural units.     

A model for photostructural changes in the amorphous AsS system

The photodarkening effect was studied in thin film, bulk glasses and powdered glasses of composition As₂₉S₇₁, As₄₀S₆₀ and As_42.5S_57.5. The amount of photodarkening produced in a sample depended strongly on the samples state and composition as well as temperature, incident light intensity and wavelength. Using Raman spectroscopy, vibrational bands at 231 and 491 cm^?1 (assigned to AsAs and SS bond vibrations) were found to be enhanced in photodarkened samples. We present a model in which photodarkening is due to the formation of As_n clusters (n ? 2) which are loosely coupled to the amorphous network.     

An XPS study of the early stages of silver photodiffusion in Ag/a-As2S3 films

X-ray induced structural changes at the Ag/As₂S₃ interface are investigated using X-ray photoelectron spectroscopy on the samples prepared within the spectrometer. The as-prepared film consists of stable heteropolar As–S bonds as well as ∼16% S (and As) atoms in lower (higher) electron density configurations such as the –S–S– (–As–As–) segments with ‘wrong’ homopolar bonds. Two distinct stages of the X-ray induced diffusion are revealed. At first, silver reacts with atoms within –S–S– like segments to form Ag–S bonds. In the second stage, the Ag–S bonds decompose due to the reaction of S with As atoms within the –As–As– ‘wrong’ segments to form As–S heteropolar bonds, and silver diffuses away from the interface into the film. The results provide guideline for enhancing silver photodiffusion in chalcogenide glass. The irradiation of the (Ag–Te)/As₂S₃ sample with X-rays shows that not only Ag, but Te also diffuses away from the surface.     

Stimulated interdiffusion and optical recording in Sb/As2S3 nanomultilayers

The role of the compositional modulation at nano-scale dimensions (2–10 nm) in the enhancement of optical recording parameters in nanomultilayers, which contain Sb as active, optical absorbing and diffusing layers and As₂S₃ as barrier (matrix) layers was investigated. Comparison was made with single homogeneous layers made of ternary (As₂S3)_xSb_1−x glasses and co-deposited from Sb and As₂S₃. It was shown that essential increase of the recording efficiency, sensitivity of the bleaching process, broadening of its spectral range occurs due to the stimulated interdiffusion of adjacent components in Sb/As₂S₃ nanomultilayers with optimized Sb layer thickness.     

Plasma etching of As2S3 films for optical waveguides

Chalcogenide glasses are good candidate materials for ultra-fast non-linear optic devices. In this work, we present the photolithographic process and the plasma etching of arsenic tri-sulphide (As₂S₃) film. The films were deposited on thermally oxidized silicon substrates by ultra-fast pulsed laser deposition. To protect As₂S₃ film from photo-resist developer, thin resist layer ∼100-200 nm was remained on the UV exposed area by controlling resist development time. After removing the protective layer in oxygen plasma, As₂S₃ waveguides were patterned in inductively coupled plasma reactive ion etching (ICP-RIE) system using CF₄-O₂ gas mixture. We investigated the etch rate and the etch selectivity to photo-resist of As₂S₃ as a function of bias power, induction power, operating pressure, and gas flow rate ratio of CF₄ and O₂. The film is mainly etched by the chemical reaction with fluorine radicals. The content of oxygen in the plasma determines the etched sidewall profiles and nearly vertical profile was obtained at high oxygen content plasma.     

Structural, electrical, and optical properties of As2S3-Cu6PS5I nanocomposites

As₂S₃-Cu₆PS₅I nanocomposites are prepared by incorporation of nanocrystals of Cu₆PS₅I superionic conductor in As₂S₃ glass matrix. Their structural studies by scanning electronic microscopy are performed and the electrical conductivity of the nanocomposites is investigated. The temperature dependence of the nanocomposite optical absorption edge is studied; a non-Urbach behaviour of the absorption edge is revealed. Influence of different types of disordering on the optical absorption edge is studied.     

The electronic properties of glasses in the Cux(As0.4Se0.6)100−x system with x between 5 and 30

Data are presented on the dc conductivity, thermopower and optical absorption of glasses in the CuAs₂Se₃ system. The electronic properties of the alloys differ markedly from those of As₂Se₃, but variations in composition do not introduce significant changes in properties, until the atomic percent of copper is greater than 25. The results are interpreted in terms of small polaron transport.     

Anomalous anisotropic deformations of As2S3 flakes induced by linearly-polarized bandgap illumination

Semi-free As₂S₃ flakes undergo visible-scale anisotropic deformations when exposed to linearly-polarized bandgap illumination. We investigate the behavior and also those in amorphous Se, GeS₂, AgAsS₂, and crystalline As₂S₃. These results suggest that the deformation occurs through photo-induced birefringence, photo-induced fluidity, and optical force.     

Raman scattering of the mixed chalcogenide glass system As2SxSe3-x

Polarized room temperature Raman spectra of glassy As₂S_xSe_3-x for 0≦×≦3 have been measured. Spectra for crystalline As₂S₁Se₂ are reported. The polarization and intensity dependence upon composition are consistent with mixed pyramids of composition As₂S_nSe_3-n and preclude phase separation in the glassy system.     

Properties and structure of glasses in the system AsS

In obtaining the glass, at first, the raw materials were mixed up and melted by using porcelain crucible, but in this case it was found by infra-red absorption method that the glass contains some oxygen impurities. Then a range of glasses was prepared by melting elementary pure As and S in definite proportions in a sealed vacuum tube. The infra-red absorption, molecular volume, molecular refraction, hardness, thermal expansion and viscosity of sample glasses with various compositions were investigated and, additionally, solubility of these glasses into CS₂ was measured. The structure of glasses in the system AsS was studied by X-ray diffraction and a structural model was set up. From the measurements the following conclusions were made. The structure of As₂S₃ glass is a distorted form of the crystalline orpiment structure. With increasing S content above As₂S₃, S is likely to exist in the chain-like form, but when the S content is greater than that in As₂S_8–10, both chain-like and ring type forms co-exist. With decreasing S content below As₂S₃, S between As and As is eliminated and AsAs bonds are formed. Consequently a deformation of layer occurs and an expansion of the layer distance was observed.     

X-ray diffraction studies of glasses in the systems Na2OMeOSiO2 (MeMg,Zn, Ca,Ba)

X-ray diffraction studies of glasses in the following ternary systems have been made: Na₂OMgOSiO₂, Na₂OZnOSiO₂, Na₂OCaOSiO₂ and Na₂OBaOSiO₂. The following heavy atom substitutions have been used: Ag for Na and Ge for Si. The changes in the electron radial distribution curves resulting from AgNa replacement can be explained as amplifications of relatively well-defined NaSi distances, which are nearly the same in all the glasses investigated. The GeSi substitution causes changes which can be explained on the basis of isostructural GeSi substitutions.     

119Sn Mössbauer studies of glassy and crystalline compounds in the chalcogenide system SeSnAs

¹¹⁹Sn Mössbauer measurements have been carried out on 18 chalcogenide glasses of different composition in the system SeSnAs. In all cases tin is four-coordinated and appears to be tetrahedrally surrounded by selenium. Two of the glasses (Se₆₀Sn₃As₃₇ and Se₄₇Sn₃As₅₀) were crystallized by heat treatment, and their Mössbauer spectra have been measured as a function of crystallization temperature and annealing time. As a result of the heat treatment, crystalline SnSe and SnSe₂ are precipitated. The amount of each compound is determined by the composition of the original glass and the remaining glassy or crystalline phase (As₂Se₃ and As₄Se₄). The degree of the crystallization depends on the temperature and the annealing time, but not the mass ratio of the tin selenides formed.