Arsenic Chalcogenides Research Articles

The mechanism of photoinduced transformations in amorphous As 2S 3 thin films

Physical photographic development is applied for visualization of the photoinduced transformations in amorphous As 2S 3 thin films. It is established that, in comparatively narrow exposure interval, the samples studied show a negative photographic response. The latter is explained by the formation of a latent image capable of initiating the development process. Simultaneously, similar catalytic activity of As clusters, vacuum deposited on the surface of As 2S 3 films, is found. On this basis, metal As is regarded as a constituting element of the latent image built up on illumination. Further, a quantitative evaluation of the photographic response is made. Thus, a higher efficiency of As cluster formation in the volume of the films as compared with the surface is found. Besides, a reduced photographic sensitivity of As 2S 3 films after annealing procedure is established. The results obtained are discussed in terms of the model for light-induced phase separation in arsenic chalcogenides.

Thin-layer chemical sensors based on chemically deposited and modified chalcogenide glasses

A new type of chemically deposited and modified thin-layer sensors has been prepared and investigated. Amorphous As 2S 3 and AsSe thin films obtained by the spin-coating technique and doped with silver were used as membrane materials of these sensors. It was found that the temperature of preliminary annealing of the films is crucial for doping efficiency. As-prepared films annealed above 120 °C remain insulating after silver doping with subsequent annealing and/or light irradiation. XPS measurements indicated some kind of decomposition of arsenic chalcogenides in this case. Properly prepared and modified thin layers are mixed conductors with a final resistivity of about 10 5 ω cm for As 2Se-based and ≈ 10 3 ω cm for AsSe-based films. Electrochemical measurements in AgNO 3 solutions revealed a reasonable sensitivity of doped AsSe films to silver ions. The ionic response of doped As 2S 3 films was found to be significantly poorer. High electronic conductivity giving rise to competitive interfacial redox processes seems to be one reason for such behaviour. The redox response of the films was studied in solutions of potassium hexacyanoferrate(II)/(III) with total redox concentration from 0.1 to 0.001 M. The parameters of the redox response of selenide glass thin-layer sensors are close to those of platinum electrode at high total redox concentration and even better in dilute solutions.

Model for bond-breaking mechanisms in amorphous arsenic chalcogenides leading to light-induced electron-spin resonance.

A model is presented for the light-induced bond-breaking processes in arsenic chalcogenides which, based on theoretical calculations of coordination defects, accounts for the details of recent experimental light-induced electron-spin resonance experiments on amorphous ${\mathrm{As}}_{\mathit{x}}$${\mathrm{S}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$ alloys. The presence of homopolar (wrong) bonds is essential in such compound materials for the optically induced creation of metastable paramagnetic dangling-bond defects, but the creation process does not involve the scission of such homopolar bonds themselves.

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

129I-Mossbauer 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-Mossbauer spectra of all glasses were fitted satisfactory, when a distribution of the electric-quadrupole coupling constant is taken into account.

Erratum: Self-consistent-field X alpha scattered-wave calculation of the electronic structure of arsenic chalcogenide molecules

We have carried out self-consistent-field X\ensuremath{\alpha} scattered-wave calculations for the arsenic chalcogenide molecules ${\mathrm{As}}_{4}$${\mathrm{S}}_{4}$, ${\mathrm{As}}_{4}$${\mathrm{Se}}_{4}$, and ${\mathrm{As}}_{4}$${\mathrm{S}}_{6}$. Results include the decomposition of the state charge with respect to the geometric partitioning of the molecules, angular momentum decomposition of the state charge around each atom, molecular ionization potentials, energies of the optical transitions, and the charge densities associated with the different bonds. Calculated densities of states compare well with the several x-ray photoemission spectra measured on the corresponding amorphous solids. The joint densities of states agree with the basic features of the ${\ensuremath{\varepsilon}}_{2}$(\ensuremath{\omega}) of the amorphous solids. The charge-density contour maps show good transferability of the arsenic-chalcogen bond among different molecules. Analysis of the arsenic homopolar bonding explains differences in the stability of the molecules.

Tables of recommended reference data. Arsenic chalcogenides. Thermal conductivity, electrical conductivity, and thermoelectric power at temperatures in the range 300-900 K Tables of recommended reference data. Lanthanum sulfides. Thermal conductivity, electrical conductivity, and thermoelectric power in the range 300-1300 K.

Tables of recommended reference data. Arsenic chalcogenides. Thermal conductivity, electrical conductivity, and thermoelectric power at temperatures in the range 300-900 K Tables of recommended reference data. Lanthanum sulfides. Thermal conductivity, electrical conductivity, and thermoelectric power in the range 300-1300 K.

Self-consistent-field X alpha scattered-wave calculation of the electronic structure of arsenic chalcogenide molecules.

We have carried out self-consistent-field X\ensuremath{\alpha} scattered-wave calculations for the arsenic chalcogenide molecules ${\mathrm{As}}_{4}$${\mathrm{S}}_{4}$, ${\mathrm{As}}_{4}$${\mathrm{Se}}_{4}$, and ${\mathrm{As}}_{4}$${\mathrm{S}}_{6}$. Results include the decomposition of the state charge with respect to the geometric partitioning of the molecules, angular momentum decomposition of the state charge around each atom, molecular ionization potentials, energies of the optical transitions, and the charge densities associated with the different bonds. Calculated densities of states compare well with the several x-ray photoemission spectra measured on the corresponding amorphous solids. The joint densities of states agree with the basic features of the ${\ensuremath{\varepsilon}}_{2}$(\ensuremath{\omega}) of the amorphous solids. The charge-density contour maps show good transferability of the arsenic-chalcogen bond among different molecules. Analysis of the arsenic homopolar bonding explains differences in the stability of the molecules.

Structural modification of arsenic chalcogenide glasses under γ-radiation

The radiation-induced changes of the molecular structure and properties of chalcogenide glassy semiconductors are analysed. The effect of γ-radiation on the mechanical properties (Young's module, internal friction) of glassy arsenic chalcogenides is investigated at various temperatures and radiation doses. At low temperatures the changes of the molecular structure and the corresponding changes of mechanical properties of the chalcogenide glasses under the influence of γ-radiation grow with the decrease of the structural network rigidity. On the other hand at higher temperatures the opposite dependence of the properties is found. [Russian Text Ignored].

The influence of the structure of different arsenic chalcogenide glasses on the dispersion parameters of a sellmeier and a Lorentz-Lorenz relation

The wavelength dependence of the refractive index of arsenic chalcogenide glasses in the series AsxSe1 − x in the transparent region was modelled using the dispersion formulae of a Sellmeier type and of a Lorentz-Lorenz type. For both cases the composition dependence of the independent parameters λ1, the resonance wavelength of the electronic absorption, and neff, the effective number of electrons taking part in the transition, and their relation to ɛ2-spectra is discussed. In the Sellmeier model the energy of the resonance wavelength λ1 is in good agreement with the energy of the strongest maximum of the ɛ2-spectra. The dependence of λ1 and neff on the composition clearly reflects structural changes. In spite of the equality of the parameter neff in both models, in the Lorentz-Lorenz model the composition dependence of λ1 is quite different and in contrast to the change of the optical bandgap. The results indicate that in the case of amorphous semiconductors a local field correction should be neglected.

Spectroscopic investigations of induced processes in arsenic sulfide chalcogenide glasses

Spectroscopic investigations of induced processes in arsenic sulfide chalcogenide glasses

Photoinduced changes of mechanical properties in amorphous arsenic chalcogenide films

The influence of illumination and annealing on the mechanical and optical properties of amorphous As-S and As-Se films has been studied. The observed compositional dependence of microhardness (Hμ) and photocontraction of the films is in good agreement with the photoinduced (PhI) changes of the optical properties. The photoinduced effects in amorphous arsenic chalcogenide films are explained by the polymerization processes due to the formation of dative bonds between polymeric networks with the concentration of 1021 cm−3.

Diffraction by Glasses With a Layer Structure

An outline is presented of the expected form of the diffraction pattern and the real space correlation function for a glass with a layer structure. The diffraction evidence for and against the presence of layers in the structure of the vitreous arsenic and germanium chalcogenides is briefly reviewed with special reference to the outrigger raft model for vitreous GeSe/sub 2/. 14 refs., 5 figs.

Evidence for As 4S 6 molecule as a structural model for amorphous arsenic sulfide from mass spectrometric analysis

Mass spectrometric analysis of arsenic trisulfide prepared by different techniques is reported. The molecular structure As 4S 6 could be resolved in samples prepared by quenching from the melt which supports the dense random packing of As 4X 6 as a structural model for amorphous arsenic chalcogenides. It has also been found that the structure is dominated by the presence of AsS and As 4S 4 molecules regardless of the preparation technique.

Surface Free Energies of α-Si<sub>3</sub>N<sub>4</sub> and β-SiC

Contact angle measurements have been carried out on powders of α-Si3N4 and β-SiC using water, formamide, methylene iodide and n-nitropropane as wetting liquids. The dispersion and polar components of the surface free energy, γsd and γsp, have been calculated from the contact angle data by geometric mean approximation which has previously been applied to estimate the surface free energies of arsenic chalcogenides. For α-Si3N4, γsd and γsp were 17 and 28-35mJ·m-2, respectively. For β-SiC, they were 37 and 2-3mJ·m-2, respectively. The present results suggest that the surface of β-SiC is much less polar than α-Si3N4.

Phosphorus and Arsenic Chalcogenides as Reagents Toward Transition Metal-Ligand Systems

Abstract The compounds obtained by reacting the P4S3, P4Se3 and As4S3 cage molecules with various transition metal-ligand moieties are reported. The transition metal-ligand systems are bound either to the intact molecules or to fragments (hexa- or tri-atomic) originating from the cage molecules. Such compounds provide examples of selective activation of cage molecules by metal moieties.

The Influence of the Structure of Different Arsenic Chalcogenide Glasses on Refractive Index and Dispersion

AbstractThe refractive index dispersion of different arsenic chalcogenide glasses is analyzed by the use of a two‐term Sellmeier dispersion formula. In a region from 3 μm up to the beginning of the absorption edge the wavelength dependence of the refractive index can be described by a single oscillator model. At wavelengths λj, determined by λ1j, = const, the molar refraction of the different glasses is a linear function of neff λ. In representations RM = RM(neff) and RM = RM(λ) the influence of the structure of the different glasses is clearly illustrated. For the glass AsSe3 a special short‐range order is indicated.

Heats of immersion of amorphous As 2S 3, As 2S 5 and As 2Se 3 in organic liquids

The heats of immersion of hydrophobic, amorphous arsenic chalcogenides have been measured in several organic liquids. For hexane, butanol, butylchloride and nitropropane, the heats of immersion with As 2S 3, As 2S 5 and As 2Se 3 showed linear dependences on the dipole moment of the wetting liquid molecule. From the results the average values of the electrostatic field strength were calculated to be 0.29 × 10 5, 0.31 × 10 5, and 0.57 × 10 5 e.s.u. cm −2. The heats of immersional wetting of As 2S 3 and As 2Se 3 in n-alkanols linearly increased with an increase of n, the number of carbon atoms in C n H 2 n+1 OH. The contributions due to polarization of the liquid molecule by the electrostatic field of the solid surface, due to the dispersion force and due to the interaction between the dipole moment of the liquid with the electrostatic field of the solid were calculated by applying the additivity of intermolecular forces. The result showed that the dispersion force was the dominant contribution to the interaction in As chalcogenides- n-alkanol systems.

Vapour phase growth of arsenic chalcogenide crystals and their characterization

Arsenic chalcogenides As2X3 (X = S, Se, Te) as a group of materials have been widely used for electronic and optoelectronic devices (1-5) and in ir spectroscopy (6-8) since long. In absence of suitable synthetic crystals these applications are restricted to glassy and amorphous materials. Intense activity in the recent years on the spectroscopy of these materials forms a promising field of research in the physics of amorphous solids. Investigations carried out on these compounds are mostly concerned with optical properties in both electronic and vibrational spectral region (9-27) and transport studies with regard to electric field, illumination, electron bombardment, etc. (28-51). Most of these investigations are confined to non-crystalline material while limited investigations on naturally occuring and synthetic crystals have been reported. (9,11,12,16,18,19,22-24,37-40, 42,43,48)

Structure of amorphous and glassy Sb 2S 3 and its connection with the structure of As 2X3 arsenic chalcogenide glasses

Two types of amorphous and glassy Sb 2S 3 were studied: amorphous orange-red powder obtained by precipitating a SbCl 3 solution using a stream of hydrogen sulphide in a bath of boiling water and a glassy material in the form of thin platelets obtained by the method of rotating cylinders. It was found by DTA that there is a great difference in the crystallization entropy and temperature between the powder and glass. Radial electron density distribution curves were measured for both modifications and a difference analysis showed that they can be considered to be much the same. From the distribution curves it follows that the basic unit is a trigonal SbS 3 pyramid which forms in the case of Sb 2S 3 glass, a covalent random network while for the amorphous powder a random ordering of crystalline-like and band-like (Sb 2S 3) n molecules can be considered as an appropriate model. A comparison of radial electron density distribution curves for As 2 X ( X=S, Se, Te and Sb 2S 3 shows that Sb 2S 3 belongs to the class of glassy As 2 X 3 structures. A rule is found that in this class of glasses the mutual ratios of diameters of corresponding coordination spheres are constant. On the basis of coordination numbers and of broadening functions for individual coordination spheres it is shown that in the series As 2S 3:As 2Se 3As 2Te 3 a gradual transition from a layer-like to a random network takes place and that glassy Sb 2S 3 can be put beside As 2Te 3. This process is a result of the difference between orpiment-like configurations and the As 2 X 5 ones, which evoke chain branching and interconnecting. This leads finally for As 2Te 3 and Sb 2S 3 to a random continuous covalent network. This process is confirmed by increase of both occupation numbers and the widths of broadening functions corresponding to individual coordination spheres.

Photoacoustic spectroscopy of solids and surfaces

After briefly reviewing the theory and instrumentation, results from a variety of experiments carried out by the authors on the photoacoustic spectroscopy of solids and surfaces by employing an indigenous spectrometer are discussed in the light of the recent literature. Some of the important findings discussed are, phase angle spectroscopy, anomalous behaviour of monolayers, unusual frequency dependence in small cell volumes, spectra of a variety of solids including amorphous arsenic chalcogenides, photoacoustic detection of phase transitions and determination of surface areas and surface acidities of oxides. Recent developments such as piezoelectric photoacoustic spectroscopy, depth profiling and subsurface imaging are also presented.