Raman spectra of As4S4 polymorphs: Structural implications for amorphous As2S3 films

Raman-scattering spectra of α-As₄S₄ and β-As₄S₄ have been determined at 300 and 10 K. Although similar in overall aspect, the spectral signatures of the two polymorphs are clearly distinct. We have made a careful comparison of these first-order crystal line spectra to the sharp features reported in the Raman spectra of freshly-deposited films of amorphous As₂S₃. Prior proposals for the presence of As₄S₄ molecules in the unannealed films are supported by these comparisons, but recent contentions that actual microcrystals of β-As₄S₄ are present in the as-deposited material are clearly contradicted by the absence of any of the lattice-phonon lines which are prominent in the crystals at frequencies below 70 cm^-1.     

Reversible photo-induced volume changes in evaporated As2S3 and As4Se5Ge1 films

Reversible photo-induced volume changes have been observed accompanying reversible optical absorption edge shift produced by successive cycles of band gap illumination and annealing for well-annealed evaporated As₂S₃ and As₄Se₅Ge₁ films. The As₂S₃ film shows an increase in its volume by illumination, while As₄Se₅Ge₁ film shows a decrease. Qualitative discussion has been given in connection with pressure-induced optical constant change.     

Thermally and photo-induced changes in the valence states of vapour-deposited As2S3 films: A comparative photoemission study of As2S3 and As4S4

During thermal annealing or light irradiation, the changes in the valence states of vapour-deposited As₂S₃ and As₄S₄ films were observed by UPS. The experimental results reveal that an as-deposited As₂S₃ film contains considerable numbers of As₄S₄ molecular units, which polymerize or cross link to form a As₂S₃ glassy network on annealing or irradiation.     

ESR in X-irradiated As2O3 glass

X-irradiation of glassy As₂O₃ at 77K or 300K produces an unusually large density (～5×10¹⁸ cm^-3) of paramagnetic centers which are stable at 300K. The average spin-Hamiltonian parameters (g = 1.998, g_⊥ = 1.984, A₆ = 243G, A_⊥ = 114G) indicate that these centers are analogous to those previously observed in As₂Se₃ and As₂S₃ glasses and that they consist of unpaired electrons localized on a non-bonding 4p orbital of an As atom. Unlike the results obtained for As₂Se₃ and As₂S₃, the concommitant holes in As₂O₃ are trapped on Fe²⁺ impurity sites which become Fe³⁺ and not on non-bonding oxygen p orbitals. The radiation induced ESR is also accompanied by a stable optical absorption tail which lies within the band gap and increases exponentially with energy. This absorption can be partially bleached with the application of sub-band-gap light.     

Infrared properties of AsχTe1−χ glasses

Infrared reflection and transmission measurements in As_χTe_1?χ glasses (45?×?55) show well-defined Gaussian vibrational absorption peaks. Comparisons with spectra observed in crystalline and glassy As₂S₃ and As₂Se₃ indicate that the local order in As_χTe_1?χ glasses is not like that found in crystalline As₂Te₃, but rather it consists primarily of AsTe₃ pyramids which are probably linked together in a fashion similar to that found in As₂S₃ and As₂Se₃.     

Electronic structure of As4S5 as a local structural model for amorphous As2S3 film

We have studied the electronic structure of As₄S₅ molecule as a model of the local pyramidal structure in amorphous As₂S₃ film. Emphasis has been put on the analysis of the behaviour of a trapped electron in this model concerning the consequent structural relaxation. It has been found that As₄S₅ species has affinity for an excess electron, and that the attachment of an excess electron promotes the cleavages of specific As-S bonds.     

Photo-synthesis of As3S2 crystal from AsAs2S2 mixture

Existence of As₃S₂ compound which is stable in a certain temperature range higher than room temperature has been confirmed in AsAs₂S₂ system. Photo-synthesis effect of As₃S₂ crystal from As and As₂S₂ mixture, namely light induced conversion from a crystalline state to another crystalline state, has also been investigated.     

Raman spectra and structure of As40−xS60Ix glasses

The Raman spectra of bulk As_40?xS₆₀I_x glasses with 0?x?20 have been studied. The obtained spectra can be successfully explained assuming the structure of these glasses to be composed of As₂S_3.45 polymer network matrix with dissolved AsBr₃ and S₈ molecules.     

Photoemission study of the density of valence states of amorphous As2S3 and Sb2S3

The densities of valence states of amorphous As₂S₃ and Sb₂S₃ have been investigated by means of X-ray photoemission and ultraviolet photoemission spectroscopy. The spectra are interpreted on the basis of existing band structure calculations.     

Photo-induced changes in the infrared vibrational spectrum of evaporated As2S3

Photo-induced changes in the infrared spectrum of amorphous, evaporated As₂S₃ films are described. The results are interpreted in terms of the photopolymerization of As₄S₄ molecular units and sulfur chains into an As₂S₃ glassy network. The role of photo-induced charged states in the polymerization process is discussed.     

Reversible photostructural change in melt-quenched As2S3 glass

Reversible phtodarkening and photostructural change accomplished by repeated cycles of band-gap illumination and annealing have been observed in melt-quenched As₂S₃ glass for the first time. The magnitudes of photo-induced shift of optical absorption edge as well as the fraction of photo-expansion observed in melt-quenched As₂S₃ glass coincide quantitatively with those observed in well-annealed evaporated As₂S₃ glass. The experimental data involving results of crystalline As₂S₃ demonstrate that the reversible photostructural change is “unique” to amorphous state and is not affected by the difference in disordered structure originated from preparation technique.     

P2S5/NH4OH处理GaAs(100)表面的电子能谱研究

采用俄歇电子能谱(AES)和X射线光电子能谱(XPS)研究了P₂S₅/NH₄OH钝化液处理的GaAs(100)表面的微观特性。AES测量表明,在钝化膜和GaAs衬底之间的界面处无O组分,只有P和S组分。XPS测量分析指出,经过P₂S₅/NH₄OH溶液处理后,GaAs表面处Ga₂O₃和As₂O_{3关键词：}     

Resonance Raman scattering from amorphous As2S3

Resonance Raman scattering from amorphous As₂S₃, obtained by temperature tuning the band edge through the He-Ne 6328 Å laser line, is reported.     

Conductivity of the chalcogenide semi-insulator system: As2S3Sb2S3

The conductivities of mixed As₂S₃Sb₂S₃ thin films are discussed. Temperature independent a.c. data are interpreted in terms of a hopping mechanism where correlation effects are important. Excepting As₂S₃, which exhibits extrinsic behaviour, the dielectric constant, a.c. conductivity and d.c. conductivity pre-exponential factor, all scale approximately linearly with composition.     

Effect of temperature and pressure on the raman spectrum of As4S3

The Raman spectrum of crystalline As₄S₃ has been investigated as a function of temperature from 4 to 430 K at ambient pressure, and as a function of pressure to 70 kbar at ambient temperature. The external mode frequencies which appear clearly separated from the internal modes exhibit stronger pressure and temperature sensitivity compared to the latter modes. At the β-As₄S₃ to α-As₄S₃ phase transition near 410 K, the external modes change discontinuously indicating a first-order phase transition. The internal mode frequencies remain practically unaffected. The $\text{dv}\text{dP}$ and $\text{dv}\text{dT}$ data are analyzed using well established approaches. Application of non-hydrostatic pressure (>60 kbar) appears to destroy the crystallinity of As₄S₃.     

Esca studies of Ga,As, GaAs,Ga2O3, As2O3 and As2O5

The binding energies of Ga 3d, As 3d, Ga L₃M₄,₅M₄,₅ and O 1s in Ga, As, GaAs, Ga₂O₃, As₂O₃ and As₂O₅ are reevaluated by means of ESCA. The calibration lines of the C 1s and the Au 4f_{$\text{7}\text{2}$} gave different binding energies for the compound materials. In order to determine the absolute binding energies, the chemical shifts in Auger and photoelectron lines from a layered structure composed of thin layer oxide and substrate of a defined material were used. An energy calibration curve, E(Ga 3d) vs. ΔE(GA LMM - Ga 3d), was found to be useful for determination of binding energies in the material which contains gallium. In the case of the GaAs sample, both the chemical etching and the ion bombardment effects on the chemical structure of the GaAs surface are also discussed.     

Studies on electrodeposited As2S3 thin films by double exposure holographic interferometry technique

Arsenic trisulphide (As₂S₃) thin films have been deposited onto stainless steel and fluorine doped tin oxide (FTO) coated glass substrates by electrodeposition technique using arsenic trioxide (As₂O₃) and sodium thiosulphate (Na₂S₂O₃) as precursors and ethylene diamine tetracetic acid (EDTA) as a complexing agent. Double exposure holographic interferometry (DEHI) technique was used to determine the thickness and stress of As₂S₃ thin films. It was observed that the thickness of the thin film increases whereas film stress to the substrate decreases with an increase in the deposition time. X-ray diffraction and water contact angle measurements showed polycrystalline and hydrophilic surface respectively. The bandgap energy increases from 1.82 to 2.45 eV with decrease in the film thickness from 2.2148 to 0.9492 μm.     

Cation ordering and crystal structures in AGa2X4 compounds (CoGa2S4, CdGa2S4, CdGa2Se4, HgGa2Se4, HgGa2Te4)

Single crystals of some AGa₂X₄ compounds (CoGa₂S₄, CdGa₂S₄, CdGa₂Se₄, HgGa₂Se₄, HgGa₂Te₄) were prepared by chemical vapour deposition and flux method.The X-ray structural investigations indicated blende or defect chalcopyrite structures.A simple relationship is suggested between the c/a ratio and the cationic sublattice ordering.     

Electronic structure and chemical bonding of phosphorus-contained sulfides InPS4, TI3PS4, and Sn2P2S6

The electronic structure of phosphorus-contained sulfides InPS₄, Tl₃PS₄, and Sn₂P₂S₆ was investigated experimentally with X-ray spectroscopy and theoretically by quantum mechanical calculations. The partial densities of electron states calculated with the ab initio multiple scattering FEFF8 code correspond well to their experimental analogues—the X-ray K- and L_2,3-spectra of sulfur and phosphorus. The good agreement between theory and experiment was also achieved for K-absorption spectra of S and P in the investigated sulfides. In spite of the difference in the crystallographic structure of InPS₄, TI₃PS₄, and Sn₂P₂S₆ that influence the form of K-absorption spectra, the electronic structure of their valence bands are rather similar. This is due to the strong interaction of the P and S atoms, which are the nearest neighbors in the compounds studied. The electron densities of p- and s-states of phosphorus are shifted by about 3 eV to lower energies in comparison to the analogous electron states of sulfur. This is connected with the greater electro-negativity of sulfur, and is confirmed by the calculated electron charge transfer from P to S.     

Valence band densities of states of CdIn2S4 and In2S3 from x-ray photoelectron spectroscopy

X-ray photoelectron spectra of the valence band of CdIn₂S₄ and In₂S₃ single crystals have been measured. The spectrum of CdIn₂S₄ has a strong resemblance to its synthesized spectrum from the In₂S₃ and CdS spectra, which is in good agreement with the theoretical density of states (DOS). The contribution of constituent atoms to the valence band DOS in CdIn₂S₄ is corresponding to those in In₂S₃ and CdS.