Ion diffusion across material interfaces is considered in a sequence of approximations with increasing complexity. First, the one-dimensional lattice gas model of particle diffusion is generalized to include a finite width interface region, and the possible existence of an energy barrier at the interface. Overvoltage measurements on InSe, and dielectric loss measurements on B2O3 - 0.5Li20 - 0.15Li2SO4 are used to determine the field-free hopping rates in the two materials. It is shown that the energy barrier is a dominant parameter. This model is then modified by considering the disorder of the glass structure and the blocking effect resulting from the ion interaction. Next, a more rigorous treatment is presented by solving the Poisson equation with appropriate boundatry conditions, and a self-consistent theory of the ionic diffusion is proposed. To clarify this problem, an intermediate step and two additional models with increasing sophistication are considered: first, the potential φ(x) of the moving charge density n(x) is calculated and it is shown that φ(x) is not negligible. Then, a feed-back is provided by including this potential in the diffusion equation. This treatment is already self-consistent and more realistic but leads to long computations even for the simple one dimensional lattice-gas model. A remedy of this difficulty is proposed whereby the theory is reformulated in order to guarantee from the beginning the self-consistency of the solution of the non-linear diffusion problem. Straightforward extensions to the two-dimensional case are then possible. The results of the computations are illustrated with numerical examples for different values of the physical parameters.

Raman scattering and IR absorption were studied in Li-intercalated MoS2 at room temperature. After intercalation, new Raman peaks were observed at low-frequency sides of the high-frequency original Raman peaks and around a rigid-layer mode. This fact indicates the formation of superlattice structure along the c-axis. An intercalation mode in which Li atoms vibrate strongly against the host lattice was observed at about 205 cm−1. Two new broad bands grow in the high-frequency region as the concentration of Li increases. The corresponding peaks were observed by IR absorption. They appears to be caused by vibrations of substitutional defects, in which the Li atoms have substituted for Mo atoms in the host lattice.

In recent years GeSe2 glass has been intensively studied by different methods. Light scattering experiments [1–10] have been used to investigate the molecular structure of the chalcogenide glasses. Diffraction studies [16–17] have shown that the short range order of this glass is similar to that of the crystalline GeSe2. Raman [9–10] and Mössbauer [11–15] spectroscopies have extended these results to include large number of atoms (intermediate range order). Glass-crystalline transition induced by laser irradiation has been investigated essentially by Raman scattering [10–16].

The layered semiconductor InSe which is a potential insertion cathode for thin film batteries can be intercalated with lithium which act as donor in the host. Chemical intercalation in n-butyllithium, leads to a drastic increase of the free carrier density in the host material, InSe single crystal. The variation of the free carrier density with intercalation shifts the plasma frequency into the region of the LO-mode vibrations and allows the observation of the plasmon-LO-phonons coupling by light scattering experiments. By varying the sample temperature, it is possible to follow the two branches of the curve ω(q) corresponding to the modes L+ and L-.

The reactivity of lithium with layered chalcogenides InSe and In2Se3 is studied using transmission electron microscopy (TEM), electrochemical potential spectroscopy (EPS) and Raman scattering (RS). It is found that for x(Li)≥0.1 in LixInSe, the host material decomposes with the formation of lithium selenide. The presence of Li2Se is confirmed by Raman spectroscopy. The insertion of Li into In2Se3 appears more stable with the occurrence of a superlattice formation at x(Li)≈0.25. The superstructure corresponding to the 2a×2a lattice is consistent with the EPS measurements of LixIn2Se3.

Comparative investigations are carried out for spectral (Raman) electrical and structural properties of V2O5 single crystals and polycrystalline samples obtained by IR laser light illumination of pure metallic samples in an oxidizing atmosphere (air). It is shown that the structures grown on metallic plates in the field of laser light are predominantly V2O5 polycrystals. Raman measurements reveal that the main peaks, which are characteristic for single crystals, are also present in laser-driven samples but with different intensities. Some peaks are attributed to laser-grown thick films, which are not present in the single-crystalline phase. There are shifts in the peak positions indicating the existence of different force constants for films as compared with crystals. The activation energies obtained from the electrical properties (conductivity, impedance versus temperature) yield similar values except for the anisotropic characteristics of the single crystal where the values are a bit different along different crystallographic axes (unlike the polycrystalline oxide films made by the laser). The single-crystalline phase has a well-defined layered structure with well-defined shapes showing formed units of truncated oktaeders, while the film structure shows randomly distributed tubular micron-size structures with empty holes at the peripheral part of the irradiated area, and nanoscaled long and thin tubes well oriented along the direction of the incoming laser light in the central part of the irradiation spot.

Analytical expressions for the velocities of the longitudinal and the torsional sound waves in single-walled carbon nanotubes are derived using Born's perturbation technique within a lattice-dynamical model. These expressions are compared to the formulas for the velocities of the sound waves in an elastic hollow cylinder from the theory of elasticity to obtain analytical expressions for the Young's and shear moduli of nanotubes. The calculated elastic moduli for different chiral and achiral (armchair and zigzag) nanotubes using force constants of the valence force field type are compared to the existing experimental and theoretical data.

In this paper, the theory of lattice dynamics of single-walled carbon nanotubes is presented. The screw symmetry of the system is used to reduce the rank of the dynamical matrix to six, independent of the number of atoms in the unit cell. Calculations of the lattice dynamics are carried out within a valence force field model and of the Raman intensity-within a bond-polarizability model. It is found that the breathing mode frequency is inversely proportional to the radius of the tube that can be used for the characterization of the samples on the basis of Raman-scattering data. The results for the Raman intensity are compared to available Raman spectra. [S0163-1829(98)06434-0].

The density and the sound velocities have been measured at room temperature in the ternary borate glasses, B2O3−xLi2O−yLinX (n=1 for X=F, Cl, Br and I; and n=2 for X=SO4), as a function of the concentration for the different ‘doping’ salts (LinX). Two series of ternary glasses with different O/B ratios, x=0.2 and 0.6, have been studied. In both series, a structural model where the anion of the ‘doping’ salts are located in interstitial positions inside the boron–oxygen network is used to explain the experimental results in borate glasses ‘doped’ with LiCl, LiBr and LiI. In the case of glasses ‘doped’ by LiF or Li2SO4, there is evidence of a direct participation of the salt anions to the boron–oxygen network. A structural modification is proposed for the LiF-‘doped’ borate glasses with x=0.2 and 0.6. Changes in the medium-range order induced by the addition of ‘doping’ salts are also discussed in these ternary glasses.

An X-ray Photoelectron Spectroscopy (XPS) and Reflection High Energy Electron Diffraction (RHEED) study of interfaces between B2O3-0.5Na(2)O and InSe has been performed as a function of the thickness of the InSe film. From RHEED and XPS, the InSe film grows mainly in a two-dimensional mode along the smooth polished berate substrate and the interface between InSe and berate glass can be considered as abrupt. The RHEED patterns indicate an in-plane misorientation of the domains. The semi-quantitative analysis of the intensities of photoelectron peaks leads to substrate attenuation and deposit uptake curves. They follow mainly an exponential law and allow an estimation of the escape depth of the photoelectrons in agreement with the calculated ones and with the flux determined from interferometry measurements although a good definition and determination of the monolayer thickness is required. Nevertheless, the phenomenological average 'monolayer' defined by Seah and Dench agrees with the experimental estimation of the escape depth, even in the case of these strong anisotropic materials. We suggest that a sodium insertion in the layered compound is plausible. (C) 1998 Elsevier Science B.V.

Thin films of vanadium pentoxide were prepared by the electron-beam evaporation technique onto Corning 7059 glass and silicon substrates maintained at Ts=553 K by varying the oxygen partial pressure in the range 0.1–20 mPa. These films have been characterized by studying their chemical state, structure, optical and electrical properties. V2O5 films of thickness 0.6 μm prepared at an oxygen partial pressure of 20 mPa exhibit an orthorhombic layered structure with an optical band gap of 2.3 eV. The room temperature electrical conductivity of the films is 2×10−5 S cm−1 with an activation energy of 0.42 eV in the temperature range 303–523 K.

Borovanadate glasses (1−x)[B2O3–yLi2O]–xV2O5 with 0≤x≤1 and 0≤y≤1 have been prepared and systematically studied by Raman spectroscopy. The results have been compared with glass transition temperature measurements. The Raman spectra exhibit a characteristic band at about 900 cm−1 whose shape and frequency are dependent on both V2O5 and Li2O concentration. The study of the line shape has shown that vanadium–oxygen structural units formed in the glasses are VO4 tetrahedra and VO5 pyramids according to the Li2O content. It is also observed that V2O5 behaves as modifier or as glass former in regard to the boron–oxygen network.

A X-ray photoelectron spectroscopy (XPS) study of the behaviour of sodium films deposited in ultra-high vacuum on InSe single-crystal or thin epitaxial films at room temperature and upon moderate annealings (up to 475 K) is reported. Major changes affect the substrate spectra, in particular indium, and clearly show the influence of the substrate morphology. For the InSe single-crystal substrate, annealing tends to restore the initial InSe surface as shown by XPS and RHEED, while for InSe films, no restoration occurs. In both cases, sodium has a partial ionic character and two phases are evidenced: one, [NaαIn0Seβ], where indium is close to metal or covalent indium, and the other, Naα'[InSe], where indium is more ionic close to InSe. The results emphasize that interdiffusion and fast chemical reaction predominate for the thin film substrate; for the bulk substrate, interfacial reaction and surface diffusion are competitive.

Ion beam modification of InSe (single crystals and molecular beam epitaxy-grown thin films on Si(111) substrate) by Ar+ and O+ (3 keV beam energy) is studied by XPS. The Ar+ ion bombardment produces surface layer enrichment in metallic indium with a gradient of concentrations, i.e. the top surface layer (10-15 Angstrom) contains less metallic indium as compared to the modified layers under it. Bombardment with O+ ions produces an indium oxide layer (similar to 20 Angstrom thick) on top of InSe. The relevance of the observed ion beam modifications to the preparation of solid state microbattery structures is discussed. (C) 1997 by John Wiley & Sons, Ltd.

Raman scattering (RS) in CdAs2 semiconducting crystals has been studied. The RS spectra have been recorded in the backscattering configuration with the lambda = 514.5 nm line of an ion argon laser at 50 mW output level, at room temperature. The recorded RS spectra have brought some evidence of the quasi-molecular character of the crystal lattice dynamics. The phonon modes at frequencies within the interval 180 to 270 cm(-1) are attributed to the arsenic atom-chain oscillations. There is some evidence of correlation splitting to occur for these high-frequency phonons. The modes at frequencies inferior to about 180 cm(-1) are attributed to the ones with important contribution of cadmium atoms and they resemble external modes in molecular crystals.

The far-IR reflectivity spectra for electrochemically lithium-intercalated layered crystal Li0.1In2Se3 exhibit a large Drude edge shift in comparison with the pristine material In2Se3. The analysis of the temperature dependence of the optical dielectric function yields a scattering rate τ−1α[(pT)2 + ω2] that is compatible with electron-electron scattering. The estimated plasma frequency ωp agrees with Hall effect data and the temperature variation of τ(T) is in accord with the d.c. resistivity.

A discussion of the electronic energy bands and lattice dynamics of pure and lithium-intercalated InSe is presented. After a review of the structure of the material and its polytypes, experimental results on both optical absorption and photoluminescence are compared for the pure and lithium-intercalated cases. A similar comparison is made for experimental Raman spectra. Electronic energy band calculations based on the tight-binding method are presented. The results indicate that InSe containing lithium has an impurity band just below the conduction band edge. The phonon dispersion curves of pure and lithium-intercalated InSe have been calculated using the rigid ion model and the results compared with the Raman spectra. Normal modes associated with lithium impurity atoms are identified. A set of conclusions is presented.

The Raman spectrum of InSe doped with GaS exhibits appreciable changes at low doping densities indicating considerable changes on introducing GaS. The photoluminescence as well as resonance Raman study shows that the exciton energy is shifted towards higher energy as a result of doping. At resonance, both the one- and two-phonon polar modes are observed, although considerably broadened. This indicates that the GaS-doped InSe develops significant topological disorder. Resonance Raman study shows that increasing the dopant broadens the resonance but the excitonic energy does not change as a result of the increase in the GaS in InSe. The scattering also exhibits considerable temperature dependence, so that it is possible to temperature tune the resonance in the doped samples at low temperatures.