Showing papers by "Christian M. Julien published in 1992"
TL;DR: It is shown that the inhomogeneous nature of percolating gold films controls the optical properties even at such long wavelengths as 500 \ensuremath{\mu}m, where the typical grain size is 10 nm, and the effective-medium theory is shown to be invalid close to the percolation threshold.
Abstract: The optical reflectance and transmittance of percolating gold films close to the metal-insulator transition were measured over an extended wavelength range: from 25 to 500 \ensuremath{\mu}m It is shown that the inhomogeneous nature of such films controls the optical properties even at such long wavelengths as 500 \ensuremath{\mu}m, where the typical grain size is 10 nm Effective-medium theory is shown to be invalid close to the percolation threshold even at 500 \ensuremath{\mu}m Comparison of the measured data of all the samples with the scaling model of Y Yagil et al [Phys Rev B 43, 11 342 (1991)] yields excellent agreement over the entire wavelength range In particular, the short length scale determined by the anomalous diffusion relation is shown to be the relevant length scale for the optical measurements This scaling model for the optical properties of such films is thus experimentally justified, both qualitatively and quantitatively
107 citations
TL;DR: In this paper, the lattice dynamics of the MoO3 crystal were studied by infrared and Raman polarized spectroscopy in the entire range of 10−1500 cm−1.
92 citations
TL;DR: In this paper, the optical and electrical properties of tin monoselenide SnSe and tin dichalcogenides SnX2 with X = S and Se were investigated by means of resistivity and Hall effect in the temperature range from 90 to 300 K.
Abstract: This work reports a study of the optical and electrical properties of tin monoselenide SnSe and tin dichalcogenides SnX2 with X = S and Se . The semiconducting character of the single crystals is investigated by means of resistivity and Hall effect in the temperature range from 90 to 300 K. The energy gap data are obtained by absorption measurements. The far-infrared reflectance spectra of the tin chalcogenide compounds have been measured. The experimental data are fitted using a four-parameter dispersion model based on the factorized form of the dielectric function.
92 citations
TL;DR: In these experiments, the resonant enhancement of the forbidden first-order LO mode at the E0 gap of pure CdTe at 17 K is shown and multiple-LO-phonon scattering up to four orders under both incoming and outgoing resonant conditions.
Abstract: We have performed experiments to show the resonant enhancement of the forbidden first-order LO mode at the ${\mathit{E}}_{0}$+${\mathrm{\ensuremath{\Delta}}}_{0}$ gap of pure CdTe at 17 K. We explain this forbidden scattering in terms of intrinsic intraband Fr\"ohlich interaction. In our experiments we also observe multiple-LO-phonon scattering up to four orders under both incoming and outgoing resonant conditions. The multiphonon spectra are briefly discussed and compared with other cadmium chalcogenides.
57 citations
TL;DR: Shallow impurities in n-type indium selenide (InSe) have been investigated by means of Fourier-transform spectroscopy in the far-infrared region and a mechanism is proposed to explain the large value of the full width at half maximum associated with the 1s-2$ p-2-3 dipole transition, which is attributed to impurity pairing.
Abstract: Shallow impurities in n-type indium selenide (InSe) have been investigated by means of Fourier-transform spectroscopy in the far-infrared region. Three electric dipole transitions have been identified: 1s-2${\mathit{p}}_{\ifmmode\pm\else\textpm\fi{}}$, 1s-2${\mathit{p}}_{0}$, and 1s-3${\mathit{p}}_{\ifmmode\pm\else\textpm\fi{}}$, corresponding to electrons bound to native donors and tin-, silicon-, and chlorine-related donors, whose ionization energies (17.6, 18.1, 18.8, and 19 meV, respectively) have been determined through the Guerlach-Pollmann model. That model was also used to calculate the oscillator strengths of those dipole transitions, and then to estimate the shallow-donor concentrations in each sample. Native donors turn out to be the most hydrogenic ones, and the energies of their related transitions are used to determine a more accurate value of the low-frequency dielectric-constant product. An absorption line is observed in the low-energy side of the spectra (80 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) for samples with a donor concentration higher than ${10}^{15}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$, which is attributed to impurity pairing. A mechanism is proposed to explain the large value of the full width at half maximum associated with the 1s-2${\mathit{p}}_{\ifmmode\pm\else\textpm\fi{}}$ absorption line (\ensuremath{\approxeq}6.6 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in the purest samples): Longitudinal-acoustic phonons polarized parallel to the c axis create dielectric-constant waves that modulate the dipole transition energies of shallow donors. In highly doped samples, compensating acceptors give rise to internal electric fields that largely broaden the absorption lines.
32 citations
TL;DR: In this article, thin films of MoO3 were prepared by the flash evaporation technique on silica glass substrates maintained in the temperature range 30-300°C and the films were systematically characterized by studying their optical, electrical and electrochemical properties.
30 citations
TL;DR: The optical absorption of substitutional Fe 2+ ions in Cd 1-x Fe x Te compounds has been measured in the far infrared and the crystal-field model is not sufficient to explain the experimental features.
Abstract: The optical absorption of substitutional Fe 2+ ions in Cd 1-x Fe x Te compounds has been measured in the far infrared (10-80 cm -1 ) at temperatures from 5 to 300 K. Electronic transitions inside the 5 E multiplet of Fe 2+ are observed at low temperature, but the crystal-field model is not sufficient to explain the experimental features. Calculations of the 5 E electron states are performed, taking into account the Jahn-Teller interaction with the vibrations of the host lattice
18 citations
TL;DR: In this article, the electrochemical and transport properties of lithium-intercalated NiPS3 were investigated and the partial ionic conductivity was estimated from the experimental determination of D ∗ and W and a value of σ i t e ( Li) is 2 × 10 −3 ω −1 cm −1 at x = 1.0.
Abstract: We have investigated the electrochemical and transport properties of lithium-intercalated NiPS3. Thermodynamic and kinetic results have been obtained by the modified galvanostatic intermittent titration technique for the long-time regime in the compositional range 0 ⩽ x ⩽ 1.5 . The chemical diffusion coefficient of lithium in Li x NiPS 3 is composition dependent and the average value is 10 −9 cm 2 s −1 at room temperature. The partial ionic conductivity is estimated from the experimental determination of D ∗ and W and a value of σ i t e ( Li) is 2 × 10 −3 ω −1 cm −1 at x = 1.0 . These transport properties are compared with those obtained in a galvanic cell with a composite electrode, i.e. a mixture of active material, solid electrolyte, acetylene black and polytetrafluoroethylene. Electrochemical titration during the discharge under moderate current drain shows lower values for the transport properties in a medium which is out of equilibrium.
12 citations
TL;DR: In this article, the applicability of the rigid-band model is used as a test for the most desirable properties of a good intercalation material for insertion electrodes in solid state batteries.
Abstract: Numerous layered compounds are interesting materials in which lithium intercalation occurs primarily without destruction of the host lattice. In many cases a rigid-band model is a useful first approximation for describing the changes in electronic properties of the host material with intercalation. This paper presents some recent experimental results obtained on transition-metal chalcogenide compounds and on transition-metal oxides as well. We shall observe, nevertheless, that the rigid-band model is not applicable to all of the intercalated materials. The applicability of the rigid-band model may be used as a test for the most desirable properties of a good intercalation material. This needs to be more extensively documented for their possible applications as insertion electrodes in solid state batteries.
8 citations
TL;DR: In this article, a study of the transport measurements on lithium intercalated InSe single crystals is presented, and the classical formalism of weak localization is applied to the weak localization.
Abstract: We present a study of the transport measurements on lithium intercalated InSe single crystals. Lithium intercalant acts as a donor species and after intercalation the resistivity falls below 0.02 Ω cm with an increase in the carrier density. At low temperature pure InSe exhibits a two-dimensional conductivity owing to weak localization as a consequence of the weak disorder introduced by the large concentration of stacking faults. The logarithmic temperature dependence is found to be general and the classical formalism of the weak localization is applied. Upon intercalation the presence of Li atoms destroys the electronic interference waves and the weak localization disappears completely. The change in the electrical properties is discussed and an electronic band model is proposed.
4 citations
TL;DR: In this paper, the optical properties of transition-metal dichalcogenides, non-transition metal chalcogens and transition metal oxides are presented and discussed with the aim of a better understanding of the intercalation process and establish some guide lines for improving the performances of these materials in their most important applications.
Abstract: Layered compounds are known to form lithium intercalation complexes as electron donor systems. A charge transfer which can strongly affect the electronic properties of the host lattice, and a change of preferential crystallographic parameters without destruction of the original structure are the main effects occuring during intercalation. Optical spectroscopies such as Raman scattering, far-infrared reflectivity, absorption measurements and photoluminescence have been carried out for the study of electronic and structural modifications. Upon lithium intercalation, lattice dynamics and electronic band structure change in numerous layered compounds. The optical properties of transition-metal dichalcogenides, non-transition metal chalcogenides and transition-metal oxides are presented and discussed with the aim of a better understanding of the intercalation process and establish some guide lines for improving the performances of these materials in their most important applications.