Two-Phonon Combination Mode Spectra of AgGaS2

Absorption spectra of (001)-oriented AgGaS₂ single crystals are measured in the wavenumber range from 400 to 900 cm⁻¹. The spectra exhibit 12 structures due to two-phonon combination modes which can be all interpreted as sum modes of zone-centre phonons. Possible frequencies for the B₁ and A₂ modes are discussed. The results obtained are compared with second-order Raman spectra of the compound.     

Photoinduced Absorption and Resonant Raman Scattering in Trans-(CD)x

The three resonantly enhanced Raman modes and the three photoinduced ir-active vibrations in trans-(CD)_x are described in terms of amplitude modes of the Peierls gap and charged induced ir-active modes, respectively. The detailed spectra are accounted for by a dressed phonon propagator and a coupling parameter. The photoinduced electronic bands and the primary Raman frequencies increase with increasing temperature; the origin of this anomaly is discussed.     

The superposition of the lattice radiation and reflectivity spectra of MoO3 and PbMoO4 crystals

The Raman scattering of MoO₃ at 300 and 77 K and the infrared reflectivity spectra of MoO₃ at 300 K have been investigated in different scattering geometries. The Raman spectra of PbMoO₄ crystals at 77 K have been investigated also. The reflectivity spectra of MoO₃ crystals were calculated for E ∥ c and E ∥ a. The phonon parameters and the effective ionic charges of anions and cations for MoO₃ and PbMoO₄ crystals are determined. The diagrams of the splitting of the vibrational levels by the Davydov resonance and by the factor group interactions have been determined. It is shown that the lattice radiation of crystals which have a number of vibrational oscillators (MoO₃, PbMoO₄) begins at low energy vibrational modes and at low values of the damping parameters.     

Vibrational properties of CdGa2S4

Polarization-dependent infrared reflectivity spectra of CdGa₂S₄ are measured at 300 K in the wavenumber range from 180 to 500 cm⁻¹. The analysis of the spectra yields three E and four B modes in this frequency range. The results are compared with previously published data and a final identification of the infrared active modes in CdGa₂S₄ is proposed. It is shown that the two-phonon absorption spectra of CdGa₂S₄ can be interpreted in terms of zone-centre two-phonon combination modes. The relation between the lattice vibrational properties of chalcopyrite and defect-chalcopyrite compounds is discussed.     

One- and two-phonon Raman spectra of amorphous AsSe systems

The polarization dependence of the one- and two-phonon Raman scatterings of the amorphous semiconductor As_xSe_1?x systems for 0 ? x ? 0.5 was measured. The analysis of the Raman data by the superposition of the vibrations of AsSe₃ pyramids and SeSe bonds suggests the existence of the intermediate range interaction in the As_xSe_1?x systems.Two phonon Raman spectra for 0.3 ? x are explained by the combination plus overtone of the first order Raman scatterings. For x ? 0.2, however, the overtone processes become predominant.The dependence of the Raman spectra on the As concentration suggests that the chemical orderings are predominant.     

Infrared optical properties and crystal structure of Cu2GeS3

Infrared reflectivity and transmission spectra of Cu₂GeS₃ are measured at room temperature in the wavenumber range from 180 to 4000 cm⁻¹. From an analysis of the spectra the parameters of the fundamental infrared active lattice modes and of the two-phonon combination modes are determined. From a comparison of the experimental data with group theoretical predictions for the structure models proposed for Cu₂GeS₃ in the literature it is concluded that Cu₂GeS₃ crystallizes in a monoclinic lattice.     

Far Infrared and Raman Optical Study of CdInGaS4, CdIn2S4, HgInGaS4 and CdIn2S2Se2 Crystals

Raman and infrared reflectivity spectra of CdInGaS₄, CdIn₂G₄, HgInGaS₄, and CdIn₂S₂Se₂ crystals have been investigated. The fiindamental phonon parameters, the limiting dielectric constants ϵ₀ and ϵ∞ and the reflectivity spectrum contours have been calculated using classical dispersion relations.     

Optical phonon modes and transmissivity in BaWO4 single crystal

Barium tungstate (BaWO₄) single crystal has been grown using Czochralski technique. It belongs to the scheelite structure, forming the space group I 4₁/a at room temperature and the primitive cell contains two molecular units. The polarized Raman spectra were recorded by a micro‐Raman spectrophotometer system in the backscattering geometry. All the observed Raman modes were assigned. The Raman mode at 924 cm^–1, which belongs to the totally symmetrical A_g optical modes, has the strongest intensity and its linewidth is 4.6 cm^–1. The infrared active lattice vibrations have been studied, eight optical modes were observed and assigned. The ultraviolet absorption edge is at 256 nm and the optical transparency range is up to 2500 nm at room temperature. The energy gap E_g of this crystal was obtained from the optical transmission spectra. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectra and structure of organophosphorus compounds,XVIII: Infrared and Raman spectra of [(CH3)2PS]2, [(CD3)2PS]2, and [(CH3CH2)2PS]2 in the solid state

The infrared (80–3500 cm^–1) and Raman (10–3500 cm^–1) spectra of solid [(CH₃)₂PS]₂, [(CD₃)₂PS]₂, and [(CH₃CH₂)₂PS]₂ have been recorded. A complete vibrational assignment is proposed for tetramethyldiphosphine disulfide on the basis ofC _2h molecular symmetry. The observed intermolecular vibrations indicate little factor group effects, and no frequency differences were observed for the normal modes of the two different molecules which exist in the crystal as reported from the x-ray study. Most of the observed bands in the spectrum of tetraethyldiphosphine disulfide have been assigned. At least two of the three optical librational modes were observed in the Raman effect.     

Adiabatic bond charge model for lattice dynamics of ternary chalcopyrite semiconductors

The adiabatic bond charge model of Rustagi and Weber is extended to study lattice dynamical properties of ternary chalcopyrite semiconductors AgGaS₂, AgGaSe₂, CuInS₂, CuInSe₂, CuGaS₂, CuGaSe₂, CuAlS₂ and CuAlSe₂. The new model calculations agree well with the results of Raman/IR and neutron measurements of Brillouin zone center phonon frequencies for both low and high frequency modes which was difficult for other phenomenological lattice dynamical models. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Multimode phonon structure of Be‐containing II ‐ VI mixed crystals determined by IR spectroscopic ellipsometry

Spectroscopic ellipsometry in the infrared spectral range 250‐5000 cm^‐1 is used for analysis of the dielectric response of Zn_1‐x‐yBe_xMg_ySe and Zn_1‐x‐yBe_xMn_ySe crystals grown by a high‐pressure Bridgman method. Ellipsometric spectra display features in the spectral range 390‐500 cm^‐1 associated with BeSe‐type phonon modes. In the optical spectra of Zn_1‐x‐yBe_xMg_ySe crystals both BeSe‐type and MgSe‐type lattice absorption bands are detected. The MgSe‐like modes are located at approximately 300 cm^‐1. The complex dielectric functions can be reproduced using a model with two or three and one or two classical damped oscillators corresponding to the BeSe‐like and the MgSe‐like transverse‐optical phonon modes, respectively. The frequencies of longitudinal‐optical phonons have been derived from the dielectric loss functions. A red‐shift of the BeSe‐like phonons frequencies with a mean rate 0.42 cm^‐1 (0.50 cm^‐1) per mole percent of Mg (Mn) incorporated to the alloy has been found for examined concentration range x, y ≤ 0.25. A noticeable damping the intensities of BeSe‐type modes with increasing fraction of Mg and Mn dopant is observed in comparison to the strengths of BeSe‐type modes in Zn_1‐xBe_xSe crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature dependence of Raman‐active mode frequencies and linewidths in TlGaSe2 layered crystals

Raman spectra of TlGaSe₂ crystal at different temperatures are discussed. The temperature dependence of frequency shifts and linewidths of the Raman peaks in the frequency region of 10‐320 cm^‐1 have been measured in the range from 50 to 320 K. The analysis of the experimental data showed that the temperature dependencies of phonon frequencies and linewidths are well described by considering the contributions from thermal expansion and lattice anharmonicity. The anharmonic contribution (phonon‐phonon coupling) is found to be due to three‐phonon processes. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of pressure on the structural stability of iron phosphate glass: Role of trace water

Raman and infrared spectroscopic measurements were carried out on 40 mol% Fe₂O₃:60 mol% P₂O₅ iron phosphate glass samples to study the effect of increasing external pressure on the local structure of both anhydrous and water trapped glasses. In-situ high‐pressure Raman measurements, done up to 24.2 GPa on anhydrous samples, revealed hardening of the phonon modes accompanied by a loss of Raman intensity and ultimately leading to complete smearing of modes at very high pressures. These changes were found to be reversible upon quenching the sample back to ambient pressure. Raman and infrared spectroscopy of pressure quenched IPG samples containing trace amounts of water have revealed definite signatures of devitrification at room temperature.     

Raman scattering study on Ga1–x Mnx As prepared by Mn ions implantation,deposition and post‐annealing

Raman scattering measurements have been performed in Ga_1–x Mn_x As crystals prepared by Mn ions implantation, deposition, and post‐annealing. The Raman spectrum measured from the implanted surface of the sample shows some weak phonon modes in addition to GaAs‐like phonon modes, where the GaAs‐like LO and TO phonons are found to be shifted by approximately 4 and 2 cm^‐1, respectively, in the lower frequency direction compared to those observed from the unimplanted surface of the sample. The weak vibrational modes observed are assigned to hausmannite Mn₃O₄ like. The coupled LO‐phonon plasmon mode (CLOPM), and defects and As related vibrational modes caused by Mn ions implantation, deposition, and post‐annealing are also observed. The compositional dependence of GaAs‐like LO phonon frequency is developed for strained and unstrained conditions and then using the observed LO_GaAs peak, the Mn composition is evaluated to be 0.034. Furthermore, by analyzing the intensity of CLOPM and unscreened LO_GaAs phonon mode, the hole density is evaluated to be 1.84×10¹⁸ cm^‐3. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical phonons and Raman scattering in ternary II–VI spheroidal nanocrystals embedded in a glass matrix

Theoretical and experimental studies of the spatial phonon confinement in ternary CdS_xSe_1−x nanocrystals embedded in a glass matrix formed by the composites (40)SiO₂₋(30)Na₂CO₃–(29)B₂O₃–(1)Al₂O₃ (mol%) + [(2)CdO + (2)S + (2)Se] (wt%) were carried out. From the analysis of the surface phonon modes, the theoretical procedure has allowed the determination of the geometrical characteristics of the nanocrystals. The calculated frequencies were compared with the experimental values obtained from the Raman spectra of CdS_xSe_1−x nanocrystals grown under different thermal treatments. A good correlation between the experimental and calculated CdS-like and CdSe-like surface optical modes was observed. The Raman selection rules and their connection with the nature of the surface optical phonons is discussed in order to use Raman spectroscopy as a probe to determine the composition x and the geometrical shape of the semiconductor nanocrystals.     

Low frequency Raman scattering in chalcogenide glasses

Low frequency Raman spectra of chalcogenide glasses are analyzed in terms of matrix element effects and modes of a layered structure. The spectra of GeSe₂ at low temperature shows no peaks which can be assigned to layer modes. The reduced spectra indicates that the density of states exhibits nearly ω² dependence for ω < 60 cm^?1, and the coupling constant approaches ω² dependence at frequencies less than 20 cm^?1.     

Infrared reflectivity of ZnIn2Te4

Infrared reflectivity spectra of ZnIn₂Te₄ single crystals are measured at room temperature in the wavenumber range from 170 to 4000 cm⁻¹. The spectra reveal a single vibrational mode the frequency of which compares well with the frequencies of the high-energy infrared active modes in HgIn₂Te₄, CuInTe₂ and AgInTe₂. It is concluded that these modes are sphalerite-like in nature and that they are essentially determined by the properties of the In—Te bond.     

Raman scattering characterization of Mn composition and strain in Ga1–x Mnx Sb/GaSb epitaxial layers

Raman scattering (RS) experiments have been performed for simultaneous determination of Mn composition and strain in Ga_1–x Mn_x Sb thin films grown on GaSb substrate by liquid phase epitaxy technique. The Raman spectra obtained from various Ga_1–x Mn_x Sb samples show only GaSb‐like phonon modes whose frequency positions are found to have Mn compositional dependence. With the combination of epilayer strain model, RS and energy dispersive x‐ray (EDX) experiments, the compositional dependence of GaSb‐like LO phonon frequency is proposed both in strained and unstrained conditions. The proposed relationships are used to evaluate Mn composition and strain from the Ga_1–x Mn_x Sb samples. The results obtained from the RS data are found to be in good agreement with those determined independently by the EDX analysis. Furthermore, the frequency positions of MnSb‐like phonon modes are suggested by reduced‐mass model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mixed alkali glass spectra and structure

The far infrared and Raman spectra of several series of mixed alkali metaphosphate glasses have been investigated as a function of the mole fraction x of the network-modifying ionic oxides in xM₂O(1?x)M₂′O · P₂O₅. The frequencies of the cation-motion bands in the far infrared spectra, which correspond to cationsite vibrations, do not shift with x, indicating that the vibrationally significant local geometry and forces associated with a particular cation are unaffected by the introduction of the second cation into the glass structure. Each Raman-active band due to vibrations of the metaphosphate network occurs at a different frequency for each pure glass (x = 0 or 1), but for mixed alkali glasses only one band occurs for each type of mode and it varies linearly with x. This indicates that the cations in these mixed alkali glasses are homogeneously distributed, there is no significant molecular-level domain formation and the phosphate chains are associated with an averaged cation environment whose effect on the chain modes varies with x. A simple vibrational model is presented which shows that the cation-dependent shifts are due to small changes in network bond angles and variation of the cationsite forces.     

Infrared and Raman spectra of potassium pentacyanonitrosylmanganate(I) dihydrate: K3[Mn(CN)5NO]· 2H2O

The infrared spectra of polycrystalline K₃[Mn(CN)₅NO]·2H₂O at different degrees of deuteration were recorded between 4000 and 200 cm^–1, both at room and low temperature. The room-temperature Raman spectrum of the isotopically normal powder was also obtained. The observed bands were assigned to the internal vibrational modes of the [Mn(CN)₅NO]^–3 ion and to the internal and librational modes of water of hydration. In accordance with X-ray diffraction studies, the spectra showed the existence of two crystallographically distinct types of water molecules located in different sets of sites ofC ₁ symmetry.A communication on this subject was presented at the XVI Latin American Chemistry Congress, Rio de Janeiro, Brazil, October 14–20, 1984.