Raman and infrared spectra of CdIn2S4 and ZnIn2S4

Four one-phonon Raman lines have been found in CdIn₂S₄ (ZnIn₂S₄) spinels at 92 (72) cm^-1, 186 (184) cm^-1, 246 (253) cm^-1, and 367 (372) cm^-1 for incident photon energies well below the energy gap E_G ～ 2.4 (2.2) eV at 300 K. For photon energies close to E_G, the 367 cm^-1 mode underwent a resonant enhancement in CdIn₂S₄ and four infrared active but Raman forbidden F_1u modes appeared in the CdIn₂S₄ and ZnIn₂S₄ Raman spectra: TO modes at 226 (221) cm^-1 and 309 (312) cm^-1, and LO modes at 274 (272) cm^-1 and 340 (342) cm^-1.     

Spin-dependent phonon Raman scattering in CdCr2Se4

Influences of ferromagnetic ordering on the phonon Raman scattering are studied for CdCr₂Se₄ through the intensity measurements of Raman spectra between 25 and 300 K with various wavelengths of excitation light (488.0–676.4 nm). Spin-dependent enhancements of Raman cross section are observed for optical phonon lines D(168 cm^?1) and F(238 cm^?1) with excitation wavelengths of about 630 and 550 nm, respectively. This kind of phenomenon in spinel-type chalcogen chromites seems to originate in spin-dependent intermediate interactions in the excited states of specific electronic transitions with which the incident or scattered light is resonant.     

First-order Raman scattering in germanium resonant with the E0 gap

We have measured the absolute Raman efficiency as well as the dispersion for first order scattering by the optical zone center phonon in germanium with the incident photon energies in the range of the E₀ gap energy. At 77 K a Raman polarizability of 68±14 Ų is found for an incident photon energy of 0.826 eV. The deformation potential d is determined to be 40 eV assuming C^″₀ ? 1 for the strength parameter of the E₀ gap.     

Variation of Raman spectrum after optical excitation in amorphous As2Se3 at 1.6°K

Several experiments, involving electronic states have shown that amorphous As₂Se₃ is modified at low temperature by the action of not very strongly absorbed light (α～10²cm^?1). This paper presents Raman scattering results before and after illumination. The shape of the Raman spectrum is changed by illumination: its high energy side has grown near 260 cm^?1. This light induced modification of the vibrational states is discussed within the framework of a previous qualitative model involving changes in local atomic configuration.     

Coupling of the CDW and the water mode in K2Pt(CN)4Br0.3⋯3.2H2O

In previous work we have observed the amplitude mode of the charge density wave (CDW) in K₂Pt(CN)₄Br_0.3?3.2H₂O (KCP) by means of Raman scattering. New measurements made on deuterated material, K₂Pt(CN)₄Br_0.3?3.2D₂O (KCP1), show the same mode but shifted from 44 to 38 cm_?1, maintaining the symmetry properties and temperature dependence of frequency and linewidth. This considerable isotope effect is interpreted in terms of a coupling of the CDW with the water stretching mode, which by the deuteration is shifted from 3494 cm^?1 in KCP to 2560 cm^?1 in KCP1 according to the change in atomic mass. Both of these modes exhibit A₁(z) symmetry. At 5 K the resulting decoupled frequency of the CDW amplitude mode is 57 cm^?1, and the coupling energy about 140 cm^?1. A discussion of the temperature dependence of various important quantities is given. The present results show that the water molecules, which are located in between the Pt chains are strongly involved in the eigenvector of the CDW amplitude mode.     

Single crystal polarized Raman spectra of the solid electrolyte Cu2HgI4; attempt frequencies for ion motion in Ag2HgI4

The polarized Raman scattering from small single crystals of Cu₂HgI₄ provided assignments for the more prominent Raman features to specific irreducible representations. The E symmetry assignment, mass dependence, and pressure dependence of the 36 cm^?1 band in Cu₂HgI₄ and 24 cm^?1 band in Ag₂HgI₄ indicate that these features approximate the attempt frequency for ion hopping. The unusually high pre-exponential factor in the Arrhenius expression for ion hopping is discussed in light of the observed attempt frequency; we conclude that despite the high activation energy the conduction mechanism is similar to other heavy-metal solid electrolytes.     

Magnon Raman scattering in the quasi 1-D antiferromagnet CsCoBr3

Raman scattering from magnons has been observed in the three magnetic phases of CsCoBr₃. In the 1-D Ising phase T > 28K a broad band at 96 cm^?1 is observed. This band grows in intensity but shows little renormalisation (100.5 cm^?1 at 14K) in the partially disordered antiferromagnetic phase 14K < T < 28K. For T < 14K additional structure at 111.5, 123.5, 133, and 141 cm^?1 is attributed to magnon-magnon combination bands. Two extra magnon branches are expected for this ferrimagnetic phase. One of these has an energy of ≈ 11 cm^?1.     

Raman scattering in K2Pt(CN)4Br0.3 · 3H2O

Raman scattering experiments on K₂Pt(CN)₄Br_0.3 · 3H₂O are reported between 5 and 300 K as a function of temperature. A line of A₁ symmetry detected at 44 cm^?1 shows interesting temperature dependent properties. It is concluded from a comparison of the frequency, symmetry, and scattering intensity of this line with theoretical predictions that the excitation concerned represents the amplitude mode of the charge density wave (the line observed in infrared absorption being the phase mode). No Peierls transition is observed, but the results are consistent with a Peierls distortion present at all temperatures. The findings are correlated with inelastic neutron scattering and infrared studies. Finally, the CN stretching modes at 2189 and 2173 cm^?1 and the water mode at 3490 cm^?1 are studied as a function of temperature.     

Observation of a soft phonon in linear chain compound (NbSe4)3I by Raman scattering

The phase transition of the linear chain compound (NbSe₄)₃I was studied by Raman scattering. At 78 K three new peaks were observed at 73 cm^?1, 205 cm^?1 and 261 cm^?1. The totally symmetric Raman peak at 73 cm^?1 shows anomalous temperature dependence. The frequency decreases with increasing temperature, and at high temperatures an anticrossing occurs with another peak observed at about 58 cm^?1. The Raman intensity decreases and the linewidth broadens remarkably as the temperature increases. These properties allow us to assign this peak to a soft phonon. This fact indicates clearly the existence of a structural phase transition of a displacive type below room temperature.     

Raman scattering of high-temperature phase transition in KH2PO4

Raman scattering was applied to study the high-temperature phase transition (near 175°C) in KH₂PO₄. Drastic temperature-dependent changes were observed to take place in the normal modes of B₁ symmetry between 1000–3400 cm^?1. The disintegration of the dominant broad feature near 2500 cm^?1 when temperature rises beyond 150°C suggests that the alteration of the hydrogen-bond network is closely connected with this high-temperature phase transition.     

Light emission at the E1 and E1+Δ1 gaps in heavily doped p-type Ge and GaAs

We report the observation in heavily doped p-type germanium (N_h ≥ 10¹⁸cm^?3) of two weak light emission bands centered at the energies of the E₁ and E₁+Δ₁ interband gaps (2.22 and 2.42 eV at 80 K). These bands, which are 100% polarized, are found only for excitation with laser frequencies slightly above the gaps. We attribute them to photon scattering by inter-valence-band excitations of the holes associated with the heavy doping. The fact that the emission bands do not shift with the exciting laser frequency is assigned to a strong resonance enhancement of this scattering near the E₁ and E₁+Δ₁ gaps. We have also observed the corresponding light emission at the E₁ gap (3.0 eV) in p-type GaAs.     

Electrical transport measurements in a quasi-onedimensional semiconductor ZrS3

We have used the technique of chemical vapour transport to prepare needle shaped single crystal of ZrS₃. Results of the measurements of d.c. resistivity. Hall coefficient and thermoelectric power of the temperature range 100–500 K are reported. All the samples exhibited semiconducting behaviour with a room temperature resistivity of about 15 Ω-cm and an activation energy of 0.20±0.02 eV. Room temperature thermoelectric power is -850 μVK^?1 and the dominant carriers are electrons. The thermoelectric power varies as (1/T), a behaviour associated with a typical semiconductor. Mobility at low temperatures is limited by ionized impurity scattering and is given by μ₁ = 6.5 × 10^?2T^3/2 cm²V^7-1 sec^?1. At high temperatures, phonon scattering is dominant and the mobility is given by μ₂ = 1.35 × 10⁺⁵T^?32 cm²V^?1 sec^?1.     

Plasmon reflectivity of n-type ferromagnetic semiconductor HgCr2Se4

The reflectivity of n-type HgCr₂Se₄ was measured between 86 and 320 K for photon wavenumber from 250 to 1000 cm^?1. A critical behaviour of the plasmon parameters (plasmon enegy and plasmon scattering energy ) was observed at about 160 K but not in the vicinity of the Curie temperature T_c = 110 K. The effective mass and the optical mobility exhibit a rapid variation between 150 and 170 K.     

High resolution Raman spectroscopy of the fundamental vibrational band of 16O2

The vibrational Raman spectrum of ¹⁶O₂ has been recorded with high resolution (0.05 cm^?1 for the Q branch). The expansion of the Hamiltonian as a sum of irreducible tensors of the O(3) group allowed us to obtain easily the expressions for the energy levels, taking into account the off-diagonal matrix elements. From the analysis of the spectrum the excited state constants have been calculated; in particular the rotational constants obtained are: B₁ = 1.421884 ± 0.000013 cm^?1 and D₁ = (?4.864 ± 0.014)10^?6 cm^?1.     

Polaritons and optical phonon assignment in orthorhombic HCOOLi·H2O crystal by Raman scattering measurement

Optical phonon modes of orthorhombic HCOOLi·H₂O crystal are investigated by laser Raman scattering technique. An A₁ mode polariton with energy between 1250 cm^-1 and 1343 cm^-1 is observed by near-forward Raman scattering using Ar laser.     

Raman scattering from magnons in CoCl2 and FeCl2

One-magnon Raman scattering has been observed in the metamagnets CoCl₂ and FeCl₂. The k = 0 magnon energies are 16 ± 1 cm^-1 at 21 K and 16.4 ± 0.4 cm^-1 at 12 K, respectively and these values are in good agreement with previous AFMR and neutron scattering results. A search for two-magnon scattering in both compounds was unsuccessful, largely because of masking from nearby first-order phonons and a weak temperature dependent broad band at 140 cm^-1 in CoCl₂, which is assigned to two-phonon scattering from acoustic phonons.     

Coherent Stokes and anti-Stokes Raman spectra of the ν1 (A1) and ν2 (E) bands of SF6 and UF6

Coherent Stokes and anti-Stokes Raman scattering are used to study the ν₁ and ν₂ spectral band profiles of UF₆ and SF₆. Most of the observed SF₆ “hot” bands are assigned, leading to evaluations of the anharmonicity constants X_ij: X₁₂ = ?(2.80 ± 0.30) cm^?1, X₁₄ = ?(1.00 ± 0.15) cm^?1, X₁₅ = ?(1.00 ± 0.15) cm^?1. For UF₆, a tentative assignment of the “hot” bands is made: X₁₂ = ?(1.80 ± 0.30) cm^?1, X₁₃ = ?(1.60 ± 0.30) cm^?1, X₁₄ = ?(0.20 ± 0.10) cm^?1, X₁₅ = ?(0.25 ± 0.10) cm^?1, and X₁₆ = ?(0.10 ± 0.05) cm^?1. Parameters such as the vibration-rotation coupling constants are determined. For SF₆: α = (7 ± 2) × 10^?5 cm^?1 for the ν₂ band and α = ?(1.02 ± 0.01) 10^?4 cm^?1 for the ν₁ band. The calculated spectral profiles of the coherent Stokes or anti-Stokes spectra, which are in good agreement with experimental results, give values for the resonant and nonresonant parts of the susceptibility in both molecules. They also show, in some cases, the influence of neighboring combination bands.     

Magnon Raman scattering in CoBr2

The one-magnon Raman spectrum of CoBr₂ has been investigated as a function of temperature, and peak frequency, integrated intensity and width parameters obtained. The results obtained for the band energy at low temperature (22.2 ± 0.2 cm^-1 at 5.7.K) are in good agreement with AFMR and neutron scattering results. The one-magnon energy renormalises relatively slowly with increasing temperature and is about 15 cm^-1 at T_N = 19 K, whereas the integrated intensity approaches zero like the magnetization at T_N and the width diverges. A low intensity band at 26.8 ± 1 cm^-1 (7.6K) may be due to two-magnon scattering from spin waves along the c-axis.     

Exponential absorption edge in hydrogenated α-Si films

Optical and photoelectric measurements demonstrate that hydrogenated amorphous silicon prepared by glow discharge decomposition of silane has an exponential optical absorption edge, over the photon energy range 1.4–1.8 eV with a slope of 0.05–0.08 eV. Evidence is presented that the photogeneration efficiency is unity at room temperature and independent of electric field (10²?10⁴ V/cm^?1) and photon energy (1.2–2.2 eV).     

Softening of charge density wave excitations at the superstructure transition in 2H-TaSe2

Raman scattering measurements performed between 5 K and 300 K on 2H-TaSe₂ reveal new modes which are assigned to the modes of the charge density wave, observed in light scattering due to the Fermi surface induced distortion. The mode at 49 cm^?1 of E_2g symmetry softens (with concurrent line-width broadening) towards 122 K, the transition temperature from the incommensurate distorted to the undistorted phase. The mode at 82 cm^?1 of A_1g symmetry appears to be connected with the transition at 90 K from the commensurate to the incommensurate superstructure. The mode at 24.5 cm^?1 of E_2g shows no temperature dependence and is clearly due to the rigid-layer vibration.