Far infrared studies of lattice and free carrier effects in CdxHg1−xSe

Far infrared reflection spectra of Cd_xHg_1−xSe are measured in the region 20 to 600 cm^-1 at temperature between 5 and 77 K. Reflection spectra are explained well by the dynamic dielectric function which is constructed as a sum of interband, intraband and phonon contributions. The plasma-LO phonon coupling and free carrier effects are discussed.     

Analysis of infrared thermoreflectance spectra of NbxTi1−xS2

Thermoreflectance spectra of Nb_xTi_1−xS₂ crystals in the infrared are reported and discussed. In particular the plasmon lineshape, an interband transition at ≅0.8 eV and the effect of cation substitution on infrared thermoreflectance spectra are examined.     

Intrinsic carrier concentration in Hg1−xCdxTe

The effective mass of heavy holes has been determined on the basis of simultaneous analysis of the Hall coefficient and conductivity data obtained in the temperature region 100–300 K on well characterized p-type Hg_1–x Cd_xTe (x0·2) samples. Its value is 0·7m₀. The calculation of intrinsic carrier concentration for 0·19 x0·3 and 50 Kg T 300 K has been carried out using the above value of the effective mass of holes, Hansen's expression for the band gap and momentum matrix element from magneto-optical measurements.     

Millimetre-wave and Fourier transform infrared spectra between 325 cm−1 and 4720 cm−1 of BrCN and global rovibrational analysis of the main isotopomers

The infrared absorption spectrum of BrCN has been recorded in the re?ion 325–4720 cm^?1 with a Bruker 120 HR interferometer. More than 30 000 lines have been measured and most of them have been assigned: 10734 lines for 151 bands and 10993 lines for 150 bands of ⁷⁹Br¹²C¹⁴N and ⁸¹Br¹²C¹⁴N, respectively. Also new millimetre-wave spectra were measured for the vibrational excited states lying between 1000 cm^?1 and 1400 cm-′. After a band by band analysis of these transitions, rovibrational global analyses have been performed for both isotopomers using all available experimental data. The rotational I-type resonance and the anharmonic resonance associated with k_l22 are taken into account in one-step diagonalization procedures. Sets of 73 molecular parameters are obtained for both isotopomers. It is shown that the existing equilibrium structure is likely to be reliable. The vibrational dependence of the quartic centrifugal distortion constant is analysed for the linear triatomic molecules studied so far.     

Temperature dependence of the electron effective mass in MnxHg1−xSe

We have investigated the temperature dependence of the electron effective mass in Mn_xHg_1–xSe crystals (0 < x 0.1) in the T=90–300 K temperature range. We have determined that the temperature-dependent changes in the band gap (_g), in the band diagram nonparabolicity, and in the conduction band carrier concentration have a strong effect on the temperature dependence of the carrier effective mass at the Fermi level m ^*=f(T).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 5–9, November, 1987.     

Electronic structure and optical spectra of YBa2Cu3O7−δ thin films in the infrared and UV region

Optical reflectance of YBa₂Cu₃O_7- thin films grown by laser ablation is measured within photon energies of 0.1 eV to 3.5 eV at room temperature. The spectra can be fit congruently with the anisotropic dielectric constants which take account of the intraband free carrier transition and interband transition. The anisotropic plasma frequencies are simulated to be _pl=2.18 eV and _ch=2.80 eV contributed from free carriers on the plane and in the chain, respectively. The interband transition occurs near 2.5 eV and is pertinent to a rather broad line width.     

Density functional calculations of Pb1−xCaxSySe1−y alloys lattice matched to different substrates

Density functional calculations are performed to study the structural and electronic properties of technologically important Pb_1?xCa_xS_ySe_1?y quaternary alloys. The calculations are based on the total-energy calculations within the full-potential augmented plane-wave (FP-LAPW) method. For exchange-correlation energy and corresponding potential, the generalized gradient approximation (GGA) by Perdew–Burke–Ernzerhof (PBE) and Engel–Vosko (EVGGA) have been used. We investigated the effect of composition on lattice constant, bulk modulus and band gap for pseudobinary as well as for quaternary alloys, which showed non-linear dependence on the composition x and y. The presented contour maps of energy band gap and lattice constants versus concentrations could be useful for designing new structures with the desired optical properties. In addition, the energy band gap and natural band offset of simple cubic Pb_1?xCa_xS_ySe_1?y quaternary alloys lattice matched to PbS and SrS substrates are investigated. The obtained results show that the quaternary alloys of interest could be appropriate materials for designing heterostructures with desired optical and interfacial properties.     

Use of the kramers — kronig method for analyzing internal reflection spectra in the region of strong infrared bands

Journal of Applied Spectroscopy -     

X-ray photoelectron spectra and atom valency distribution in oxide BaPb1−xBixO3 superconductor

X-ray photoelectron spectra of valent regions and inner atomic levels for BaPb_0.8Bi_0.2O₃, PbO, PbO₂, BaPbO₃, BaBiO₃, NaBiO₃, Bi₂O₃ have been measured. On the basis of the comparison of bond energy values 4f_7/2 Pb for PbO (137.9 eV), PbO₂ (136.9 eV), BaPbO₃ (137.8 and 136.6 eV) and bond energy values 4f_7/2 Bi for BaBiO₃ (158.4 and 157.5 eV), NaBiO₃ (157.6 eV), Bi₂O₃ (158.2 eV) with analogous values 4f_7/2 Pb (137.7 and 136.9 eV) and 4f_7/2 Bi (158.2 and 157.4 eV) for studied BaPb_0.8Bi_0.2O₃ it is strictly shown that two valent forms of lead atoms Pb^IV, Pb^II and two valent forms of bismuth atoms Bi^V, Bi^III are simultaneously present in the structure of the high temperature oxide superconductor BaPb_0.8Bi_0.2O₃. The parameters of X-ray photoelectron spectra of valent regions of all studied compounds do not contradict this conclusion about the valent states of lead and bismuth atoms in the BaPb_0.8Bi_0.2O₃ structure.     

Structural,electrical and optical properties of Cdx Zn1−xSe thin films

X-ray diffraction and electron diffraction techniques indicate that Cd_x Zn_1–xSe thin films on glass substrates have a polycrystalline nature, with sphalerite structure for x0.5 and wurtzite structure for x0.6. The crystalline size in each composition increases with increasing the film thickness. The room temperature dark resistivity varies from one composition to another showing a transition at x=0.55The temperature dependence of of the deposited films revealed two conduction mechanisms, one below 352 K due to shallow levels, surface states, and defects introduced during the film growth, and over 352 K due to deep-level ionization following the ordinary semiconducting behaviour.The thermal activation energy of the free charge carriers decreases linearly with increasing the molar fraction x of the CdSe content up to x=0.55, above which it increases with increasing x.The optical constants of Cd_x Zn_1–xSe thin films of different compositions were determined in the spectral range 400–2000 nm. The analysis of the absorption coefticient at and near the absorption edge indicates the existence of allowed direct transition energy gaps decreasing with increasing x.     

Low-frequency lattice dynamics in Ba1−x KxBiO3 oxides according to 39K NMR data

The spin-lattice relaxation times T ₁ in Ba_1−x K_xBiO₃ (x=0.3, 0.4, 0.5) were measured in the normal temperature range (20–300 K).A substantial contribution to the spin-lattice relaxation rate from dynamic local distortions of the crystal lattice near potassium atoms is found. The activation energy of this process increases with decreasing potassium concentration, and the frequency of lattice excitations decreases. The nature of the low-frequency lattice dynamics is discussed. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 344–349 (10 September 1999)     

Near infrared magneto-absorption in the laser material KZn1−xCoxF3

Infrared absorption (1.4–2μm) of KZn_1−xCo_xF₃ (0⩽ x<0.15) at 4.2 K has been studied in a magnetic field (B⩽7 T). Large field-induced splittings were observed for Co²⁺-ion lines. Details of the cobalt concentration dependence of the absorptivity at B = 0 and at field are given along with the dependences on field direction and strength. Assignments are made of the observed Co²⁺ single-ion and pair transitions. The data has enabled the determination of the infrared (IR) transition g values.     

Optical study of semiconductor to metal transition in Sm1−xLnxS and SmS1−xAsx films

We have optically probed the Semiconductor to Metal transition (SC-MT) in Sm_1−xLn_xS and SmS_1−xAs_x films. For Ln = Yb, Sm²⁺4f⁶→4f⁵5d transitions (E₁, E₂) are well preserved for 0 ⩽ x ⩽ 1 showing the stability of Sm²⁺ and the absence of a SC-MT. For Ln = Tm, the definition of E₁ and E₂ disappears as x increases from 0 to 0.3, the 4f levels of Sm²⁺ seem to broaden or 5d band gets filled up leading to a SC-MT. For As substitution, SC-MT occurs for x ⩽ 0.10.     

Low-cost set-up for Fourier-transform infrared spectroscopy in diamond anvil cell from 4000 to 400 cm−1

An experimental set-up for Fourier-transform infrared (FTIR) studies at high pressure in the mid-IR region (400–4000 cm^?1) is constructed using a compact TEO-400 FTIR interferometer module and an external microscopic optical bench with cassegrain focusing objectives. Cassegrain-type reflective objectives act as an excellent beam condenser that facilitates the interfacing between FTIR spectrometer and diamond anvil cell. This set-up is capable of recording transmission and reflection infrared spectra at high pressure. Preliminary results are reported both in the reflection (pressure dependence of polar phonons in CuWO₄) and transmission configuration (polarized light absorption of polar phonons across the wurtzite-to-rocksalt transition in ZnO).     

Stress evolution and lattice distortion induced by thickness variation and lattice misfit in La0.67Sr0.33MnO3−δ films

La_0.67Sr_0.33MnO_3?δ thin films with different thicknesses are prepared in order to investigate the structural variation induced by film thickness and lattice misfit. The X-ray diffraction results show the in-built stress evolution from a full strained thin layer (～10 nm) to a completely relaxed thick layer (～150 nm), which can be well explained by the Poisson effect. Raman spectroscopy measurements reveal the complicated correlation between the Jahn–Teller (JT) distortion and film thickness. Important octahedron modes reflecting JT distortion are completely caused by the relaxed layer. It is observed that broad JT bands are formed in the films with large thickness of the relaxed layer and the residual stress in the layer leads to an obvious blue shift. In contrast, for films with the thin relaxed layer, JT modes are present as a sharper structure and move to low frequency, indicating towards a much better oxygen stoichiometry.     

Composition and lattice mismatch dependent dielectric constants and optical phonon modes of InAs1−x−ySbxPy quaternary alloys

Based on the pseudopotential formalism under the virtual crystal approximation, the dielectric and lattice vibration properties of zinc-blende InAs_1−x−ySb_xP_y quaternary system under conditions of lattice matching and lattice mismatching to InAs substrates have been investigated. Generally, a good agreement is noticed between our results and the available experimental and theoretical data reported in the literature. The variation of all features of interest versus either the composition parameter x or the lattice mismatch percentage is found to be monotonic and almost linear. The present study provides more opportunities to get diverse high-frequency and static dielectric constants, longitudinal and transversal optical phonon modes and phonon frequency splitting by a proper choice of the composition parameters x and y (0 ⩽ x ⩽ 0.30, 0 ⩽ y ⩽ 0.69) and/or the lattice mismatch percentage.