Resonant Raman scattering in mixed GaSxSe1−x crystals

One- and two-phonon resonant Raman scattering around the absorption edge in mixed GaS_xSe_1?x crystals with 0 ? x < 0.23 has been measured. The results can be explained by a simple theory in which the dispersion of RRS is dominate by exciton resonances.     

Emission spectra of iron doped ZnSxSe1-x solid solutions

The photoluminescence of ZnS_xSe_1?x:Fe has been investigated in the visible and near infrared (λ ? 1.2 μm) region. The doping dependence shows, that the incorporation of iron in ZnS produces, in addition to the well-known red luminescence (λ_max = 660 nm), another emission band at 980 nm, which was hitherto unknown for ZnS: Fe. The energetic position of this new band is proved to be independent of composition of the ZnS_xSe_1?x solid solution. Therefore, it is interpreted as an internal transition in iron centres. On the other hand, the red Fe-band shifts to lower energy with increasing selenium concentration. This result shows clearly, that the red Fe-band of zincsulfide cannot be interpreted by an internal transition in iron centres [3], but favors the donor-acceptor model, which was already suggested by other authors [4].     

Raman scattering from GaSe1−xTex

The long-wavelength optical phonons of the layer GaSe_1?xTe_x have been investigated at room temperature by means of Raman scattering spectroscopy. The spectra of the Bridgman grown crystals were excited with the 1,06 μm line of the continuously operated YAG:Nd³⁺ laser. Detailed study of the Raman spectra of GaSe_1?xTe_x solid solutions showed that there is an abrupt change in the frequency-composition dependences for all observed modes. It is shown, that a phase transition from hexagonal ?-GaSe to monoclinic GaTe in GaSe_1?xTe_x solid solutions takes place in the composition range 0.27 ? × ? 0.72. Only one mode behaviour of the optical phonons was observed in GaSe_1?xTe_x system.     

Effect of substitution-type disorder in GaS1-xSex layer solid solutions on Raman scattering spectra

An experimental study has been carried out to investigate Raman scattering spectra of GaS_1-xSe_x solid solutions in which a one-dimensional localization of interlayer mode due to a disorder in the layer stacking was observed.     

Thermo-optical response of VxTi1-xSe2 in the plasmon reion

It is shown that some structure growing on the high energy side of the plasmon when cooling TiSe₂ crystals through the transition temperature is smeared out with vanadium concentrations of the order of 1% and that the plasmon lifetime is considerably affected both by temperature and vanadium content.     

Magnetic properties of system HgxZn1-xCr2Se4

Magnetic moments, magnetic susceptibilities and optical absorption of the system Hg_xZn_1-xCr₂Se₄ have been measured. A correlation is found between the optical and the magnetic properties.     

Core hole satellites in NixPd1-x alloys

The two and three hole satellites accompanying the main Ni 2p and Pd 3d XPS core lines in Ni_xPd_1-x alloys have been measured as function of the alloy concentration. The changes in satellite distance with concentration cannot be explained by the thermochemical approach, which has recently been shown to describe successfully the one hole core level binding energy shifts (main line) in alloys. The reason is probably, that in this approach, which uses thermochemical data of Z + 1, Z + 2 and Z + 3 elements - where Z stands for Ni or Pd and Z + n is the nth element following them in the periodic table - d-band contributions to the cohesive energies of the final d-hole states are neglected.     

Ge1-xCx double-layer antireflection and protection coatings

The antireflection Germanium carbide (Ge_1-xC_x) coating, deposited using RF reactive sputtering, on both sides of ZnS substrate wafer has been developed. The infrared (IR) transmittance spectra show that the IR transmittance in the wavelength region between 8 and 12 μm for the designed system Ge_1-xC_x/ZnS/Ge_1-xC_x is greatly enhanced compared to that for ZnS substrate. In addition, the double-layer coated ZnS substrate is approximately four times as hard as uncoated ZnS substrate. This investigation indicates that a double-layer Ge_1-xC_x coating can be used as an effective antireflection and protection coating on ZnS infrared window.     

Raman scattering from GaAs-InxGa1−xAs strained-layer superllatices

Measurements of Raman scattering were performed on GaAs-In_xGa_1?xAs strained-layer superlattices, grown by molecular beam epitaxy, with lattice periods ranging from 30 ～ 250 Å and In concentrations x, 0.22 and 0.37. Only one GaAs-like longitudinal optical phonon peak was observed in each strained-layer superlattice, in contrast to the well-known result that two peaks were observed in GaAs-Al_xGa_1?xAs superlattices. The GaAs-like phonon frequencies shifted from those of bulk GaAs to those of bulk In_xGa_1?xAs alloys as the ratio of the one-layer thickness of In_xGa_1?xAs to the lattice period increases from zero to one. We conclude that the GaAs-like phonon mode is a uniform mode of the whole strained-layer superlattice and the phonon frequency is determined by the averaged In concentration.     

NMR and magnetization study of the mixed systems (Pd1-xCux)2 MnIn and (Pd1-xNix)2 MnIn

Systematic NMR and magnetization data with concentration show that for decreasing x these systems go from ferromagnetic (F) to anti-ferromagnetic (AF) order by passing a mixed phase region where both magnetic orders coexist in different domains. The magnetic phase diagrams for both alloy series are nearly coincident. The NMR spectra show that the Cu or Ni atoms substitute randomly onto Pd sites and we find no evidence that the participation of Mn atoms in F or AF domains is at all correlated with their nearest neighbour environments. In the limit where the AF order becomes largely dominant the samples exhibit a magnetic anisotropy after field cooling.     

Resonant Raman scattering of CdCr2Se4

The scattering cross section of the Raman-active phonons at 156 cm^?1 (Eg) and 169 cm^?1 (F2g) in the ferromagnetic semiconductor CdCr₂Se₄ (T_c=130 K) has been measured as a function of incident photon energy between 1.55 and 2.81 eV, both in the ferromagnetic and paramagnetic phases. The resonance curve peaks sharply near 2 eV and shows a broadening for temperatures below the Curie point. The relative line intensities change significantly with photon energy. The results show that the concept of spin-dependent Raman scattering in the ferromagnetic spinels has to be revised in terms of exchange-splitting-induced resonant Raman scattering.     

Thermochemical analysis of PdxAg1-x alloys from XPS core-level binding energy shifts

XPS core level binding energy shifts of the $\text{3d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ energy levels of Pd and Ag for a large number of coevaporated Pd_xAg_1-x alloys with 0?x?1 have been measured. An analysis of the Pd level shifts yields the heats of formation of the PdAg alloy system in good agreement with those reported from calorimetric measurements. Combining these data with the Ag level shifts one obtains the heat of formation of Cd diluted into Pd_xAg_1-x.     

Structural and optical properties of amorphous GexSn1-x alloys

The structural and optical properties of amorphous Ge_xSn_1-x alloys have been studied in the range x ? 0.5. The atomic arrangement is found to be tetrahedral with a random nearest neighbor environment. Both the average and the minimum optical gaps decrease with increasing Sn content, with the latter extrapolating to 0 at x ≈ 0.0. It is suggested that the variation of the optical and electronic properties with Sn concentration will provide a sensitive test of current theories of amorphous solids.     

Study of polycrystalline bulk CuIn1-xGaxTe2

Polycrystalline CuIn_1−xGa_xTe₂ bulk films were synthesized by reacting, in stoichiometric proportions, high purity Cu, In, Ga and Te in a vacuum sealed quartz ampoule. The phase structure and composition of the bulk films were analysed by X-ray diffraction and energy-dispersive X-ray analysis, respectively. The bulk samples, of p-type conductivity, are found to be near-stoichiometric, polycrystalline, with tetragonal chalcopyrite structure, predominantly oriented along a direction perpendicular to the (1 1 2) plane. Photoluminescence spectra were recorded at 7 K and 700 mW to characterize the defects and the structural quality. The main peak as a function of composition has been studied.     

Raman scattering from mixed crystals (HgBr2)1−x(HgI2)x

The behavior of long wavelength optic phonons in mixed system HgBr₂-HgI₂ has been investigated in Raman scattering. Different types of behavior, i.e. ‘persistent type’ and ‘amalgamation type’ were observed. Three strong Raman bands were observed for persistent type mode. These correspond to stretching vibration of HgBr₂, HgBrI, HgI₂ molecules. Intensity of these bands showed striking concentration dependence. A model based on nearly free molecular approximation have been proposed to explain the dependence. The analysis indicated that the distribution of anions on the sublattices is essentially random. For amalgamation (one-mode) type behavior, it is suggested that the intramolecular force relevant to the vibration is comparable to the intermolecular force and that the band width of the corresponding phonon branch in the parent crystal is broad enough to be degenerate with impurity mode at the low concentration limit.     

Electronic Raman scattering from inter-valence band transition in photo-excited GaP and GaAs1−xPx crystals

Raman scattering from photo-created free carriers in undoped GaP and GaAs_1?xP_x (x = 0.85, 0.73 and 0.66) under high excitation intensity has been studied. Two new Raman bands have been observed and assigned to electronic transitions from the split-off hole band to the heavy hole band and from the light hole band to the heavy hole band. The spin-orbit splitting energies in these crystals have been determined from the analysis of observed Raman bands, and compared with other experimental values.     

Raman scattering from 1T-TaS2

Raman measurements on the 1T-polytype of TaS₂ are reported. In the commensurate charge density wave state, a large number of Raman-active peaks are observed below 400 cm^-1. Most of these peaks are attributed to k = 0 optic phonons resulting from superlattice formation.     

Wavelength and concentration dependence of Raman scattering from CdS1−xSex

We present measurement of the resonant Raman effect in the alloy system CdS_1?xSe_x for laser photon energies both above and below the concentration-dependent energy gap. Our data show that the Raman intensities are not simply functions of the difference between the photon energy and the gap energy. These results may be partially understood in terms of a simple theoretical model which elucidates the role of local electric fields in determining Raman intensities in alloys.     

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.     

Electronic structure of nin-isocoric transition metal alloys: CuxRh1-x

The electronic structure of the copper—rhodium alloys is determined in the frame of recently developed LCAO-based theory which allows to treat also non-isocoric alloys with strong off-diagonal disorder exactly within the single-site approximation. The total and component densities of states are calculated and compared with available experimental data.