Transition-metal dichalcogenides have been investigated using Raman spectroscopy both being off-resonance and in resonance. The first-order Raman spectra of MoS 2 , MoSe 2 , WS 2 and WSe 2 single crystal synthesized by vapor transport technique have been studied as a function of hydrostatic pressure (0-20 GPa) and temperature (80-300 K). Isobaric and isothermal mode-Grüneisen parameters have been determined from the temperature and pressure-dependent Raman spectra. The pressure dependence of the chalcogen-chalcogen and metal-chalcogen force constant has been obtained using a central force model. Separation of the temperature dependence of Raman mode wavenumbers into quasi-harmonic and purely anharmonic contributions using measured high-pressure Raman data allows us to extract the changes in the phonon wavenumbers arising exclusively due to anharmonic interactions.

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The authors report the synthesis of Fe3O4 nanoparticles by wet chemical reduction technique at ambient temperature and its characterization. Ferric chloride hexa-hydrate (FeCl3 · 6H2O) and sodium boro-hydrate (NaBH4) were used for synthesis of Fe3O4 nanoparticles at ambient temperature. The elemental composition of the synthesized Fe3O4 nanoparticles was determined by energy dispersive analysis of x-rays technique. The x-ray diffraction (XRD) technique was used for structural characterization of the nanoparticles. The crystallite size of the nanoparticles was determined using XRD data employing Scherrer’s formula and Hall–Williamson’s plot. Surface morphology of as-synthesized Fe3O4 nanoparticles was studied by scanning electron microscopy. High resolution transmission electron microscopy analysis of the as-synthesized Fe3O4 nanoparticles showed narrow range of particles size distribution. The optical absorption of the synthesized Fe3O4 nanoparticles was studied by UV–vis–NIR spectroscopy. The as-synthesized nanoparticles were analyzed by Fourier transform infrared spectroscopy technique for absorption band study in the infrared region. The magnetic properties of the as-synthesized Fe3O4 nanoparticles were evaluated by vibrating sample magnetometer technique. The thermal stability of the as-synthesized Fe3O4 nanoparticles was studied by thermogravimetric technique. The obtained results are elaborated and discussed in details in this paper.

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The transport properties of ternary mixed WS x Se 2-x single crystals have been studied by measuring the thermo power, electrical conductivities and Hall parameters in a small temperature range 303-423 K. The electrical conductivity was highest for selenium rich WSe 2 and lowest for sulphur rich WS 2 crystals. All the crystals showed semiconducting behaviour from the temperature dependence of 'ρ', 'R H ' and 'S'. The Hall coefficients showed that the samples are p-type conducting. The temperature dependence of resistivity, Hall coefficients, carrier concentration showed that all of them are thermally activated. The values of activation energies, pre-exponential factors and the scattering parameters have been determined. The dominant scattering mechanism for the charge carriers has been explained. The relation between the TEP and the concentration of charge carriers and electrical conductivity was studied. The effective masses of holes and the effective density of states have been determined. These parameters show an increase with increase in sulphur content.

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