S. G. Patel

High pressure effect on MoS2 and MoSe2 single crystals grown by CVT method

Single crystals of MoS2 and MoSe2 were grown by chemical vapour transport method using iodine as a transporting agent and characterized by optical microscopy, energy dispersive analysis (EDAX), X-ray powder diffraction (XRD) and Hall mobility at room temperature. The variation of electrical resistance under pressure was monitored in a Bridgman anvil set-up up to 6.5 GPa to identify occurrence of any structural transition. MoS2 and MoSe2 do not undergo any structural transitions under pressure.

X-ray diffraction studies of NbTe2 single crystal

NbTe2 is a member of transition metal dichalcogenide (TMDC) group. Single crystals of niobium ditelluride (NbTe2) have been grown by a chemical vapour transport technique using iodine as transporting agent. The composition of the grown crystals was confirmed on the basis of energy dispersive analysis by X-ray (EDAX) and remaining structural characterization was also accomplished by X-ray diffraction (XRD) studies. Lattice parameters, volume and X-ray density have been carried out for the grown crystals. The particle size for a number of reflections has been calculated using Scherrer’s formula.

Growth of molybdenum disulphide using iodine as transport material

In the present paper an attempt has been made to describe the chemical vapor transport (CVT) technique used for the growth of molybdenum disulphide (MoS2) single crystals. Iodine (I2) is used as transporting material for this purpose. The energy dispersive analysis by X-ray (EDAX) confirmed the stoichiometry of the as-grown crystals. The lattice parameters of these crystals were determined from the X-ray diffraction analysis. The grown crystals were examined under the optical zoom microscope for their surface microstructure study.

Effect of pressure on electrical properties of SnS x Se1−x single crystals

The single crystals of tin monosulphoselenides in the form of a series SnS x Se1−x (where x = 0, 0.25, 0.50,0.75 and 1) have been grown using the direct vapor transport technique (DVT). The analysis of the X-ray diffraction patterns reveals that all crystals belong to the orthorhombic crystal structure. Hall effect measurements were carried out on grown crystals at room temperature. The optical absorption measurements at room temperature have been carried out for all crystals. The values of the band gap were determined at atmospheric pressure and also calculated at high-pressure. Simultaneous thermoelectric power (TEP) and a.c. resistance measurements up to 8 GPa were carried out. The results of the effect of high-pressure on the electrical resistance of the grown crystals are reported in this paper.

Optical and electrical properties of ZrSe3 single crystals grown by chemical vapour transport technique

Single crystals of the lamellar compound, ZrSe3, were grown by chemical vapour transport technique using iodine as a transporting agent. The grown crystals were characterized with the help of energy dispersive analysis by X-ray (EDAX), which gave confirmation about the stoichiometry. The optical band gap measurement of as grown crystals was carried out with the help of optical absorption spectra in the range 700–1450 nm. The indirect as well as direct band gap of ZrSe3 were found to be 1.1 eV and 1.47 eV, respectively. The resistivity of the as grown crystals was measured using van der Pauw method. The Hall parameters of the grown crystals were determined at room temperature from Hall effect measurements. Electrical resistivity measurements were performed on this crystal in the temperature range 303–423 K. The crystals were found to exhibit semiconducting nature in this range. The activation energy and anisotropy measurements were carried out for this crystal. Pressure dependence of electrical resistance was studied using Bridgman opposed anvils set up up to 8 GPa. The semiconducting nature of ZrSe3 single crystal was inferred from the graph of resistance vs pressure. The results obtained are discussed in detail.

Two- and three-dimensional models for analysis of optical absorption in tungsten disulphide single crystals

The optical energy gaps of WS2single crystal were determined from the analysis of the absorption spectrum near the fundamental absorption edge at room temperature using light parallel to c-axis incident normally on the basal plane. On the basis of two- and three-dimensional models it was found that both direct and indirect band transitions took place in WS2 bdand the indirect transition was of the allowed type. The optical energy gaps corresponding to both transitions were determined and the phonon energies associated with the indirect transitions estimated. The implications of the results have been discussed.

CVT growth of zirconium sulphoselenide single crystals

Large single crystals of a few important members (x=0, 1, 2) of the series ZrSxSe2−x compounds have been obtained by chemical vapour (iodine) transport method. The crystals have been characterized for several properties. Their semiconducting nature is inferred from resistivity vs temperature measurements, their optical absorption data reveal indirect gap transitions, their thermoscans indicate their stability over a limited temperature range, and they essentially grow by the mechanism of two dimensional layer propagation.

Anisotropic behaviour of semiconducting tin monosulphoselenide single crystals

Single crystals of ternary mixed compounds of group IV-VI in the form of a series, SnSxSe1-x (wherex = 0, 0.25, 0.50, 0.75 and 1), have been grown using direct vapour transport technique. The grown crystals were characterized by the X-ray diffraction analysis for their structural parameter determination. All the grown crystals were found to be orthorhombic. The microstructure analysis of the grown crystals reveals their layered type growth mechanism. From the Hall effect measurements Hall mobility, Hall coefficient and carrier concentration were calculated with all crystals showingp-type nature. The d.c. electrical resistivity measurements perpendicular toc-axis (i.e. along the basal plane) in the temperature range 303–453 K were carried out for grown crystals using four-probe method. The d.c. electrical resistivity measurements parallel to c-axis (i.e. perpendicular to basal plane) in the temperature range 303–453 K were carried out for the same crystals. The electrical resistivity measurements showed an anisotropic behaviour of electrical resistivity for the grown crystals. The anisotropic behaviour and the effect of change in stoichiometric proportion of S and Se content on the electrical properties of single crystals of the series, SnSxSe1-x (wherex = 0, 0.25, 0.50, 0.75 and 1), is presented systematically.

Photoelectrochemical Study of Zirconium Dichalcogenides

Publisher Summary Use of transition metal dichalcogenides (TMDCs) as a photoelectrode in photoelectrochemical (PEC) solar cell has significant importance toward renewable conversion of solar energy into electrical energy. In comparison with solid state solar cells, the fabrication of PEC device is cheaper and easy. The search for better materials in this field investigates ZrSxSe1-x. The n-type single crystals of ZrS2, ZrSSe, and ZrSe2 have been grown by chemical vapor transport technique. Photoresponse measurements were carried out at different intensities of light source to illuminate the photoanode. The best photoelectrode was used to determine the capacitance formed at the solid–liquid interface with Hewlett-Packard multi-frequency LCR meter. The energetic locations of the valence and conduction band edges as well as the doping levels and fiat band potentials are determined in the chapter.

Metallic behavior of ZrS 0.5 Se 1.5 single crystals

The electrical resistivity measurement on ZrS0.5Se1.5 has shown a metallic behavior in the range 333-363 K followed immediately by metal-semiconductor transition. It is verified using percolation model and Mott-Hamilton- Pollack relation that this particular composition of zirconium sulphoselenides is 3D. Details show a sine wave potential which is indicative of the prevalence of charge density wave. Umpklapp processes are found to dominate giving rise to T6 power law for resistivity in the metallic range.