Study of chemical vapour transport (CVT) grown WSe1.93 single crystals

In the present study, the single crystals of WSe1.93 were grown by chemical vapour transport (CVT) technique. Iodine was used as transporting agent. The purity and stoichiometry of the as-grown WSe1.93 single crystals were determined by energy dispersive analysis of X-ray (EDAX). The structural characterization was done by X-ray diffraction (XRD) technique. The scanning electron microscopy (SEM) of the as-grown single crystal surfaces showed that the crystal growth took place by layer growth mechanism. The thermogravimetric (TG), differential thermogravimetric (DTG) and differential thermal analysis (DTA) of as-grown WSe1.93 single crystal in inert N2 atmosphere showed two stages decomposition. The thermal parameters like activation energy (Ea), Arrhenius constant (A), enthalpy change (ΔH), the entropy change (ΔS) and the free energy change (Gibbs function) (ΔG) were calculated using Kissinger method. The optical bandgaps were determined from the optical absorption spectrum. The d.c. electrical resistivity measurements in the temperature range of 303-483 K showed that the resistivity value decreases with increase of temperature, in line with semiconducting behavior. The p - type semiconducting nature of the sample was confirmed by Hall effect and thermoelectric power (TEP) measurements. The obtained results are discussed in details.