ELECTRONIC PROPERTIES OF LAYERED DICHALCOGENIDE COMPOUNDS

Abstract

In this thesis we present a study of the electronic properties of transition metal dichalcogenide compounds (TMDC). A number of important physical properties, such as heat capacity, thermal conductivity and metallic succeptibility of solids can be understood from their electronic structure. TMDC show a variety of interesting physical properties. They can exist in various crystallographic structures. They display semiconduct- _ ing, metallic, superconducting and magnetic behaviour. This thesis deals with disulphides and diselenides of the group IVB, VB and VIB transition metals. The TMDC formed from group IVB and VIB transition metal atoms exhibit semiconducting or insulating behaviour whereas group VB compounds tend to be metallic and are reportedly superconducting at low temperatures. These compounds show profound anisotropy in physical properties aris-ing from the formation of MX2 layers with covalent bonding within layers and weak Van der Waals bonding between the layers. As a result of this the TMDC, which behave as two di-mensional solids, can be intercalated with foreign atoms and molecules leading to significant and dramatic changes in their electronic properties. Electrical and thermal conductivities are found to be significantly lower along c-axis compared to in the basal plane. The study of electronic properties of TMDC has been actively pursued during-the past few decades due to their potential for a variety of technological applications. 2H-WSe2, which is a interesting member of TMDC family, is a semiconductor with a measured indirect gap of 1.2eV and is useful for photovoltaic and optoelectronic applications [80]. Electrochemical devices based on WSe2 have been reported to posses conversion efficiency up to 17% [83] and is known for their remarkable stability against photo-corrosion. Hollow nano-particles of MoS2 and WSe2 have great potential of being used as solid state lubricants, displaying large life times [118,60].