ABSTRACT
There are many different types of layered semiconductors and semimetals. Their bulk crystallographic, electrical, and optical properties have been extensively studied and several texts and review articles are available [1-4]. Most of these materials are binary compounds: metal chalcogenides and halides. All of these materials are characterized as having highly anisotropic physical and electrical properties. Among the most heavily studied materials are the dichalcogenides of the group IVB, VB, VIB, and VIII transition metals and the group IIIA and IVA metals. Much of this interest comes from their use as catalysts. In particular, MoS2 is widely used a hydrodesulfurization catalyst. There has recently been great interest in nanoparticles (quantum dots) and “inorganic fullerenes” of these materials, particularly the group VIB dichalcogenides. The layered structures of these materials are analogous to graphitic carbon. Extending this analogy, inorganic fullerenes are the structural analogs of carbon nanotubes. As such, inorganic fullerenes have extremely interesting structural, physical, and electronic properties [5-13]. The most extensively studied inorganic fullerene materials are those in the MoS2 family, specifically MoS2, MoSe2, WS2, and WSe2. Very recently, inorganic fullerenes of GaSe has also received theoretical attention [14]. Inorganic fullerenes have either single-layer or multilayer tube-type morphologies. The electronic structures of single-wall and multiwall inorganic fullerenes approximate two-dimensional thin films of these materials. However, the curvature necessary to produce the tube morphology also results in a modest perturbation of the electronic structure.
