Dichalcogenides, transition metal layered compound

IV layered transition metal dichalcogenide-alkali metal intercalation compounds. The advantage of this method is that it is carried out at room temperature and, consequently, there is less likelihood of reaction between sodium and the reaction vessel. On the other hand, this method is more difficult in that it involves the use of liquid NH3. Furthermore, undesirable side reactions may occur if the NH3 is not dried thoroughly or if the reaction vessel is not clean. For example,... 

Omloo and Jellinek7 have described the synthesis and characterization of intercalation compounds of alkali metals with the group V layered transition metal dichalcogenides. Typically, these types of intercalation complexes are sensitive to moisture and must be handled in dry argon or nitrogen atmospheres. The alkali metal atoms occupy either octahedral or trigonal prismatic holes between X-M—X slabs. There are two principal means by which these compounds may be prepared. 

DiSalvo et al.9 have carried out a systematic survey of intercalation compounds of 2H(a)-TaS2 with post-transition metals. In particular, the system SnxTaS2 was found to exist in two composition domains, 0 < x < /3 and x = 1. The following discussion briefly describes the techniques used by DiSalvo to synthesize the compound SnTaS2. Syntheses of other transition and post-transition metal intercalation complexes with the layered transition metal dichalcogenides are discussed in References 9 and 20-24. 

In summary, it has been demonstrated that surface morphology is critically important in determining the performance of solar cells with layered compound semiconductors. Steps on structured surfaces of transition metal dichalcogenides have been identified as carrier recombination sites. The region defined by the depth of the space charge layer parallel to the van der Waals planes can be considered as essentially "dead" in the sense that its photoresponse is negligible. As the "step model" predicts, marked improvement in solar cell performance is found on samples with smooth surfaces. 

In the case of oxides the repulsion between adjacent layers would be quite strong and very destabilizing. Instead of the layered model observed for numerous transition-metal dichalcogenides, most of the MO2 oxides take the rutile arrangement. However, A,M02 derivatives are often isostructural with A,MS2 intercalation compounds. The sodium ions located in the van der Waals gap stabilize the two-dimensional arrangement. 

The class of layered transition metal dichalcogenides has been of great interest because of their varied electronic properties and chemical reactions. Most compounds of this class may be prepared by stoichiometric reactions of the elements above 500°. However, the highest vanadium sulfide that can be made in this manner is VjSg. An amorphous VS has been prepared by the metathetical reaction of LijS and VC. The method presented here allows preparation of polycrystalline VSj with the Cdiz structure. ... 

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