Diameter and Morphology Dependent Raman Signatures of WS2 Nanostructures

Abstract

structures are usually constituted of several {XMX} triple layers stacked in hexagonal (2H) order, which encage a compact or a hollow core. They are synthesized by the sulphurisation of trioxides, chlorides, or metal-chalcogen-halogen compounds in a H2S/H2 atmosphere, chemical transport reactions of metal disulphide powder, or by the reduction of trisulphides. [4–6] The development of a bulk synthesis method paved the way for technical applications of WS2 and MoS2 nanostructures. [7] Meanwhile, kilograms of these materials can be commercially purchased. [8] Due to their caged morphology WS2 and MoS2 nanomaterials attracted a particular strong interest for applications as dry lubricants and grease additives. Experimental studies showed lower coefficients of friction and less wear for IFWS2 and IF-MoS2 then for microcrystalline WS2 and MoS2 standard mineral oil additives. [9] Very recent molecular-dynamics calculations indicate that the tribological effect of MoS2 nanotubes at high loads is due to bursting and subsequent platelet formation at positions of the closest contact between the sliding materials. [10] From this point of view the conservation of the IF structures is of crucial importance for the fabrication of tribological thin films based on IF nanostructures. Due to a large cross-section, resonance Raman spectroscopy is a very sensitive method for the chemical identification and the structural analysis of small amounts of WS2. 2H-WS2 single crystals belong to the space group P 63= mmc ðD 4hÞ and have 4 Raman active crystal vibrations at the G-point of the recipro