Anomalous SiO2 layer formed on crystalline MoS2 films grown on Si by thermal vapor sulfurization of molybdenum at elevated temperatures

Abstract

We have synthesized crystalline MoS2 thin films on Si substrates by thermal processing of molybdenum layers in sulfur vapor environment at elevated temperatures. The molybdenum layers were deposited at room temperature by magnetron sputtering. X-ray diffraction, Raman scattering spectroscopy, and transmission-electron microscopy characterizations revealed that the synthesized MoS2 thin films are of hexagonal crystal with van der Waals layered structures that bended into bell-like domains. Amorphous SiO2 layers have been observed not only at the MoS2/Si interface but also anomalously on top of the MoS2 layer. Secondary ion mass spectroscopy has been employed to investigate the elemental depth profiles, which, together with the structural properties, provides evidence that the surface SiO2 was grown out from its bottom layers rather than deposited from the growth environments. A mechanism based on solid-state reactions and atomic diffusions is introduced to explain the formation of the observed SiO2/MoS2/SiO2 sandwich structures, which may have important consequences when fabricating and/or processing MoS2/Si heterostructures for electrical and optoelectronic applications.