The Spiral Growth of Few Layer Transition Metal Dichalogenides

A new class of materials called transition metal dichalcogenides have made waves in study of semiconductors in the recent years because of their enhanced optical and electronic properties in a two dimensional limit. These materials are composed of a transition metal (e.g. tungsten, molybdenum) and a chalogen pair (e.g. sulfur, selenium, tellurium), which can form a single atomic layer when grown properly on a substrate. The purpose of this study is to optimize the growth of transition metal dichalogenides onto a silicon dioxide substrate using chemical vapor deposition. In this method, the precursor materials (sulfur, metal oxide) and substrate are heated in a quartz tube furnace at a pressure of 5 torr under flux of hydrogen and argon gas. The chalogen evaporates and reduces the metal oxide and ideally deposits a single atomic layer or few layer transition metal dichalogenide onto the SiO2 substrate. The film is characterized using optical and atomic force microscopy, and Raman spectroscopy. Atomic layer MoS2 islands are found to be triangularly shaped with sizes ranging from tens to hundreds of micrometers, which also exhibits the characteristic Raman bands at 403.36 and 385.05 cm-1 corresponding to the A1g and E2g modes, respectively. Atomic force microscopy imaging further confirms the single atomic layer thickness to be 0.8 nm. For few layer MoS2 films, triangular spirals are observed with both left and right handed chirality. Raman spectra show interesting features of these growth spirals, the details of which will be presented at the conference