Large Area Synthesis of WS$_2$ Crystalline Sheets Directly on SiO$_2$ and Their Transfer to Other Substrates

Metal dichalcogenides (e.g. MoS$_2$, WS$_2$, NbS$_2)$ have attracted attention because they are layered materials that could exhibit either semiconducting or metallic properties. These properties could be significantly modified when these materials become monolayers. Here we report for the first time the synthesis of large area few-layer WS$_2$ by a two step method. WO$_{\mathrm{x}}$ thin films were first grown on a Si/SiO$_2$ substrate and these films were sulfurized in a second step. Furthermore, we have developed an efficient route to transfer these WS$_2$ films onto different substrates. WS$_2$ films of different thicknesses have been analyzed by Raman spectroscopy, HRTEM and AFM. Characterization techniques demonstrate the presence of mono-, bi- and few-layered WS$_2$ in the as-grown samples. The novel photoluminescence properties of the films will also be discussed.