Processing Stability of Monolayer WS2 on SiO2

Using internal photoemission of electrons, the energy position of the valence band top edge in 1 monolayer WS2 films on top of SiO2 thermally-grown on Si was monitored to evaluate the stability of the WS2 layer with respect to two critically important technological factors: exposure to air and the transfer of WS2 from the growth substrate (sapphire) onto SiO2. Contrary to previous results obtained for WS2 and MoS2 layers synthesized by metal film thermal sulfurization in H2S, the valence band top of metal-organic chemical vapor deposition grown WS2 is found to remain at 3.7 ± 0.1 eV below the conduction band bottom edge of SiO2 through different growth runs, transfer processing, and storage in air for several months. This exceptional stability indicates WS2 as a viable candidate for the wafer-scale technology implementation.