Atomic layer deposition of Al2O3 and TiO2 on MoS2 surfaces

In this work, the authors compare the surface coverage obtained in the initial and intermediate steps of Al2O3 and TiO2 atomic layer deposition on MoS2 surfaces prepared by either mechanical exfoliation or chemical vapor deposition (CVD). They find that the film surface coverage is highly dependent on the origin and preparation of the MoS2 starting surface. While mechanical exfoliation can be used to quickly obtain few-layer MoS2 surfaces, these surfaces exhibit significant variability in quality and cleanliness, leading to unpredictable film growth. Conversely, MoS2 grown by CVD provides a more reliable starting surface resulting in significantly improved scattering in the surface coverage. They find that, on CVD MoS2, neither Al2O3 nor TiO2 film growth strongly exhibits temperature dependence described by the Langmuir adsorption model. For both processes, films up to 6 nm thick deposited on CVD MoS2 are not fully coalesced and exhibit a large concentration of pinhole type features.