Direct Identification of Surface Bound MoO3 on Single MoS2 Flakes Heated in Dry and Humid Air

Abstract The chemical presence of the MoO x species on single microscopic MoS 2 flakes is shown at two conditions, which are of interest for future MoS 2 ‐based devices and where their presence is not previously confirmed. First, the case of thick MoS 2 flakes oxidatively etched at 350–370 °C in air is treated. Atomic force microscopy (AFM), high resolution X‐ray photoelectron spectroscopy, and X‐ray absorption spectroscopy are combined to unambiguously confirm the chemical presence of the α‐MoO 3 species on such samples, mostly in the form of loose particles. Second, it is shown that MoS 2 flakes heated at temperatures of only 220 °C display a quite uniform ≈2 nm thick MoO x layer at already 10% relative humidity. The presence of such MoO x oxide layers is confirmed by scratching the sample with AFM tips and performing comparative Kelvin probe force microscopy and Auger photoelectron spectroscopy on scratched‐out and untouched parts of the flakes.