Native and induced surface charge-transfer doping of MoTe₂

In this work, the surface charge transfer doping (SCTD) of air-exposed MoTe₂ surfaces was investigated by means of Kelvin probe force microscopy (KPFM). The induced changes in the surface potential of MoTe₂ due to air adsorbates were detailed as a function of the thickness of exfoliated MoTe₂ flakes all the way down to a single atomic layer. It was found that the SCTD driven by adsorbates can be easily adjusted through thermal annealing and, in this way, have an effective modulation on the surface potential of MoTe₂. Furthermore, the SCTD was controlled locally at the nanoscale by using the probe of an electrostatic force microscope as a floating gate. Following either thermal annealing or contact electrification, the air-exposed MoTe₂ surfaces exhibited slow reversal processes of re-adsorption with the restoration of the original positively charged doping. The KPFM measurements were paired with X-ray photoelectron spectroscopy measurements and density functional theory calculations to assess the contribution of physisorbed molecules to the observed variations in the measured surface potential. The study emphasizes that, as a reversible and controllable nanoscale physisorption, the SCTD can add significant progress to the paradigm of emerging 2D-TMDC electronics.