Research About Effect Of Low Temperature Oxygen Plasma Treatments On Properties Of Single Layer Molybdenum Disulfide

Two-dimensional materials are attractive for use in next-generation nanoelectronic devices.In this work,the electrical and mechanical properties of single-layer MoS₂ film?SLM?obtained by micro-mechanical stripping was investigated.Low-temperature oxygen plasma treatment was employed on the SLMs.Their optical properties before and after the treatments were observed by using the optical microscopy which could distinguish a desired high-quality monolayer MoS₂ film from the randomly distributed samples.Similarly,Raman spectroscopy was used to provide the Raman spectra of SLMs before and after the treatments.Furthermore,Kelvin scanning probe microscope was applied to investigate the surface potential of the samples before and after the oxygen plasma treatments.With the increase of reaction time,the surface potential continuously decreases.There are two reasons for this phenomenon.One is the specialty of transition metal d electrons and the other is that as the processing time increases,a large number of negative ions are adsorbed on the sample surfaces.The surface potentials of the few-layered and multi-layered micro domain samples were demonstrated.It was shown that there was a large potential difference in the interface micro domains,indicating that the lattice distortion and dislocation caused by the stacking resulted in an increase at the potential difference.The potential difference after the low temperature oxygen plasma treatment decreased at the step,showing that the low temperature oxygen plasma treatment changed the stress and lattice state of the sample.The SLMs with great quality were transferred onto SiO₂/Si substrates with an oxide layer thickness of 300 nm.The difference value of E₂¹ _g and A_1g peaks spacing of the MoS₂ films showed less than 20 cm^-1,and there were apparent LAM peaks at 450cm^-1.After treatments,it was discovered that the E₂¹ _g and A_1g peaks shifted,and the LAM peak disappeared after oxygen plasma treatments.This illustrates that major changes happened on surface properties of the samples,such as surface modification,lattice distortion,and surface oxidation.The samples adhesion was also observed under irradiation for a short time.This resulted in an increase in surface dangling bonds and Mo-O bonds,which added adhesion and roughness of the samples.Since the irradiation time increases,etching and further oxidation effects occurred,leading to a reduction in roughness and adhesion.A friction probe force microscopy was employed to reveal the friction of samples before or after treatments with oxygen plasma.Due to the minimized self-lubricating properties of the samples after treatments,there was an increasing trend of the friction force.According to Ruan's nano-friction model,it can be concluded that the friction increases with the slope of the particle,symbolizing that the slope of the sample surface morphology will affect the instant friction changes.These finding could be important for producing electronic device based on SLMs.