Thickness-Dependent Enhancement of Electronic Mobility of MoS2 Transistors via Surface Functionalization

The thickness dependence of the chemical and physical properties is one fundamental characteristic shared by many two-dimensional layered transition-metal dichalcogenides, including molybdenum disulfide (MoS2). Recently, in order to expand the scope of applications of MoS2, surface functionalization has been employed to engineer its chemical and electrical properties for the purposes of drug delivery, photothermal therapy, gas sensing, and biosensing. Here, we report a facile method for controlled functionalization of MoS2 field-effect transistors of a wide range of thicknesses with alpha-lipoic acid (LA). Atomic force microscopy (AFM), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) show evidence of chemical bonding. After functionalization, a significant increase of on current is observed in the MoS2 transistors, caused by the enhancement of electronic mobility. The maximum increase of mobility can reach similar to 100% for monolayer devices. The thickness dependence of the mobility enhancement is analyzed, and a theoretical model based on vacancy filling and charge impurity scattering is proposed to reveal the microscopic origin. These results provide new opportunities of controlling the electronic properties of MoS2 by surface functionalization.