Influence of removing PMMA residues on surface of CVD graphene using a contact-mode atomic force microscope

For device fabrication based on 2D materials such as graphene, hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDs), polymethyl methacrylate (PMMA) is conventionally used in the wet transfer and lithography processes. All these processes are sources of polymer residue, which degrade the intrinsic electrical and optical properties of devices. In this work, we report the effect of mechanical cleaning via contact mode atomic force microscopy (AFM) on the surface morphology and electrical behavior of chemical-vapor-deposition grown graphene. An AFM tip with large contact force was used to scan, and multiple scanning was performed to remove the residues of PMMA. Raman mapping was incorporated to confirm the cleaning effect using AFM. Transconductance properties associated with a field-effect-transistor device based on the cleaned graphene were analyzed. It was observed that charge-neutrality point was shifted towards zero gate voltage and the charge carrier mobility was increased. We claim that our technique provides a facile route to fabricate devices with less polymer residue and higher efficiency.