Colossal vertical conductivity enhancement in graphene by wrinkle engineering

Wrinkles are out-of-plane deformations, commonly seen in chemical vapor deposition (CVD) grown graphene, that mostly arise from thermal expansion mismatches. These one-dimensional corrugations are believed to be centers of altered electrical and electronic properties for graphene. Herein, high-resolution electrical modes of Atomic Force Microscopy (AFM) were employed to measure the nanoscale current and work function distribution of graphene wrinkles. Tapping current measurements showcased an unforeseen increase up to two orders of magnitude compared to flat regions. As revealed by extensive first principles calculations (density functional theory employing CAM-B3LYP and PBE0 functionals) and experimental data (AFM advanced electrical modes), an interplay of mechanisms between polarization, separation from the substrate and strain gradients result in an impressive increase in vertical conductivity with possible implications for analogous surge also along wrinkle axes. Furthermore, characteristic variations in the work function of wrinkles, with respect to various substrates, could be clearly identified. The implications of our findings may pave the way for fine-regulation of conductivity via wrinkle engineering for the previously unexplored out-of-plane direction, as well as for the controlled formation of conductive channels.