Morphological effect and conductivity tunability of different regions in a single graphene film by surface steps

Abstract

Surface step is a fascinating aspect of chemical vapor-deposited graphene. Although the Cu surface steps influence graphene nucleation, they limit the domain expansion at lower temperatures. In this study, we report surface steps and nanoscale surface roughness that can be used to control the electrical properties of two regions in the same graphene film. Higher processing temperatures such as 1000 °C produced an ultra-smooth surface (below 0.1 nm roughness), whereas lower temperatures of 700 °C showed minimal step height due to lack of surface rearrangement. In order to introduce two different surface step conditions, the selected regions were individually subjected to electropolishing (smooth) and Ar plasma (nanoscale surface steps) treatments. At a moderate temperature of 800 °C, a smooth area eases diffusion-driven graphene growth, which results in a continuous film of monolayer graphene with better electrical properties (mobility ≈ 700 cm2/V). However, the region with surface steps showed no conductivity whereas Raman spectra confirmed the existence of multilayer graphene. This phenomenon was observed with fabricated graphene micro-ribbons at 800 °C; a 40 μm ribbon showed an approximate resistance of 3.5 kΩ mm−1. Most importantly, the resistance was precisely controlled by physical parameters of the ribbon or during graphene processing in a single film.