Wafer-scale few-layer graphene growth on Cu/Ni films for gas sensing applications

Pristine, few-layer graphene (FLG)/Si nanopillar assemblies are introduced as gas sensitive chemiresistors showing unprecedented sensitivity towards NO2 when operated at room temperature (25 °C) and in humid air. To achieve this, we first developed wafer-scale (∼50 cm2) FLG growth using sub-micrometer thick films of thermally evaporated Cu/Ni on a SiO2/Si substrate. The Ni film was deposited and annealed to induce the formation of a Cu-rich binary alloy. This alloy formation limited the inter-diffusion of Cu and SiO2, a phenomenon known to take place during the CVD growth of graphene on Cu/SiO2/Si. The as-grown high structural quality FLG was transferred, using a conventional wet chemical method, to lithographically patterned arrays of Si nanopillars (non-flat substrate). Testing of the FLG/Si assembly revealed a NO2 sensitivity that outperforms what is reported in the literature for pristine graphene. Overall, our growth and device fabrication work-flow demonstrate a way to design graphene-based gas sensing systems without incurring inconvenient processing steps such as metal foil etching, surface functionalization or particle loading.