Tunneling and Josephson coupling studies of n-layer graphene

We investigate planar tunnel and superconductor-graphene-superconductor (SGS) junctions involving n-layer graphene. We fabricate our devices using an ultrathin quartz filament as a shadow mask over mechanically exfoliated graphene as an alternative to lithographic procedures so as to avoid possible contamination in a wet lithography process. Our tunnel junctions use Al$_2$O$_3$ as the tunnel barrier and Pb or Au as the counter-electrode. We observed a reduction of density of states in the n-layer graphene and the superconducting energy gap of Pb when Pb was an electrode. Results from work on SGS junctions and other atomically thin materials such as NbSe$_2$ will also be presented.