Fabrication of High Quality Suspended Graphene devices

Suspended graphene devices have been demonstrated to have ultra-high mobility, enabling the recent obsevation of fractional quantum Hall effect. Here we report a lithography-free technique for fabrication of suspended graphene devices. Graphene sheets are exfoliated over pre- defined trenches on the substrate. Hard shadow masks are etched from Si wafers and aligned to the trenches. Metals are evaporated through the masks to form clean suspended devices, eliminating contaminants introduced by lithography and etching processes. The completed devices have high mobilities $\sim $100,000 cm$^2$/Vs.