FIG. 4: (a) Optical micrograph of (1 ¯ 10 n ) facet with graphene ribbon. Scale bar is 2 µ m. (b) Raman map ( ∼ 1 µ m lat. res., 0.5 µ m grid) of graphene 2D intensity at this location indicates presence of graphene essentially exclusively on the facet. (c) Conductance vs. source-drain voltage as a function of temperature. Band gap is observed at 4K as expected for a ribbon of this width (200 nm). Inset: optical micrograph of test structure. Scale bar is 5 µ m. 12 (b) (c) 77 K 20 K 15 K 10 K 4 K − 20 − 10 0 10 20 30 40 50 60 70 80 90 V$_{sd}$ (mV) G( µ S)