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Graphene synthesized by CVD. (a) Optical micrograph of graphene flakes transferred onto a silicon wafer with a 300 nm-thick oxide. (b) Typical Raman spectrum measured on a graphene flake. (c) Conductance-gate voltage characteristic of a single flake sample measured using the substrate as a backgate. The carrier mobility of 2000–3000 cm2/V-s is comparable to that for exfoliated graphene on a similar substrate. Inset: Optical micrograph of a graphene flake contacted by two gold electrodes using shadow mask method.
UV doping of CVD graphene. (a) The conductance (G) versus gate voltage (Vg) curves for different doping time, measured at room temperature and a pressure of 10−2 Torr. Dotted lines are linear fits used to obtain the carrier mobilities shown in the inset table. (b) Injected carrier concentrations obtained in (a) as a function of photon flux and an exponential fit. Inset shows the plot of inverse carrier mobilities as a function of doping time.
UV doping of CVD-graphene is fully reversible. The plot shows conductance (G) versus gate voltage (Vg) curves for the same sample when (1) as-made device (solid blue line), (2) after 16 min of UV-doping (solid red line) and (3) after annealing in air at 80 °C for 45 min (black dashed line), and (4) re-doped by exposure to UV for 16 min (dashed green line). All measurements are done at 295 K at a pressure of 10 mTorr.
(a) Schematic of a graphene device showing electron-trapping species adsorbed on the graphene surface (b) The linear dispersion relation characteristic of graphene. Upon UV irradiation, photo-generated holes recombine with the negatively charged adsorbates at the surface and consequently shift the Fermi level to higher energy.
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