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Comparison of the surface topographies and roughness by AFM in tapping mode. (a) Topography of graphene after exfoliation: roughness = 0.1 nm RMS. (b) Topography after the sputtering on graphene of an Al thin film and its complete oxidation in O2 (film thickness = 1 nm): roughness = 0.2 nm RMS and no pinholes are observed. (c) Topography after the evaporation on graphene of an Al thin film and its complete oxidation in O2 (film mean thickness = 1 nm): roughness >0.3 nm RMS and large density of pinholes are observed (few 100/μm2).
(a) Topography (AFM contact mode) of graphene deposited on highly doped Si wafer after sputtering of Al2O3 (inset: before deposition). (b) Impedance (CTAFM) of the same graphene flakes after sputtering of Al2O3 (inset: before deposition). (c) Impedance (CTAFM) of the standard sputtered structure Al2O3/Co. (d) Impedance (CTAFM) of graphene flakes after evaporation of Al2O3.
(a) Bias dependence of the resistance-area product of sputtered Al2O3 tunnel barriers on graphene measured locally by CTAFM. (b) Spatial homogeneity of the bias dependence. Left panels: 300 nm by 300 nm CTAFM scans at 1 V, 2 V, and 3 V. Right panel: scan of the whole graphene flake at 2 V. (c) Typical CTAFM line scans for each bias.
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