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(Color online) The concomitant time evolution of (a) S and (b) R (red and blue circles – plotted on the left axis) and the corresponding temperature profile (orange dotted lines – plotted on the right axis) of a CVD-grown graphene sample during vacuum annealing. (c) The time evolution of concomitant S and R during the degassing in a blown-up scale.
(Color online) (a) Graphene on a SiO2/Si substrate is p-type under ambient conditions: EF is pinned by the redox potential of oxygen dissolved in the mildly acidic water adsorbed on the SiO2 surface, causing electron transfer from the graphene to the oxygen/water layer. (b) Graphene becomes n-type under degassed conditions: EF is located in the conduction band due to electron doping by the surface states of the SiO2/Si substrate.
(Color online) The temperature dependence of (a) S and (b) R of a graphene device during heating (red, prior to the oxygen desorption) and cooling (blue, after degassing). Solid black lines are the fits for quadratic (heating) and linear (cooling) dependences. The data during desorption are excluded in both plots.
(Color online) The concomitant time evolution of (a) S and (b) R of CVD-grown graphene upon exposure to air, N2O, and NH3. After each exposure, the sample was degassed to recover the original values of S and R before the subsequent exposure.
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