In this work we present the effect of low dose gallium (Ga) deposition (<4 ML) performed in UHV (10 Pa) on the electronic doping and charge carrier scattering in graphene grown by chemical vapor deposition. In situ graphene transport measurements performed with a graphene field-effect transistor structure show that at low Ga coverages a graphene layer tends to be strongly n-doped with an efficiency of 0.64 electrons per one Ga atom, while the further deposition and Ga cluster formation results in removing electrons from graphene (less n-doping). The experimental results are supported by the density functional theory calculations and explained as a consequence of distinct interaction between graphene and Ga atoms in case of individual atoms, layers, or clusters.

Hysteresis is a problem in field-effect transistors (FETs) often caused by defects and charge traps inside a gate isolating (e.g., SiO 2 ) layer. This work shows that graphene-based FETs also exhibit hysteresis due to water physisorbed on top of graphene determined by the relative humidity level, which naturally happens in biosensors and ambient operating sensors. The hysteresis effect is explained by trapping of electrons by physisorbed water, and it is shown that this hysteresis can be suppressed using short pulses of alternating gate voltages.

The article shows how the dynamic mapping of surface potential (SP) measured by Kelvin probe force microscopy (KPFM) in combination with calculation by a diffusion-like equation and the theory based on the Brunauer-Emmett-Teller (BET) model of water condensation and electron hopping can provide the information concerning the resistivity of low conductive surfaces and their water coverage. This is enabled by a study of charge transport between isolated and grounded graphene sheets on a silicon dioxide surface at different relative humidity (RH) with regard to the use of graphene in ambient electronic circuits and especially in sensors. In the experimental part, the chemical vapor-deposited graphene is precisely patterned by the mechanical atomic force microscopy (AFM) lithography and the charge transport is studied through a surface potential evolution measured by KPFM. In the computational part, a quantitative model based on solving the diffusion-like equation for the charge transport is used to fit the experimental data and thus to find the SiO surface resistivity ranging from 10 to 10 Ω and exponentially decreasing with the RH increase. Such a behavior is explained using the formation of water layers predicted by the BET adsorption theory and electron-hopping theory that for the SiO surface patterned by AFM predicts a high water coverage even at low RHs.