Enhanced sensing response of oxidized graphene formed by UV irradiation in water

A small amount of defects (less than 0.01%) were introduced into graphene by irradiating it with ultraviolet (UV) light in water. The chemisorbed oxygen species caused a limited amount of degradation in the charge carrier mobility, while the physisorbed water molecules caused both a reduction in the mobility and hole doping. The oxidation was nonuniform, owing to variations in the potential caused by the metal contacts. Raman spectroscopy measurements revealed that UV irradiation in water promoted mild oxidation of graphene's basal plane, which enhanced the electrical sensing response of the adsorption of water molecules. The enhanced electrical response was achieved by the high binding energy of the water molecules at the oxidized sites and the near-zero Dirac point voltage, easily obtained by desorbing the physisorbed water molecules.