Robust reduction of graphene fluoride using an electrostatically biased scanning probe

We report a novel and easily accessible method to chemically reduce graphene fluoride (GF) sheets with nanoscopic precision using high electrostatic fields generated between an atomic force microscope (AFM) tip and the GF substrate. Reduction of fluorine by the electric field produces graphene nanoribbons (GNR) with a width of 105-1,800 nm with sheet resistivity drastically decreased from > 1 T Omega center dot sq.(-1) (GF) down to 46 k Omega center dot sq.(-1) (GNR). Fluorine reduction also changes the topography, friction, and work function of the GF. Kelvin probe force microscopy measurements indicate that the work function of GF is 180-280 meV greater than that of graphene. The reduction process was optimized by varying the AFM probe velocity between 1.2 mu m center dot s(-1) and 12 mu m center dot s(-1) and the bias voltage applied to the sample between -8 and -12 V. The electrostatic field required to remove fluorine from carbon is similar to 1.6 V center dot nm(-1). Reduction of the fluorine may be due to the softening of the C-F bond in this intense field or to the accumulation and hydrolysis of adventitious water into a meniscus.