Graphene Transistors Are Insensitive to pH Changes in Solution. Nano Lett

We observe very small gate-voltage shifts in the transfer characteristic of as-prepared graphene field-effect transistors (GFETs) when the pH of the buffer is changed. This ob-servation is in strong contrast to Si-based ion-sensitive FETs. The low gate-shift of a GFET can be further reduced if the graphene surface is covered with a hydrophobic fluorobenzene layer. If a thin Al-oxide layer is applied instead, the opposite happens. This suggests that clean graphene does not sense the chemical potential of protons. A GFET can therefore be used as a reference electrode in an aqueous electrolyte. Our finding sheds light on the large variety of pH-induced gate shifts that have been published for GFETs in the recent literature. Graphene1 is an extremely interesting and important material with startling new physical and unique chemical characteristics.2 It is a one-atom-thick crystal of carbon atoms arranged into a two-dimensional (2D) hexagonal lattice. Compared with carbon nanotube (CNT), wafer-scale high-quality graphene can readily be produced by chemical vapor deposition (CVD) on copper ∗To whom correspondence should be addressed 1 a