Effect of epoxy exposure on the electronic properties of graphene

The effect of epoxy exposure and its curing agent (trimethyl-1, 6-hexanediamine), widely used for the biocompatible packaging of graphene-based devices, on the electrical characteristics of a graphene field effect transistor is investigated in this work. Upon 5 min of the epoxy curing agent exposure, the Dirac point shifted from 60 to 13 V, while for 15 min of the epoxy curing agent exposure, the Dirac point changed more than 130 V, from 63 to -68 V, completely changing the doping of graphene from strong p-type to strong n-type due to the electron donating nature of the adsorbed molecules. Additionally, due to exposure, the hole mobility was found to reduce from 1243 to 401 cm(2) V-1 s(-1), indicating the strong impact of ionized impurity scattering. The temperature-dependent Hall measurement of single layer graphene before and after the epoxy curing agent exposure also exhibited a change in the dominant scattering mechanism from surface optical phonon scattering to Coulomb scattering near room temperature due to epoxy exposure. Reduction of initial p-type doping in chemical vapor deposited (CVD) graphene after epoxy exposure is also confirmed by Raman spectroscopy. We found that the Dirac point recovered very slowly upon storage of the epoxy (or curing agent) exposed devices, changing by only similar to 11 V after 4 months without significant change in carrier mobility.