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We study the change in transport properties of graphene field effect transistor devices as a result of in situ electron beam irradiation followed by molecular adsorption. We find that the observed change in transport is not due to direct irradiation effects but instead can be attributed to electron beam induced molecular adsorption, governed by a Redox process. Subsequent to the exposure of graphene devices with electrons, the onset of negative doping is observed. This doping is attributed to adsorbate species on graphene generated during the electron irradiation process. As the irradiated graphene is subsequently exposed to ambient conditions, Redox coupling with environmental molecules deteriorates the transport properties while concomitantly changing the surface topography of graphene, as observed by atomic force microscopy. In addition, the resistivity shows hysteresis in gate voltage, which arises from the polarity of some of the adsorbate species. The enhanced control of the transport properties by electron beam induced molecular adsorption provides a novel approach to graphene transistors as sensors for chemical and biological materials. |
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