Filippos Farmakis

Effect of vacuum thermal annealing to encapsulated graphene field effect transistors

Water vapor barriers used for graphene encapsulation can both exclude water from the environment and trap water in the device, preventing annealing from improving device performance. In this paper, the authors investigate the effects of vacuum annealing on encapsulated single layer graphene field effect transistors (SLG-FETs). The stability of GFETs is monitored for a period of up to six months, and different annealing times and atmospheres are tested to recover lost electronic performance. Fabricated encapsulated devices based on a parylene-C/aluminum passivation layers offer increased stability over exposed back-gated devices, but still suffer from a significant Dirac point shift over extended air exposure. Our results show that GFETs subjected to varying annealing times exhibit similar initial behavior, characterized by a substantial reduction of their doping profile due to desorption of oxygen/water molecules, but drastically different long term stability. This suggests that moderate vacuum annealing ...

Amorphous silicon-graphene anodes for lithium ion batteries

For the development of the next generation lithium-ion batteries it is primordial to investigate new materials as potential candidates towards the increase of the specific capacity of the anode and the new lighter and efficient cells. In this paper we present our investigation on amorphous silicon (a-Si) deposited by DC-sputtering on top of Single Layer Graphene (SLG) grown by Chemical Vapor Deposition (CVD). Our aim being to improve the mechanical properties of the silicon volume change during charging and discharging cycles, it is found that half cells fabricated with such electrodes can achieve specific capacity values above 2000 mAh/g while avoiding large pulverization phenomena. However, it is also found that the a-Si/SLG interface results in high resistance electrodes and decreases cell performance. We suggest that by improving the a-Si/SLG contact resistance, the performance will further improve.