Graphene Synthesis on Electrodeposited Substrates and Its Integration in MEMS for Sensor Applications

Graphene has become a promising material for many different applications, such as nanoelectronic devices, physical, chemical and biochemical sensors, transparent conductive films, clean energy scavenging and storage devices, and nanocomposite formulation. Recently, gas sensing, as a critical application in intelligent systems, is receiving increasing attention in both industry and academia. Sensing applications using graphene sheets as transducers have experienced a surge of activities in recent years, especially for gas sensing platforms and electrochemical sensing, because of the high electrical conductivity and high surface area of graphene.  Despite the significant amount of work on graphene electronic devices such as the field effect transistor, its use in sensors, actuators or micro and nano-electromechanical systems (MEMS/NEMS) in general, is relatively less explored. By combining graphene's electronic and mechanical properties, monolithic sensors can be developed with superior sensitivity. Furthermore, proper functionalization of graphene enables enhanced selectivity. In this work, we investigate the synthesis of graphene by methane decomposition at 1000 °C onto free standing electrodeposited substrates, studying the effects of the electrochemical synthesis onto graphene quality. The growth of good quality graphene layers is also discussed in terms of the role played by grain boundaries and diffusion at the grain boundaries. Results on graphene properties when grown on ruthenium, copper and Ni-Cu alloys are reported, together with the possibility to grow 3D graphene layers on porous substrates, obtained by selective electrochemical de-alloying in the Ni-Cu system. Our results demonstrate the synthesis of graphene on Cu with presence of the D-peak and with the 2D-peak not higher than the G-peak (shifting of the 2D-peak) and on Ru with a high D-peak but with the 2D-peak still higher than the G-peak. The growth of graphene on NiCu is affected by the amount of copper in the alloy: a transition from graphitic to graphenic layers is observed with increasing copper content. Transfer procedures in order to integrate thus-produced graphene layers into MEMS device are presented, including the electrochemical approaches to decorate the graphene sheets with catalytic nanoparticles. The possibility of using this simple approach to develop new transducing materials for sensing applications integrated with a silicon microdevices is demonstrated.