Industrially-safe, Nitrogen-buffered Graphene CVD and its Application in Sensing Devices

Abstract

Graphene is a two-dimensional carbon material, which has been suggested for use within many next-generation electronic applications due to its outstanding electronic and mechanical properties. Copper-catalysed chemical vapour deposition (Cu-CVD) is currently the most promising method for upscaling graphene production. However, there are safety and cost aspects which have not yet been fully explored and which are desirable to have in place prior to moving graphene production from batch- to industrial-scale production. This thesis presents research aimed at the development of Cu-CVD graphene growth recipes, using processes which mitigate against explosive risk and reduce cost via the dilution of precursor species within nitrogen, rather than the almost universally used argon. Process development is presented for graphene growth within a nitrogen-buffered atmosphere, which demonstrates that graphene growth follows the same trends with nitrogen as is observed within argon and also provides a guideline for others wishing to develop their own graphene CVD processes. Investigation of graphene films grown within nitrogen-buffered and argon-buffered atmospheres via Raman Spectroscopy, X-ray Photoelectron Spectroscopy and Time-ofFlight Secondary Ion Spectroscopy are presented, demonstrating that atomic nitrogen does not become incorporated within the graphene film when CVD is carried out within an N2 atmosphere, within spectroscopically detectable limits. The use of nitrogen, rather than argon, within CVD opens possibilities for significant cost reduction, particularly within mass-production which is likely to require high volumes of process gases. The electronic properties of the CVD graphene is explored via analysis of graphene field effect transistor (GFET) where it is shown that graphene grown via nitrogen-buffered CVD and argon-buffered CVD is indistinguishable. GFETs are used as the basis for gas-sensing devices, operating on a basis of resistance change due to charge-transfer. Decoration of GFETs with catalytically active nanoparticles to improve device sensitivity is explored, but quality variation of graphene layers is shown to be a limiting factor.