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

Ph. D. ThesisGraphene 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.Newcastle University SAgE DT

Dynamics of Droplets Impacting on Aerogel, Liquid Infused, and Liquid-Like Solid Surfaces

Droplets impacting superhydrophobic surfaces have been extensively studied due to their compelling scientific insights and important industrial applications. In these cases, the commonly reported impact regime was that of complete rebound. This impact regime strongly depends on the nature of the superhydrophobic surface. Here, we report the dynamics of droplets impacting three hydrophobic slippery surfaces, which have fundamental differences in normal liquid adhesion and lateral static and kinetic liquid friction. For an air cushion-like (super)hydrophobic solid surface (Aerogel) with low adhesion and low static and low kinetic friction, complete rebound can start at a very low Weber (We) number (∼1). For slippery liquid-infused porous (SLIP) surfaces with high adhesion and low static and low kinetic friction, complete rebound only occurs at a much higher We number (>5). For a slippery omniphobic covalently attached liquid-like (SOCAL) solid surface, with high adhesion and low static friction similar to SLIPS but higher kinetic friction, complete rebound was not observed, even for a We as high as 200. Furthermore, the droplet ejection volume after impacting the Aerogel surface is 100% across the whole range of We numbers tested compared to other surfaces. In contrast, droplet ejection for SLIPs was only observed consistently when the We was above 5–10. For SOCAL, 100% (or near 100%) ejection volume was not observed even at the highest We number tested here (∼200). This suggests that droplets impacting our (super)hydrophobic Aerogel and SLIPS lose less kinetic energy. These insights into the differences between normal adhesion and lateral friction properties can be used to inform the selection of surface properties to achieve the most desirable droplet impact characteristics to fulfill a wide range of applications, such as deicing, inkjet printing, and microelectronics