  A bottom-up chemical vapor deposition (CVD) process for the growth of
graphene nanomesh films is demonstrated. The process relies on silicon
nanospheres to block nucleation sites for graphene CVD on copper substrates.
These spheres are formed in a self-organized way through silicon diffusion
through a 5 $\mu$m copper layer on a silicon wafer coated with 400 nm of
silicon nitride. The temperature during the growth process disintegrates the
$Si_3$$N_4$ layer and silicon atoms diffuse to the copper surface, where they
form the nanospheres. After graphene nanomesh growth, the Si nanospheres can be
removed by a simple hydrofluoric acid etch, leaving holes in the graphene film.
The nanomesh films have been successfully transferred to different substrates,
including gas sensor test structures, and verified and characterized by Auger,
TEM and SEM measurements. Electrical/gas-exposure measurements show a 2-fold
increase in ammonia sensitivity compared to plain graphene sensors. This
improvement can be explained by a higher adsorption site density (edge sites).
This new method for nanopatterned graphene is scalable, inexpensive and can be
carried out in standard semiconductor industry equipment. Furthermore, the
substrates are reusable.
