Metal-catalyst-free growth of graphene on insulating substrates by ammonia-assisted microwave plasma-enhanced chemical vapor deposition

Abstract

We study the metal-catalyst-free growth of uniform and continuous graphene films on different insulating substrates by microwave plasma-enhanced chemical vapor deposition (PECVD) with a gas mixture of C 2 H 2 , NH 3 , and H 2 at a relatively low temperature of 700-750 C. Compared to growth using only C 2 H 2 and H 2 , the use of NH 3 during synthesis is found to be beneficial, in transforming vertical graphene nano-walls into a layer-by-layer film, reducing the density of defects, and improving the graphene quality. The effect of different insulating substrates (including Al 2 O 3 and SiO 2 ) on the growth of graphene was studied under different growth temperatures, implying that the growth-temperature window and catalytic effect vary among insulators. The low activation energy barrier of Al 2 O 3 proves it to be a more suitable substrate for the metal-catalyst-free growth of graphene at low temperature. These directly grown graphene films on insulators can be conveniently integrated into various electronic and optoelectronic applications avoiding any post-growth transfer processes.

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