  The direct growth of high-quality, large single-crystalline domains of
graphene on a dielectric substrate is of vital importance for applications in
electronics and optoelectronics. Traditionally, graphene domains grown on
dielectrics are typically only ~1 nm with a growth rate of ~1 nm/min or less,
the main reason is the lack of a catalyst. Here we show that silane, serving as
a gaseous catalyst, is able to boost the graphene growth rate to ~1 um/min,
thereby promoting graphene domains up to 20 um in size to be synthesized via
chemical vapor deposition on hexagonal boron nitride. Hall measurements show
that the mobility of the sample reaches 20,000 cm2/Vs at room temperature,
which is among the best for CVD-grown graphene. Combining the advantages of
both catalytic CVD and the ultra-flat dielectric substrate, gaseous
catalyst-assisted CVD paves the way for synthesizing high-quality graphene for
device applications while avoiding the transfer process.
