We
investigated the growth of twisted graphene on graphene/silicon
carbide (SiC-G) templates by metal-free chemical vapor deposition
(CVD) through a sequential thermal (ST) process, which exploits the
ultraclean surface of SiC-G without exposing the surface to air before
CVD. By conducting control experiments with SiC-G templates exposed
to air (AirE process), structural analysis by atomic force microscopy
revealed that the nucleation density of CVD-grown graphene (CVD-G)
was significantly suppressed in the ST process under the same growth
conditions. The nucleation behavior on SiC-G surfaces was observed
to be very sensitive to the carbon source concentration and process
temperature. Nucleation on the ultraclean surface of SiC-G prepared
by the ST process requires a higher partial pressure of the carbon
source compared to that on the surface of SiC-G prepared by the AirE
process. Moreover, an analysis of CVD-G growth over a wide temperature
range indicated that the nucleation phenomena change dramatically
with a threshold temperature of 1300 °C, possibly due to arising
etching effects. The successful synthesis of twisted few-layer graphene
(tFLG) was affirmed by Raman spectroscopy, in which an analysis of
the G′-band proved thre was a high ratio of twisted structure
in CVD-G. These results demonstrate that metal-free CVD utilizing
ultraclean templates is an effective approach for the scalable production
of large-domain tFLG, which is valuable for electronic applications.