64 research outputs found
Selective epitaxial growth of graphene on SiC
We present an innovative method of selective epitaxial growth of few layers
graphene (FLG) on a pre-patterned SiC substrate. The methods involves,
successively, the sputtering of a thin AlN layer on top of a mono-crystalline
SiC substrate and, then, patterning it with e-beam lithography (EBL) and wet
etching. The sublimation of few atomic layers of Si from the SiC substrate
occurs only through the selectively etched AlN layer. The presence of the Raman
G-band at ~1582 cm-1 in the AlN-free areas is used to validate the concept, it
gives absolute evidence of the selective FLG growth.Comment: comments: 3 pages, reference 3 replace
Controlled epitaxial graphene growth within amorphous carbon corrals
Structured growth of high quality graphene is necessary for technological
development of carbon based electronics. Specifically, control of the bunching
and placement of surface steps under epitaxial graphene on SiC is an important
consideration for graphene device production. We demonstrate lithographically
patterned evaporated amorphous carbon corrals as a method to pin SiC surface
steps. Evaporated amorphous carbon is an ideal step-flow barrier on SiC due to
its chemical compatibility with graphene growth and its structural stability at
high temperatures, as well as its patternability. The amorphous carbon is
deposited in vacuum on SiC prior to graphene growth. In the graphene furnace at
temperatures above 1200C, mobile SiC steps accumulate at these
amorphous carbon barriers, forming an aligned step free region for graphene
growth at temperatures above 1330C. AFM imaging and Raman spectroscopy
support the formation of quality step-free graphene sheets grown on SiC with
the step morphology aligned to the carbon grid
Early stage formation of graphene on the C-face of 6H-SiC
An investigation of the early stage formation of graphene on the C-face of
6H-SiC is presented. We show that the sublimation of few atomic layers of Si
out of the SiC substrate is not homogeneous. In good agreement with the results
of theoretical calculations it starts from defective sites, mainly dislocations
that define nearly circular flakes, which have a pyramidal, volcano-like, shape
with a center chimney where the original defect was located. At higher
temperatures, complete conversion occurs but, again, it is not homogeneous.
Within the sample surface the intensity of the Raman G and 2D bands, evidences
non-homogeneous thickness.Comment: 12 pages, 3 figure
Investigation of Long Monolayer Graphene Ribbons grown on Graphite Capped 6H-SiC (000-1)
We present an investigation of large, isolated, graphene ribbons grown on the
C-face of on-axis semi-insulating 6H-SiC wafers. Using a graphite cap to cover
the SiC sample, we modify the desorption of the Si species during the Si
sublimation process. This results in a better control of the growth kinetics,
yielding very long (about 300 microns long, 5 microns wide), homogeneous
monolayer graphene ribbons. These ribbons fully occupy unusually large terraces
on the step bunched SiC surface, as shown by AFM, optical microscopy and SEM.
Raman spectrometry indicates that the thermal stress has been partially relaxed
by wrinkles formation, visible in AFM images. In addition, we show that despite
the low optical absorption of graphene, optical differential transmission can
be successfully used to prove the monolayer character of the ribbons
Micro-Raman and micro-transmission imaging of epitaxial graphene grown on the Si and C faces of 6H-SiC
Micro-Raman and micro-transmission imaging experiments have been done on epitaxial graphene grown on the C- and Si-faces of on-axis 6H-SiC substrates. On the C-face it is shown that the SiC sublimation process results in the growth of long and isolated graphene ribbons (up to 600 μm) that are strain-relaxed and lightly p-type doped. In this case, combining the results of micro-Raman spectroscopy with micro-transmission measurements, we were able to ascertain that uniform monolayer ribbons were grown and found also Bernal stacked and misoriented bilayer ribbons. On the Si-face, the situation is completely different. A full graphene coverage of the SiC surface is achieved but anisotropic growth still occurs, because of the step-bunched SiC surface reconstruction. While in the middle of reconstructed terraces thin graphene stacks (up to 5 layers) are grown, thicker graphene stripes appear at step edges. In both the cases, the strong interaction between the graphene layers and the underlying SiC substrate induces a high compressive thermal strain and n-type doping
Growth and Characterization of Graphene on Polycrystalline SiC Substrate Using Heating by CO2 Laser Beam
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