posted on 2021-05-05, 14:33authored byJosé
V. Anguita, Thomas R. Pozegic, Muhammad Ahmad, S. Ravi P. Silva
We report an in situ imaging method and use it
to reveal the mechanism for the formation of extended size sheets
of graphene (carpets) in few-layer graphene using the solid-state
process, taking place via a layer-by-layer growth mechanism, which
can result in a stack of separate individual layers of graphene. This
mechanism is revealed by an imaging method that allows the use of
conventional (unmodified) scanning electron microscopy to image graphene
growth in situ and in real time. With this dynamic
imaging, we reveal for the first time the dynamics of flake nucleation
and growth and show the dynamics of flake coalescence to form extended
size polycrystalline graphene carpets, allowing one to deduce a growth
model. This growth method produces graphene flakes with Raman spectral
characteristics that closely resemble those from exfoliated flakes
obtained using the “Scotch-tape” method. The material
is highly electronically intrinsic, with I2D/IG ratios as high as 5. The kinetics
of electronic interconnectivity between flakes during blanket formation
is imaged dynamically using a doping level contrast in an electron
microscope in real time. Furthermore, the observations reveal that
it is possible to maximize the time between the formation of each
individual blanket, up to several minutes, thus facilitating the production
of multiple decoupled graphene layers of precise thickness. This allows
one to control the number of layers produced even when using catalysts
of high activity and high-carbon solubility such as Fe.