9,757 research outputs found
Laser-induced etching of few-layer graphene synthesized by Rapid-Chemical Vapour Deposition on Cu thin films
The outstanding electrical and mechanical properties of graphene make it very
attractive for several applications, Nanoelectronics above all. However a
reproducible and non destructive way to produce high quality, large-scale area,
single layer graphene sheets is still lacking. Chemical Vapour Deposition of
graphene on Cu catalytic thin films represents a promising method to reach this
goal, because of the low temperatures (T < 900 Celsius degrees) involved during
the process and of the theoretically expected monolayer self-limiting growth.
On the contrary such self-limiting growth is not commonly observed in
experiments, thus making the development of techniques allowing for a better
control of graphene growth highly desirable. Here we report about the local
ablation effect, arising in Raman analysis, due to the heat transfer induced by
the laser incident beam onto the graphene sample.Comment: v1:9 pages, 8 figures, submitted to SpringerPlus; v2: 11 pages,
PDFLaTeX, 9 figures, revised peer-reviewed version resubmitted to
SpringerPlus; 1 figure added, figure 1 and 4 replaced,typos corrected,
"Results and discussion" section significantly extended to better explain
etching mechanism and features of Raman spectra, references adde
Understanding and optimising the packing density of perylene bisimide layers on CVD-grown graphene
The non-covalent functionalisation of graphene is an attractive strategy to
alter the surface chemistry of graphene without damaging its superior
electrical and mechanical properties. Using the facile method of aqueous-phase
functionalisation on large-scale CVD-grown graphene, we investigated the
formation of different packing densities in self-assembled monolayers (SAMs) of
perylene bisimide derivatives and related this to the amount of substrate
contamination. We were able to directly observe wet-chemically deposited SAMs
in scanning tunnelling microscopy (STM) on transferred CVD graphene and
revealed that the densely packed perylene ad-layers adsorb with the conjugated
{\pi}-system of the core perpendicular to the graphene substrate. This
elucidation of the non-covalent functionalisation of graphene has major
implications on controlling its surface chemistry and opens new pathways for
adaptable functionalisation in ambient conditions and on the large scale.Comment: 27 pages (including SI), 10 figure
The influence of residual oxidizing impurities on the synthesis of graphene by atmospheric pressure chemical vapor deposition
The growth of graphene on copper by atmospheric pressure chemical vapor
deposition in a system free of pumping equipment is investigated. The emphasis
is put on the necessity of hydrogen presence during graphene synthesis and
cooling. In the absence of hydrogen during the growth step or cooling at slow
rate, weak carbon coverage, consisting mostly of oxidized and amorphous carbon,
is obtained on the copper catalyst. The oxidation originates from the
inevitable occurrence of residual oxidizing impurities in the reactor's
atmosphere. Graphene with appreciable coverage can be grown within the
vacuum-free furnace only upon admitting hydrogen during the growth step. After
formation, it is preserved from the destructive effect of residual oxidizing
contaminants once exposure at high temperature is minimized by fast cooling or
hydrogen flow. Under these conditions, micrometer-sized hexagon-shaped graphene
domains of high structural quality are achieved.Comment: Accepted in Carbo
Comeback of epitaxial graphene for electronics: large-area growth of bilayer-free graphene on SiC
We present a new fabrication method for epitaxial graphene on SiC which
enables the growth of ultra-smooth defect- and bilayer-free graphene sheets
with an unprecedented reproducibility, a necessary prerequisite for wafer-scale
fabrication of high quality graphene-based electronic devices. The inherent but
unfavorable formation of high SiC surface terrace steps during high temperature
sublimation growth is suppressed by rapid formation of the graphene buffer
layer which stabilizes the SiC surface. The enhanced nucleation is enforced by
decomposition of polymer adsorbates which act as a carbon source. With most of
the steps well below 0.75 nm pure monolayer graphene without bilayer inclusions
is formed with lateral dimensions only limited by the size of the substrate.
This makes the polymer assisted sublimation growth technique the most promising
method for commercial wafer scale epitaxial graphene fabrication. The
extraordinary electronic quality is evidenced by quantum resistance metrology
at 4.2 K with until now unreached precision and high electron mobilities on mm
scale devices.Comment: 20 pages, 6 Figure
Optical Probing of Electronic Interaction between Graphene and Hexagonal Boron Nitride
Even weak van der Waals (vdW) adhesion between two-dimensional solids may
perturb their various materials properties owing to their low dimensionality.
Although the electronic structure of graphene has been predicted to be modified
by the vdW interaction with other materials, its optical characterization has
not been successful. In this report, we demonstrate that Raman spectroscopy can
be utilized to detect a few % decrease in the Fermi velocity (vF) of graphene
caused by the vdW interaction with underlying hexagonal boron nitride (hBN).
Our study also establishes Raman spectroscopic analysis which enables
separation of the effects by the vdW interaction from those by mechanical
strain or extra charge carriers. The analysis reveals that spectral features of
graphene on hBN are mainly affected by change in vF and mechanical strain, but
not by charge doping unlike graphene supported on SiO2 substrates. Graphene on
hBN was also found to be less susceptible to thermally induced hole doping.Comment: 19 pages, 4 figure
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