Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userGraphene on insulating crystalline substrates
99
0
0.0
(
0
)
Added by
Marika Schleberger Y
Publication date
2009
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
We show that it is possible to prepare and identify ultra--thin sheets of graphene on crystalline substrates such as SrTiO$_3$, TiO$_2$, Al$_2$O$_3$ and CaF$_2$ by standard techniques (mechanical exfoliation, optical and atomic force microscopy). On the substrates under consideration we find a similar distribution of single, bi- and few layer graphene and graphite flakes as with conventional SiO$_2$ substrates. The optical contrast $C$ of a single graphene layer on any of those substrates is determined by calculating the optical properties of a two-dimensional metallic sheet on the surface of a dielectric, which yields values between $C=$ ~- 1.5% (G/TiO$_2$) and $C=$ ~- 8.8% (G/CaF$_2$). This contrast is in reasonable agreement with experimental data and is sufficient to make identification by an optical microscope possible. The graphene layers cover the crystalline substrate in a carpet-like mode and the height of single layer graphene on any of the crystalline substrates as determined by atomic force microscopy is $d_{SLG}=0.34$ nm and thus much smaller than on SiO$_2$.
rate research
Read More
This paper describes the behavior of top gated transistors fabricated using carbon, particularly epitaxial graphene on SiC, as the active material. In the past decade research has identified carbon-based electronics as a possible alternative to silicon-based electronics. This enthusiasm was spurred by high carbon nanotube carrier mobilities. However, nanotube production, placement, and control are all serious issues. Graphene, a thin sheet of graphitic carbon, can overcome some of these problems and therefore is a promising new electronic material. Although graphene devices have been built before, in this work we provide the first demonstration and systematic evaluation of arrays of a large number of transistors entirely produced using standard microelectronics methods. Graphene devices presented feature high-k dielectric, mobilities up to 5000 cm2/Vs and, Ion/Ioff ratios of up to 7, and are methodically analyzed to provide insight into the substrate properties. Typical of graphene, these micron-scale devices have negligible band gaps and therefore large leakage currents.
The graphene-enhanced Raman scattering of Rhodamine 6G molecules on pristine, fluorinated and 4-nitrophenyl functionalized graphene substrates was studied. The uniformity of the Raman signal enhancement was studied by making large Raman maps. The relative enhancement of the Raman signal is demonstrated to be dependent on the functional groups, which was rationalized by the different doping levels of pristine, fluorinated and 4-nitrophenyl functionalized graphene substrates. The impact of the Fermi energy of graphene and the phonon energy of the molecules was considered together for the first time in order to explain the enhancement. Such approach enables to understand the enhancement without assuming anything about the uniformity of the molecules on the graphene surface. The agreement between the theory and our measured data was further demonstrated by varying excitation energy.
We report the synthesis of single and bi layer graphene films by low pressure chemical vapor deposition technique on Cu and Au substrates. The as grown films were characterized by transmission electron microscopy, scanning electron microscopy and Raman spectroscopy techniques. The large lateral area graphene deposited on Cu can easily be transferred on Si SiO2. In the case of Au substrate both the adsorption and diffusion-precipitation leads to the growth of graphene.
In graphene growth, island symmetry can become lower than the intrinsic symmetries of both graphene and the substrate. First-principles calculations and Monte Carlo modeling explain the shapes observed in our experiments and earlier studies for various metal surface symmetries. For equilibrium shape, edge energy variations $delta E$ manifest in distorted hexagons with different ground-state edge structures. In growth or nucleation, energy variation enters exponentially as $sim e^{delta E / k_{B} T}$, strongly amplifying the symmetry breaking, up to completely changing the shapes to triangular, ribbon-like, or rhombic.
We demonstrate the growth of graphene nanocrystals by molecular beam methods that employ a solid carbon source, and that can be used on a diverse class of large area dielectric substrates. Characterization by Raman and Near Edge X-ray Absorption Fine Structure spectroscopies reveal a sp2 hybridized hexagonal carbon lattice in the nanocrystals. Lower growth rates favor the formation of higher quality, larger size multi-layer graphene crystallites on all investigated substrates. The surface morphology is determined by the roughness of the underlying substrate and graphitic monolayer steps are observed by ambient scanning tunneling microscopy.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
