102 research outputs found
Penetration of alkali atoms throughout graphene membrane: theoretical modeling
Theoretical studies of penetration of various alkali atoms (Li, Na, Rb, Cs)
throughout graphene membrane grown on silicon carbide substrate are reported
and compared with recent experimental results. Results of first principles
modeling demonstrate rather low (about 0.8 eV) energy barrier for the formation
of temporary defects in carbon layer required for the penetration of Li at high
concentration of adatoms, higher (about 2 eV) barrier for Na, and barriers
above 4 eV for Rb and Cs. Experiments prove migration of lithium adatoms from
graphene surface to the buffer layer and SiC substrate at room temperature,
sodium at 100{\deg}C and impenetrability of graphene membrane for Rb and Cs.
Differences between epitaxial and free standing graphene for the penetration of
alkali ions are also discussed.Comment: 16 pages, 3 figure, accepted to Nanoscal
Directed self-organization of graphene nanoribbons on SiC
Realization of post-CMOS graphene electronics requires production of
semiconducting graphene, which has been a labor-intensive process. We present
tailoring of silicon carbide crystals via conventional photolithography and
microelectronics processing to enable templated graphene growth on
4H-SiC{1-10n} (n = 8) crystal facets rather than the customary {0001} planes.
This allows self-organized growth of graphene nanoribbons with dimensions
defined by those of the facet. Preferential growth is confirmed by Raman
spectroscopy and high-resolution transmission electron microscopy (HRTEM)
measurements, and electrical characterization of prototypic graphene devices is
presented. Fabrication of > 10,000 top-gated graphene transistors on a 0.24 cm2
SiC chip demonstrates scalability of this process and represents the highest
density of graphene devices reported to date.Comment: 13 pages, 5 figure
Surface Chemistry Involved in Epitaxy of Graphene on 3C-SiC(111)/Si(111)
Surface chemistry involved in the epitaxy of graphene by sublimating Si atoms from the surface of epitaxial 3C-SiC(111) thin films on Si(111) has been studied. The change in the surface composition during graphene epitaxy is monitored by in situ temperature-programmed desorption spectroscopy using deuterium as a probe (D2-TPD) and complementarily by ex situ Raman and C1s core-level spectroscopies. The surface of the 3C-SiC(111)/Si(111) is Si-terminated before the graphitization, and it becomes C-terminated via the formation of C-rich (6√3 × 6√3)R30° reconstruction as the graphitization proceeds, in a similar manner as the epitaxy of graphene on Si-terminated 6H-SiC(0001) proceeds
Probing Mechanical Properties of Graphene with Raman Spectroscopy
The use of Raman scattering techniques to study the mechanical properties of
graphene films is reviewed here. The determination of Gruneisen parameters of
suspended graphene sheets under uni- and bi-axial strain is discussed and the
values are compared to theoretical predictions. The effects of the
graphene-substrate interaction on strain and to the temperature evolution of
the graphene Raman spectra are discussed. Finally, the relation between
mechanical and thermal properties is presented along with the characterization
of thermal properties of graphene with Raman spectroscopy.Comment: To appear in the Journal of Materials Scienc
Quantum Resistance Standard Based on Epitaxial Graphene
We report development of a quantum Hall resistance standard accurate to a few
parts in a billion at 300 mK and based on large area epitaxial graphene. The
remarkable precision constitutes an improvement of four orders of magnitude
over the best results obtained in exfoliated graphene and is similar to the
accuracy achieved in well-established semiconductor standards. Unlike the
traditional resistance standards the novel graphene device is still accurately
quantized at 4.2 K, vastly simplifying practical metrology. This breakthrough
was made possible by exceptional graphene quality achieved with scalable
silicon carbide technology on a wafer scale and shows great promise for future
large scale applications in electronics.Comment: Submitte
Transition metals on the (0001) surface of graphite: Fundamental aspects of adsorption, diffusion, and morphology
In this article, we review basic information about the interaction of transition metal atoms with the (0001) surface of graphite, especially fundamental phenomena related to growth. Those phenomena involve adatom-surface bonding, diffusion, morphology of metal clusters, interactions with steps and sputter-induced defects, condensation, and desorption. General traits emerge which have not been summarized previously. Some of these features are rather surprising when compared with metal-on-metal adsorption and growth. Opportunities for future work are pointed out
Changes induced in the surface electronic structure of Be(0001) after Si adsorption
A study of effects induced in the Be is core level spectrum and in the surface band structure after Si adsorption on Be(0001) is reported. The changes in the Be is spectrum are quite dramatic. The number of resolvable surface components and the magnitude of the shifts do decrease and the relative intensities of the shifted components are drastically different compared to the clean surface. The surface band structure is also strongly affected after Si adsorption and annealing. At (&UGamma;) under bar the surface state is found to move down from 2.8 to 4.1 eV. The band also splits at around 0.5 Angstrom(-1) along both the (&UGamma;-K) under bar and (&UGamma;-M) under bar directions. At (M) under bar and beyond (K) under bar only one surface state is observed in the band gap instead of the two for the clean surface. Our findings indicate that a fairly small amount of Si in the outer atomic layers strongly modifies the electronic properties of these layers
- …