171 research outputs found
Ultraviolet Raman Spectroscopy of Single and Multi-layer Graphene
We investigated Raman spectra of single-layer and multi-layer graphene under
ultraviolet laser excitation at the wavelength of 325 nm. It was found that
while the G peak of graphene remains pronounced in UV Raman spectra, the 2D
band intensity undergoes severe quenching. The evolution of the ratio of the
intensities of the G and 2D peaks, I(G)/I(2D), as the number of graphene layers
n changes from n=1 to n=5, is different in UV Raman spectra from that in
conventional visible Raman spectra excited at the 488 nm and 633 nm
wavelengths. The 2D band under UV excitation shifts to larger wave numbers and
is found near 2825 1/cm. The observed UV Raman features of graphene were
explained by invoking the resonant scattering model. The obtained results
contribute to the Raman nanometrology of graphene by providing an additional
metric for determining the number of graphene layers and assessing its quality.Comment: 18 pages; 5 figures; submitted for publication on February 20, 200
Negative Thermal Expansion Coefficient of Graphene Measured by Raman Spectroscopy
The thermal expansion coefficient (TEC) of single-layer graphene is estimated
with temperature-dependent Raman spectroscopy in the temperature range between
200 and 400 K. It is found to be strongly dependent on temperature but remains
negative in the whole temperature range, with a room temperature value of
-8.0x10^{-6} K^{-1}. The strain caused by the TEC mismatch between graphene and
the substrate plays a crucial role in determining the physical properties of
graphene, and hence its effect must be accounted for in the interpretation of
experimental data taken at cryogenic or elevated temperatures.Comment: 17 pagese, 3 figures, and supporting information (4 pages, 3
figures); Nano Letters, 201
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
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