924 research outputs found
Multiphonon Raman Scattering in Graphene
We report multiphonon Raman scattering in graphene samples. Higher order
combination modes involving 3 phonons and 4 phonons are observed in
single-layer (SLG), bi-layer (BLG), and few layer (FLG) graphene samples
prepared by mechanical exfoliation. The intensity of the higher order phonon
modes (relative to the G peak) is highest in SLG and decreases with increasing
layers. In addition, all higher order modes are observed to upshift in
frequency almost linearly with increasing graphene layers, betraying the
underlying interlayer van der Waals interactions.Comment: Accepted for publication in Phys. Rev.
Hooge's Constant of Carbon Nanotube Field Effect Transistors
The 1/f noise in individual semiconducting carbon nanotubes (s-CNT) in a
field effect transistor configuration has been measured in ultra-high vacuum
and following exposure to air. The amplitude of the normalized current spectral
noise density is independent of source-drain current, indicating the noise is
due to mobility rather than number fluctuations. Hooge's constant for s-CNT is
found to be 9.3 plus minus 0.4x10^-3. The magnitude of the 1/f noise is
substantially degreased by exposing the devices to air
Building Fuzzy Elevation Maps from a Ground-based 3D Laser Scan for Outdoor Mobile Robots
Mandow, A; Cantador, T.J.; Reina, A.J.; MartĂnez, J.L.; Morales, J.; GarcĂa-Cerezo, A. "Building Fuzzy Elevation Maps from a Ground-based 3D Laser Scan for Outdoor Mobile Robots," Robot2015: Second Iberian Robotics Conference, Advances in Robotics, (2016) Advances in Intelligent Systems and Computing, vol. 418. This is a self-archiving copy of the author’s accepted manuscript. The final publication is available at Springer via
http://link.springer.com/book/10.1007/978-3-319-27149-1.The paper addresses terrain modeling for mobile robots with fuzzy elevation maps by improving computational
speed and performance over previous work on fuzzy terrain identification from a three-dimensional (3D) scan. To this end,
spherical sub-sampling of the raw scan is proposed to select training data that does not filter out salient obstacles. Besides,
rule structure is systematically defined by considering triangular sets with an unevenly distributed standard fuzzy partition
and zero order Sugeno-type consequents. This structure, which favors a faster training time and reduces the number of rule
parameters, also serves to compute a fuzzy reliability mask for the continuous fuzzy surface. The paper offers a case study
using a Hokuyo-based 3D rangefinder to model terrain with and without outstanding obstacles. Performance regarding error
and model size is compared favorably with respect to a solution that uses quadric-based surface simplification (QSlim).This work was partially supported by the Spanish CICYT project DPI 2011-22443, the Andalusian project PE-2010 TEP-6101, and Universidad de Málaga-AndalucĂa Tech
Atomic Structure of Graphene on SiO2
We employ scanning probe microscopy to reveal atomic structures and nanoscale
morphology of graphene-based electronic devices (i.e. a graphene sheet
supported by an insulating silicon dioxide substrate) for the first time.
Atomic resolution STM images reveal the presence of a strong spatially
dependent perturbation, which breaks the hexagonal lattice symmetry of the
graphitic lattice. Structural corrugations of the graphene sheet partially
conform to the underlying silicon oxide substrate. These effects are obscured
or modified on graphene devices processed with normal lithographic methods, as
they are covered with a layer of photoresist residue. We enable our experiments
by a novel cleaning process to produce atomically-clean graphene sheets.Comment: 13 pages, 4 figure
Diffusive Charge Transport in Graphene on SiO2
We review our recent work on the physical mechanisms limiting the mobility of
graphene on SiO2. We have used intentional addition of charged scattering
impurities and systematic variation of the dielectric environment to
differentiate the effects of charged impurities and short-range scatterers. The
results show that charged impurities indeed lead to a conductivity linear in
density in graphene, with a scattering magnitude that agrees quantitatively
with theoretical estimates [1]; increased dielectric screening reduces
scattering from charged impurities, but increases scattering from short-range
scatterers [2]. We evaluate the effects of the corrugations (ripples) of
graphene on SiO2 on transport by measuring the height-height correlation
function. The results show that the corrugations cannot mimic long-range
(charged impurity) scattering effects, and have too small an
amplitude-to-wavelength ratio to significantly affect the observed mobility via
short-range scattering [3, 4]. Temperature-dependent measurements show that
longitudinal acoustic phonons in graphene produce a resistivity linear in
temperature and independent of carrier density [5]; at higher temperatures,
polar optical phonons of the SiO2 substrate give rise to an activated, carrier
density-dependent resistivity [5]. Together the results paint a complete
picture of charge carrier transport in graphene on SiO2 in the diffusive
regime.Comment: 28 pages, 7 figures, submitted to Graphene Week proceeding
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