617 research outputs found
Introducing Nonuniform Strain to Graphene Using Dielectric Nanopillars
A method for inducing nonuniform strain in graphene films is developed.
Pillars made of a dielectric material (electron beam resist) are placed between
graphene and the substrate, and graphene sections between pillars are attached
to the substrate. The strength and spatial pattern of the strain can be
controlled by the size and separation of the pillars. Application of strain is
confirmed by Raman spectroscopy as well as from scanning electron microscopy
(SEM) images. From SEM images, the maximum stretch of the graphene film reaches
about 20%. This technique can be applied to the formation of band gaps in
graphene.Comment: Appl. Phys. Express, in pres
Fluctuations of Quantum Radiation Pressure in Dissipative Fluid
Using the generalized Langevin equations involving the stress tensor
approach, we study the dynamics of a perfectly reflecting mirror which is
exposed to the electromagnetic radiation pressure by a laser beam in a fluid at
finite temperature. Based on the fluctuation-dissipation theorem, the minimum
uncertainty of the mirror's position measurement from both quantum and thermal
noises effects including the photon counting error in the laser interferometer
is obtained in the small time limit as compared with the "standard quantum
limit".
The result of the large time behavior of fluctuations of the mirror's
velocity in a dissipative environment can be applied to the laser
interferometer of the ground-based gravitational wave detector.Comment: 8 pages. Version published in Physics Letters
Strained graphene: tight-binding and density functional calculations
We determine the band structure of graphene under strain using density
functional calculations. The ab-initio band strucure is then used to extract
the best fit to the tight-binding hopping parameters used in a recent
microscopic model of strained graphene. It is found that the hopping parameters
may increase or decrease upon increasing strain, depending on the orientation
of the applied stress. The fitted values are compared with an available
parametrization for the dependence of the orbital overlap on the distance
separating the two carbon atoms. It is also found that strain does not induce a
gap in graphene, at least for deformations up to 10%
Surface energy engineering of graphene
Contact angle goniometry is conducted for epitaxial graphene on SiC. Although
only a single layer of epitaxial graphene exists on SiC, the contact angle
drastically changes from 69{\deg} on SiC substrates to 92{\deg} with graphene.
It is found that there is no thickness dependence of the contact angle from the
measurements of single, bi, and multi layer graphene and highly ordered
pyrolytic graphite (HOPG). After graphene is treated with oxygen plasma, the
level of damage is investigated by Raman spectroscopy and correlation between
the level of disorder and wettability is reported. By using low power oxygen
plasma treatment, the wettability of graphene is improved without additional
damage, which can solve the adhesion issues involved in the fabrication of
graphene devices
Differential Conductance Fluctuation of Curved Nanographite Sheets in the Mesoscopic Regime
Excess conductance fluctuations with peculiar temperature-dependence from 1.4
to 250 K were observed in curved nano-graphite sheets with an electrode gap
length of 300 and 450 nm, whereas the conductance fluctuation is greatly
suppressed above 4.2 K when the electrode gap length increases to 800 and 1000
nm. The former is discussed in the context of the presence of a small energy
bandgap in the nano-graphite sheets, while the latter is attributed to the
crossover from coherent transport to diffusive transport regime.Comment: 12 pages, 3 figure
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
Strain- and Adsorption-Dependent Electronic States and Transport or Localization in Graphene
The chapter generalizes results on influence of uniaxial strain and
adsorption on the electron states and charge transport or localization in
graphene with different configurations of imperfections (point defects):
resonant (neutral) adsorbed atoms either oxygen- or hydrogen-containing
molecules or functional groups, vacancies or substitutional atoms, charged
impurity atoms or molecules, and distortions. To observe electronic properties
of graphene-admolecules system, we applied electron paramagnetic resonance
technique in a broad temperature range for graphene oxides as a good basis for
understanding the electrotransport properties of other active carbons. Applied
technique allowed observation of possible metal-insulator transition and
sorption pumping effect as well as discussion of results in relation to the
granular metal model. The electronic and transport properties are calculated
within the framework of the tight-binding model along with the Kubo-Greenwood
quantum-mechanical formalism. Depending on electron density and type of the
sites, the conductivity for correlated and ordered adsorbates is found to be
enhanced in dozens of times as compared to the cases of their random
distribution. In case of the uniaxially strained graphene, the presence of
point defects counteracts against or contributes to the band-gap opening
according to their configurations. The band-gap behaviour is found to be
nonmonotonic with strain in case of a simultaneous action of defect ordering
and zigzag deformation. The amount of localized charge carriers (spins) is
found to be correlated with the content of adsorbed centres responsible for the
formation of potential barriers and, in turn, for the localization effects.
Physical and chemical states of graphene edges, especially at a uniaxial strain
along one of them, play a crucial role in electrical transport phenomena in
graphene-based materials.Comment: 16 pages, 10 figure
Aharonov-Bohm interferences from local deformations in graphene
One of the most interesting aspects of graphene is the tied relation between
structural and electronic properties. The observation of ripples in the
graphene samples both free standing and on a substrate has given rise to a very
active investigation around the membrane-like properties of graphene and the
origin of the ripples remains as one of the most interesting open problems in
the system. The interplay of structural and electronic properties is
successfully described by the modelling of curvature and elastic deformations
by fictitious gauge fields that have become an ex- perimental reality after the
suggestion that Landau levels can form associated to strain in graphene and the
subsequent experimental confirmation. Here we propose a device to detect
microstresses in graphene based on a scanning-tunneling-microscopy setup able
to measure Aharonov-Bohm inter- ferences at the nanometer scale. The
interferences to be observed in the local density of states are created by the
fictitious magnetic field associated to elastic deformations of the sample.Comment: Some bugs fixe
Bird-spiders (Arachnida, Mygalomorphae) as perceived by the inhabitants of the village of Pedra Branca, Bahia State, Brazil
This paper deals with the conceptions, knowledge and attitudes of the inhabitants of the county of Pedra Branca, Bahia State, on mygalomorph spiders locally known as 'caranguejeiras' (bird-spiders). It is launched here a new filed within ethnozoology: ethnoarachnology, which is defined as the transdisciplinary study of the relationships between human beings and bird-spiders. Data were collected from February to June 2005 by means of open-ended interviews carried out with 30 individuals, which ages ranged from 13 to 86 years old. It was recorded some traditional knowledge regarding the following items: taxonomy, biology, habitat, ecology, seasonality, and behavior. Results show that bird-spiders are classified as "insects". The most commented aspect of the interaction between bird-spiders and inhabitants of Pedra Branca is related to their dangerousness, since they said these spiders are very venomous and can cause health problems. In general, the traditional zoological knowledge of Pedra Branca's inhabitants concerning these spiders is coherent with the academic knowledge
Clar's Theory, STM Images, and Geometry of Graphene Nanoribbons
We show that Clar's theory of the aromatic sextet is a simple and powerful
tool to predict the stability, the \pi-electron distribution, the geometry, the
electronic/magnetic structure of graphene nanoribbons with different hydrogen
edge terminations. We use density functional theory to obtain the equilibrium
atomic positions, simulated scanning tunneling microscopy (STM) images, edge
energies, band gaps, and edge-induced strains of graphene ribbons that we
analyze in terms of Clar formulas. Based on their Clar representation, we
propose a classification scheme for graphene ribbons that groups configurations
with similar bond length alternations, STM patterns, and Raman spectra. Our
simulations show how STM images and Raman spectra can be used to identify the
type of edge termination
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