43 research outputs found
Mapping the nanomechanical properties of graphene suspended on silica nanoparticles
Using nanoparticles to impart extrinsic rippling in graphene is a relatively
new method to induce strain and to tailor the properties of graphene. Here we
study the structure and elastic properties of graphene grown by chemical vapour
deposition and transferred onto a continuous layer of SiO2 nanoparticles with
diameters of around 25 nm, prepared by Langmuir-Blodgett technique on Si
substrate. We show that the transferred graphene follows only roughly the
morphology induced by nanoparticles. The graphene membrane parts bridging the
nanoparticles are suspended and their adhesion to the AFM tip is larger
compared to that of supported graphene parts. These suspended graphene regions
can be deformed with forces of the order of 10 nN. The elastic modulus of
graphene was determined from indentation measurements performed on suspended
membrane regions with diameters in the 100 nm range.Comment: in Journal of Experimental Nanoscience (2016
Effect of the disorder in graphene grain boundaries: A wave packet dynamics study
Chemical vapor deposition (CVD) on Cu foil is one of the most promising methods to produce graphene samples despite of introducing numerous grain boundaries into the perfect graphene lattice. A rich variety of GB structures can be realized experimentally by controlling the parameters in the CVD method. Grain boundaries contain non-hexagonal carbon rings (4, 5, 7, 8 membered rings) and vacancies in various ratios and arrangements. Using wave packet dynamic (WPD) simulations and tight-binding electronic structure calculations, we have studied the effect of the structure of GBs on the transport properties. Three model GBs with increasing disorder were created in the computer: a periodic 5-7 GB, a "serpentine" GB, and a disordered GB containing 4, 8 membered rings and vacancies. It was found that for small energies (E = EF ± 1 eV) the transmission decreases with increasing disorder. Four membered rings and vacancies are identified as the principal scattering centers. Revealing the connection between the properties of GBs and the CVD growth method may open new opportunities in the graphene based nanoelectronics. © 2013 Elsevier B.V. All rights reserved
Canonical Ensemble of Initial States Leading to Chiral Fluctuations
In energetic heavy ion collisions, if quark-gluon plasma is formed, its
hadronization may lead to observable critical fluctuations, i.e., DCC
formation. The strength and observability of these fluctuations depend on the
initial state. Here we study the canonical ensemble of initial states of chiral
fluctuations in heavy ion collisions and the probability to obtain observable
domains of chiral condensates.Comment: 13 pages (figures included) Accepted for publication in Phys. Rev.
Optical structure and function of the white filamentary hair covering the edelweiss bracts
The optical properties of the inflorescence of the high-altitude
''Leontopodium nivale'' subsp. ''alpinum'' (edelweiss) is investigated, in
relation with its submicrometer structure, as determined by scanning electron
microscopy. The filaments forming the hair layer have been found to exhibit an
internal structure which may be one of the few examples of a photonic structure
found in a plant. Measurements of light transmission through a self-supported
layer of hair pads taken from the bracts supports the idea that the wooly layer
covering the plant absorbs near-ultraviolet radiation before it reaches the
cellular tissue. Calculations based on a photonic-crystal model provides
insight on the way radiation can be absorbed by the filamentary threads.Comment: 9 pages, 13 figures. Published pape
Dynamical Evolution of the Scalar Condensate in Heavy Ion Collisions
We derive the effective coarse-grained field equation for the scalar
condensate of the linear sigma model in a simple and straightforward manner
using linear response theory. The dissipative coefficient is calculated at tree
level on the basis of the physical processes of sigma-meson decay and of
thermal sigma-mesons and pions knocking sigma-mesons out of the condensate. The
field equation is solved for hot matter undergoing either one or three
dimensional expansion and cooling in the aftermath of a high energy nuclear
collision. The results show that the time constant for returning the scalar
condensate to thermal equilibrium is of order 2 fm/c.Comment: 19 pages, 3 figures are embedded at the end. The effect of the time
dependence of the condensate v is included in this revised version. Numerical
work is redone accordingl
Influence of Native Defects on the Electronic and Magnetic Properties of CVD Grown MoSe<sub>2</sub> Single Layers
The intrinsic defect structure of exfoliated MoS2 single layers revealed by Scanning Tunneling Microscopy
MoS2 single layers have recently emerged as strong competitors of graphene in electronic and optoelectronic device applications due to their intrinsic direct bandgap. However, transport measurements reveal the crucial role of defect-induced electronic states, pointing out the fundamental importance of characterizing their intrinsic defect structure. Transmission Electron Microscopy (TEM) is able to image atomic scale defects in MoS2 single layers, but the imaged defect structure is far from the one probed in the electronic devices, as the defect density and distribution are substantially altered during the TEM imaging. Here, we report that under special imaging conditions, STM measurements can fully resolve the native atomic scale defect structure of MoS2 single layers. Our STM investigations clearly resolve a high intrinsic concentration of individual sulfur atom vacancies, and experimentally identify the nature of the defect induced electronic mid-gap states, by combining topographic STM images with ab intio calculations. Experimental data on the intrinsic defect structure and the associated defect-bound electronic states that can be directly used for the interpretation of transport measurements are essential to fully understand the operation, reliability and performance limitations of realistic electronic devices based on MoS2 single layers
Tailoring the atomic structure of graphene nanoribbons by STM lithography
The practical realization of nano-scale electronics faces two major
challenges: the precise engineering of the building blocks and their assembly
into functional circuits. In spite of the exceptional electronic properties of
carbon nanotubes only basic demonstration-devices have been realized by
time-consuming processes. This is mainly due to the lack of selective growth
and reliable assembly processes for nanotubes. However, graphene offers an
attractive alternative. Here we report the patterning of graphene nanoribbons
(GNRs) and bent junctions with nanometer precision, well-defined widths and
predetermined crystallographic orientations allowing us to fully engineer their
electronic structure using scanning tunneling microscope (STM) lithography. The
atomic structure and electronic properties of the ribbons have been
investigated by STM and tunneling spectroscopy measurements. Opening of
confinement gaps up to 0.5 eV, allowing room temperature operation of GNR-based
devices, is reported. This method avoids the difficulties of assembling
nano-scale components and allows the realization of complete integrated
circuits, operating as room temperature ballistic electronic devices.Comment: 8 pages text, 5 figures, Nature Nanotechnology, in pres