10,078 research outputs found
Raman spectroscopy as probe of nanometer-scale strain variations in graphene
Confocal Raman spectroscopy is a versatile, non-invasive investigation tool
and a major workhorse for graphene characterization. Here we show that the
experimentally observed Raman 2D line width is a measure of nanometer-scale
strain variations in graphene. By investigating the relation between the G and
2D line at high magnetic fields we find that the 2D line width contains
valuable information on nanometer-scale flatness and lattice deformations of
graphene, making it a good quantity for classifying the structural quality of
graphene even at zero magnetic field.Comment: 7 pages, 4 figure
Multi-shell gold nanowires under compression
Deformation properties of multi-wall gold nanowires under compressive loading
are studied. Nanowires are simulated using a realistic many-body potential.
Simulations start from cylindrical fcc(111) structures at T=0 K. After
annealing cycles axial compression is applied on multi-shell nanowires for a
number of radii and lengths at T=300 K. Several types of deformation are found,
such as large buckling distortions and progressive crushing. Compressed
nanowires are found to recover their initial lengths and radii even after
severe structural deformations. However, in contrast to carbon nanotubes
irreversible local atomic rearrangements occur even under small compressions.Comment: 1 gif figure, 5 ps figure
Crack fronts and damage in glass at the nanometer scale
We have studied the low speed fracture regime for different glassy materials
with variable but controlled length scales of heterogeneity in a carefully
mastered surrounding atmosphere. By using optical and atomic force microscopy
(AFM) techniques we tracked in real-time the crack tip propagation at the
nanometer scale on a wide velocity range (mm/s - pm/s and below). The influence
of the heterogeneities on this velocity is presented and discussed. Our
experiments reveal also -for the first time- that the crack progresses through
nucleation, growth and coalescence of nanometric damage cavities within the
amorphous phase. This may explain the large fluctuations observed in the crack
tip velocities for the smallest values. This behaviour is very similar to what
is involved, at the micrometric scale, in ductile fracture. The only difference
is very likely due to the related length scales (nanometric instead of
micrometric). Consequences of such a nano-ductile fracture mode observed at a
temperature far below the glass transition temperature in glass is finally
discussed.Comment: 12 pages, 8 figures, submitted to Journal of Physics: Condensed
Matter; Invited talk at Glass and Optical Materials Division Fall 2002
Meeting, Pittsburgh, Pa, US
Fluorescent nanodiamonds for FRET-based monitoring of a single biological nanomotor FoF1-ATP synthase
Color centers in diamond nanocrystals are a new class of fluorescence markers
that attract significant interest due to matchless brightness, photostability
and biochemical inertness. Fluorescing diamond nanocrystals containing defects
can be used as markers replacing conventional organic dye molecules, quantum
dots or autofluorescent proteins. They can be applied for tracking and
ultrahigh-resolution localization of the single markers. In addition the spin
properties of diamond defects can be utilized for novel magneto-optical imaging
(MOI) with nanometer resolution. We develop this technique to unravel the
details of the rotary motions and the elastic energy storage mechanism of a
single biological nanomotor FoF1-ATP synthase. FoF1-ATP synthase is the enzyme
that provides the 'chemical energy currency' adenosine triphosphate, ATP, for
living cells. The formation of ATP is accomplished by a stepwise internal
rotation of subunits within the enzyme. Previously subunit rotation has been
monitored by single-molecule fluorescence resonance energy transfer (FRET) and
was limited by the photostability of the fluorophores. Fluorescent nanodiamonds
advance these FRET measurements to long time scales.Comment: 10 pages, 4 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
Atomically sharp non-classical ripples in graphene
A fundamental property of a material is the measure of its deformation under
applied stress. After studying the mechanical properties of bulk materials for
the past several centuries, with the discovery of graphene and other
two-dimensional materials, we are now poised to study the mechanical properties
of single atom thick materials at the nanoscale. Despite a large number of
theoretical investigations of the mechanical properties and rippling of single
layer graphene, direct controlled experimental measurements of the same have
been limited, due in part to the difficulty of engineering reproducible ripples
such that relevant physical parameters like wavelength, amplitude, sheet length
and curvature can be systematically varied. Here we report extreme (>10%)
strain engineering of monolayer graphene by a novel technique of draping it
over large Cu step edges. Nanoscale periodic ripples are formed as graphene is
pinned and pulled by substrate contact forces. We use a scanning tunneling
microscope to study these ripples to find that classical scaling laws fail to
explain their shape. Unlike a classical fabric that forms sinusoidal ripples in
the transverse direction when stressed in the longitudinal direction, graphene
forms triangular ripples, where bending is limited to a narrow region on the
order of unit cell dimensions at the apex of each ripple. This non-classical
bending profile results in graphene behaving like a bizarre fabric, which
regardless of how it is pulled, always buckles at the same angle. Using a
phenomenological model, we argue that our observations can be accounted for by
assuming that unlike a thin classical fabric, graphene undergoes significant
stretching when bent. Our results provide insights into the atomic-scale
bending mechanisms of 2D materials under traditionally inaccessible strain
magnitudes and demonstrate a path forward for their strain engineering.Comment: 22 pages, 4 figure
Nonharmonic oscillations of nanosized cantilevers due to quantum-size effects
Using a one-dimensional jellium model and standard beam theory we calculate
the spring constant of a vibrating nanowire cantilever. By using the asymptotic
energy eigenvalues of the standing electron waves over the nanometer-sized
cross-section area, the change in the grand canonical potential is calculated
and hence the force and the spring constant. As the wire is bent more electron
states fits in its cross section. This has an impact on the spring"constant"
which oscillates slightly with the bending of the wire. In this way we obtain
an amplitude-dependent resonance frequency of the oscillations that should be
detectable.Comment: 6 pages, 5 figure
Hydrogen-Induced Deformations of Metals Followed by in Situ Scanning Tunneling Microscopy : Palladium Electrolytic Hydrogen Charging and Discharging in Alkaline Solution
In situ scanning tunneling microscopy measurements of Pd single-crystal domains during hydrogen charging/discharging cycles in 0.25 M KOH at 298 K allowed us to follow deformations produced by the Pd ↔ S β(H-Pd) phase transition in real time. The stress produced by this transition leads to elastic deformations involving reversible volume changes and plastic deformations resulting in one- or two-atom high slip lines and slip bands. These results demonstrate the capability of nanoscopies to investigate solid deformations on the nanometer scale in different environments, discriminate different types of deformations, and distinguish possible additional steps that are involved in the dynamics of solids.Instituto de Investigaciones FisicoquĂmicas TeĂłricas y Aplicada
The Escape Problem in a Classical Field Theory With Two Coupled Fields
We introduce and analyze a system of two coupled partial differential
equations with external noise. The equations are constructed to model
transitions of monovalent metallic nanowires with non-axisymmetric intermediate
or end states, but also have more general applicability. They provide a rare
example of a system for which an exact solution of nonuniform stationary states
can be found. We find a transition in activation behavior as the interval
length on which the fields are defined is varied. We discuss several
applications to physical problems.Comment: 24 page
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