8,648 research outputs found
Investigation of ion induced bending mechanism for nanostructures
Ion induced bending is a promising controlled technique for manipulating nanoscale structures. However, the underlying mechanism of the process is not well understood. In this letter, we report a detailed study of the bending mechanism of Si nanowires (NWs) under Ga+ irradiation. The microstructural changes in the NW due to ion beam irradiation are studied and molecular dynamics simulations are used to explore the ion–NW interaction processes. The simulation results are compared with the microstructural studies of the NW. The investigations inform a generic understanding of the bending process in crystalline materials, which we suggest to be feasible as a versatile manipulation and integration technique in nanotechnology
High-Quality Planar high-Tc Josephson Junctions
Reproducible high-Tc Josephson junctions have been made in a rather simple
two-step process using ion irradiation. A microbridge (1 to 5 ?m wide) is
firstly designed by ion irradiating a c-axis-oriented YBa2Cu3O7-? film through
a gold mask such as the non-protected part becomes insulating. A lower Tc part
is then defined within the bridge by irradiating with a much lower fluence
through a narrow slit (20 nm) opened in a standard electronic photoresist.
These planar junctions, whose settings can be finely tuned, exhibit
reproducible and nearly ideal Josephson characteristics. This process can be
used to produce complex Josephson circuits.Comment: 4 pages, 5 figures, to be published in Applied Physics Letter
Hardy type spaces on certain noncompact manifolds and applications
In this paper we consider a complete connected noncompact Riemannian manifold
M with Ricci curvature bounded from below, positive injectivity radius and
spectral gap b. We introduce a sequence X^1(M), X^2(M), ... of new Hardy spaces
on M, the sequence Y^1(M/, Y^2(M), ... of their dual spaces, and show that
these spaces may be used to obtain endpoint estimates for purely imaginary
powers of the Laplace-Beltrami operator and for more general spectral
multipliers associated to the Laplace--Beltrami operator L on M. Under the
additional condition that the volume of the geodesic balls of radius r is
controlled by C r^a e^{2\sqrt{b} r} for some real number a and for all large r,
we prove also an endpoint result for first order Riesz transforms D L^{-1/2}.
In particular, these results apply to Riemannian symmetric spaces of the
noncompact type.Comment: 27 pages, v2: the first version has been revised and rearranged, with
additions, in two papers, of which this new version is the first. The second
paper is posted as arXiv:1002.1161v
THE ADMITTANCE AND TRANSFER FUNCTIONS OF SOLID CORE ELECTROMAGNETS (thesis)
The admittance and transfer functions of large, solidcore electromagnets were determined. The effects of eddy currents and hysteresis were considered in deriving the functions. The study was concerned with the type of magnet employed in nuclear physics research which requires very precise regulation of the magnetic field. The study originated during the design of an analyzing magnet regulator for the ORNL 63-inch cyclotron. (W.D.M.
Gaps and tails in graphene and graphane
We study the density of states in monolayer and bilayer graphene in the
presence of a random potential that breaks sublattice symmetries. While a
uniform symmetry-breaking potential opens a uniform gap, a random
symmetry-breaking potential also creates tails in the density of states. The
latter can close the gap again, preventing the system to become an insulator.
However, for a sufficiently large gap the tails contain localized states with
nonzero density of states. These localized states allow the system to conduct
at nonzero temperature via variable-range hopping. This result is in agreement
with recent experimental observations in graphane by Elias {\it et al.}.Comment: 16 pages, 7 figure
Lifetime measurements of Triaxial Strongly Deformed bands in Tm
With the Doppler Shift Attenuation Method, quadrupole transition moments,
, were determined for the two recently proposed Triaxial Strongly Deformed
(TSD) bands in Tm. The measured moments indicate that the
deformation of these bands is larger than that of the yrast, signature
partners. However, the measured values are smaller than those predicted by
theory. This observation appears to be valid for TSD bands in several nuclei of
the regionComment: 8 pages, 5 figures. Submitted to Physical Review
Swift heavy ion damage to sodium chloride: synergy between excitation and thermal spikes
Systematic data on the effect of irradiation with swift ions (Zn at 735 MeV and Xe at 929 MeV) on NaCl single crystals have been analysed in terms of a synergetic two-spike approach (thermal and excitation spikes). The coupling of the two spikes, simultaneously generated by the irradiation, contributes to the operation of a non-radiative exciton decay model as proposed for purely ionization damage. Using this scheme, we have accounted for the π-emission yield of self-trapped excitons and its temperature dependence under ion-beam irradiation. Moreover, the initial production rates of F-centre growth have also been reasonably simulated for irradiation at low temperatures ( < 100 K), where colour centre annealing and aggregation can be neglected
Optical Hall conductivity of systems with gapped spectral nodes
We calculate the optical Hall conductivity within the Kubo formalism for
systems with gapped spectral nodes, where the latter have a power-law
dispersion with exponent n. The optical conductivity is proportional to n and
there is a characteristic logarithmic singularity as the frequency approaches
the gap energy. The optical Hall conductivity is almost unaffected by thermal
fluctuations and disorder for n=1, whereas disorder has a stronger effect on
transport properties if n=2
Influence of ion implantation on the magnetic and transport properties of manganite films
We have used oxygen ions irradiation to generate controlled structural
disorder in thin manganite films. Conductive atomic force microscopy CAFM),
transport and magnetic measurements were performed to analyze the influence of
the implantation process in the physical properties of the films. CAFM images
show regions with different conductivity values, probably due to the random
distribution of point defect or inhomogeneous changes of the local Mn3+/4+
ratio to reduce lattice strains of the irradiated areas. The transport and
magnetic properties of these systems are interpreted in this context.
Metal-insulator transition can be described in the frame of a percolative
model. Disorder increases the distance between conducting regions, lowering the
observed TMI. Point defect disorder increases localization of the carriers due
to increased disorder and locally enhanced strain field. Remarkably, even with
the inhomogeneous nature of the samples, no sign of low field magnetoresistance
was found. Point defect disorder decreases the system magnetization but doesn t
seem to change the magnetic transition temperature. As a consequence, an
important decoupling between the magnetic and the metal-insulator transition is
found for ion irradiated films as opposed to the classical double exchange
model scenario.Comment: 27 pages, 11 Figure
Bose-Einstein Condensation in a Trap: the Case of a Dense Condensate
We consider the Bose-Einstein condensation of atoms in a trap where the
density of particles is so high that the low density approach of Gross and
Pitaevskii will not be applicable. For this purpose we use the slave boson
representation which is valid for hard-core bosons at any density. This
description leads to the same results as the Gross-Pitaevskii approach in the
low density limit, but for higher densities, it predicts the depletion of the
order parameter field condensate in the regions where the density of the atomic
cloud is high.Comment: 6 pages RevTeX, 3 eps-figure
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