25,238 research outputs found
An interaction theory for scattering by defects in arrays
Wave scattering by an array of bodies that is periodic except for a finite number
of missing or irregular elements is considered. The field is decomposed into contributions from a
set of canonical problems, which are solved using a modified array scanning method. The resulting
interaction theory for defects is very efficient and can be used to construct the field in a large number
of different situations. Numerical results are presented for several cases, and particular attention is
paid to the amplitude with which surface waves are excited along the array. We also show how other
approaches can be incorporated into the theory so as to increase the range of problems that can be solved
Engineering Fano resonances in discrete arrays
We study transmission properties of discrete arrays composed of a linear waveguide coupled to a system of N side defect states. This simple system can be used to model discrete networks of coupled defect modes in photonic crystals, complex waveguide arrays in two-dimensional nonlinear lattices, and ring-resonator structures. We demonstrate the basic principles of the resonant scattering management through engineering Fano resonances and find exact results for the wave transmission coefficient. We reveal conditions for perfect reflections and transmissions due to either destructive or constructive interferences, and associate them with Fano resonances, also demonstrating how these resonances can be tuned by nonlinear defects
Understanding the interaction between energetic ions and freestanding graphene towards practical 2D perforation
We report experimentally and theoretically the behavior of freestanding
graphene subject to bombardment of energetic ions, investigating the ability of
large-scale patterning of freestanding graphene with nanometer sized features
by focused ion beam technology. A precise control over the He+ and Ga+
irradiation offered by focused ion beam techniques enables to investigate the
interaction of the energetic particles and graphene suspended with no support
and allows determining sputter yields of the 2D lattice. We find strong
dependency of the 2D sputter yield on the species and kinetic energy of the
incident ion beams. Freestanding graphene shows material semi-transparency to
He+ at high energies (10-30 keV) allowing the passage of >97% He+ particles
without creating destructive lattice vacancy. Large Ga+ ions (5-30 keV), in
contrast, collide far more often with the graphene lattice to impart
significantly higher sputter yield of ~50%. Binary collision theory applied to
monolayer and few-layer graphene can successfully elucidate this collision
mechanism, in great agreement with experiments. Raman spectroscopy analysis
corroborates the passage of a large fraction of He+ ions across graphene
without much damaging the lattice whereas several colliding ions create single
vacancy defects. Physical understanding of the interaction between energetic
particles and suspended graphene can practically lead to reproducible and
efficient pattern generation of unprecedentedly small features on 2D materials
by design, manifested by our perforation of sub-5-nm pore arrays. This
capability of nanometer scale precision patterning of freestanding 2D lattices
shows practical applicability of the focused ion beam technology to 2D material
processing for device fabrication and integration.Comment: 31 pages of main text (with 4 figures) plus 4 pages of supporting
information (with 2 figures). Original article submitted to a journal for
consideration for publicatio
Spatial storage of discrete dark solitons
The interaction between a mobile discrete dark soliton (DDS) and impurities
in one-dimensional nonlinear (Kerr) photonic lattices is studied. We found that
the scattering is an inelastic process where the DDS can be reflected or
transmitted depending on its transversal speed and the strength of the
impurities. In particular, in the reflection regime, the DDS increases its
transversal speed after each scattering. A method for spatial storage of DDS
solutions using two impurities is discussed, where the soliton can be trapped
within a storage region until it reaches the critical speed needed to be
transmitted. We show, numerically, that this method allows the storage of
multiple DDS simultaneously.Comment: 6 pages and 6 figure
Fano resonance in quadratic waveguide arrays
We study resonant light scattering in arrays of channel optical waveguides
where tunable quadratic nonlinearity is introduced as nonlinear defects by
periodic poling of single (or several) waveguides in the array. We describe
novel features of wave scattering that can be observed in this structure and
show that it is a good candidate for the first observation of Fano resonance in
nonlinear optics.Comment: 3 pages, 3 figures, submitted to Optics Letters, slightly revise
THEORY OF REGULAR ARRAYS OF DEFECTS - VOID LATTICE
Defects in crystals may form a regular array, rather than a random distribution. The lattice of voids produced in irradiated molybdenum is a remarkable example of this. We give a general method of calculating the energy per defect in the array which exploits the periodicity of the defect lattice. The existence of the void lattice depends on the elastic interaction between voids. The present approach can treat both arbitrarily anisotropic elastic continua and discrete lattices, and is readily extended to discuss the stability of the defect lattice. The results predict that a void lattice should occur in molybdenum, and compare a number of models for the void. Stability against shear of the void lattice is not discussed in the present paper. The ratio of the void lattice spacing to void radius predicted is 2.2 to 4.5 and is smaller than the value of about 10 observed. The results are in general agreement with the more approximate Malén-Bullough treatment
Temperature dependence of the resistance of metallic nanowires (diameter 15 nm): Applicability of Bloch-Gr\"{u}neisen theorem
We have measured the resistances (and resistivities) of Ag and Cu nanowires
of diameters ranging from 15nm to 200nm in the temperature range 4.2K-300K with
the specific aim to assess the applicability of the Bloch-Gr\"{u}neisen formula
for electron phonon resistivity in these nanowires. The wires were grown within
polymeric templates by electrodeposition. We find that in all the samples the
resistance reaches a residual value at T=4.2K and the temperature dependence of
resistance can be fitted to the Bloch-Gr\"{u}neisen formula in the entire
temperature range with a well defined transport Debye temperature
(). The value of Debye temperature obtained from the fits lie
within 8% of the bulk value for Ag wires of diameter 15nm while for Cu
nanowires of the same diameter the Debye temperature is significantly lesser
than the bulk value. The electron-phonon coupling constants (measured by
or ) in the nanowires were found to have the same
value as that of the bulk. The resistivities of the wires were seen to increase
as the wire diameter was decreased. This increase in the resistivity of the
wires may be attributed to surface scattering of conduction electrons. The
specularity p was estimated to be about 0.5. The observed results allow us to
obtain the resistivities exactly from the resistance and gives us a method of
obtaining the exact numbers of wires within the measured array (grown within
the template).Comment: 9 pages, 10 figure
Similarities Between Proton and Neutron Induced Dark Current Distribution in CMOS Image Sensors
Several CMOS image sensors were exposed to neutron or proton beams (displacement damage dose range from 4 TeV/g to 1825 TeV/g) and their radiation-induced dark current distributions are compared. It appears that for a given displacement damage dose, the hot pixel tail distributions are very similar, if normalized properly. This behavior is observed on all the tested CIS designs (4 designs, 2 technologies) and all the tested particles (protons from 50 MeV to 500 MeV and neutrons from 14 MeV to 22 MeV). Thanks to this result, all the dark current distribution presented in this paper can be fitted by a simple model with a unique set of two factors (not varying from one experimental condition to another). The proposed normalization method of the dark current histogram can be used to compare any dark current distribution to the distributions observed in this work. This paper suggests that this model could be applied to other devices and/or irradiation conditions
Nonradiating Photonics with Resonant Dielectric Nanostructures
Nonradiating sources of energy have traditionally been studied in quantum
mechanics and astrophysics, while receiving a very little attention in the
photonics community. This situation has changed recently due to a number of
pioneering theoretical studies and remarkable experimental demonstrations of
the exotic states of light in dielectric resonant photonic structures and
metasurfaces, with the possibility to localize efficiently the electromagnetic
fields of high intensities within small volumes of matter. These recent
advances underpin novel concepts in nanophotonics, and provide a promising
pathway to overcome the problem of losses usually associated with metals and
plasmonic materials for the efficient control of the light-matter interaction
at the nanoscale. This review paper provides the general background and several
snapshots of the recent results in this young yet prominent research field,
focusing on two types of nonradiating states of light that both have been
recently at the center of many studies in all-dielectric resonant meta-optics
and metasurfaces: optical {\em anapoles} and photonic {\em bound states in the
continuum}. We discuss a brief history of these states in optics, their
underlying physics and manifestations, and also emphasize their differences and
similarities. We also review some applications of such novel photonic states in
both linear and nonlinear optics for the nanoscale field enhancement, a design
of novel dielectric structures with high- resonances, nonlinear wave mixing
and enhanced harmonic generation, as well as advanced concepts for lasing and
optical neural networks.Comment: 22 pages, 9 figures, review articl
- …