238,652 research outputs found
Optimized Superconducting Nanowire Single Photon Detectors to Maximize Absorptance
Dispersion characteristics of four types of superconducting nanowire single
photon detectors, nano-cavity-array- (NCA-), nano-cavity-deflector-array-
(NCDA-), nano-cavity-double-deflector-array- (NCDDA-) and
nano-cavity-trench-array- (NCTA-) integrated (I-A-SNSPDs) devices was optimized
in three periodicity intervals commensurate with half-, three-quarter- and one
SPP wavelength. The optimal configurations capable of maximizing NbN
absorptance correspond to periodicity dependent tilting in S-orientation
(90{\deg} azimuthal orientation). In NCAI-A-SNSPDs absorptance maxima are
reached at the plasmonic Brewster angle (PBA) due to light tunneling. The
absorptance maximum is attained in a wide plasmonic-pass-band in
NCDAI_1/2*lambda-A, inside a flat-plasmonic-pass-band in NCDAI_3/4*lambda-A and
inside a narrow plasmonic-band in NCDAI_lambda-A. In NCDDAI_1/2*lambda-A bands
of strongly-coupled cavity and plasmonic modes cross, in NCDDAI_3/4*lambda-A an
inverted-plasmonic-band-gap develops, while in NCDDAI_lambda-A a narrow
plasmonic-pass-band appears inside an inverted-minigap. The absorptance maximum
is achieved in NCTAI_1/2*lambda-A inside a plasmonic-pass-band, in
NCTAI_3/4*lambda-A at inverted-plasmonic-band-gap center, while in
NCTAI_lambda-A inside an inverted-minigap. The highest 95.05% absorptance is
attained at perpendicular incidence onto NCTAI_lambda-A. Quarter-wavelength
type cavity modes contribute to the near-field enhancement around NbN segments
except in NCDAI_lambda-A and NCDDAI_3/4*lambda-A. The polarization contrast is
moderate in NCAI-A-SNSPDs (~10^2), NCDAI- and NCDDAI-A-SNSPDs make possible to
attain considerably large polarization contrast (~10^2-10^3 and ~10^3-10^4),
while NCTAI-A-SNSPDs exhibit a weak polarization selectivity (~10-10^2).Comment: 26 pages, 8 figure
Maximizing the quality factor to mode volume ratio for ultra-small photonic crystal cavities
Small manufacturing-tolerant photonic crystal cavities are systematically
designed using topology optimization to enhance the ratio between quality
factor and mode volume, Q/V. For relaxed manufacturing tolerance, a cavity with
bow-tie shape is obtained which confines light beyond the diffraction limit
into a deep-subwavelength volume. Imposition of a small manufacturing tolerance
still results in efficient designs, however, with diffraction-limited
confinement. Inspired by numerical results, an elliptic ring grating cavity
concept is extracted via geometric fitting. Numerical evaluations demonstrate
that for small sizes, topology-optimized cavities enhance the Q/V-ratio by up
to two orders of magnitude relative to standard L1 cavities and more than one
order of magnitude relative to shape-optimized L1 cavities. An increase in
cavity size can enhance the Q/V-ratio by an increase of the Q-factor without
significant increase of V. Comparison between optimized and reference cavities
illustrates that significant reduction of V requires big topological changes in
the cavity
Hydrogen Fluoride Capture by Imidazolium Acetate Ionic Liquid
Extraction of hydrofluoric acid (HF) from oils is a drastically important
problem in petroleum industry, since HF causes quick corrosion of pipe lines
and brings severe health problems to humanity. Some ionic liquids (ILs)
constitute promising scavenger agents thanks to strong binding to polar
compounds and tunability. PM7-MD simulations and hybrid density functional
theory are employed here to consider HF capture ability of ILs. Discussing the
effects and impacts of the cation and the anion separately and together, I will
evaluate performance of imidazolium acetate and outline systematic search
guidelines for efficient adsorption and extraction of HF
Importance of van der Waals interactions for ab initio studies of topological insulators
We investigate the lattice and electronic structures of the bulk and surface
of the prototypical layered topological insulators BiSe and
BiTe using ab initio density functional methods, and systematically
compare the results of different methods of including van der Waals (vdW)
interactions. We show that the methods utilizing semi-empirical energy
corrections yield accurate descriptions of these materials, with the most
precise results obtained by properly accounting for the long-range tail of the
vdW interactions. The bulk lattice constants, distances between quintuple
layers and the Dirac velocity of the topological surface states (TSS) are all
in excellent agreement with experiment. In BiTe, hexagonal warping of
the energy dispersion leads to complex spin textures of the TSS at moderate
energies, while in BiSe these states remain almost perfectly helical
away from the Dirac point, showing appreciable signs of hexagonal warping at
much higher energies, above the minimum of the bulk conduction band. Our
results establish a framework for unified and systematic self-consistent first
principles calculations of topological insulators in bulk, slab and interface
geometries, and provides the necessary first step towards ab initio modeling of
topological heterostructures.Comment: 26 pages, 7 figures. This is the Accepted Manuscript version of an
article accepted for publication in Journal of Physics: Condensed Matter. IOP
Publishing Ltd is not responsible for any errors or omissions in this version
of the manuscript or any version derived from it. The Version of Record is
available online at https://dx.doi.org/10.1088/1361-648X/abbdb
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