391 research outputs found
Enhancement of optical response in nanowires by negative-tone PMMA lithography
The method of negative-tone-PMMA electron-beam lithography is investigated to
improve the performance of nanowire-based superconducting detectors. Using this
approach, the superconducting nanowire single-photon detectors (SNSPDs) have
been fabricated from thick 5-nm NbN film sputtered at the room temperature. To
investigate the impact of this process, SNSPDs were prepared by positive-tone
and negative-tone-PMMA lithography, and their electrical and photodetection
characteristics at 4.2 K were compared. The SNSPDs made by negative-tone-PMMA
lithography show higher critical-current density and higher photon count rate
at various wavelengths. Our results suggest a higher negative-tone-PMMA
technology may be preferable to the standard positive-tone-PMMA lithography for
this application
Measuring thickness in thin NbN films for superconducting devices
We present the use of a commercially available fixed-angle multi-wavelength
ellipsometer for quickly measuring the thickness of NbN thin films for the
fabrication and performance improvement of superconducting nanowire single
photon detectors. The process can determine the optical constants of absorbing
thin films, removing the need for inaccurate approximations. The tool can be
used to observe oxidation growth and allows thickness measurements to be
integrated into the characterization of various fabrication processes
Optimized polar-azimuthal orientations for polarized light illumination of different Superconducting Nanowire Single-Photon Detector designs
The optimal orientations are determined for polarized substrate side
illumination of three superconducting nanowire single-photon detector (SNSPD)
designs: (1) periodic niobium-nitride (NbN) stripes standing in air with
dimensions according to conventional SNSPDs, (2) same NbN patterns below
~quarter-wavelength hydrogensilsesquioxane-filled nano-cavity, (3) analogous
NbN patterns in HSQ nano-cavity closed by a thin gold reflector. Numerical
computation results have shown that the optical response and near-field
distribution vary significantly with polar-angle, fi, and these variations are
analogous across all azimuthal-angles, gamma, but are fundamentally different
in various device designs. Larger absorptance is available due to p-polarized
illumination of NbN patterns in P-structure configuration, while s-polarized
illumination results in higher absorptance in S-structure arrangement. As a
result of p-polarized illumination a global maximum appears on absorptance of
bare NbN pattern at polar angle corresponding to NbN-related ATIR; integration
with HSQ nano-cavity results in a global absorptance maximum at polar angle
corresponding to TIR at sapphire-air interface; while the highest absorptance
is observable at perpendicular incidence on P-structures aligned below gold
reflector covered HSQ nano-cavity. S-polarized light illumination results in a
global absorptance maximum at TIR on bare NbN patterns; the highest absorptance
is available below HSQ nano-cavity at polar angle corresponding to ATIR
phenomenon; while the benefit of gold reflector is large and polar angle
independent absorptance.Comment: 24 pages, 7 figure
Source shot noise mitigation in scanned beam microscopy
Accepted manuscrip
Frequency pulling and mixing of relaxation oscillations in superconducting nanowires
Many superconducting technologies such as rapid single flux quantum computing
(RSFQ) and superconducting quantum interference devices (SQUIDs) rely on the
modulation of nonlinear dynamics in Josephson junctions for functionality. More
recently, however, superconducting devices have been developed based on the
switching and thermal heating of nanowires for use in fields such as single
photon detection and digital logic. In this paper, we use resistive shunting to
control the nonlinear heating of a superconducting nanowire and compare the
resulting dynamics to those observed in Josephson junctions. We show that
interaction of the hotspot growth with the external shunt produces high
frequency relaxation oscillations with similar behavior as observed in
Josephson junctions due to their rapid time constants and ability to be
modulated by a weak periodic signal. In particular, we use a microwave drive to
pull and mix the oscillation frequency, resulting in phase locked features that
resemble the AC Josephson effect. New nanowire devices based on these
conclusions have promising applications in fields such as parametric
amplification and frequency multiplexing
Drift Correction for Scanning-Electron Microscopy by
Scanning electron micrographs at high magnification (100,000x and up) are distorted by motion of the sample during image acquisition, a phenomenon called drift. We propose a method for correcting drift distortion in images obtained on scanning electron and other scanned-beam microscopes by registering a series of images to create a drift-free composite. We develop a drift-distortion model for linear drift and use it as a basis for an affine correction between images in the sequence. The performance of our correction method is evaluated with simulated datasets and real datasets taken on both scanning electron and scanning helium-ion microscopes; we compare performance against translation only correction. In simulation, we exhibit a 12.5 dB improvement in SNR of our drift-corrected composite compared to a non-aligned composite, and a 3 dB improvement over translation correction. A more modest 0.
A nanofabricated, monolithic, path-separated electron interferometer
We report a self-aligned, monolithic electron interferometer, consisting of
two 45 nm thick silicon layers separated by 20 m. This interferometer was
fabricated from a single crystal silicon cantilever on a transmission electron
microscope grid by gallium focused ion-beam milling. Using this interferometer,
we demonstrate beam path-separation, and obtain interference fringes in a
Mach-Zehnder geometry, in an unmodified 200 kV transmission electron
microscope. The fringes have a period of 0.32 nm, which corresponds to the
lattice planes of silicon, and a maximum
contrast of 15 %. This design can potentially be scaled to millimeter-scale,
and used in electron holography. It can also be applied to perform fundamental
physics experiments, such as interaction-free measurement with electrons.Comment: 21 pages (including supplementary info), 8 figures; Corrected typos,
added references for introduction and conclusion, changed ordering of
paragraphs of Discussion, results unchange
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