Light management is one of the main challenges to address when designing a sensor from a nanocrystal (NC) array. Indeed, the carrier diffusion length, limited by hopping mechanism, is much shorter than the absorption depth. Several types of resonators (plasmon, Bragg mirror, guided mode, Fabry–Perot cavity) have been proposed to reduce the volume where light is absorbed. All of them are inherently narrow bands, while imaging applications focus on broadband sensing. Here, an infrared sensor in the short and mid‐wave infrared (SWIR and MWIR) that combines three different photonic modes is proposed to achieve broadband enhancement of the light absorption. Moreover, it is shown that these three modes can be obtained from a simple structure where the NC film is coupled only to a grating and a top metallic layer. The obtained device achieves a high responsivity of >700 mA W–1, a detectivity up to 2 × 1010 Jones at 80 K, and a short response time of 11 µs.
The present paper is concerned with a special group of approximants with B2 superstructures. In the first part, recent work on structural features of the B2 superstructure approximants is summarized. Experimental results obtained in AI-Cu-Mn and AI-Cu systems are presented, where a series of B2-based approximants are observed. These phases all have similar valence electron concentrations, in full support of the e/a-constant definition of approximants. Special emphasis is laid on the chemical twinning modes of the B2 basic structure in relation to the AI-Cu approximants. It is revealed that the B2 twinning mode responsible for the formation of local pentagonal atomic arrangements is of 180°/[111] type. This is also the origin of 5-fold twinning of the B2 phase on quasicrystal surfaces. Crystallographic features of phases B2, ~2, z3, y, and other newly discovered phases are also discussed. In all these phases, local pentagonal configurations are revealed. In the second part, dry trihological properties of some AICuFe samples containing the B2-type phases are presented. The results indicated that the B2 phase having their valence ratio near that of the quasicrystal possesses low friction coefficient under various loads, comparable with the annealed quasicrystalllne ingot. Such a result indicates that the B2-type phase with e/a near that of quasicrystal is indeed an approximant, which is in full support of the valence electron criterion for approximants.
Thanks to their narrow band gap nature
and fairly high carrier
mobility, HgTe nanocrystals (NCs) are of utmost interest for optoelectronics
beyond the telecom window (λ > 1.55 μm). In particular,
they offer an interesting cost-effective alternative to the well-developed
InGaAs technology. However, in contrast to PbS, far less work has
been dedicated to the integration of this material in photodiodes.
In the short-wave infrared region, HgTe NCs have a more p-type character than in the mid-wave infrared region, thus promoting
the development of new electron transport layers with an optimized
band alignment. As for perovskites, HgTe NCs present a fairly deep
band gap with respect to vacuum. Thus, we were motivated by the strategy
developed for perovskite solar cells, for which SnO2 has
led to the best performing devices. Here, we explore the following
stack made of SnO2/HgTe/Ag2Te, in which the
SnO2 and Ag2Te layers behave as electron and
hole extractors, respectively. Using X-ray photoemission, we show
that SnO2 presents a nearly optimal band alignment with
HgTe to efficiently filter the hole dark current while letting the
photoelectrons flow. The obtained I–V curve exhibits an increased rectifying behavior, and the
diode stack presents a high internal efficiency for the diode (above
60%) and an external quantum efficiency that is mostly limited by
the absorption magnitude. Furthermore, we tackle a crucial challenge
for the transfer of such a diode onto readout circuits, which prevents
back-side illumination. We also demonstrate that the diode stack is
reversible with a partially transparent conducting electrode on the
top, while preserving the device’s responsivity. Finally, we
show that such a SnO2 layer is also beneficial for electron
injection and leads to an enhanced electroluminescence signal as the
diode is operated under forward bias. This work is an essential step
toward the design of a focal plane array with a HgTe NC-based photodiode.
The integration of photonic structures
in nanocrystal (NC)-based
photodetectors has been demonstrated to improve device performances.
Furthermore, bias-dependent photoresponse can be observed in such
devices as a result of the interplay between hopping transport and
inhomogeneous electromagnetic field. Here, we investigate the main
physical concepts leading to a voltage-dependent photoresponse. We
first bring evidence of bias-dependent carrier mobilities in a NC
array over a wide range of temperatures. Then, we fabricate an infrared
sensing device using HgTe NCs, where the electrodes also play the
role of a grating, inducing a spatially inhomogeneous absorption.
The obtained device exhibits a significant bias-dependent photoresponse
while possessing a competitive detection performance in the extended
short-wave and mid-wave infrared, with detectivity reaching 7 ×
1010 Jones at 80 K and a fast response time of around 70
ns. This work provides the foundation for further advancements in
NC-based-active photonics devices.
Purpose
The purpose of this paper is to evaluate the effect of micro-nano mixed super-hydrophobic structure on corrosion resistance and mechanism of magnesium alloys.
Design/methodology/approach
A super-hydrophobic surface was fabricated on AZ91 and WE43 magnesium alloys by laser etching and micro-arc oxidation (MAO) with SiO2 nanoparticles coating and low surface energy material modification. The corrosion resistance properties of the prepared super-hydrophobic surfaces were studied based on polarization curves and immersion tests.
Findings
Compared with bare substrates, the corrosion resistance of super-hydrophobic surfaces was improved significantly. The corrosion resistance of super-hydrophobic surface is related to micro-nano composite structure, static contact angle and pretreatment method. The more uniform the microstructure and the larger the static contact angle, the better the corrosion resistance of the super-hydrophobic surface. The corrosion resistance of super-hydrophobic by MAO is better than that of laser machining. Corrosion of super-hydrophobic surface can be divided into air valley action, physical shielding, pretreatment layer action and substrate corrosion.
Originality/value
The super-hydrophobic coatings can reduce the contact of matrix with water so that a super-hydrophobic coating would be an effective way for magnesium alloy anti-corrosion. Therefore, the corrosion resistance properties and mechanism of the prepared super-hydrophobic magnesium alloys were investigated in detail.
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