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1. Ensemble GaAsSb/GaAs axial configured nanowire-based separate absorption, charge, and multiplication avalanche near-infrared photodetectors

   https://doi.org/10.1039/D2NA00359G  

   Parakh, M.; Pokharel, R.; Dawkins, K.; Devkota, S.; Li, J.; Iyer, S. (January 2022, Nanoscale Advances)

   In this study, molecular beam epitaxially grown axially configured ensemble GaAsSb/GaAs separate absorption, charge, and multiplication (SACM) region-based nanowire avalanche photodetector device on non-patterned Si substrate is presented. Our device exhibits a low breakdown voltage ( V BR ) of ∼ −10 ± 2.5 V under dark, photocurrent gain ( M ) varying from 20 in linear mode to avalanche gain of 700 at V BR at a 1.064 μm wavelength. Positive temperature dependence of breakdown voltage ∼ 12.6 mV K −1 further affirms avalanche breakdown as the gain mechanism in our SACM NW APDs. Capacitance–voltage ( C – V ) and temperature-dependent noise characteristics also validated punch-through voltage ascertained from I – V measurements, and avalanche being the dominant gain mechanism in the APDs. The ensemble SACM NW APD device demonstrated a broad spectral room temperature response with a cut-off wavelength of ∼1.2 μm with a responsivity of ∼0.17–0.38 A W −1 at −3 V. This work offers a potential pathway toward realizing tunable nanowire-based avalanche photodetectors compatible with traditional Si technology. 

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2. Stretchable and Transparent Metal Nanowire Microelectrodes for Simultaneous Electrophysiology and Optogenetics Applications

   https://doi.org/10.3390/photonics8060220  

   Tian, Jinbi; Lin, Zexu; Chen, Zhiyuan; Obaid, Sofian N.; Efimov, Igor R.; Lu, Luyao (June 2021, Photonics)

   Recently developed optically transparent microelectrode technology provides a promising approach for simultaneous high-resolution electrical and optical biointerfacing with tissues in vivo and in vitro. A critically unmet need is designing high-performance stretchable platforms for conformal biointerfacing with mechanically active organs. Here, we report silver nanowire (Ag NW) stretchable transparent microelectrodes and interconnects that exhibit excellent electrical and electrochemical performance, high optical transparency, superior mechanical robustness and durability by a simple selective-patterning process. The fabrication method allows the direct integration of Ag NW networks on elastomeric substrates. The resulting Ag NW interface exhibits a low sheet resistance (Rsh) of 1.52–4.35 Ω sq−1, an advantageous normalized electrochemical impedance of 3.78–6.04 Ω cm2, a high optical transparency of 61.3–80.5% at 550 nm and a stretchability of 40%. The microelectrode arrays (MEAs) fabricated with this approach exhibit uniform electrochemical performance across all channels. Studies on mice demonstrate that both pristine and stretched Ag NW microelectrodes can achieve high-fidelity electrophysiological monitoring of cardiac activity with/without co-localized optogenetic pacing. Together, these results pave the way for developing stretchable and transparent metal nanowire networks for high-resolution opto-electric biointerfacing with mechanically active organs, such as the heart. 

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3. Gallium Nitride (GaN) Nanostructures and Their Gas Sensing Properties: A Review

   https://doi.org/10.3390/s20143889  

   Khan, Md Ashfaque; Rao, Mulpuri V. (July 2020, Sensors)

   null (Ed.)

   In the last two decades, GaN nanostructures of various forms like nanowires (NWs), nanotubes (NTs), nanofibers (NFs), nanoparticles (NPs) and nanonetworks (NNs) have been reported for gas sensing applications. In this paper, we have reviewed our group’s work and the works published by other groups on the advances in GaN nanostructures-based sensors for detection of gases such as hydrogen (H2), alcohols (R-OH), methane (CH4), benzene and its derivatives, nitric oxide (NO), nitrogen dioxide (NO2), sulfur-dioxide (SO2), ammonia (NH3), hydrogen sulfide (H2S) and carbon dioxide (CO2). The important sensing performance parameters like limit of detection, response/recovery time and operating temperature for different type of sensors have been summarized and tabulated to provide a thorough performance comparison. A novel metric, the product of response time and limit of detection, has been established, to quantify and compare the overall sensing performance of GaN nanostructure-based devices reported so far. According to this metric, it was found that the InGaN/GaN NW-based sensor exhibits superior overall sensing performance for H2 gas sensing, whereas the GaN/(TiO2–Pt) nanowire-nanoclusters (NWNCs)-based sensor is better for ethanol sensing. The GaN/TiO2 NWNC-based sensor is also well suited for TNT sensing. This paper has also reviewed density-functional theory (DFT)-based first principle studies on the interaction between gas molecules and GaN. The implementation of machine learning algorithms on GaN nanostructured sensors and sensor array has been analyzed as well. Finally, gas sensing mechanism on GaN nanostructure-based sensors at room temperature has been discussed. 

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4. Resistance of single domain walls in half-metallic CrO ₂ epitaxial nanostructures

   https://doi.org/10.1039/d1nr05555k  

   Qian, Lijuan; Zhou, Shiyu; Wang, Kang; Xiao, Gang (December 2021, Nanoscale)

   Magnetic domain structures are active electron transport agents and can be used to induce large magnetoresistance (MR), particularly in half-metallic solids. We have studied the excess resistance induced by a single magnetic domain wall in a one-dimensional half-metallic CrO 2 nanoscale conductor with a built-in constriction whose channel width ( d ) ranges from 30 to 200 nm. We observed that the domain wall-induced MR is enhanced by 70 fold when d decreases from 200 nm to 30 nm. We speculate that the enhancement is due to the increased domain wall resistance (DWR) and the extra contribution of ballistic magnetoresistance (BMR). We have uncovered a large size effect of d on the MR induced by the domain wall, which scales with d as d −1.87±0.32 . Accordingly, we predict that the MR ratio of a simple CrO 2 nanowire impregnated with a constriction at a 150 nm 2 cross-section could reach 100%. This large MR far exceeds that of a conventional ferromagnetic nanowire, confirming the role of half metallicity on enhanced magneto-transport. 

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5. Molecular composition of comet 46P/Wirtanen from millimetre-wave spectroscopy

   https://doi.org/10.1051/0004-6361/202040125  

   Biver, N.; Bockelée-Morvan, D.; Boissier, J.; Moreno, R.; Crovisier, J.; Lis, D. C.; Colom, P.; Cordiner, M. A.; Milam, S. N.; Roth, N. X.; et al (April 2021, Astronomy & Astrophysics)

   null (Ed.)

   We present the results of a molecular survey of comet 46P/Wirtanen undertaken with the IRAM 30-m and NOEMA radio telescopes in December 2018. Observations at IRAM 30-m during the 12–18 December period comprise a 2 mm spectral survey covering 25 GHz and a 1 mm survey covering 62 GHz. The gas outflow velocity and kinetic temperature have been accurately constrained by the observations. We derive abundances of 11 molecules, some being identified remotely for the first time in a Jupiter-family comet, including complex organic molecules such as formamide, ethylene glycol, acetaldehyde, or ethanol. Sensitive upper limits on the abundances of 24 other molecules are obtained. The comet is found to be relatively rich in methanol (3.4% relative to water), but relatively depleted in CO, CS, HNC, HNCO, and HCOOH. 

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