Low NEP Research Articles

Plasmonic hot electron-induced WO3 films for a highly responsive visible photodetector

Visible photodetectors have found significant applications in various fields that require rapid and precise detection of visible light. These fields encompass optical communication, high-speed imaging, LIDAR systems, biomedical imaging, and industrial process monitoring. Semiconductors play a crucial role in photodetection applications by efficiently converting light into electrical signals, offering high sensitivity and rapid response time. Among various semiconductor metal oxides, WO3 is commonly used as a visible photodetector due to its unique properties like high chemical & thermal stability, and it possesses a direct bandgap making it suitable for efficient detection of visible light. Here we report the surface plasmon resonance induced visible light detection using Au NPs on WO3 film. The WO3 film was grown on SiO2 substrate by DC magnetron sputtering while monodispersed (⁓20 nm) Au NPs were chemically synthesised. MSM based Au NPs functionalized WO3 film was tested under 455 nm wavelength with changing optical power and applied bias. The interaction of Au NPs and visible light lead to generation of hot electrons leading to enhancement in the photocurrent. The fabricated device exhibits large bias-dependent responsivity, low NEP, and high EQE of 23.45 A/W, 2.6 × 10−13 WHz−1/2, and 126%, respectively. The study not only provides understanding of plasmon-enhanced visible light detection but also underscores the significance of Au NPs as a powerful tool for enhancing the performance of WO3-based visible photodetectors. The implications of this study extend beyond fundamental research, paving the way for novel applications in the field of optoelectronics appliances.

Genetic diversity, asexual reproduction and conservation of the edible fruit tree Spondias purpurea L. (Anacardiaceae) in the Costa Rican tropical dry forest.

The term circa situm has been used to describe different conservation strategies within agricultural landscapes. Circa situm conserves planted or remnant species in farmlands, where natural vegetation has been modified through anthropogenic intervention. It has been proposed that trees planted or retained under circa situm conditions may contribute to maintaining genetic diversity, however information on the role of this strategy in preserving genetic diversity is scarce. The aim of this study was to determine the levels of genetic diversity and structure, and mating patterns in planted and unmanaged stands of the tropical fruit tree Spondias purpurea L. in north western Costa Rica. In three localities, we used seven polymorphic microsatellite loci and genotyped 201 adults and 648 seeds from planted and wild stands. We found no differences in genetic diversity among planted and wild stands. Genetic structure analysis revealed that gene flow occurs among planted and wild stands within localities. Clones were present and their diversity and evenness were both high and similar between planted and wild stands. The number of pollen donors per progeny array was low (Nep = 1.01) which resulted in high levels of correlated paternity (rp = 0.9). Asexual seeds were found in 4.6% of the progeny arrays, which had multilocus genotypes that were identical to the maternal trees. Our results show that although planted stands under circa situm conditions can maintain similar levels of genetic diversity than wild stands, the low number of sires and asexual seed formation could threaten the long term persistence of populations.

MoS2-on-GaN Plasmonic Photodetector Using a Bowtie Striped Antenna Structure

The layered semiconductor material molybdenum disulfide (MoS2) has led to an upsurge in research for applications in optoelectric devices that benefit from its excellent optical and electrical properties. The application of the plasmonic structure to enhance light–matter interaction and intensity of the light field via localized surface plasmon resonance provides a promising method for MoS2-based devices for improving performance. In this work, we have prepared a plasmon-enhanced few-layer MoS2 photodetector based on a gallium nitride substrate using a bowtie equal grid antenna structure, and the large-scale few-layer MoS2 growth on the GaN substrate is realized by chemical vapor deposition. The enhancement MoS2 plasmonic photodetector achieves a high responsivity R of 0.82 A/W, a low noise equivalent power NEP of 6.58 × 10–14 W/Hz1/2, and a detectivity of 1.56 × 1012 Jones under 365 nm at 5 V bias and a corresponding rise/fall time of 18/10 ms. With the enhanced performance of the photodetector demonstrated, the as-fabricated plasmonic structure proposed a feasibility method to achieve enhanced photoresponse and is applicable to other high-efficiency photoelectric devices.

Ultra-sensitive THz microwave kinetic inductance detectors for future space telescopes

Aims. Future actively cooled space-borne observatories for the far-infrared, loosely defined as a 1–10 THz band, can potentially reach a sensitivity limited only by background radiation from the Universe. This will result in an increase in observing speed of many orders of magnitude. A spectroscopic instrument on such an observatory requires large arrays of detectors with a sensitivity expressed as a noise equivalent power NEP = 3 × 10−20 W/√Hz. Methods. We present the design, fabrication, and characterisation of microwave kinetic inductance detectors (MKIDs) for this frequency range reaching the required sensitivity. The devices are based on thin-film NbTiN resonators which use lens-antenna coupling to a submicron-width aluminium transmission line at the shorted end of the resonator where the radiation is absorbed. We optimised the MKID geometry for a low NEP by using a small aluminium volume of ≈1 µm3 and fabricating the aluminium section on a very thin (100 nm) SiN membrane. Both methods of optimisation also reduce the effect of excess noise by increasing the responsivity of the device, which is further increased by reducing the parasitic geometrical inductance of the resonator. Results. We measure the sensitivity of eight MKIDs with respect to the power absorbed in the detector using a thermal calibration source filtered in a narrow band around 1.5 THz. We obtain a NEPexp(Pabs) = 3.1 ± 0.9 × 10−20 W/√Hz at a modulation frequency of 200 Hz averaged over all measured MKIDs. The NEP is limited by quasiparticle trapping. Conclusions. The measured sensitivity is sufficient for spectroscopic observations from future, actively cooled space-based observatories. Moreover, the presented device design and assembly can be adapted for frequencies up to ≈10 THz and can be readily implemented in kilopixel arrays.

Improved photodetection capabilities of Ag@CeO2 Nanorod composite array using GLAD technique

This work reports the growth of an Ag@CeO2 nanorod (NR) composite array using the glancing angle deposition (GLAD) technique for UV photodetector application. It showed improvement in performance by decorating plasmonic nanoparticles (NPs) on the semiconductor surface. The interaction between the plasmonic NPs and the semiconductor under the influence of light manifested a localised surface plasmon resonance (LSPR) effect. This allowed for strong absorption, scattering and inducement of an intense electric field, which resulted in the enhancement of photocurrent and, consequently, the device performance. The use of the GLAD technique also allowed the growth of vertically oriented NR composite structures, which assisted in increased absorption. It was found that the fabricated structure exhibited an increase in the responsivity at 370 nm with a value of 18.74 AW-1 as compared to the previous work of only 4.51 AW-1. A comparably high detectivity of 3.94 × 1012 Jones and a low NEP value of 10.67 fW at −6 V were also exhibited by the device on account of low dark current and enhanced photocurrent. The maximum internal gain obtained for the device was 62.92. The presence of Ag NPs all around the semiconductor NR structure had led to a substantial increase in the photoresponse with a rise time and fall time of 65 ms and 58 ms respectively. These results are believed to offer new ways of harnessing light to boost the functioning of 1D nanostructure-based UV photodetectors.

Low-Noise Balanced Photoreceiver With InP-on-Si Photodiodes and SiGe BiCMOS Transimpedance Amplifier

A photoreceiver consisting of indium phosphide (InP) balanced photodiodes (PD) on Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> waveguides and a transimpedance amplifier (TIA) fabricated in a silicon germanium (SiGe) BiCMOS process is demonstrated. The InP PDs, heterogeneously integrated on a silicon substrate, achieve external (internal) responsivities of 0.75 (0.9) A/W, bandwidths of 4 GHz, and common mode rejection ratios (CMRR) of greater than 40 dB when illuminated differentially. The TIA achieves 74 dBΩ of transimpedance gain with a 1 dB peak, a bandwidth of 3 GHz, and a low equivalent input noise current density of 7.2 pA/√{Hz} when loaded with a C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">PD</sub> of 380 fF. The full photoreceiver achieves high conversion gain of more than 2 kV/W up through 2 GHz, and a low NEP of 8 pW/√{Hz} up through 1.6 GHz. The photoreceiver optical CMRR is measured to be 36 dB.

Extending KIDs to the Mid-IR for Future Space and Suborbital Observatories

The galaxy evolution probe (GEP) is a concept for a probe-class space observatory to study the physical processes related to star formation over cosmic time. To do so, the mid- and far-infrared (IR) spectra of galaxies must be studied. These mid- and far-IR observations require large multi-frequency arrays, sensitive detectors. Our goal is to develop low NEP aluminum kinetic inductance detectors (KIDs) for wavelengths of 10–400 {upmu }{{hbox {m}}} for the GEP and a pathfinder long-duration balloon (GEP-B) that will perform precursor GEP science. KIDs for the lower wavelength range (10–100 {upmu }{{hbox {m}}}) have not been previously implemented. We present an absorber design for KIDs sensitive to wavelengths of 10 {upmu }{{hbox {m}}} shown to have around 75–80% absorption efficiency through ANSYS HFSS (high-frequency structure simulator) simulations, challenges that come with optimizing our design to increase the wavelength range, initial tests on our design of fabricated 10 {upmu }{{hbox {m}}} KIDs, and theoretical NEP calculations.

AC Bias Characterization of Low Noise Bolometers for SAFARI Using an Open-Loop Frequency Domain SQUID-based Multiplexer Operating Between 1 and 5 MHz

SRON is developing the Frequency Domain Multiplexing (FDM) read-out and the ultra low NEP TES bolometers array for the infra-red spectrometer SAFARI on board of the Japanese space mission SPICA. The FDM prototype of the instrument requires critical and complex optimizations. For single pixel characterization under AC bias we are developing a simple FDM system working in the frequency range from 1 to 5 MHz, based on the open loop read-out of a linearized two-stage SQUID amplifier and high Q lithographic LC resonators. We describe the details of the experimental set-up required to achieve low power loading (<1 fW) and low noise ( $\mathrm{NEP}\sim 10^{-19}~\mathrm{W}/\sqrt{\mathrm{Hz}}$ ) in the TES bolometers. We conclude the paper by comparing the performance of a $4\times 10^{-19}~\mathrm{W}/\sqrt{\mathrm{Hz}}$ TES bolometer measured under DC and AC bias.

Registration of TTU 0782, an Upland Cotton Germplasm Line with Superior Fiber Quality

Improvement of fiber quality is essential if cotton farmers in the United States are to compete in the world market. A high‐quality cotton (Gossypium hirsutum L.) germplasm designated as TTU 0782 (Reg. No. GP‐930, PI 659504) was developed and released by the Department of Soil Science, Texas Tech University, on 25 May 2010. TTU 0782 was derived from the cross of TTU 202‐1107B with ‘Acala 1517‐95’, and it possesses highly favorable fiber length, high fiber‐bundle strength, and a desirable fiber‐length uniformity index as determined by high‐volume‐instrument testing. In addition, TTU 0782 exhibits low short‐fiber content, a high maturity ratio, and low nep counts as determined by the Advanced Fiber Information System. Spinning tests indicate that TTU 0782 had improved yarn tenacity and fewer thin and thick places, fewer neps, and less hairiness of yarn when compared with previously registered germplasm lines from Texas Tech University and with ‘FiberMax 958’.

Long‐pollen Movement and Deviation of Random Mating in a Low‐density Continuous Population of a Tropical Tree Hymenaea courbaril in the Brazilian Amazon

ABSTRACTMating system and pollen flow are two key elements to understand the genetic structure of tree species. Mating and pollen‐dispersal patterns of a low‐density population of bat pollinated Hymanea courbaril were examined before logging in a 546‐ha plot in the Brazilian Amazon. The multilocus genotypes of nine microsatellite loci were determined for 130 adult‐trees and 367 seeds collected from 20 seed‐trees. Mating system analysis, using mixed‐mating model and paternity analysis showed that the studied population is perfectly outcrossed (tm= 1.002), and probably self‐incompatible. However, significant deviations from random mating were detected for mating among relatives (tm−ts= 0.096, P &lt; 0.05) and correlated matings (rp= 0.289, P &lt; 0.05), indicating inbreeding in the population and that part of offspring are full‐sibs (28.9%). Inbreeding was reflected in the positive and significant fixation index observed in adult trees (F= 0.137, P &lt; 0.05), although no significant inbreeding was detected in offspring (F= 0.074, P &gt; 0.05). The effective number of pollen donors mating with each seed‐tree was determined to be low (Nep≈ 4). The average of pollen flow distance was measured inside of the plot by both paternity (827 ± 429 m) and TwoGener analysis (115–363 m). However, this underestimated pollen dispersal distance, since the detected rate of pollen immigration inside of the plot was high (55%). The observed long‐pollen dispersal distance is probably related to pollination by bats and the low density of reproductive trees in the site.

OVULE DISCOUNTING IN AN OUTCROSSING, CRYPTICALLY DIOECIOUS TREE

Abstract Ovule discounting denotes the reduction in the number of ovules available for cross-fertilization due to the interference of inferior pollen. Traditionally, ovule discounting has been discussed solely from the perspective of compromised outcrossing opportunities as a result of selfing, but the principle is more general. Here, we extend its applicability beyond the simple contrast between selfing and outcrossing by showing that, in the cryptically dioecious tree species Fraxinus ornus, ovule discounting through frequent outcrossing with inferior fathers also constitutes a substantial cost of mating. In F. ornus, hermaphrodites produce pollen capable of siring offspring, but these offspring are less viable than those sired by males and are inferred to produce few, if any, surviving progeny. In this paper, we used microsatellite markers to analyze the mating system and paternity in a wild population of F. ornus. We found that the effective number of sires per mother was low (Nep= 2.93 to 4.95), and that paternity was correlated among progeny sampled from the same mother, but not among progeny sampled from neighboring mothers. Despite the existence of a local spatial genetic structure (up to 30 m), we found no evidence of biparental inbreeding. There was negligible selfing by hermaphrodites, but they sired approximately one fourth of the seeds produced by other hermaphrodites. Given that these progeny are not inferred to reach reproductive maturity, this constitutes a substantial cost of ovule discounting in the broad sense. We discuss the possible reasons for why hermaphrodites invest resources into inferior pollen.

Reciprocal regulation of angiotensin converting enzyme and neutral endopeptidase in rats with experimental hypertension.

Angiotensin I is a substrate for both the angiotensin converting enzyme (ACE) and neutral endopeptidase 24.11 (NEP). The present study examined the hypothesis that a high ACE expression is associated with a low NEP activity. Male Sprague-Dawley rats had two-kidney, one-clip (2K1C), N(G)-nitro-L-arginine methyl ester (L-NAME) or deoxycorticosterone acetate (DOCA)-salt hypertension, which were either angiotensin-dependent or -independent. The expression of ACE and NEP mRNA was determined in the thoracic aorta by a reverse transcription-polymerase chain reaction. The catalytic activity of NEP was measured by fluorometry. The expression of ACE was increased in 2K1C and L-NAME hypertension, and decreased in DOCA-salt hypertension. Conversely, the expression of NEP was decreased in 2K1C and L-NAME hypertension, and increased in DOCA-salt hypertension. The catalytic activity of NEP was altered similarly as its expression. These results suggest that ACE expression is inversely related to vascular NEP activity in certain forms of hypertension.

Angiotensin I-converting enzyme modulates neutral endopeptidase activity in the rat.

Angiotensin I is a substrate for both ACE and for neutral endopeptidase 24.11 (NEP). We hypothesized that high ACE expression is related to low NEP activity. Accordingly, circulating and tissue NEP and ACE activities were measured by fluorometry in homozygous rats (F(0) and F(2)) for the Lewis microsatellite allele (LL, low ACE) and for the Brown Norway microsatellite allele (BB, high ACE). Plasma, lung, and aortic ACE activities in F(0) and F(2) were higher in BB rats than in LL rats (P<0.01), whereas left ventricular ACE activity was similar in both genotypes. In contrast, NEP activity in the LL group was higher in the serum, aorta, and lungs in F(0) and F(2) homozygous (P<0.05). Plasma ACE activity was inversely correlated with serum (r=-0.6 and -0.598 in F(0) and F(2), respectively; P<0.03) and lung NEP activities (r=-0.77 in F(0) and r=-0.59 in F(2), P<0.01). Aortic ACE and NEP activities were also correlated (r=-0.696 and -0.584 in F(0) and F(2), respectively; P<0.03). In conclusion, genetically determined high ACE expression in rats is inversely related to tissue NEP activity, which could determine lower angiotensin-(1-7) tissue levels.

Neutrophil neutral endopeptidase variation and its regulation by opioid peptides

The opioid peptide methionine-enkephalin (MENK) has significant immunomodulatory ability in addition to its neurotransmitter function. Since neutral endopeptidase (NEP, CD10, enkephalinase EC 3.4.24.11) cleaves opioid peptides, the presence and activity of NEP in neutrophils from different persons might be responsible for the diverse, neuropeptide-induced, responses of neutrophils from different donors [Ann. N. Y. Acad. Sci. 650 (1992) 146]. The results obtained showed statistically significant differences in NEP activity among donors (high, medium and low). A 10-fold higher NEP activity in neutrophils (160–280 nmol/10 6 cells/h) and in their corresponding membrane preparations (550 nmol/mg protein/min) in our study, as compared to literature data, was a result of high specificity and affinity of Suc-Ala-Ala-Phe–pNA as substrate. In control nontreated neutrophils, the number of CD10 positive cells were not correlated with NEP activity. However, in neutrophils treated with a physiological (10 −10 M) concentration of MENK, two main events occurred; not only did the number of CD10 positive cells correlate with NEP activity, but contrary to control samples, MENK upregulated the expression of CD10 marker as demonstrated by an increase of mean florescence intensity ( F-mean) in donors with low NEP activity. Taken together, these data add some clarity to the diverse activity of enkephalins in association with enzyme cleavage of those molecules.

Infrared detector fabricated by YBCO Josephson junctions in series

The infrared detectors were fabricated by YBCO bicrystal and step-edge junctions in series. The detectors exhibited an high responsivity of 780 V/W at 77K and low NEP of 9.0 × 10−13 W/√Hz. The optical response of the detectors below Tc is mainly of nonequilibrium origin.

A low noise highly integrated bolometer array for absolute measurement of VUV and soft x radiation

A new low noise miniaturized multichannel bolometer module for absolute measurements in the VUV and soft x spectral ranges is described. Highly integrated four-channel modules (2×3.3×1.5 cm3) each comprising four independent ac-excited (50 kHz) metal resistor bolometer bridges were successfully tested on a large tokamak (Tore Supra in Cadarache) and on an electron synchrotron (BESSY in Berlin). The bolometer system features a linear response to the absorbed radiation power, a low detection limit (≤1.0×10−6 W cm−2 on Tore Supra with an integration time of τint=10×10−3 s) and a low NEP (≤10×10−9 W on BESSY). The thermal cross-talk between adjacent detectors is negligible (&amp;lt;0.003) and a low thermal drift ΔUBr/ΔT &amp;lt; 10−4 V °C−1 is achieved. It can be operated at a maximum temperature of 150 °C, at high magnetic fields (tested up to B=4.5 T in the laboratory) and survives high nuclear radiation doses. The system offers the possibility of detecting low-power VUV and soft x-radiation with sampling rates of up to 10 kHz on plasma machines and of absolutely calibrating VUV and soft x instruments. Effective suppression of electric, thermal and nuclear radiation interferences is characteristic of the bolometer system.Strain gauge effects, which could affect the behavior of the bolometers at high magnetic fields, are suppressed by the ac-excitation technique.

EFFECT OF CRACKS ON THE PRESSURE-VELOCITY RELATIONSHIP OF AIR FORCED THROUGH BALED ALFALFA HAY

ABSTRACT Imperfections in lint cotton, particularly neps and seed-coat fragments, reduce processing efficiency in the textile mill and detract from appearance in yam and fabric. This study identified fiber properties and varieties which are consistently associated with low nep and seed-coat fragment levels in ginned lint, yam, and fabric. Growth conditions and maturity of the cottons were considered; the level of imperfections were measured in both dyed and undyed fabric. Correlations were determined and definite trends established between many of the variables. The information obtained will aid breeders in selecting for further development those cottons which have a low potential for imperfection formation during processing.

PROPENSITY OF COTTON VARIETIES TO NEPPINESS

ABSTRACT Imperfections in lint cotton, particularly neps and seed-coat fragments, reduce processing efficiency in the textile mill and detract from appearance in yam and fabric. This study identified fiber properties and varieties which are consistently associated with low nep and seed-coat fragment levels in ginned lint, yam, and fabric. Growth conditions and maturity of the cottons were considered; the level of imperfections were measured in both dyed and undyed fabric. Correlations were determined and definite trends established between many of the variables. The information obtained will aid breeders in selecting for further development those cottons which have a low potential for imperfection formation during processing.

Sensitive LiTaO3 pyroelectric detector

We have constructed and tested a sensitive LiTaO3 pyroelectric detector with a measured NEP of 1.3×10−10 W/(Hz)1/2, which is in good agreement with the theoretical value. LiTaO3 has the advantages of being nonhygroscopic, relatively insensitive to ambient temperature, and has sufficient mechanical strength to polish to 10-μ-thick samples. We show that no one figure of merit is sufficient for evaluating pyroelectric materials for use in low NEP detectors.

Radiant-Energy Detection by Superconducting Films

Superconducting films offer promise as fast, sensitive detectors at intermediate frequencies from millimeter waves to near infrared. The superconductor's marked temperature dependence of resistance about its transition temperature suggests that it would have a high responsivity as a bolometer, and operation at cryogenic temperatures suggests that a low NEP can be achieved. In addition, placing the sample in the liquid-helium bath should result in very short response times (τ) on the order of 10 nsec. Films have been studied with sheet resistances from 200 Ω/sq to &amp;gt; 1000 Ω/sq. These films achieve NEP ≈ 10−9 W·Hz−1/2 as bolometers with τ≈20 nsec. There is an enhanced microwave response, NEP ≈ 10−11 W·Hz−1/2 with τ = 20 nsec, which is especially pronounced for high-resistance films. This mode shows promise for use in the far-infrared and submillimeter region. The bolometer mode compares favorably with other bolometers.