Non-volatile rippled-assisted optoelectronic array for all-day motion detection and recognition.

In-sensor processing has the potential to reduce the energy consumption and hardware complexity of motion detection and recognition. However, the state-of-the-art all-in-one array integration technologies with simultaneous broadband spectrum image capture (sensory), image memory (storage) and image processing (computation) functions are still insufficient. Here, macroscale (2 × 2 mm2) integration of a rippled-assisted optoelectronic array (18 × 18 pixels) for all-day motion detection and recognition. The rippled-assisted optoelectronic array exhibits remarkable uniformity in the memory window, optically stimulated non-volatile positive and negative photoconductance. Importantly, the array achieves an extensive optical storage dynamic range exceeding 106, and exceptionally high room-temperature mobility up to 406.7 cm2 V-1 s-1, four times higher than the International Roadmap for Device and Systems 2028 target. Additionally, the spectral range of each rippled-assisted optoelectronic processor covers visible to near-infrared (405 nm-940 nm), achieving function of motion detection and recognition.

Unraveling the strain tuning mechanism of interlayer excitons in WSe2/MoSe2heterostructure.

Atomically thin transition metal dichalcogenides (TMDs) exhibit rich excitonic physics, due to reduced dielectric screening and strong Coulomb interactions. Especially, some attractive topics in modern condensed matter physics, such as correlated insulator, superconductivity, topological excitons bands, are recently reported in stacking two monolayer (ML) TMDs. Here, we clearly reveal the tuning mechanism of tensile strain on interlayer excitons (IEXs) and intralayer excitons (IAXs) in WSe2/MoSe2heterostructure (HS) at low temperature. We utilize the cryogenic tensile strain platform to stretch the HS, and measure by micro-photoluminescence (µ-PL). The PL peaks redshifts of IEXs and IAXs in WSe2/MoSe2HS under tensile strain are well observed. The first-principles calculations by using density functional theory reveals the PL peaks redshifts of IEXs and IAXs origin from bandgap shrinkage. The calculation results also show the Mo-4d states dominating conduction band minimum shifts of the ML MoSe2plays a dominant role in the redshifts of IEXs. This work provides new insights into understanding the tuning mechanism of tensile strain on IEXs and IAXs in two-dimensional (2D) HS, and paves a way to the development of flexible optoelectronic devices based on 2D materials.

Reconfigurable, non-volatile neuromorphic photovoltaics.

The neural network image sensor-which mimics neurobiological functions of the human retina-has recently been demonstrated to simultaneously sense and process optical images. However, highly tunable responsivity concurrent with non-volatile storage of image data in the neural network would allow a transformative leap in compactness and function of these artificial neural networks. Here, we demonstrate a reconfigurable and non-volatile neuromorphic device based on two-dimensional semiconducting metal sulfides that is concurrently a photovoltaic detector. The device is based on a metal-semiconductor-metal (MSM) two-terminal structure with pulse-tunable sulfur vacancies at the M-S junctions. By modulating sulfur vacancy concentrations, the polarities of short-circuit photocurrent can be changed with multiple stable magnitudes. The bias-induced motion of sulfur vacancies leads to highly reconfigurable responsivities by dynamically modulating the Schottky barriers. A convolutional neuromorphic network is finally designed for image processing and object detection using the same device. The results demonstrated that neuromorphic photodetectors can be the key components of visual perception hardware.

Synergistic effects of extrinsic photoconduction and photogating in a short-wavelength ZrS3 infrared photodetector.

Two-dimensional (2D) material-based photodetectors, especially those working in the infrared band, have shown great application potential in the thermal imaging, optical communication, and medicine fields. Designing 2D material photodetectors with broadened detection band and enhanced responsivity has become an attractive but challenging research direction. To solve this issue, we report a zirconium trisulfide (ZrS3) infrared photodetector with enhanced and broadened response with the assistance of the synergistic effects of extrinsic photoconduction and photogating effect. The ZrS3 photodetectors can detect infrared light up to 2 µm by extrinsic photoconduction and exhibit a responsivity of 100 mA W-1 under 1550 nm illumination. Furthermore, the ZrS3 infrared photodetectors with an oxide layer show a triple enhanced responsivity due to the photogating effect. Additionally, the infrared imaging capability of the ZrS3 infrared photodetectors is also demonstrated. This work provides a potential way to extend the response range and improve the responsivity for nanomaterial-based photodetectors at the same time.

First-Principles Study of Structural and Electronic Properties of Monolayer PtX2 and Janus PtXY (X, Y = S, Se, and Te) via Strain Engineering.

In this work, the structural parameters and electronic properties of PtX2 and Janus PtXY (X, Y = S, Se, and Te) are studied based on the density functional theory. The phonon spectra and the Born criteria of the elastic constant of these six monolayers confirm their stability. All PtX2 and Janus PtXY monolayers show an outstanding stretchability with Young's modulus ranging from 61.023 to 82.124 N/m, about one-fifth that of graphene and half that of MoS2, suggesting highly flexible materials. Our first-principles calculations reveal that the pristine PtX2 and their Janus counterparts are indirect semiconductors with their band gap ranging from 0.760 to 1.810 eV at the Perdew-Burke-Ernzerhof level (1.128-2.580 eV at the Heyd-Scuseria-Ernzerhof level). By applying biaxial compressive and tensile strain, the electronic properties of all PtX2 and Janus PtXY monolayers are widely tunable. Under small compressive strain, PtX2 and Janus PtXY structures remain indirect semiconductors. PtTe2, PtSeTe, and PtSTe monolayers undergo a semiconducting to metallic transition when the strain reaches -6, -8, and -10%, respectively. Interestingly, there is a transition from the indirect semiconductor to a quasi-direct one for all PtX2 and Janus PtXY monolayers when the tensile strain is applied.

Uniaxial Strain-Induced Tunable Mid-infrared Light Emission from Thin Film Black Phosphorus.

Strain engineering is a powerful tool that can modulate semiconductor device performance. Here, we demonstrate that the bandgap of thin film (∼40 nm) black phosphorus (bP) can be continuously tuned from 2.9 to 3.9 µm by applying an in-plane uniaxial strain, as evidenced by mid-infrared photoluminescence (PL) spectroscopy. The deduced bandgap strain coefficients are ∼103 meV %-1, which coincide with those obtained in few-layer bP. On the basis of first-principles calculations, the origin of the uniaxial tensile strain-induced PL enhancement is suggested to be due to the increase in both the effective mass ratio (me*/mh*) and the bandgap, leading to the increment of the radiative efficiency. Moreover, the mid-infrared PL emission remains perfectly linear-polarized along the armchair direction regardless of tensile or compressive strain. The highly tunable bandgap of bP in the mid-infrared regime opens up opportunities for the realization of mid-infrared light-emitting diodes and lasers using layered materials.

Momentum-matching and band-alignment van der Waals heterostructures for high-efficiency infrared photodetection.

Two-dimensional (2D) infrared photodetectors always suffer from low quantum efficiency (QE) because of the limited atomically thin absorption. Here, we reported 2D black phosphorus (BP)/Bi2O2Se van der Waals (vdW) photodetectors with momentum-matching and band-alignment heterostructures to achieve high QE. The QE was largely improved by optimizing the generation, suppressing the recombination, and improving the collection of photocarriers. Note that momentum-matching BP/Bi2O2Se heterostructures in k-space lead to the highly efficient generation and transition of photocarriers. The recombination process can be largely suppressed by lattice mismatching-immune vdW interfaces. Furthermore, type II BP/Bi2O2Se vdW heterostructures could also assist fast transport and collection of photocarriers. By constructing momentum-matching and band-alignment heterostructures, a record-high QE of 84% at 1.3 micrometers and 76.5% at 2 micrometers have been achieved in BP/Bi2O2Se vdW photodetectors.

Monolayer WS2 Lateral Homosuperlattices with Two-dimensional Periodic Localized Photoluminescence.

Homojunctions and homosuperlattices are essential structures and have been widely explored for use in advanced electronic and optoelectronic devices. However, artificially manipulating crystalline phases in two-dimensional (2D) monolayers is still challenging, especially when attempting to engineer lateral homogeneous junctions in a single monolayer of transition metal dichalcogenides (TMDs). Herein, we demonstrate a lateral homosuperlattice (MLHS) with alternating 1T and 2H domains in a 2D WS2 monolayer plane. In MLHSs, the 2H domains, which are laterally localized and isolated by potential wells, manifest junction interfaces and irradiated photoluminescence (PL) with a lateral periodic distribution in the two-dimensional plane. The studies on MLHSs here can provide further understanding of lateral homojunctions and homosuperlattices in a monolayer plane, providing an alternative route to modulate optical and electronic behaviors in TMD monolayers.

Substitutionally Doped MoSe2 for High-Performance Electronics and Optoelectronics.

2D materials, of which the carrier type and concentration are easily tuned, show tremendous superiority in electronic and optoelectronic applications. However, the achievements are still quite far away from practical applications. Much more effort should be made to further improve their performance. Here, p-type MoSe2 is successfully achieved via substitutional doping of Ta atoms, which is confirmed experimentally and theoretically, and outstanding homojunction photodetectors and inverters are fabricated. MoSe2 p-n homojunction device with a low reverse current (300 pA) exhibits a high rectification ratio (104 ). The analysis of dark current reveals the domination of the Shockley-Read-Hall (SRH) and band-to-band tunneling (BTB) current. The homojunction photodetector exhibits a large open-circuit voltage (0.68 V) and short-circuit currents (1 µA), which is suitable for micro-solar cells. Furthermore, it possesses outstanding responsivity (0.28 A W-1 ), large external quantum efficiency (42%), and a high signal-to-noise ratio (≈107 ). Benefiting from the continuous energy band of homojunction, the response speed reaches up to 20 µs. Besides, the Ta-doped MoSe2 inverter exhibits a high voltage gain (34) and low power consumption (127 nW). This work lays a foundation for the practical application of 2D material devices.

Slowing Hot-Electron Relaxation in Mix-Phase Nanowires for Hot-Carrier Photovoltaics.

Hot carrier harvest could save 30% energy loss in solar cells. So far, however, it is still unreachable as the photoexcited hot carriers are short-lived, ∼1 ps, determined by a rapid relaxation process, thus invalidating any reprocessing efforts. Here, we propose and demonstrate a feasible route to reserve hot electrons for efficient collection. It is accomplished by an intentional mix of cubic zinc-blend and hexagonal wurtzite phases in III-V semiconductor nanowires. Additional energy levels are then generated above the conduction band minimum, capturing and storing hot electrons before they cool down to the band edges. We also show the superiority of core/shell nanowire (radial heterostructure) in extracting hot electrons. The strategy disclosed here may offer a unique opportunity to modulate hot carriers for efficient solar energy harvest.

Blackbody-sensitive room-temperature infrared photodetectors based on low-dimensional tellurium grown by chemical vapor deposition.

Blackbody-sensitive room-temperature infrared detection is a notable development direction for future low-dimensional infrared photodetectors. However, because of the limitations of responsivity and spectral response range for low-dimensional narrow bandgap semiconductors, few low-dimensional infrared photodetectors exhibit blackbody sensitivity. Here, highly crystalline tellurium (Te) nanowires and two-dimensional nanosheets were synthesized by using chemical vapor deposition. The low-dimensional Te shows high hole mobility and broadband detection. The blackbody-sensitive infrared detection of Te devices was demonstrated. A high responsivity of 6650 A W-1 (at 1550-nm laser) and the blackbody responsivity of 5.19 A W-1 were achieved. High-resolution imaging based on Te photodetectors was successfully obtained. All the results suggest that the chemical vapor deposition-grown low-dimensional Te is one of the competitive candidates for sensitive focal-plane-array infrared photodetectors at room temperature.

Emotion matters for academic success: Implications of the Article by Jarrell, Harley, Lajoie, and Naismith (2017) for creating nurturing and supportive learning environments to help students manage their emotions.

This paper is in response to the published article entitled "Success, failure and emotions: examining the relationship between performance feedback and emotions in diagnostic reasoning" (Jarrell, Harley, Lajoie, & Naismith, Education Technology & Research Development, 65, 1263-1284: 2017) focusing on its implications to inform educational practice and research as learning and instruction are shifted to digital environments in times of emergencies and crisis. The study explored the relationships between learners' retrospective performance outcome emotions and their academic performance (i.e., efficiency and accuracy). The results revealed that positive emotions were associated with higher performance while negative emotions were associated with poorer performance, and the low intensity emotions were associated with performance between high and low levels. A summary of the study reported by the article is provided, including the purpose, methods, measures, data analysis and findings. Following the summary, the paper focuses on the discussion about the focused perspective, values and impact of the study on digital learning environments with implications for education during the COVID-19 pandemic and other emergency situations. Based on Jarrell and her colleagues' study, suggestions are made for designing and developing instructional strategies to support students with negative or low intensity emotions and for creating learning environments to cultivate positive emotions. This paper concludes with recommendations for future research.

Notes on attribution functions.

Let Q,Kσ be the knowledge space derived from an attribution function σ on Q. Under an assumption for σ, this paper gives some necessary and sufficient conditions such that Q,Kσ is discriminative. It also discusses the resolubility of σ when Q is an infinite set. More precisely, this paper proves that σ is not resoluble if Q is uncountable, and gives a necessary and sufficient condition such that σ is resoluble when Q,Kσ is ∞ -well-graded. By way of applications of these results, discriminativeness and resolubility are discussed around the merge of skill multimaps and the meshing of the delineated knowledge spaces.

Air-Stable Low-Symmetry Narrow-Bandgap 2D Sulfide Niobium for Polarization Photodetection.

Low-symmetry 2D materials with unique anisotropic optical and optoelectronic characteristics have attracted a lot of interest in fundamental research and manufacturing of novel optoelectronic devices. Exploring new and low-symmetry narrow-bandgap 2D materials will be rewarding for the development of nanoelectronics and nano-optoelectronics. Herein, sulfide niobium (NbS3 ), a novel transition metal trichalcogenide semiconductor with low-symmetry structure, is introduced into a narrowband 2D material with strong anisotropic physical properties both experimentally and theoretically. The indirect bandgap of NbS3 with highly anisotropic band structures slowly decreases from 0.42 eV (monolayer) to 0.26 eV (bulk). Moreover, NbS3 Schottky photodetectors have excellent photoelectric performance, which enables fast photoresponse (11.6 µs), low specific noise current (4.6 × 10-25 A2 Hz-1 ), photoelectrical dichroic ratio (1.84) and high-quality reflective polarization imaging (637 nm and 830 nm). A room-temperature specific detectivity exceeding 107 Jones can be obtained at the wavelength of 3 µm. These excellent unique characteristics will make low-symmetry narrow-bandgap 2D materials become highly competitive candidates for future anisotropic optical investigations and mid-infrared optoelectronic applications.

High Quality Pyrazinoquinoxaline-Based Graphdiyne for Efficient Gradient Storage of Lithium Ions.

N-doping of graphdiyne with atomic precision is very important for the study of heteroatom doping effect and the structure-properties relationships of graphdiyne. Here we report the bottom-up synthesis and characterizations of high-quality pyrazinoquinoxaline-based graphdiyne (PQ-GDY) film. First-principle studies of the layered structure were performed to examine the stacking mode, lithium binding affinity, and bulk lithium storage capacity. Three-stage insertion of 14 lithium atoms with binding affinities in the order of pyrazine nitrogen > diyne carbon > central aromatic ring were confirmed by both lithium-ion half-cell measurements and DFT calculations. More than half of the lithium atoms preferentially bind to pyrazine nitrogen, and a reversible capacity of 570.0 mA h g-1 at a current density of 200 mA g-1 after 800 cycles was achieved. Such a high capacity utilization rate of 97.2% provides a good case study of N-doped GDY with atomic precision.

The strain effect on the electronic properties of the MoSSe/WSSe van der Waals heterostructure: a first-principles study.

The structural, mechanical and electronic properties of the MoSSe/WSSe van der Waals (vdW) heterostructure under various degrees of horizontal and vertical strain are systematically investigated based on first-principles methods. It is found that the MoSSe/WSSe vdW heterostructure of the most stable AB stacking is a direct band gap semiconductor and exhibits a type-II band alignment, which demonstrates an effective separation of photogenerated electron-hole pairs and increases their lifetime accordingly. The high angle-dependent Young's modulus and normal Poisson's ratios show the mechanical stability and anisotropy. It is found that the band gap of the heterostructure can be modulated effectively by applying strain, exhibiting a decreasing trend with increasing strain, and even lead to an intriguing semiconductor-metal transition under a certain large tensile strain. In particular, a negative correlation between the band gap and structure pressure provides a theoretical basis for experimentally regulating the electronic properties. Moreover, different strains can induce two different conditions of direct-indirect transition or can maintain the characteristics of the direct-band-gap. All these interesting results provide a detailed understanding of the MoSSe/WSSe vdW heterostructure under strain and indicate that it is a good candidate for low-dimensional electronic, nano-electronic and optoelectronic devices.

End-tidal carbon dioxide monitoring improves patient safety during propofol-based sedation for breast lumpectomy: A randomised controlled trial.

BACKGROUND: The use of sedation is becoming more commonplace. Although pulse oximetry is a standard monitoring procedure during sedation, it cannot accurately detect early hypoventilation. End-tidal carbon dioxide (EtCO2) monitoring can be an earlier indicator of airway compromise; however, the existing literature is limited to a few studies with varying outcomes. OBJECTIVES: To evaluate whether EtCO2 monitoring decreases the incidences of CO2 retention and apnoeic events in propofol-based sedation. DESIGN: Randomised controlled study. SETTING: A tertiary hospital. PATIENTS: Two hundred women (aged 18 to 65 years, ASA physical status 1 or 2) who were scheduled for breast lumpectomy between June 2017 and August 2017. INTERVENTIONS: Patients were allocated randomly to receive either standard monitoring or standard monitoring and EtCO2 monitoring. MAIN OUTCOME MEASURES: The primary outcome was the incidence of CO2 retention. The secondary outcomes were the number of actions taken to restore ventilation, variations in PaCO2 and pH, the frequency of apnoea and the recovery time. RESULTS: CO2 retention occurred significantly less often in the EtCO2 monitoring group (10 vs. 87%; P < 0.0001). In the standard monitoring group, the mean PaCO2 was more than 6 kPa (45 mmHg) and the pH was less than 7.35 at 5, 10, 20 and 30 min after induction of anaesthesia and at the end of the procedure. Both values were within the normal range in the EtCO2 monitoring group. The number of airway interventions performed was significantly higher in the EtCO2 monitoring group (9.8 ±â€Š1.8 vs. 1.9 ±â€Š1.0; P < 0.0001). Apnoea occurred significantly less often in the EtCO2 monitoring group (0 vs. 10%; P < 0.0001) and recovery time was shorter (9.9 ±â€Š1.4 vs. 11.4 ±â€Š2.1 min; P = 0.048). CONCLUSION: The addition of EtCO2 monitoring to standard monitoring during propofol-based sedation can improve patient safety by decreasing the incidence of CO2 retention, and therefore the risk of hypoxaemia through early recognition of apnoea, and can also shorten recovery time. TRIAL REGISTRATION: This trial is registered with http://www.chictr.org.cn (ChiCTR-INR-17011537).

Topologies on superspaces of TVS-cone metric spaces.

This paper investigates superspaces 𝒫0(X) and 𝒦0(X) of a tvs-cone metric space (X, d), where 𝒫0(X) and 𝒦0(X) are the space consisting of nonempty subsets of X and the space consisting of nonempty compact subsets of X, respectively. The purpose of this paper is to establish some relationships between the lower topology and the lower tvs-cone hemimetric topology (resp., the upper topology and the upper tvs-cone hemimetric topology to the Vietoris topology and the Hausdorff tvs-cone hemimetric topology) on 𝒫0(X) and 𝒦0(X), which makes it possible to generalize some results of superspaces from metric spaces to tvs-cone metric spaces.