Slow Response Speed Research Articles

Effect of surface oxygen vacancy defects on the performance of ZnO quantum dots ultraviolet photodetector* *Project supported by the National Natural Science Foundation of China (Grant Nos. 62074148, 61875194, 11727902, 12074372, 11774341, 11974344, 61975204, and 11804335), the Youth Innovation Promotion Association of the Chinese Academy of Sciences (Grant No. 2020225), the Open Project of the State Key Laboratory of Luminescence

The slower response speed is the main problem in the application of ZnO quantum dots (QDs) photodetector, which has been commonly attributed to the presence of excess oxygen vacancy defects and oxygen adsorption/desorption processes. However, the detailed mechanism is still not very clear. Herein, the properties of ZnO QDs and their photodetectors with different amounts of oxygen vacancy (VO) defects controlled by hydrogen peroxide (H2O2) solution treatment have been investigated. After H2O2 solution treatment, VO concentration of ZnO QDs decreased. The H2O2 solution-treated device has a higher photocurrent and a lower dark current. Meanwhile, with the increase in VO concentration of ZnO QDs, the response speed of the device has been improved due to the increase of oxygen adsorption/desorption rate. More interestingly, the response speed of the device became less sensitive to temperature and oxygen concentration with the increase of VO defects. The findings in this work clarify that the surface VO defects of ZnO QDs could enhance the photoresponse speed, which is helpful for sensor designing.

Morphology changes of In-doped ZnO nanosheets via ZnCl2 and InCl3 vapor formation during thermal dissipation annealing process and improved UV photoresponse properties

Ultraviolet (UV) photodetectors that are fabricated using ZnO thin films exhibit higher photocurrent stability, without a complex filter, than that exhibited by Si-based UV photodetectors. However, the ZnO-based UV photodetectors possess several drawbacks such as slow response speed, low on/off current ratio, and low sensitivity. These drawbacks can be overcome by regulating the number of free carriers and point defects that affect the photocurrent increment and the response speed of the UV photodetectors. In this study, indium (In)-doped ZnO (IZO) thin films were deposited via sol-gel spin coating. Subsequently, the amorphous IZO thin films were crystallized via thermal dissipation annealing (TDA). This facilitated the regulation of the number of point defects and free carriers, and the surface roughness of the IZO thin films decreased with the increase in the doping concentration. The UV photosensitivity of the IZO thin films was higher than that of the undoped ZnO thin films. The IZO thin films also exhibited the highest photoresponsivity and UV photoresponse speed. The technique that was devised in the study was concluded to be a feasible route for the fabrication of ZnO-based UV photodetectors with high photosensitivity, photoresponsivity, and UV photoresponse speed.

Highly sensitive solar-blind deep ultraviolet photodetector based on graphene/PtSe2/β-Ga2O3 2D/3D Schottky junction with ultrafast speed

There is an emerging need for high-sensitivity solar-blind deep ultraviolet (DUV) photodetectors with an ultra-fast response speed. Although nanoscale devices based on Ga2O3 nanostructures have been developed, their practical applications are greatly limited by their slow response speed as well as low specific detectivity. Here, the successful fabrication of two-/three-dimensional (2D/3D) graphene (Gr)/PtSe2/β-Ga2O3 Schottky junction devices for high-sensitivity solar-blind DUV photodetectors is demonstrated. Benefitting from the high-quality 2D/3D Schottky junction, the vertically stacked structure, and the superior-quality transparent graphene electrode for effective carrier collection, the photodetector is highly sensitive to DUV light illumination and achieves a high responsivity of 76.2 mA/W, a large on/off current ratio of ~ 105, along with an ultra-high ultraviolet (UV)/visible rejection ratio of 1.8 × 104. More importantly, it has an ultra-fast response time of 12 µs and a remarkable specific detectivity of ~ 1013 Jones. Finally, an excellent DUV imaging capability has been identified based on the Gr/PtSe2/β-Ga2O3 Schottky junction photodetector, demonstrating its great potential application in DUV imaging systems.

Speed enhancement of ultraviolet photodetector base on ZnO quantum dots by oxygen adsorption on surface defects

Applications of ZnO quantum dots (QDs) in photodetectors are generally limited by a slower response speed and a higher dark current. The corresponding mechanism is not very clear, and how to resolve these problems is still in big challenge. Herein, we have demonstrated a photodetector on 700 nm-thick ZnO QDs film with a large number of oxygen vacancy defects by adjusting the ratio of the reactants and the reaction time. The device exhibits a quick response speed with a rise time of ~1.00 s and a recovery time of ~0.19 s. Meanwhile, the dark current and the responsivity under 730 μW/cm2 UV light illumination were found to be 20 pA and 260 mA/W under 10 V bias, respectively. The mechanism of these phenomena has been investigated, and the fast response speed of ZnO QDs photodetector in the air should originate from the adsorption/desorption of oxygen on the surface oxygen vacancy defects of ZnO QDs. The findings in this work can be used to guide design of high-performance photodetectors based on ZnO QDs and other nanomaterials with large surface to volume ratio.

Enhanced response speed of TiO2 nanoarrays based all solid-state ultraviolet photodetector via SiO2 dielectric layer

All solid-state ultraviolet photodetector based on TiO2 nanoarrays always suffers from slow response speed, which seriously limits its actual application. In this work, a novel all solid-state hybrid structure ultraviolet photodetector based on nano-tree TiO2 nanoarrays and SiO2 dielectric layer was prepared. The response speed of the device can be improved significantly by the addition of SiO2 layer. The obtained TiO2/SiO2 hybrid device demonstrates large responsivity of 1.15 A/W, high detection sensitivity of 7.74 × 1013 Jones and fast photoresponse time of 1.13 s/0.75 s for PD4 under UV light illumination. The existence of the SiO2 layer widen the depletion layer on the surface of TiO2, which increases the loss rate of the photo-generated carrier and reduces the response time of the device. This device based on nano-tree TiO2 nanoarrays and SiO2 layer provides a certain fundamental for the future development of all solid-state photodetectors.

Direct observation of enhanced performance in suspended ReS2 photodetectors.

Rhenium disulfide (ReS2) has emerged as a promising material for future optoelectric applications due to its extraordinary electrical, mechanical, and optoelectrical properties. However, the ReS2-based photodetectors are severely restricted by their slow response speed (>10 s). Here, we demonstrate a high-performance polarization-sensitive photodetector based on suspended ReS2. Such a transistor shows an n-type behavior with the mobility of about 14.1 cm2V-1s-1, an on/off ratio of 105, and a responsivity of 0.22 A/W. Benefitting from well-developed contact between Au and the ReS2 channel and reduced interface scattering from the Si substrate, the response time of the device can be as short as 83.5 and 325.3µs, respectively, which are three orders of magnitude faster than that reported earlier. Furthermore, the suspended ReS2 photodetector also has the capability to detect polarized light (Imax/Imin ≈ 1.4 at 532 nm) due to the robust in-plane anisotropy of the material. These findings offer an efficient approach for improving the performance of ReS2-based photodetectors.

Visual Servoing of Flying Robot Based on Fuzzy Adaptive Linear Active Disturbance Rejection Control

Visual servoing is the most common control scheme for military and civil robots. For the flying robot, a nonlinear and strongly coupled system, the traditional control methods have the problems of poor adaptive ability and sensitivity to the disturbance in the complex environment. This brief deals with the disadvantages of slow response speed and weak anti-interference ability of flying robot visual servoing by using a fuzzy adaptive linear active disturbance rejection control (FLADRC) scheme. To improve the response speed and robustness of the system, the effect of the controller parameters on the performance is analyzed and quantified into fuzzy rules, and the fuzzy adaptive method is used to adjust the parameters of the linear extended state observer in real-time. Furthermore, a high-speed and high-precision visual positioning algorithm based on YOLOv4 and efficient large-scale stereo matching (ELAS) is proposed. Finally, the performances of FLADRC, LADRC, PID, and Fuzzy-PID are compared by simulation experiments, and the effectiveness of the proposed scheme is proved.

NiO/GaN p-n junction ultraviolet photodetector and self-powered technology

<sec> Ultraviolet photodetector plays an important role in fire warning, missile tracking and dose detecting of ultraviolet sterilization and disinfection, which is closely related to human lives. With the development of integrated detection system, the requirements for the size and energy consumption of the detector are becoming more and more stringent. Traditional detector that requires an external power supply can no longer meet these requirements. Moreover, a traditional ultraviolet detector is mainly composed of first-generation semiconductors and second-generation semiconductors. These semiconductors have small band gaps and large cut-off wavelengths, and are more suitable for infrared detection. When used for implementing the ultraviolet detection, an additional layer is often required, which increases not only the volume but also the cost. </sec><sec> Gallium nitride (GaN), as a third-generation semiconductor, has a band gap of 3.4 eV and a corresponding absorption edge of 365 nm. It is a natural ultraviolet detection material. At the same time, the excellent physical and chemical properties make the devices prepared by GaN have high stability. In recent years, some studies have shown that the GaN-based ultraviolet photodetectors have excellent responsiveness, but each of these detectors usually requires an external bias and has a slow response speed. Here, we propose a high responsivity, fast response speed and self-powered ultraviolet photodetector based on NiO/GaN p-n junction. By using the magnetron sputtering, a layer of 70 nm thick p-NiO film is deposited on a high-quality n-GaN film that has been grown on a sapphire substrate by the metal-organic chemical vapor deposition. The fabricated p-n junction shows obvious rectification characteristics at ± 0.5 V. Due to the existence of the built-in electric field, the device can work without externally applied bias. Under zero bias, the detector shows a responsivity of 272.3 mA/W for 365 nm ultraviolet light while the intensity is 50 μW/cm<sup>2</sup>, and has a detectivity as high as 2.83 × 10<sup>14</sup> Jones. This indicates that the detector has a high sensitivity even for very weak light. Owing to the good crystallinity of the film, the dark current is as low as 10<sup>–10</sup> A, the switching ratio is > 10<sup>3</sup>, and the response speed reaches 31 ms. These excellent properties show the broad application prospects of the devices based on NiO/GaN p-n junctions in the field of self-powered ultraviolet detection, and thus providing new ideas for the future development of intelligent integration. </sec>

Optimization of fuel cell thermal management system based on back propagation neural network

Two thermal management control strategies, namely flow following current and power mode and back propagation neural network auto-disturbance rejection method, were proposed to solve significant temperature fluctuation problems, long regulation time, and slow response speed in fuel cell thermal management system variable load. The results show that the flow following current and power control strategy can effectively weaken the coupling effect between pump and radiator fan and significantly reduce the overshoot and adjustment time of inlet and outlet cooling water temperature and temperature difference reactor. Although the control effect of the neural network and strategy is insufficient under maximum power, the overall control effect is better than that of the flow following the current control strategy.

Path Planning of Mobile Robot Based on Improved Multiobjective Genetic Algorithm

Path planning is the core technology of mobile robot decision‐making and control and is also a research hotspot in the field of artificial intelligence. Aiming at the problems of slow response speed, long planning path, unsafe factors, and a large number of turns in the conventional path planning algorithm, an improved multiobjective genetic algorithm (IMGA) is proposed to solve static global path planning in this paper. The algorithm uses a heuristic median insertion method to establish the initial population, which improves the feasibility of the initial path and generates a multiobjective fitness function based on three indicators: path length, path security, and path energy consumption, to ensure the quality of the planned path. Then, the selection, crossover, and mutation operators are designed by using the layered method, the single‐point crossover method, and the eight‐neighborhood‐domain single‐point mutation method, respectively. Finally, the delete operation is added, to further ensure the efficient operation of the mobile robot. Simulation experiments in the grid environment show that the algorithm can improve the defects of the traditional genetic algorithm (GA), such as slow convergence speed and easy to fall into local optimum. Compared with GA, the optimal path length obtained by planning is shortened by 17%.

Design and Integration of a Layered MoS2/GaN van der Waals Heterostructure for Wide Spectral Detection and Enhanced Photoresponse.

Molybdenum disulfide (MoS2) as a typical two-dimensional (2D) transition-metal dichalcogenide exhibits great potential applications for the next-generation nanoelectronics such as photodetectors. However, most MoS2-based photodetectors hold obvious disadvantages including a narrow spectral response in the visible region, poor photoresponsivity, and slow response speed. Here, for the first time, we report the design of a two-dimensional MoS2/GaN van der Waals (vdWs) heterostructure photodetector consisting of few-layer p-type MoS2 and very thin n-type GaN flakes. Thanks to the good crystal quality of the 2D-GaN flake and the built-in electric field in the interface depletion region of the MoS2/GaN p-n junction, photogenerated carriers can be rapidly separated and more excitons are collected by electrodes toward the high photoresponsivity of 328 A/W and a fast response time of 400 ms under the illumination of 532 nm light, which is seven times faster than pristine MoS2 flake. Additionally, the response spectrum of the photodetector is also broadened to the UV region with a high photoresponsivity of 27.1 A/W and a fast response time of 300 ms after integrating with the 2D-GaN flake, exhibiting an advantageous synergetic effect. These excellent performances render MoS2/GaN vdWs heterostructure photodetectors as promising and competitive candidates for next-generation optoelectronic devices.

A near-infrared fluorogenic probe with fast response for detecting sodium dithionite in living cells.

Developing a reliable fluorescence probe is crucial for accurately monitoring sodium dithionite (Na2S2O4, SDT) in biosystems, but the current reported azo-based ones suffers from short excitation/emission wavelengths and relative slow response speed. To address this issue, we herein present a novel near-infrared emissive fluorescence probe for SDT, namely DCM-MQ, consisting of a dicyanomethylene-benzopyran fluorogenic reporter and a 1-methylquinolinium as recognition moiety. On the basis of the specific reduction mechanism, DCM-MQ exhibited a rapid colorimetric and fluorescent recognition for SDT (less than 3s) with large Stokes shift (112nm) and high sensitivity (detection limit was 19nM). The fluorescence imaging results demonstrate that DCM-MQ is competent for monitoring SDT in living systems.

A Photoactuator Based on Stiffness-Variable Carbon Nanotube Nanocomposite Yarn.

Actuators based on carbon nanotube (CNT) yarn have attracted extensive attention due to their great properties and potential applications such as artificial muscles, sensors, intelligent robots, and so on. However, the CNT yarn actuators with one-dimensional structure were often only used to drive through electrochemical, thermal, or electrical stimulation, which limits the applications of CNT yarn actuators. In addition, the slow response speed, low output stress, uncontrollable driving deformation, and self-recovery without an external stimulus are also great challenges. Here, we propose a photoactuator with large output stress, fast response speed, large and reversible driving deformation, and good reusability based on stiffness-variable CNT nanocomposite yarn (CNT-NCY). Such a CNT-NCY photoactuator can achieve torsional and contractive actuation under irradiation of near-infrared (NIR) light; it is important that the actuation is reversible and controllable. The maximum rotation rate of the CNT-NCY photoactuator during the torsional actuation is about 45 rpm, and the contractive deformation can reach more than 9%. This CNT-NCY photoactuator can create more than 12 MPa output stress, which is 40 times higher than that of the human skeletal muscle. The driving mechanism of this CNT-NCY photoactuator has been analyzed, and its potential application has also been demonstrated.

Unlock the Flexibility of Combined Heat and Power for Frequency Response by Coordinative Control With Batteries

Owners of combined heat and power (CHP), e.g., industrial manufacturers, are motivated to provide frequency response to power grids due to clear financial benefits. Yet, the slow response speed of CHP limits its capability in providing such services. Moreover, frequent adjustments would cause a faster lifetime reduction of CHP and rapid pressure fluctuation in the gas network. To further unlock the flexibility of CHP, this article integrates a battery unit with CHP via a power electronic interface. A filter-based coordinative controller is designed for smoothing short-term fluctuations in CHP outputs. Based on the filter parameters and frequency response requirements, the minimum required capacity of the battery is identified. The results show that the proposed system enhances the capability of CHP for frequency response and mitigates the associated adverse effects on the gas network. The required capacity of the battery is economically feasible considering the benefit it brings to the CHP.

Response Speed in Executive Tasks Predicts Social Motivation and Communication in School-Aged Children With Autism Spectrum Disorder (ASD)

Abstract Date Presented 03/27/20 Our results show that a slower response speed, not accuracy, on executive function (EF) tasks is related to better social interaction in school-age children with ASD. Children with ASD reduce their response speed to maintain good accuracy. Therefore, the response speed could be a correlate of social motivation and communication for school-age children with ASD and should be included in their evaluation for better intervention planning. Primary Author and Speaker: Yen-Ting Yu Contributing Authors: Chien-Ho Lin, Ching-Lin Hsieh, Cheng-Chun Kuei-Cheng, Kuan-Lin Chen

52‐4: Late‐News‐Paper: Development of 240Hz Refresh Rate ADS Mode Gaming Product

The ADS display mode shows significant advantages of high transmittance, wide viewing angle, small color shift at large view angle, etc., and thus has been widely used in all kinds of display product such as mobile phone, tablet, notebook, monitor and television. However, ADS mode shows shortcomings of slow response speed. In this work, we made extreme optimization research and breakthroughs in improving ADS mode response speed from the aspects of LC material, cell gap, and pixel ITO slit angle. Based on the research, 27 inch FHD 240Hz refresh rate gaming product was successfully developed. It has been achieved gray to gray average response time 1.9ms with over driving as well as contrast ratio 1214:1 fulfilling static CR requirements of VESA HDR standard.

Multi-timescale robust dispatching for coordinated automatic generation control and energy storage

The increasing penetration of renewable energy into power grids is reducing the regulation capacity of automatic generation control (AGC). Thus, there is an urgent demand to coordinate AGC units with active equipment such as energy storage. Current dispatch decision-making methods often ignore the intermittent effects of renewable energy. This paper proposes a two-stage robust optimization model in which energy storage is used to compensate for the intermittency of renewable energy for the dispatch of AGC units. This model exploits the rapid adjustment capability of energy storage to compensate for the slow response speed of AGC units, improve the adjustment potential, and respond to the problems of intermittent power generation from renewable energy. A column and constraint generation algorithm is used to solve the model. In an example analysis, the proposed model was more robust than a model that did not consider energy storage at eliminating the effects of intermittency while offering clear improvements in economy and efficiency

Energy level gradient trapping based on different work functions of ZnO enhancing response and stablity for lateral photodetectors

Abstract The slow response speed and instability of the lateral photodetectors (L-PDs), often caused by the persistence of the excess minority carriers in the long channel after the termination of the illumination (called Persistent Photoconductivity effects) are the main factors that hinder the practical application of this type of device. In this research, two types of ZnO with different work functions, including ZnO nanoparticles (ZnO-NPs) doped in bulk heterojunction (BHJ) and thermal annealed ZnO nanocrystalline film (ZnO–NF), are incorporated into the L-PDs to construct an energy gradient, which could facilitate the quick transfer of the minority carriers and restrict their release into the active layer. The structure of L-PDs are optimized as quartz/ZnO–NF/PffBT4T-2OD:PC61BM:ZnO-NPs (component ratio = 5:6:1)/Au–Au electrodes. Compared with the control device, the test results show that the optimized L-PDs exhibit higher stability with much lower fall time (3.7 ms, boosted 200-fold) and gentler rise slope of dark current versus time (Kdark) (8.3 × 10−6 nA/s, reduced four orders of magnitude). Meanwhile, the very low dark current (

Research on Simulation Analysis of Valveless Hydraulic Servo System

The hydraulic transmission technology is widely used in the industrial field. With the continuous development of microelectronic technology, valveless electro-hydraulic servo technology came into being. Aiming at the problems such as slow response speed and poor displacement tracking accuracy, this paper builds a simulation model of the forward and reverse displacement of the valveless electro-hydraulic servo system, and uses AMESim and simulink software to build the hydraulic part simulation and motor part simulation of the system respectively. A fuzzy PID controller is introduced and simulation is performed with the addition of the fuzzy PID controller to improve the overall performance of the valveless electro-hydraulic servo system.

Subacute and chronic neuropsychological sequalae of acute organophosphate pesticide self-poisoning: a prospective cohort study from Sri Lanka

Context Some epidemiological evidence implicates acute organophosphate (OP) pesticide poisoning in long-term neurocognitive deficits. However, no study has prospectively followed up poisoned patients long-term from the time of intoxication. We aimed to determine whether clinically significant acute OP self-poisoning leads to subacute and chronic neurocognitive deficits, in a prospective follow up study. Methods Employing Mini Mental State Examination, Digit Span and Cambridge Neuropsychological Test Automated Battery (CANTAB), we compared multiple cognitive functions in 222 patients hospitalized with acute OP pesticide self-poisoning with a control group of 52 patients hospitalized with paracetamol overdose, at three time points: on discharge following clinical recovery, 6 weeks and 6 months post-ingestion. Intergroup comparisons at each time point were done in multiple regression models, adjusting for sex, age, education and psychiatric comorbidities. OP within-group analysis was done to determine a dose–response relationship. Results After adjusting for covariates, the OP poisoned group had significantly poorer working memory (Digit Span) and episodic memory (CANTAB Paired Associates Learning); impaired spatial planning (CANTAB Stocking of Cambridge); and slower response speed in the sustained attention task (CANTAB Rapid Visual Information Processing), in the post-discharge assessment. Only working memory and episodic memory measures were impaired in the OP group at 6 weeks, whereas no significant intergroup differences were observed at 6 months. The OP subgroup who had complete red cell acetylcholinesterase inhibition on admission had poorer episodic memory when tested post-discharge than those who had partial inhibition, but no significant subgroup differences were observed at 6 weeks or 6 months. Discussion Acute OP pesticide poisoning may cause neuropsychological impairment that outlasts the cholinergic phase on a subacute time scale; but does not cause measurable chronic neuropsychological deficits.