BaTiO_(3)/p-GaN/Au self-driven UV photodetector with bipolar photocurrent controlled by ferroelectric polarization

Ferroelectric materials are promising candidates for ultraviolet photodetectors due to their ferroelectric effect.In this work,a BaTiO_(3)/p-GaN/Au hybrid heterojunction-Schottky self-driven ultraviolet photodetector was fabricated with excellent bipolar photoresponse property.At 0 V bias,the direction of the photocurrent can be switched by flipping the depolarization field of BaTiO_(3),which allows the performance of photodetectors to be controlled by the ferroelectric effect.Meanwhile,a relatively large responsivity and a fast response speed can be also observed.In particular,when the depolarization field of BaTiO_(3) is in the same direction of the built-in electric field of the Au/p-GaN Schottky junction(up polarized state),the photodetector exhibits a high responsivity of 18 mA/W at 360 nm,and a fast response speed of<40 ms at 0 V.These findings pave a new way for the preparation of high-performance photodetectors with bipolar photocurrents.

Ultraviolet photodetectors based on wide bandgap oxide semiconductor films

Ultraviolet(UV) photodetectors have attracted more and more attention due to their great potential applications in missile tracking, flame detecting, pollution monitoring, ozone layer monitoring, and so on. Owing to the special characteristics of large bandgap, solution processable, low cost, environmentally friendly, etc., wide bandgap oxide semiconductor materials, such as ZnO, ZnMgO, Ga_2O_3, TiO_2, and Ni O, have gradually become a series of star materials in the field of semiconductor UV detection. In this paper, a review is presented on the development of UV photodetectors based on wide bandgap oxide semiconductor films.

Minimum Cost Multi-Path Parallel Transmission with Delay Constraint by Extending Openflow

Sometimes user has the requirement to run a high bandwidth application over a low bandwidth network. But its implementation is not easy as the traditional network transmits data with only one path where its bandwidth is lower than the demand. Although the current network technology like SDN has the ability to precisely control the data transmission in the network, but till now the standard openflow protocol does not support splitting one flow to multiple flows. In this paper, a flow splitting algorithm is proposed. The algorithm splits a data flow to multiple sub-flows by extending the openflow protocol. A multiple paths routing algorithm is also proposed to implement the multi-path parallel transmission in the paper. The algorithm selects multiple paths and minimizes the cost of transmission under the constraint of maximum delay and delay variance. The simulations show the algorithms can significantly improve the transmission performance.

Boosting the performance of crossed ZnO microwire UV photodetector by mechanical contact homo-interface barrier

One-dimensional(1D)micro/nanowires of wide band gap semiconductors have become one of the most promising blocks of high-performance photodetectors.However,in the axial direction of micro/nanowires,the carriers can transport freely driven by an external electric field,which usually produces large dark current and low detectivity.Here,an UV photodetector built from three cross-intersecting ZnO microwires with double homo-interfaces is demonstrated by the chemical vapor deposition and physical transfer techniques.Compared with the reference device without interface,the dark current of this ZnO double-interface photodetector is significantly reduced by nearly 5 orders of magnitude,while the responsivity decreases slightly,thereby greatly improving the normalized photocurrent-to-dark current ratio.In addition,ZnO double-interface photodetector exhibits a much faster response speed(~0.65 s)than the no-interface device(~95 s).The improved performance is attributed to the potential barriers at the microwire-microwire homo-interfaces,which can regulate the carrier transport.Our findings in this work provide a promising approach for the design and development of high-performance photodetectors.

Effect of surface oxygen vacancy defects on the performance of ZnO quantum dots ultraviolet photodetector

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(H_(2)O_(2))solution treatment have been investigated.After H_(2)O_(2) solution treatment,VO concentration of ZnO QDs decreased.The H_(2)O_(2) 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.

Urchin-like Na-doped zinc oxide nanoneedles for low-concentration and exclusive VOC detections

In the early-stage diagnosis of lung cancer,the low-concentration(<5 ppm)volatile organic compounds(VOCs)are extensively identified to be the biomarkers for breath analysis.Herein,the urchin-like sodium(Na)-doped zinc oxide(ZnO)nanoneedles were synthesized through a hydrothermal strategy with the addition of different contents of citric acid.The Na-doped ZnO gas sensor with a 3:1 molar ratio of Na^(+)and citric acid showed outstanding sensing properties with an optimal selectivity to various VOCs(formaldehyde(HCOH),isopropanol,acetone,and ammonia)based on working temperature regulation.Specifically,significantly enhanced sensitivity(21.3@5 ppm)compared with pristine ZnO(~7-fold),low limit of detection(LOD)(298 ppb),robust humidity resistance,and long-term stability of formaldehyde sensing performances were obtained,which can be attributed to the formation of a higher concentration of oxygen vacancies(20.98%)and the active electron transitions.Furthermore,the improved sensing mechanism was demonstrated by the exquisite band structure and introduction of the additional acceptor level,which resulted in the narrowed bandgap of ZnO.

Mechanical Behavior of Bamboo,and Its Biomimetic Composites and Structural Members:A Systematic Review

Bamboo is a typical biological material widely growing in nature with excellent physical and mechanical properties.It is lightweight with high strength and toughness.The naturally optimized bamboo structure,which has inspired global material scientists and engineers for decades,is significantly important for the bionic design of novel structural materials with ultra-light,ultra-strong,or ultra-tough and comprehensive properties.Typical literature on innovative composite materials and structural members inspired by bamboo are reviewed in this paper,and the research progress and prospects in this field are expounded in three parts.First,the structural characteristics of the bamboo wall layer along the thickness and height directions are described in terms of chemical composition,gradient structure,pore structure,and hollow structure with variable cross-section.Second,this paper summarizes the research progress on new composite materials and structural components by applying bamboo’s structural features from the perspective of sustainability,designability,and customization.Finally,given the limitations of current research,the biomimetic scientific research on bamboo’s structural characteristics is prospected from the interpretation of bamboo structure,new bamboo-like materials,and structural design optimization perspectives,providing a reference for future research on biomimetic aspects of biomass.

Mitigating fast thermal instability by engineered laser sweep in AlN soliton microcomb generation

Transient thermal instability represents a significant challenge in generating soliton microcombs.Fast laser sweep can be an efficient method to mitigate thermal instability,but it requires an ultrahigh laser sweep rate for crystalline microresonators with fast thermal relaxation.Here,we engineer a laser sweep waveform to generate AlNon-sapphire soliton microcombs with an intermediate sweep speed(<30 GHz∕μs).Two laser sweep methods with backward plus forward tuning or two-step backward tuning added after the fast forward laser sweep were demonstrated to stabilize solitons.Reducing the soliton number is found to be useful to stabilize solitons in fast laser sweep.The effectiveness of the methods was numerically verified.Our measurements and simulations also reveal the impacts of different thermal relaxation processes occurring at quite different time scales on thermal instability.The requirement of the laser sweep protocols is discussed.

Ultrasensitive room-temperature geranyl acetone detection based on Fe@WO_(3−x) nanoparticles in cooked rice flavor analysis

In the assessment of food quality,geranyl acetone plays a crucial role as a volatile organic compound(VOC)biomarker for diverse agricultural products,while the ultralow concentration detection meeting application requirements has been barely studied.Herein,an iron(Fe)-doped WO_(3−x) gas sensor was employed for greatly sensitive,selective,and scalable geranyl acetone detection.The results proved that precisely-regulated oxygen vacancy(OV)and sophisticatedly-active electron transition of Fe-doped WO_(3−x) nanoparticles were fulfilled by modifying the doping amount of Fe^(3+),leading to the prominently enhanced sensitivity(23.47 at 6 ppm),low limit of detection(LOD)(237 ppb),optimal selectivity,and outstanding long-term stability.Furthermore,the enhancing mechanism of gas sensing performance was substantiated through density functional theory(DFT)calculation,while the practical application for the evaluation of spoiled cooked rice was conducted as well.This study demonstrates a reliable method for detecting a VOC biomarker in cooked rice,which can ensure food security and improve palatability of cooked rice.

Spatiotemporal mode-locking and dissipative solitons in multimode fiber lasers

Multimode fiber(MMF)lasers are emerging as a remarkable testbed to study nonlinear spatiotemporal physics with potential applications spanning from high energy pulse generation,precision measurement to nonlinear microscopy.The underlying mechanism for the generation of ultrashort pulses,which can be understood as a spatiotempoal dissipative soliton(STDS),in the nonlinear multimode resonators is the spatiotemporal mode-locking(STML)with simultaneous synchronization of temporal and spatial modes.In this review,we first introduce the general principles of STML,with an emphasize on the STML dynamics with large intermode dispersion.Then,we present the recent progress of STML,including measurement techniques for STML,exotic nonlinear dynamics of STDS,and mode field engineering in MMF lasers.We conclude by outlining some perspectives that may advance STML in the near future.

Numerical study on the effect of in-situ stress on smoothwall blasting in deep tunnelling

In the present study,a numerical model is first calibrated against the crack networks and pressure attenuation data in laboratory blasting test.Then,based on the calibrated numerical model,two-hole plane models are developed and used to perform a series of sim-ulations of smoothwall blasting in deep tunnelling subjected to in-situ stress.The evolutions of rock fracture and excavation damage zone in the roof/floor and sidewalls under different far-field hydrostatic pressure and anisotropic in-situ stress conditions are numerically investigated.The findings in numerical modelling are also analytically interpreted with the stress distributions around the designed tunnel perimeter and perimeter borehole.The numerical and analytical results show that the variations of rock cracking and excavation dam-aged zone induced by smoothwall blasting with in-situ stress are mainly attributed to the high tangential compressive stress concentration around the remaining rock after inner primary blasts and the tensile stress acting on the wall of perimeter hole,which control the crack propagation and initiation respectively.At last,the implications of findings for practical smoothwall blasting in deep tunnelling are discussed.

Buildup dynamics of multiple solitons in spatiotemporal mode-locked fiber lasers

Spatiotemporal mode locking is a nonlinear process of multimode soliton self-organization.Here the real-time buildup dynamics of the multiple solitons in a spatiotemporal mode-locked multimode fiber laser are investigated,assisted by the time-stretch technique.We find that the buildup processes are transverse mode dependent,especially during the stages of relaxation oscillation and Q-switching prior to multiple soliton formation.Furthermore,we observe that the transverse modal composition of these generated pulses among the multiple solitons can be different from each other,indicating the spatiotemporal structure of the multiple soliton.A simplified theoretical model based on pulse energy evolution is put forward to interpret the role of 3D saturable absorber on spatiotemporal structures of spatiotemporal mode-locking multiple solitons.Our work has presented the spatiotemporal nonlinear dynamics in multimode fiber lasers,which are novel to those inside the single transverse mode fiber lasers.

Observation of transition between multimode Q-switching and spatiotemporal mode locking

We report experimental observation of multimode Q-switching and spatiotemporal mode locking in a multimode fiber laser.A typical steady Q-switching state is achieved with a 1.88μs pulse duration,a 70.14 kHz repetition rate,and a 215.8 mW output power,corresponding to the single pulse energy of 3.08μJ.We find weak spatial filtering is essential to obtain stable Q-switched pulses,in contrast to the relatively stronger spatial filtering for spatiotemporal mode locking.Furthermore,a reversible transition process,as well as a critical bistable state,between multimode Q-switching and spatiotemporal mode locking,is achieved with specific spatial coupling and waveplates sets.We believe the results will not only contribute to understanding the complicated nonlinear dynamics in multimode,fiber-based platforms,but also benefit the development of promising high-pulse energy lasers.

Computational Identification of Small Interfering RNA Targets in SARS CoV-2

Dear Editor,At the end of 2019,a new virus,called Severe Acute Respiratory Syndrome Coronavirus 2(SARS-CoV-2)was reported(Benvenuto et al.2020;Zhu et al.2020).The sequences of SARS-CoV-2 reported by different research groups demonstrated that it is a positive strand RNA virus.The sequence of SARS-CoV-2 is approximately 30 kb long,and could encodes spike,envelope,membrane,nucleocapsid proteins,etc.(Phan 2020).These proteins are responsible for replicating the viral genome as well as generating nested transcripts that are used in the synthesis of the viral proteins.