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.

Photoresponse Characteristics of Chamaenerion spp. in Mount Shergyla

Chamaenerion spp.( Onagraceae) are a class of ecological restoration medicinal herbs. Mount Shergyla has three species and one variant of Chamaenerion. Studying their photoresponse characteristics and elucidating their adaptation and physiological response to the photosynthetic characteristics of the environment is the basis for the development and protection of the plant resources of the genus Chamaenerion. In this experiment,Li-6400 portable photosynthesis instrument was used to study the photoresponse characteristics of C. spp. in Mount Shergyla,and the photoresponse curves were fitted using a right-angle hyperbolic correction model. The results showed that Chamaenerion conspersum has low light compensation point[4. 931 μmol/( m^2·s) ],high light saturation point[1 000 μmol/( m^2·s) ],and strongest adaptability to light,which is one of the determinants of its distribution at each elevation of Mount Shergyla. Chamaenerion angustifolium subsp. circumvagum has higher light compensation point [11. 848 μmol/( m^2·s) ],low light saturation point[800 μmol/( m^2·s) ],and weakest adaptability to light,and it is a typical sciophilous plant. This result is consistent with the habitats( Rhododendron wardii shrub and spruce forest margin) that C. angustifolium are distributed in Mount Shergyla. C. angustifolium and Chamaenerion latifolium have higher light compensation points and higher light saturation points,suggesting that the adaptability of C. angustifolium and C. latifolium to the light environment is weak. This can also explain the narrow distribution of C. angustifolium and C. latifolium in Mount Shergyla. There are certain degree of differences in the responses of net photosynthetic rate( Pn),intercellular CO_2 concentration( Ci),stomatal conductance( Gs) and transpiration rate( Tr) of the three species and one variant of Chamaenerion to different photosynthetically active radiation( PAR). With the increase of light intensity,the Pn,Gs and Tr of Chamaenerion spp. increased significantly,and the Ci decreased. The Pn of C. conspersum and C. latifolium differed insignificantly,but they were both higher than that of C. angustifolium. The Pn of C. angustifolium subsp. circumvagum was the lowest. The Gs of C. conspersum and C. latifolium differed insignificantly,but they were both higher than that of C. angustifolium subsp. circumvagum. The Gs of C. angustifolium was the lowest. There was no obvious difference in Ci between C. angustifolium and C. latifolium,of which the Ci was both higher than that of C. conspersum. The Ci of C. angustifolium subsp. circumvagum was the lowest. C. angustifolium subsp. circumvagum had the highest Tr,followed by C. angustifolium and C. conspersum( no obvious difference),and C. latifolium had the lowest Tr. The light utilization efficiency of C. spp. ranked as C. angustifolium subsp. circumvagum < C. angustifolium < C. latifolium < C. conspersum. The light suppression phenomenon was evident in C. angustifolium,C. angustifolium subsp. circumvagum and C. latifolium. C. conspersum is most suitable for application under high light intensity conditions in Tibet. C. angustifolium,C. angustifolium subsp. circumvagum and C. latifolium should be shaded properly under conditions of high light intensity in the cultivation process,while C. conspersum needs to be supplemented with light during the cultivation process.

Effects of surface adsorbed oxygen, applied voltage, and temperature on UV photoresponse of ZnO nanorods

The ultraviolet(UV) photoresponses of ZnO nanorods directly grown on and between two micro Au-electrodes by using electric-field-assisted wet chemical method are measured comprehensively under different conditions, including ambient environment, applied bias voltage, gate voltage and temperature. Experimental results indicate that the photoresponses of the ZnO nanorods can be modulated by surface oxygen adsorptions, applied voltages, as well as temperatures. A model taking into account both surface adsorbed oxygen and electron-hole activities inside ZnO nanorods is proposed. The enhancement effect of the bias voltage on photoresponse is also analyzed. Experimental results shows that the UV response time(to 63%) of ZnO nanorods in air and at 59°C could be shortened from 34.8 s to 0.24 s with a bias of 4 V applied between anode and cathode.

An Experimental Setup for Study of Photoresponse of High T_c Superconductors

We have developed an experimental setup that has been proven suitable for the study of photoresponse of high Tc superconductors. The distinguish feature of this experimental setup lies mainly in the data acquisition system which is equipped with computer as well as the IEEE-488 interface bus. which ensures the accuracy to experimental results. Using the experimental setup, the optical response to laser radiation in high-Tc superconductors has been examined, both of bolometric effect and nonequilibrium optical response are revealed.

Photoresponse Process and Model Comparison of Paeonia ludlowii under Saline-alkali Stress

The research aimed to analyze changes in photosynthetic characteristics of Paeonia ludlowii under saline-alkali stress, and annual seedlings of P. ludlowii were taken as the materials. Photoresponse process of P. ludlowii leaves under saline-alkali stress was simulated, and different models were used to fit photoresponse curve. The results showed that P n of P. ludlowii leaves showed the trend of first rising and then declining with PAR increased under saline-alkali stress;both G s and T r showed a rising trend with PAR increased;C i showed the trend of first declining and then rising with PAR increased. Photoresponse curve fitted by modified rectangular hyperbolic model had the best effect, and it was the optimal fitting model. P. ludlowii could adapt to saline-alkali stress in lower concentration, showing that P. ludlowii could be introduced and cultivated in saline-alkali land at a lower level.

Anisotropic photoresponse of layered rhenium disulfide synaptic transistors

Layered ReS_(2) with direct bandgap and strong in-plane anisotropy shows great potential to develop high-performance angle-resolved photodetectors and optoelectronic devices.However,systematic characterizations of the angle-dependent photoresponse of ReS_(2) are still very limited.Here,we studied the anisotropic photoresponse of layered ReS_(2) phototransistors in depth.Angel-resolved Raman spectrum and field-effect mobility are tested to confirm the inconsistency between its electrical and optical anisotropies,which are along 120°and 90°,respectively.We further measured the angle-resolved photoresponse of a ReS_(2) transistor with 6 diagonally paired electrodes.The maximum photoresponsivity exceeds 0.515 A·W^(-1) along b-axis,which is around 3.8 times larger than that along the direction perpendicular to b axis,which is consistent with the optical anisotropic directions.The incident wavelength-and power-dependent photoresponse measurement along two anisotropic axes further demonstrates that b axis has stronger light-ReS_(2) interaction,which explains the anisotropic photoresponse.We also observed angle-dependent photoresistive switching behavior of the ReS_(2) transistor,which leads to the formation of angle-resolved phototransistor memory.It has simplified structure to create dynamic optoelectronic resistive random access memory controlled spatially through polarized light.This capability has great potential for real-time pattern recognition and photoconfiguration of artificial neural networks(ANN)in a wide spectral range of sensitivity provided by polarized light.

Trap induced slow photoresponse of single CdS nanoribbons

Wurtzite CdS nanoribbons are prepared by using a simple thermal evaporation method. Electron microscopy shows that the ribbons are smooth in surface and uniform in size. Besides the intrinsic emission, the photoluminescence spectrum of a CdS nanoribbon shows a peak at about 580 nm, which may arise from the defect- and the trap- related transitions. The photoresponse of single CdS nanoribbons is researched. When these nanoribbons are exposed to a laser with a wavelength of 400 nm, their conductivity is enhanced greatly. The conductivity of CdS nanoribbons cannot be restored to a value without any illumination even at 5 minutes after the illumination. A model is proposed to explain this phenomenon, which may be due to a slow photoresponse induced by the trap.

Edge assisted epitaxy of CsPbBr_(3)nanoplates on Bi_(2)O_(2)Se nanosheets for enhanced photoresponse

Bi_(2)O_(2)Se has been proved to be a promising candidate for electronic and optoelectronic devices due to their unique physical properties.However,it is still a great challenge to construct the heterostructures with direct epitaxy of hetero semiconductor materials on Bi_(2)O_(2)Se nanosheets.Here,a two-step chemical vapor deposition(CVD)route was used to directly grow the CsPbBr_(3)nanoplate-Bi_(2)O_(2)Se nanosheet hetero structures.The CsPbBr_(3)nanoplates were selectively grown on the Bi_(2)O_(2)Se nanosheet along the edges,where the dangling bonds provide the nucleation sites.The epitaxial relationships between CsPbBr3 and Bi_(2)O_(2)Se were determined as[200]_(Bi_(2)O_(2)Se)‖[110]_(CsPbBr_(3))and[110]_(Bi_(2)O_(2)Se)‖[200]_(CsPbBr_(3))by transmission electron microscopy characterization.The photoluminescence(PL)results reveal that the formation of heterostructures results in the remarkable PL quenching due to the type-Ⅰband arrangement at CsPbBr_(3)/Bi_(2)O_(2)Se interface,which was confirmed by ultraviolet photoelectron spectroscopy(UPS)and Kelvin probe measurements,and makes the photogenerated carriers transfer from CsPbBr_(3)to Bi_(2)O_(2)Se.Importantly,the photodetectors based on the heterostructures exhibit a 4-time increase in the responsivity compared to those based on the pristine Bi_(2)O_(2)Se sheets,and the fast rise and decay time in microsecond.These results indicate that the direct epitaxy of the CsPbBr_(3)plates on the Bi_(2)O_(2)Se sheet may improve the optoelectronic performance of Bi_(2)O_(2)Se based devices.

Enhanced ultraviolet photoresponse based on ZnO nanocrystals/Pt bilayer nanostructure

The development of solution strategies for Zinc oxide(Zn O) quantum dots provides a pathway to utilizing Zn O nanocrystal thin films in optoelectronic devices.In this work,quasi-spherical Zn O quantum dots with a diameter of 5 nm are synthesized by using ethanol as a solvent.Zn O nanocrystal thin film is obtained by spin-coating Zn O quantum dots on a Au interdigital electrode(IDE)/Al2O3 substrate and annealing at different temperatures in order to yield the optimal photosensitive on/off ratio of Zn O.For further enhancing the responsivity,ion sputtering is utilized to deposit Pt nanoparticles on the surface of Zn O nanocrystal thin film,the responsivity of the Zn O/Pt bilayer nanostructure increases from 0.07 A/W to 54 A/W,showing that the metal/inorganic nanocrystal bilayer nanostructure can be used to improve the performance of optoelectronic devices.The excellent properties of Zn O/Pt bilayer nanostructure have important applications in future electronic and optoelectronic devices.

A self-driven photodetector based on a SnS_(2)/WS_(2) van der Waals heterojunction with an Al_(2)O_(3) capping layer

Photodetectors based on two-dimensional(2D) materials have attracted considerable attention because of their unique properties. To further improve the performance of self-driven photodetectors based on van der Waals heterojunctions, a conductive band minimum(CBM) matched self-driven SnS_(2)/WS_(2) van der Waals heterojunction photodetector based on a SiO2/Si substrate has been designed. The device exhibits a positive current at zero voltage under 365 nm laser illumination.This is attributed to the built-in electric field at the interface of the SnS_(2) and WS_(2) layer, which will separate and transport the photogenerated carriers, even at zero bias voltage. In addition, the Al_(2)O_(3) layer is covered by the surface of the SnS_(2)/WS_(2) photodetector to further improve the performance, because the Al_(2)O_(3) layer will introduce tensile stress on the surface of the 2D materials leading to a higher electron concentration and smaller effective mass of electrons in the films. This work provides an idea for the research of self-driven photodetectors based on a van der Waals heterogeneous junction.

宽光谱响应范围的氮化碳纳米片的制备及其光催化产氢性能研究

以块体氮化碳(CN)为前驱物,采用氧化剥离制备氧化型氮化碳纳米片(o-CN NSs),将o-CN NSs还原制得了还原型氮化碳纳米片(r-CN NSs)。o-CN NSs和r-CN NSs厚度均约2 nm,且都保留了纯CN的庚嗪环骨架结构;相比于o-CN NSs,r-CN NSs具有更小的禁带宽度(2.62 eV)、更宽的光响应范围(485 nm)和更高的产氢速率(1700μmol/(g·h));r-CN NSs的光催化产氢速率是CN的8.5倍、o-CN NSs的2.1倍。经过20 h的循环测试,r-CN NSs的光催化产氢速率没有衰减,具备良好的光催化稳定性。实验和理论分析表明,r-CN NSs是边缘基团为氨基的纳米片结构,氨基的引入改善了纳米片的结晶性,提高了电子和空穴的分离效率、拓宽了纳米片的光响应范围,从而导致光催化性能增强。

单层SnS的光电效应及应变工程的第一性原理研究

光电探测器在工业制造和军事国防等各领域用途广泛。近年来,研究者在寻找一种兼具极化灵敏度高与光响应强的特点的光电探测器。在可见光范围内,SnS是一种制作具有各向异性光电探测器的半导体材料。本文基于第一性原理,采用非平衡态格林函数(NEGF)与密度泛函理论(DFT)结合的方法对单层SnS两个器件方向(Armchair和Zigzag)的光电性质进行理论计算。研究发现,在零偏压下,两个方向的光电流数值均较小,通过加偏压的方法可以获得稳定的光电流。计算了小偏压0.1~1.0 V(间隔0.1 V)、线性偏振光照射下最大光响应随光子能量的变化,发现单层SnS在光子能量为2.4与3.2 V时最大光响应数值较大且十分稳定,并结合能带图和态密度图分析了光响应产生的微观机制。本文通过计算消光比,发现单层SnS具有极强的偏振灵敏度。最后,通过施加双轴应变的方法,器件的不对称性显著增加,极大增强器件在零偏压下的光电流,其中压缩应力数值为-6%时对光电流的提升十分明显。希望以上结果能为单层SnS设计用于光电探测器提供理论参考。

水凝胶中的抗菌技术

细菌感染及其耐药性是当今世界面临的巨大健康难题之一,每年给全世界造成了巨大的人员伤亡和经济损失。水凝胶是一种三维聚合物网络结构胶体,其亲水性好,具备独特的三维网络、良好的生物相容和细胞粘附性,因而水凝胶是一种适用于抗菌领域的新型生物材料,也有望于成为解决抗生素耐药性的潜力抗菌材料。根据相应的抗菌方式,水凝胶中的抗菌技术可以大致归纳为以下几类:(i)负载抗菌物质水凝胶;(ii)具有固有抗菌活性水凝胶;(iii)利用光响应疗法的抗菌水凝胶。文章简略介绍各种水凝胶抗菌技术的基本原理,方法和应用,并对未来存在的困难和挑战进行初步探讨。

载阿霉素光响应纳米锆基MOFs构建及细胞毒性研究

为了克服乳腺癌治疗药物阿霉素存在毒副作用大、作用时间短等限制,本研究采用含偶氮苯侧链结构的联苯羧酸与Zr4+构建了一种新型光响应纳米金属有机框架(U67-AZO-COOH)作为药物载体,成功地将阿霉素负载其中。通过粉末X射线衍射、扫描电镜、傅里叶变换红外光谱、全自动比表面及孔隙度分析等技术手段对其结构进行了详细表征,得到在紫外光照射下阿霉素的载药率可由18.57%降至7.31%。体外释放实验和细胞毒性实验结果表明,该纳米药物复合物具有高载药量、良好的生物相容性,其在微酸环境下的释放率57.02%高于生理条件39.26%,表现出显著的缓释效果,能够减少对正常细胞的损害,存活率从39.88%提高到81.73%。这为新型光响应纳米金属有机框架在药物传递领域的广泛应用提供了新的可能性。

Mixed-dimensional stacked nanocomposite structures for a specific wavelength-selectable ambipolar photoresponse

Mixed-dimensional composite structures using zero-dimensional(0D)quantum dots(QDs)and two-dimensional(2D)transition metal dichalcogenides(TMDs)materials are expected to attract great interest in optoelectronics due to the potential to generate new optical properties.Here,we report on the unique optical characteristics of a devices with mixed dimensional vertically stacked structures based on tungsten diselenide(WSe_(2))/CdSeS QDs monolayer/molybdenum disulfide(MoS_(2))(2D/0D/2D).Specifically,it exhibits an ambipolar photoresponse characteristic,with a negative photoresponse observed in the 400-600 nm wavelength range and a positive photoresponse appeared at 700 nm wavelength.It resulted in the high negative responsivity of up to 52.22 mA·W^(−1)under 400 nm,which is 163 times higher than that of the photodetector without CdSeS QDs.We also demonstrated the negative photoresponse,which could be due to increased carrier collision probability and non-radiative recombination.Device modeling and simulation reveal that Auger recombination among the types of non-radiative recombination is the main cause of negative photocurrent generation.Consequently,we discovered ambipolar photoresponse near a specific wavelength corresponding to the energy of quantum dots.Our study revealed interesting phenomenon in the mixed low-dimensional stacked structure and paved the way to exploit it for the development of innovative photodetection materials as well as for optoelectronic applications.

MgBi-LDHs和NiBi-LDHs光催化降解罗丹明B性能

通过共沉淀法制备MgBi-LDHs和NiBi-LDHs两种光催化剂,采用紫外可见分光光度计对催化剂进行表征分析,并探究了溶液初始pH值、催化剂物质的量之比和光照类型对罗丹明B(RhB)降解效果的影响;采用扫描电子显微镜(SEM)对材料进行形貌和元素分布进行分析。实验结果表明:溶液初始pH值为6时,在长弧氙灯照射条件下,光照4 h,Mg-Bi(3∶1)降解效果最佳,去除率达91.24%;在紫外高压汞灯照射条件下,光照4 h,Mg-Bi(5∶1)降解效果最佳,去除率达92.16%。该光催化剂的制备为降解罗丹明B提供了一种廉价、简便的措施,对其他高效光催化剂的合成具有一定的指导意义。

光致异构分子修饰改性富勒烯复合材料的合成及性能研究

C60富勒烯为零维碳纳米材料,具有笼状空间结构和优异物化特性(如超导、光催化等),在能源、电子、医药及太阳能等领域中具有极大应用潜力。然而,C60自身特殊的分子结构决定了其本征较差的溶解性和加工性能,限制了其实际应用。因此,高效的表面修饰和表面功能化成为C60复合材料当今的研究热点。针对传统C60复合材料制备方法需要使用有机溶剂、产率不高的现状,提出了一种简便的水相合成法,即通过表面羟基化和自由基加成反应,合成具有光敏特性的偶氮苯分子修饰的富勒烯复合材料AZOC-FC60。利用红外光谱、X射线光电子能谱、紫外可见光谱等技术,对复合材料的结构和光致异构特性进行表征。结果表明,AZOC-FC60复合材料中,AZOC与FC60为共价接枝方式,AZOC分子的功能密度约为1∶41(即每41个C原子接枝1个AZOC分子),使AZOC-FC60复合材料具有较高的功能密度。AZOC-FC60复合材料的结构与FC60类似,为球状团聚结构,但其表面凹凸不平,这是由于AZOC接枝在FC60表面所导致。通过增强分子间相互作用,提高了AZOC-FC60复合材料的光响应特性和结构稳定性,使其回复半衰期提高了4个数量级。综上研究,开发了一种工艺简便的富勒烯复合材料的水相合成法,极大拓展了该复合材料在光热存储/光催化等领域中的应用潜力。

STUDY ON PHOTODYNAMIC AND PHOTORESPONSIVE AZO POLYELECTROLYTES

Several kinds of novel azobenzene-containing polyelectrolytes with special molecular design have been developedfrom acryloyl chloride or epoxy based precursor polymers. The acryloyl chloride based precursor polymer, poly(acryloylchloride), was prepared by free radical polymerization of acryloyl chloride. The azo polyelectrolytes were prepared by anesterification reaction between the precursor polymer and corresponding azo chromophores containing a reactive hydroxylgroup, followed by hydrolysis of the unreacted acyl chloride groups. The epoxy based precursor polymer was prepared by thereaction between 1,4-cyclohexanedimethanol diglycidyl ether and aniline, and postfunctionalized by azo coupling reaction toform azo polymers containing chromophores with ionizable groups. The polyelectrolytes were characterized by elementalanalysis, ~1H-NMR, IR and UV-Vis spectroscopy. The photodynamic and photoresponsive properties, as well as self-assemblyof these azo polyelectrolytes are reported in this paperp.

Synthesis, Characterisation and Photoresponsive Studies of Lignin Functionalised with 2-(5-(4-dimethylamino-benzylidin)-4-oxo-2-thioxo- thiazolidin-3-yl)-acetic Acid

A chromophoric system 2-(5-(4-dimethylamino-benzylidin)-4-oxo-2-thioxo-thiazoli din-3-yl)acetic acid with push-pull electron modulation was synthesised and incorporated onto lignin core (technical lignin, lignin sulphonic acid M.W. 52,400) and the photo responsive behaviour was investigated. The product was characterised by UV-visible, fluores-cence, FT-IR, and NMR spectroscopic methods. The results of the studies show that the incorporation of the chromo-phoric system on to the lignin core enhanced the light absorption and light stabilization properties of the chromophoric system. The remarkable stability on irradiation provides a novel photo responsive system with excellent light fastening properties which would find application in coating materials, dyes, paints etc.

Characterization of Self-driven Cascode-Configuration Synchronous Rectifiers

This paper presents a cascode configuration synchronous rectifier device based on silicon MOSFET and Schottky diode,which can replace traditional power diode directly.This structure has self-driven ability with simple external circuit,and the conduction characteristic is preferable to a power diode.Static characterization and switching behavior analysis of proposed structure are conducted in this paper.The switching process is illustrated in detail using real model which considers the parasitic inductances and the nonlinearity of junction capacitors.The real time internal voltage and current value during switching transition are deduced with the equivalent circuit.To validate the analysis,two voltage specification rectifiers are built.Finally,double-pulse test results and the practical design example verify the performance advantages of proposed structure.