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.

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.

Enhanced ultraviolet photoresponse based on ZnO nanocrystals/Pt bilayer nanostructure

The development of solution strategies for Zinc oxide （ZnO） quantum dots provides a pathway to utilizing ZnO nanocrystal thin films in optoelectronic devices. In this work, quasi-spherical ZnO quantum dots with a diameter of 5 nm are synthesized by using ethanol as a solvent. ZnO nanocrystal thin film is obtained by spin-coating ZnO quantum dots on a Au interdigital electrode （IDE）/AI203 substrate and annealing at different temperatures in order to yield the optimal pho- tosensitive on/off ratio of ZnO. For further enhancing the responsivity, ion sputtering is utilized to deposit Pt nanoparticles on the surface of ZnO nanocrystal thin film, the responsivity of the ZnO/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 ZnO/Pt bilayer nanostructure have important applications in future electronic and optoelectronic devices.

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.

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.

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.

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.

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.

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.

A self-powered solar-blind UV-enhanced Bi_(2)Se_(3)/a-Ga_(2)O_(3)/p-Si heterojunction photodetector for full spectral photoresponse and imaging

Self-powered full-spectrum photodetectors(PDs)offer numerous advantages,such as broad application fields,high precision,efficiency,and multi-functionality,which represent a highly promising and potentially valuable class of detectors for future development.However,insensitive response to solar-blind ultraviolet(UV)and complex and expensive preparation processes greatly limit their performance and practical application.In this study,a self-powered full-spectrum Bi_(2)Se_(3)/a-Ga_(2)O_(3)/p-Si heterojunction PD with high sensitivity for solar-blind UV band prepared by a simple and low-cost two-step synthesis method is presented.Experiments results reveal that the developed PD has an excellent performance,such as high sensitivity from 200 to 850 nm,and a responsivity of 1.38 mA/W as well as a detectivity of 3.22×10^(10) Jones under 254 nm light at zero bias.Additionally,the unencapsulated device displays exceptional stability and imaging capabilities.It is expected that Bi_(2)Se_(3)/a-Ga_(2)O_(3)/p-Si heterojunction PD with a simple and low-cost synthesis method has great potential for self-powered full-spectrum photodetectors.

Tune the photoresponse of monolayer MoS_(2) by decorating CsPbBr_(3) perovskite nanoparticles

Tuning the photoresponse of monolayer MoS_(2) could extend its potential application in many fields,however,it is still a challenge.In this study,CsPbBr_(3) nanoparticles were prepared and spin-coated on the surface of monolayer MoS_(2) to fabricate hybrid CsPbBr_(3)/MoS_(2) photodetectors.By combing the photoelectrical property of the CsPbBr_(3),the synergistic effect has been systematically studied from its carrier mobility,photoresponse and detectivity.It was found that nanofilm-coating of CsPbBr_(3)would impede the photoelectric performance due to the electron-hole recombination facilitated by the defects at the interface of C PbBr_(3) and MoS_(2) films.While the nanoparticles decorating was observed to significantly improve the conductivity of the monolayer Mo S_(2),which also increased the on/off ratio of the MoS_(2) transistor from 8.2×10~3 to 4.4×10^(4),and enhanced the carrier mobility from 0.090 cm^(2)V^(-1)s^(-1)to 0.202 cm^(2)V^(-1)s^(-1),ascribing to a mixed electron recombination-injection process.Furthermore,the CsPbBr_(3) nanofilm would decrease the responsivity to 136 and 178 A/W under the light wavelength of 400 and 500 nm,respectively,while decorating CsPbBr_(3) nanoparticles improve the photoresponse to 948 and 883 A/W with the detectivity at the level of 10^(11)Jones.This work may provide an easy and cost-efficient way to tune the photoresponse of MoS_(2) photodetectors.

Observation of ambipolar photoresponse from 2D MoS_(2)/MXene heterostructure

Two-dimensional materials have been demonstrated as promising toolboxes for optoelectronics.Transition metal carbides and nitrides(MXenes),members of an emerging family of two-dimensional materials,have drawn extensive attention in optoelectronics owing to their excellent conductivity and tunable electronic properties.Herein,a photodetector based on the two-dimensional van der Waals heterostructure of Ti_(3)C_(2)T_(x)MXene and a MoS_(2)monolayer was constructed to observe the ambipolar photoresponse,which showed a positive photoresponse in the visible spectrum(500-700 nm)and a negative photoresponse at longer wavelengths(700-800 nm).The device exhibited a high negative responsivity of 1.9 A/W and a detectivity of 2.1×10^(10)Jones under 750 nm light illumination.Detailed experiments demonstrate that the negative photoresponse arises from the heterostructureinduced trap energy level,which confines the excited photoelectrons and leads to an inverse current.This work demonstrates a unique optoelectronic phenomenon in MoS_(2)/MXene heterostructures and provides valuable insights into the development of new photodetection materials.

Plasmon-enhanced photoresponse of deep-subwavelength GaAs NW photodetector

According to optical diffraction limit, the photoresponsity of nanowire(NW)-based photodetector exponentially decreases when its NW diameter reduces to the range of deep subwavelength. In this paper, we demonstrate a photoresponse-enhanced method of the deep-subwavelength Ga As NW photodetector by using a plasmon-driven dipole antenna. Considering that the enhancement is extremely influenced by the shape and size of antenna, the structure of antenna is optimized by finite difference time domain(FDTD) solutions. The optimal structure of antenna optimizes the responsivity-enhanced factors to 1123.3 and 224.7 in NW photodetectors with NW diameters of 20 nm and 60 nm, respectively. This photoresponse-enhanced method is promising for easy-integration high-performance nanoscale photodetectors.

STUDY ON PHOTORESPONSE MECHANISM OF HIGH T_c YBa_2 Cu_3O_(7-x) SUPERCONDUCTING FILMS AT TEMPERATURES IN THE TRANSITION REGION

Since the discovery of high temperature oxide superconductors in 1986, it is possible to adapt superconducting materials for technological applications at liquid nitrogen. One of the important applications is the fabrication of superconducting optical detector. This kind of device has good performances of wide response spectrum (from the visible to the millimeter),

Annealing Effects on the Structural, Optical, and UV Photoresponse Properties of ZnO Nanostructures Prepared by RF-Magnetron Sputtering at Different Deposition Temperatures

Undoped ZnO nanostructures were deposited on SiO2/Si substrates via radio 11：equency magnetron sputtenng at different deposition temperatures （room temperature, 200, 300, and 400 ℃）. The prepared samples were annealed at 500 ℃ for 2 h under an N2 flow. The structural, surface morphological, optical, and photoresponse characteristics of ZnO nanostructures as deposited and after annealing were then investigated. The energy bandgaps of all samples after annealing （3.22-3.28 eV） decreased compared with those of the as-deposited specimens. The barrier height increased when the deposition temperature increased and reached 0.77 eV at 400 ℃ after annealing with a leakage current of 0.17 gA at a 5 V bias. The UV photodetector device which was deposited at the optimal temperature of 300 ℃, has 12.51 × 10^3% pho- tosensitivity, 2.259 pA dark current, 0.508 s response time, and 0.466 s recovery time. The dark current significantly decreased for all samples after annealing. The proposed UV photodetectors exhibit high performance, high photosensi- tivity, shorter response and recovery times, and excellent stability at lower bias voltages of 5 and 2 V.

Wavelength-selectivity polarization dependence of optical absorption and photoresponse in SnS nanosheets

The optical and optoelectronic characteristics of SnS nanosheets with strong anisotropic crystal structure are researched.Transmission electron microscopy and polarized Raman spectra are used to determine the crystal orientation of SnS nanosheets.The photodetector based on SnS nanosheets exhibits the carrier mobility of 37.75 cm^(2)/V·s,photoresponsivity of 310.5 A/W and external quantum efficiency of 8.56×10^(4)%at 450 nm.Optical absorption around the absorption edge presents obvious polarization sensitivity with the highest optical absorption dichroic ratio of 3.06 at 862 nm.Due to anisotropic optical absorption,the polarized photocurrent appears as the periodic change affected by the polarized direction of the incident light at 808 nm.Overall,SnS nanosheets show good potential in the future application of the polarized photodetectors for specific wavelength.

A dynamic photoresponse model for a pinned photodiode in CMOS image sensors

A novel dynamic photoresponse model for complementary metal-oxide-semiconductor(CMOS)image sensors with pinned photodiode(PPD)structures is proposed.The PPD is regarded as the bonding structure of the two p-n junctions.The transient current equation of the two junctions is calculated by the current-voltage formula of the p-n junction,and the photoresponse curve of the PPD is calculated and drawn by the numerical solution.Simulation results show that the dynamic model successfully restores the entire process of the electron accumulation in the PPD.The difference between the full well capacity(FWC)values which were calculated by the proposed model and the simulation results is less than 5%,which is much smaller than the error of 40%for the traditional model.

Construction of n-TiO_(2)/p-Ag_(2)O Junction on Carbon Fiber Cloth with Vis-NIR Photoresponse as a Filter-Membrane-Shaped Photocatalyst

The development of effective and reusable photocatalysts with broad-spectra activity has attracted attention.Herein,we have constructed n-TiO_(2)/p-Ag_(2)O junction on carbon fiber(CF)cloth as an efficient and recyclable photocatalyst.With CF cloth as the substrate,TiO_(2) nanorods(length:1-2μm)are prepared by a hydrothermal process,and the in-situ growth of Ag_(2)O nanoparticles(10-20 nm)is then realized by chemical bath deposition route.The flexible CF/TiO_(2)/Ag_(2)O cloth(area:4×4 cm^(2))shows a broad and strong photo-absorption(200-1000 nm).Under the illumination of visible-light(λ>400 nm),CF/TiO_(2)/Ag_(2)O cloth can efficiently eliminate 99.2%rhodamine B(RhB),99.4%acid orange 7(AO7),87.6%bisphenol A(BPA),and 89.5%hexavalent chromium(Cr^(6+))in 100 min,superior to CF/Ag_(2)O cloth(83.5%RhB,60.0%AO7,31.2%BPA and 41.8%Cr^(6+)).In particular,under the NIR-light illumination(980 nm laser),CF/TiO_(2)/Ag_(2)O cloth can remove 70.9%AO7 and 60.0%Cr^(6+) in 100 min,which are significantly higher than those by CF/Ag_(2)O cloth(19.8%AO7 and 18.9%Cr^(6+)).In addition,CF/TiO_(2)/Ag_(2)O cloth(diameter:10 cm),as a filter-membrane,can effectively wipe off 94.4%flowing RhB solution(rate:~1 L h^(−1))at 6th filtering/degrading grade.Thus,CF/TiO_(2)/Ag_(2)O cloth can be used as a Vis-NIR-responded filter-membrane-shaped photocatalyst with high-efficiency for purifying wastewater.

Analysis of optoelectronic properties of TiO_2 nanowiers/Si heterojunction arrays

The optoelectronic properties of n-TiO2NW/p-Si heterojunction fabricated by depositing TiO2 nanowires on a p-Si substrate are studied. Under excitation at a wavelength of 370 nm, the TiO2 nanowires produce a light emission at 435 nm due to the emission of free excitons. The I-V characteristics are measured to investigate the heterojunction effects under the dark environment and ultraviolet （UV） illumination, n-TiOzNW/p-Si has a p-n junction formed in the n-TiOz/p-Si beterojunction. TiO2NW/Si photodiode produces a pbotocurrent larger than dark current under UV illumination. It is observed that UV photons are absorbed in TiO2 and the heterojunction shows a 0.034-A/W responsivity at 4-V reverse bias.

Fabrication of azobenzene-functionalized porous polymers for selective CO_(2) capture

Many solid adsorbents have been prepared for the CO_(2)capture.In particular,the photoresponsive adsorbents have attracted extensive interests because of their tunable pore structure and variable responsive behaviors provoked by the external light.However,it is challenging to fabricate the photoresponsive adsorbents featured the big CO_(2)capacity and high CO_(2)selectivity.Herein,copolymerized between 4-phenylazobenzoyl chloride,2,4,6-trichloro-1,3,5-triazine and melamine,a series of azobenzenefunctionalized porous polymers(PTM-AZOs)are successfully synthesized.The PTM-AZOs are verified in possession of proper pore structures,large surface area and photoconductive properties through a series of characterization.The PTM-AZO-2 with the trans-isomerization exhibits the best CO_(2)adsorption amount of 2.7 mmol·g^(-1)(273 K and 0.1 MPa),while the CO_(2)/N_(2)selectivity can reach 2459 and 607 on the trans-and cis-isomerization,respectively.The regulatable pore structures controlled by the photoresponsive azobenzene groups affect the CO_(2)capture performance of the PTM-AZOs.