Fast Ultraviolet Research Articles

Influence of oxygen partial pressure on the performance of MoO3-based ultraviolet photodetectors

To save our motherland from the harmful ultraviolet (UV) ray, the essentiality of UV photodetectors is increasing gradually. Herein, the MoO3-x thin films are deposited onto the SiO2/Si substrates through a sputtering technique by varying the oxygen partial pressure (pO2) at a substrate temperature of 200°C to examine the UV photodetector performance. It is observed that the thickness of the thin film is decreased with an increase in the pO2 due to the less ejection of atoms from the oxidized target surface. Structural study confirms the improved crystalline nature of the thin film deposited at 5.0% of pO2 and results in better electrical properties. The photodetector performance under UV illumination is studied as a function of pO2. The linear behavior of the current-voltage (I-V) characteristics attests to the ohmic contact nature between the photoactive layer (MoO3-x) and the metal (Ag) electrode interface. The fabricated photodetector test-device achieves a high photocurrent of 11.22 µA, a fast response time of 100 ms, and a superior responsivity of 1.537 A/W even at a lower optical power density of 0.0292 mW/cm2. Finally, these enhanced figures of merit of the MoO3-based photodetector could show a significant path toward the development of fast UV photodetector and optoelectronic devices.

Dynamic ultraviolet harmonic beam pattern control by programmable spatial wavefront modulation of near-infrared fundamental beam.

The ultraviolet (UV) wavelength regime is attracting increasing attention because of its growing demand in semiconductor lithography, spectroscopy, and imaging applications owing to its high spatial resolution and high photon energy. However, beam shape control, beam delivery, and wavefront manipulation of UV laser beams usually require highly dedicated optics because of the strong UV absorption of most optical materials and the high surface precision required for tailoring short wavelengths, thus limiting a broader application of UV wavelengths. Here, we demonstrate a novel dynamic UV harmonic beam pattern control by manipulating the near-infrared (NIR) wavefront of the fundamental wavelength of a femtosecond pulse laser. The temporal and spatial coherences in an optical harmonic generation are known to be well preserved. Therefore, the spatial beam distribution of UV harmonic beams (λ = 400 and 266 nm for second and third harmonics, respectively) could be readily controlled by tailoring the wavefront of the driving infrared (IR) beam, and this approach can be expanded to higher-order harmonics in the vacuum ultraviolet (VUV) or extreme ultraviolet (EUV) regimes. Moreover, this enables fast polarization-sensitive UV beam switching at a speed of 6.7 frames/s in a depth-resolving manner. To efficiently separate the UV beam from the strong fundamental IR background beam, a non-collinear harmonic generation configuration is introduced. This facile dynamic UV beam control technique enables arbitrary wavefront control of UV laser beams for high-precision laser patterning, polarization-sensitive encryption, and 3D holograms.

Fast Outflowing Warm Absorbers in Narrow-line Seyfert 1 Galaxy PG 1001+054 Revealed by HST/COS Spectra

Narrow-line Seyfert 1 (NLS1) galaxies are an important type of active galactic nucleus (AGN), generally expected to be accreting at a high Eddington rate. The properties of their outflows and importance of AGN feedback remain intriguing. We report on the discovery of fast outflowing warm absorbers (WAs) in the NLS1 PG 1001+054 with velocities in the range of ∼7000–9000 km s−1. They are identified with blueshifted Lyα, N v, and Si iv lines in the high-resolution ultraviolet (UV) spectra taken with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. We perform photoionization modeling using XSTAR with three WAs. The derived physical properties are typical of WAs in terms of ionization and column density, whereas the outflow velocities are significantly higher. The estimated location of these WAs ranges from 1 to 73 parsecs away from the AGN. Together with previous detection of high ionization absorbers in the X-ray for PG 1001+054, we suggest that fast outflowing UV absorbers are probably part of a multiphase outflow. Such a structure is likely produced by the outflow launched from the AGN at an accretion disk scale, which shocks the ambient interstellar medium (ISM), producing stratified absorbers. Assuming contribution from the three WAs at tens of parsecs, the estimated ratio between the kinetic power of the outflow and AGN Eddington luminosity could reach 1.7%, raising the possibility of sufficient influence on the host galaxy when compared to some theoretical models for efficient AGN feedback.

Development of spectrophotometric method for simultaneous estimation of dexketoprofen and dicyclomine

Objectives: The objective of this work was to develop a simple, fast, and reliable ultraviolet (UV) spectrophotometric method for simultaneous estimation of dexketoprofen and dicyclomine in tablet dosage forms. Materials and Methods: Dexketoprofen and dicyclomine solutions were prepared separately in the range of 2 µg/mL–10 µg/mL. The solutions were scanned over a range of 200–400 nm. The isoabsorptive point for both drugs was determined. The developed method was evaluated for accuracy, precision, and linearity. In linearity correlation coefficient was found. Results: A simple, fast, and reliable UV spectrophotometric method was developed for quantitative estimation of dexketoprofen and dicyclomine. The precision study showed that the percent relative standard deviation was within the range of acceptable limits, and the percent recovery was found to be in the range of 0.3–1.5 (intraday) and 0.23–1.7 (interday). In the accuracy study, the percent recovery was found to be 97 (50%), 96 (100%), and 95 (150%). Conclusion: The developed spectrophotometric method in this study was simple, accurate, precise, specific, sensitive, and reproducible and can be directly and easily applied to pharmaceutical dosage forms.

Robust and fast response solar-blind UV photodetectors based on the transferable 4H-SiC free-standing nanowire arrays

Wide band gap semiconductor 4 H -SiC has been considered as the most promising candidate for developing solar blind ultraviolet (UV) photodetectors (PDs). However, the absence of PDs constructed by the desired 4 H -SiC nanostructures greatly limits their performance and practical application. In this study, the free-standing 4 H -SiC bamboo-like nanowire arrays with an even diameter/height of 30 nm/35 µm prepared by the anodic oxidation of 4 H -SiC bulk single crystal in a top-down manner are used to develop the solar-blind PDs. Experiment results reveal that the developed PDs can have an excellent solar-blind detection performance such as high sensitivity to 275 and 365 nm UV light, a considerable light-dark ratio (∼44.3), remarkably low dark current, fast response (47.3 ms), excellent repeatability and stability. Additionally, the unencapsulated PDs can have an excellent high-temperature stability up to 300 ºC. It is expected that the 4 H -SiC nanowire arrays-based PDs can have more potential than their counterpart bulk material for the future optoelectronic device applications. • The MSM solar-blind UV photodetectors based on bamboo-like 4 H -SiC nanowire arrays have been successfully fabricated. • The developed photodetectors can have a large light-dark ratio, high photoresponsivity, and remarkably low dark current. • The resulting photodetectors can achieve the fast response and an excellent high-temperature stability up to 300 ºC.

Synthesis of interface modified MoS2/ZnO heterostructure via simple hydrothermal method and their enhanced UV photodetection characteristics with ultrafast photoresponse speed

Ultraviolet (UV) photodetectors employing ZnO nanorods (NRs) exhibit high photocurrent stability; however, UV photodetectors fabricated using ZnO NRs have several disadvantages. In this study, we fabricated high-performance UV photodetector using hydrothermally grown MoS2/ZnO heterostructure. The surface morphology of MoS2/ZnO heterostructure exhibited sea-urchin structure with a greater length and diameter than ZnO NRs. In addition, the formation of MoS2/ZnO heterostructure can form a type-II band alignment at interface between MoS2 and ZnO, which facilitates the regulation of electron movement with large surface area. With respect to UV photoresponse, MoS2/ZnO heterostructure exhibited a significantly improved photocurrent value compared to ZnO NRs and MoS2/ZnO heterostructure had extremely fast UV photoresponse speed with highly improved photoresponsivity, photosensitivity, and photoselectivity. Therefore, it was concluded that hydrothermally grown MoS2/ZnO heterostructure is a suitable solution to drawbacks of ZnO-based UV photodetectors; consequently, the proposed method can be used to fabricate ZnO-based high-performance optoelectronics applied in various fields.

Enhanced Ultraviolet Photoresponse Characteristics of Indium Gallium Zinc Oxide Photo-Thin-Film Transistors Enabled by Surface Functionalization of Biomaterials for Real-Time Ultraviolet Monitoring.

Indium gallium zinc oxide (IGZO) is one of the most promising materials for diverse optoelectronic applications based on thin-film transistors (TFTs) including ultraviolet (UV) photodetectors. In particular, the monitoring of UV-A (320-400 nm) exposure is very useful for healthcare applications because it can be used to prevent various human skin and eye-related diseases. However, the relatively weak optical absorption in the UV-A range and the persistent photoconductivity (PPC) arising from the oxygen vacancy-related states of IGZO thin films limit efficient UV monitoring. In this paper, we report the enhancement of the UV photoresponse characteristics of IGZO photo-TFTs by the surface functionalization of biomolecules on an IGZO channel. The biomaterial/IGZO interface plays a crucial role in enhancing UV-A absorption and suppressing PPC under negative gate bias, resulting in not only increased photoresponsivity and specific detectivity but also a fast and repeatable UV photoresponse. In addition, turning off the device without external bias completely eliminates PPC due to the internal electric field induced by the surface functionalization of biomaterials. Such a volatile feature of PPC enables the fast and repeatable UV photoresponse. These results suggest the potential of IGZO photo-TFTs combined with biomaterials for real-time UV monitoring.

Fast Response UV Detector by Vertically Allied ZrO2 Nanowire Array Through Glancing Angle Deposition

Vertically aligned zirconium dioxide (ZrO2) nanowire (NW) array based fast response ultraviolet (UV) detector has been fabricated upon ZrO2 thin film (TF) by glancing angle deposition (GLAD) technique. The detector shows ~1.4 fold lesser dark current and ~1.5 fold enhanced light current than the ZrO2 TF due to the formation of oxygen vacancies. Improved detector performances through ~1.8 fold high photosensitivity, low ideality, high barrier height and fast response (Tr = 0.26 sec and Tf = 0.25 sec) was also observed for ZrO2 TF/ZrO2 NW based device. Therefore, these improved optoelectronic performances will ensure that the vertically aligned ZrO2 TF/ZrO2 NW based device demonstrated good reliability in optoelectronic device applications.

UV response characteristics of mixed-phase MgZnO thin films with different structure distributions, high Iuv/Idark ratios, and fast speed MgZnO UV detectors with tunneling breakdown mechanisms

High-performance ultraviolet (UV) detectors with both high responses and fast speeds are hard to make on homogeneous crystal semiconductor materials. Here, the UV response characteristics of mixed-phase MgZnO thin films with different internal structure distributions are studied. The mixed-phase MgZnO-based detector with the given crystal composition has a high response at both deep UV light (96 A W−1 at 240 nm) and near UV light (80 A W−1 at 335 nm). Meanwhile, because of the quasi-tunneling breakdown mechanism within the device, the high-response UV detector also shows a fast response speed (tr = 0.11 μs) and recovery speed (td1 = 26 μs) at deep UV light, which is much faster than both low-response mixed-phase MgZnO-based UV detectors with other structure constitutions and reported high-response UV devices on homogenous crystal materials. The Idark of the device is just 4.27 pA under a 5 V bias voltage, so the signal-to-noise ratio of the device reached 23852 at 5.5 uW cm−2 235 nm UV light. The new quasi-tunneling breakdown mechanism is observed in some mixed-phase MgZnO thin films that contain both c-MgZnO and h-MgZnO parts, which introduce a high response, signal-to-noise ratio, and fast speed into mixed-phase MgZnO-based UV detectors at weak deep UV light.

Gamma radiation shielding properties of poly (methyl methacrylate) / Bi2O3 composites

This work investigated the gamma-ray shielding performance, and the physical and mechanical properties of poly (methyl methacrylate) (PMMA) composites embedded with 0–44.0 wt% bismuth trioxide (Bi2O3) fabricated by the fast ultraviolet (UV) curing method. The results showed that the addition of Bi2O3 had significantly improved the gamma shielding ability of PMMA composites. Mass attenuation coefficient and half-value layer were examined using five gamma sources (Cs-137, Ba-133, Cd-109, Co-57, and Co-60). The high loading of Bi2O3 in the PMMA samples improved the micro-hardness to nearly seven times that of the pure PMMA. With these enhancements, it was demonstrated that PMMA/Bi2O3 composites are promising gamma shielding materials. Furthermore, the fast UV curing exerts its great potential in significantly shortening the production cycle of shielding material to enable rapid manufacturing.

The high-speed ultraviolet photodetector of ZnO nanowire Schottky barrier based on the triboelectric-nanogenerator-powered surface-ionic-gate

Nanowires have a high specific surface area and high surface activity, and the surface states are key factors controlling the nanowire Schottky barrier. Therefore, adjusting the surface states is an important strategy for developing high-performance electronic and optoelectronic devices based on nanowire Schottky barriers. Here, a surface-ionic-gate modulation technique was developed to modulate the surface states and Schottky barrier of nanowires, based on the gas discharge induced by triboelectric nanogenerators (TENGs). It is demonstrated that the Schottky barrier height and electrical transport characteristics of the Ag/ZnO nanowires can be modulated by effectively controlling the surface states. The experimental results from different atmospheres show that O2− ions and electrons generated by gas discharge can form local ions on nanowires surface, which is the source for modulating surface states. Reversible modulation of the surface states and barrier height could be achieved by combining the surface-ionic-gate modulation with ultraviolet (UV) light. In addition, the recovery time of the ZnO nanowire Schottky barrier UV photodetector was reduced from 87 s to 0.3 s using the surface-ionic-gate modulation technique, the recovery speed increased 290 times, making it a universal method for achieving fast UV detection in different environments, such as in air, in oxygen, and in nitrogen. The TENG-based surface-ionic-gate modulation technique proposed here can modulate the surface states of nanowires in real time and in situ. This provides a novel method to study the dynamic generation and relaxation process of surface states and to develop high-performance electronic and optoelectronic nanodevices with broad application prospects.

Synthesis and characterization of Cu doped ZnO nanoparticles for stable and fast response UV photodetector at low noise current

The rising demand for optoelectronic devices to be operable in adverse environments necessitates the sensing of ultraviolet (UV) radiation. Here, a highly sensitive, fast responding Cu doped zinc oxide nanoparticles (Nps) based UV photodetector (PD) is reported. For the first time, Cu doped ZnO Nps are grown via forced hydrolysis of acetate salt of metals in a polyol medium. Various characterization methods including X-Ray diffraction, high resolution transmission electron microscopy and Fourier infrared spectroscopy are used to testify the presence of Cu element in ZnO Nps, although the diffuse reflectance and PL characterization are used to study the optical properties. The performance of the PD has been established by photocurrent measurements under different power density. Our device exhibited good photoresponse under UV illumination (375 nm) at 1 V bias voltage. Furthermore, the response of the PD is much better than other detectors based on oxide semiconductors nanostructures, and, especially, it shows a higher responsivity as compared with other photodetectors. In addition, achieved a highest responsivity of 40.12 A/W, quick response (rise/decay time of 0.8 s/3 s) and high sensitivity (2 × 104) for the Cu doped ZnO Nps annealed at 300 °C. It is established that the devices under higher power incident light show much lower 1/f noise. These results are meaningful to the noise control and performance improvement in the development of Schottky diode based PD-devices.

Fast response UV detection based on waveguide characteristics of vertically grown ZnO nanorods partially embedded in anodic alumina template

Zinc oxide (ZnO)-based ultraviolet (UV) detector has been fabricated and its photoresponse is studied in an out-of-plane contact configuration. Porous anodic aluminum oxide (AAO) template-based deposition method is adopted for the aligned and well-separated growth of ZnO nanorods (NRs). Through-hole in silicon (Si) by modified metal assisted chemical etching is used as a window for the electrochemical deposition of ZnO in the template and for out-of-plane electrical contacts during device analysis. The fabricated photodetector shows a fast response under UV (365 nm) light illumination, with rise and decay times of 31 ± 2 ms and 85 ± 3 ms, respectively. This fast response is analysed in terms of vertical growth and the waveguide nature of ZnO NRs embedded in anodic alumina. These results are further supported by a simulation comparing the electric field distribution of ZnO NR embedded in AAO with that of bare ZnO NR.

Highly sensitive and fast UV sensor based on fiber grating with easily producible photoreactive material

In this paper, a newly synthesized material has been proposed to improve the ultraviolet (UV) sensitivity of a non-etched fiber Bragg grating (FBG) for UV sensors, comparable to the high sensitivity of a previously reported UV sensor based on a diameter-downsized FBG. The photomechanical material was prepared simply by mixing an azobenzene compound and curing agent. An FBG was subsequently coated with the functional polymer using the UV curing process. We determined the best combination of the azobenzene compound exhibiting UV-induced mechanical stretching and the curing agent as a commercially available coating polymer to achieve the highest sensitivity in many combinations. The maximum wavelength shift of the non-etched FBG was 2.5 nm at a UV power of ∼2.5 mW/cm2. The sensitivity of the sensor was found to be related to the hardness of the coating material. In addition, we suggested a simple algorithm to determine the presence and absence of UV radiation using the change in the slope of the wavelength shift over time obtained through the first derivative of the measured data. The proposed method is very easy to use, providing the information at a glance, and our fast UV sensor is sufficiently powerful for applications such as corona discharge detection and lightning strike monitoring.

Halide Perovskites for Selective Ultraviolet-Harvesting Transparent Photovoltaics

Summary Halide perovskite materials have emerged as a potential Si replacement with excellent photovoltaic properties. There has been growing interest in applying halide perovskites to semitransparent and spatially segmented transparent photovoltaics (TPVs) to enable a greater range of deployment routes. However, the continuous-band absorption of these semiconductors prevents near-infrared selective harvesting typically targeted for TPVs with the highest efficiency and transparency needed to meet the aesthetic demands of many potential applications. In this work, we demonstrate TPVs based on perovskite semiconductors where the band gap is sensitively tuned with a range of compositions to selectively harvest only ultraviolet photons with band gaps between 410 and 440 nm. This approach offers theoretical efficiencies up to 7% with >99% visible transparency when precisely targeting band gaps around 435 nm. Practical optimization of these perovskite cells could quickly yield TPVs with power conversion efficiencies rivaling state-of-the-art near-infrared harvesting TPVs today while also providing a route to higher-efficiency multi-junction TPVs.

UV sensitive pulsed laser deposited ZnO thin films: Influence of growth temperature

The thin films of zinc oxide (ZnO) were grown on sapphire (0 0 1) substrates using pulsed laser deposition (PLD) in O2 gas ambient and at different growth (substrate) temperatures (200, 300, 400, 500 and 600 °C). The effect of growth temperature on the crystallographic and morphological and photoluminescence properties of the films were investigated using X-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM) and photoluminescence spectrometer. All the films reveal a wurtzite ZnO structure. The XRD results are well supported by the surface morphological and photoluminescence studies. The film characteristics were interrelated to their ultraviolet (UV) photo-sensing properties. The UV photodetection properties of the films were investigated at room temperature in metal–semiconductor–metal (MSM) planar configurations and are observed to be strongly driven by the growth temperature dependent crystallographic properties. The dark-current and the photocurrent of the ZnO film-based UV photodetectors are relational to the crystallite/grain size and the quality of ZnO thin films. For the photodetector based on ZnO film with a greater crystallite size, a lower dark current, and a higher photocurrent were achieved under 5 V bias voltage. The time-dependent photoresponse investigations illustrate a highly stable and fast switching UV photoresponse for the photodetector with ZnO film grown at 400°C growth temperature, which exhibits the maximum responsivity of ∼21.65 mA/W upon 2 mW/cm2 UV light exposure (365 nm), at a bias voltage of 5 V.

Fast Intra Bunch Train Charge Feedback for FELs Based on Photo Injector Laser Pulse Modulation

Bunch charge variations in free electron lasers such as the free electron laser (FEL) in Hamburg (FLASH) or the European X-ray FEL (E-XFEL) impact the longitudinal phase space distribution of the electrons resulting in different bunch peak currents, bunch durations, and bunch shapes. The electron bunches are generated by short ultraviolet (UV) laser pulses impinging onto a photocathode inside a radio frequency (RF) accelerating cavity. At FLASH, bursts of bunches up to 800 pulses with an intra train repetition rate of 1 MHz are used and even higher repetition rates (up to 4.5 MHz) are planned at the E-XFEL. Charge variations along these bunch trains can be caused by variations of the laser pulse energies, instabilities of the accelerating fields in the RF cavity, and time-dependent effects in the photoemission process. To improve the intra bunch train charge flatness and to compensate train-to-train fluctuations, a dedicated digital control system, based on the Micro Telecommunication Computing Architecture (MicroTCA.4) standard, was designed, implemented, and successfully tested at FLASH. The system consists of a bunch charge detection module which analyzes data from a toroid system and provides the input signal for the controller which drives a fast UV Pockels cell installed in the optical path of the photocathode laser. The Pockels cell alters the laser polarization and thus the transmission through a polarizer. The modulation of UV laser pulse energy with an iterative learning feedforward minimizes the repetitive errors from bunch train to bunch train. A fast feedback algorithm implemented in a field-programmable gate array allows for fast tuning of bunch charge inside the bunch train. In this paper, a detailed description of the system and the first preliminary measurement results are presented.

Toward Understanding the Role of VZn Defect on the Photoconductivity of Surface-Passivated ZnO NRs

The point defects in ZnO nanorods (NRs) play very crucial role in its photoconductivity (PC) properties and thus it is essential to understand the sub-band gap carrier dynamics in order to have efficient ultraviolet (UV) photodetection. In order to understand the role of a dominant point defect, Zn vacancy (VZn) which is prevalent on the surface of the NRs, we employ a high temperature annealing step in air and also an excess hydration step for one set of annealed NRs, each followed by a final surface passivation step by poly-vinyl butyral (PVB). A comprehensive study on the photocurrent spectra, photocurrent transients under different sub-band gap excitations and power dependence of photocurrent of aqueous chemically grown ZnO NRs treated under various conditions have been carried out and demonstrates the superiority (extraordinarily high and fast UV response) of the point defect rich but surface passivated NRs as compared to ones with absence or less VZn defects. Further a good support on the major role...

Ultrafast Solar-Blind Ultraviolet Detection by Inorganic Perovskite CsPbX3 Quantum Dots Radial Junction Architecture.

Inorganic CsPbX3 (X = Cl, Br, I, or hybrid among them) perovskite quantum dots (IPQDs) are promising building blocks for exploring high performance optoelectronic applications. In this work, the authors report a new hybrid structure that marries CsPbX3 IPQDs to silicon nanowires (SiNWs) radial junction structures to achieve ultrafast and highly sensitive ultraviolet (UV) detection in solar-blind spectrum. A compact and uniform deployment of CsPbX3 IPQDs upon the sidewall of low-reflective 3D radial junctions enables a strong light field excitation and efficient down-conversion of the ultraviolet incidences, which are directly tailored into emission bands optimized for a rapid photodetection in surrounding ultrathin radial p-i-n junctions. A fast solar-blind UV detection has been demonstrated in this hybrid IPQD-NW detectors, with rise/fall response time scales of 0.48/1.03 ms and a high responsivity of 54 mA W-1 @200 nm (or 32 mA W-1 @270 nm), without the need of any external power supply. These results pave the way toward large area manufacturing of high performance Si-based perovskite UV detectors in a scalable and low-cost procedure.

Intense and fast UV emitting ZnO microrods fabricated by low temperature aqueous chemical growth method

Intense and fast ultraviolet (UV) emitting zinc oxide (ZnO) microrods are successfully fabricated by low temperature aqueous chemical growth (ACG) method. Uniform and hexagonal microrods of varying dimensions are synthesized using different zinc acetate dihydrate (ZnAc) and hexamethelynetetramine (HMTA) molar concentration ratios. Although exhibiting broad orange emissions, the microrods have intense UV emissions with lifetimes as fast as 30–40ps. Analyses show that there is no definite correlation between the microrod dimensions and the optical emissions. Nevertheless, with the ease on the microcrystal fabrication, these ZnO microrods with intense and fast UV emissions have potential use for future scintillator applications.