ZnO UV Research Articles

Ultraviolet photodetectors based on ZnO nanowires with SiO2/ZnO multilayers

Ultraviolet photodetectors (UV PDs) have been a frequently studied focus of optoelectronic semiconductor devices because of their large range of applications. As one of the most famous materials in third-generation semiconductors, ZnO-based UV PDs have received a great deal of attention in various research areas. Due to the carrier transport channel and higher exciton bond energy, ZnO nanowires (NWs) have better photoelectron sensitivity under UV light than ZnO films. Here, well-organized ZnO NWs were fabricated on ZnO-seeded substrates via a hydrothermal method. Multilayers of double SiO2/ZnO(S/Z) layers were designed on the NWs, and the Schottky barrier was introduced by the close contact of the ZnO NWs and gold electrodes to improve the performance of ZnO UV PDs. Characteristics of the dark current, photocurrent, rise time, decay time, photo-to-current ratio (S), and responsivity values (Rs) of the PDs were studied. Furthermore, multilayer UV PDs were achieved on both Si and quartz substrates. S of the ZnO S/Z-based UV PDs fabricated on a silica substrate can reach 55.57, which is better than the values of ZnO UV PDs reported previously. Compared with silica-based UV PDs with S/Z layers, quartz-based UV PDs with S/Z layers show a higher performance of Rs, which reach 12.62 A/W. ZnO NWs with multilayers and the Schottky contact between ZnO NWs and Au are promising candidates in high-sensitivity UV PDs.

Hydrothermal Synthesis of ZnO Nanospheres Using Apple Pectin as Biotemplate and Application for UV Sensing

In this study, spherical-like ZnO UV photodetectors based on the facile hydrothermal method, induced different concentrations of apple pectin as the biotemplate. Apple pectin can react with zinc particles and change the pH value, which plays an essential role in modifying surface morphology. Moreover, apple pectin extracted from apple peels as carbon and nitrogen sources can also be used to improve absorption properties and increase depletion region to reduce dark current. The best results were obtained when 150 mg of apple pectin was used, showing a high UV-to-dark current ratio and fast response and recovery times. The UV-to-dark current ratio is as high as 80106.1, which is better than that of pure ZnO (4.47). Fast response and recovery times are also swift. The physical properties were evaluated using various techniques, including scanning electron microscopy, photoluminescence (PL), X-ray diffraction, and energy-dispersive X-ray (EDX), respectively. The results of this study suggest that the use of apple pectin in the hydrothermal synthesis of ZnO may offer a promising approach for modifying ZnO materials.

Sensing Performance of Ethanol Microfiber Probe Augmented by ZnO Nanosheet and UV Glue Film

A microfiber reflective ethanol gas sensing probe was designed and fabricated. The single-mode fiber was heated and stretched to prepare a microfiber taper, on which a mixed material of ZnO nanosheets and UV glue was built by the dip-coating method. The influencing factors on its sensing performance for ethanol have been discussed, including the dozen ratio of ZnO nanosheets, UV glue materials, and end-face morphology. As the concentration of ethanol gas increased, the intensity of the reflection spectrum increased with the responding sensitivity of 7.28 × 10−4 dBm/ppm. The exchanging efficiency of the optical signal is enhanced by the strong evanescent field of the microfiber taper. This sensing probe is convenient for high-density integration and working in a small space and is capable of high-performance monitoring for ethanol at room temperature.

ZnO UV sensor photoresponse enhancement by coating method optimization

Modern high-performance photodetector research is driven by the need to simultaneously improve multiple parameters, but also fit the decreasing size of electronics and maintain low production price. Here, we demonstrated how our synthesized ZnO tetrapod (ZnO-T) nanostructure was deposited on electrodes with variating gap by four coating methods including drop casting, microdrop casting, spray coating and slot-die coating with the same thickness. Optimizing the inter-electrode gap and coating method the record IUV/IDark ratio per unit area value of 8.73 × 106 was obtained. The fastest rise time 0.78 s and fastest decay time 0.94 s were obtained by slot-die coated sensors. High photoresponse of ZnO-Ts, the inter-electrode gap size influences formation of ZnO-T microstructure during coating process and morphology influence on photoresponse was explained. We demonstrate that even with the same optimized ZnO-T nanostructures photoresponse can be improved by 2 orders of magnitude. Our work shows the importance of coating morphology and inter-electrode gap optimization.

A Safe-by-Design Approach to "Reef Safe" Sunscreens Based on ZnO and Organic UV Filters.

In recent years, the issue of coral bleaching has led to restrictions in some tropical locations (i.e., Palau, Hawaii, etc.) on the use of some organic UV sunscreen filters, such as oxybenzone and ethyl hexyl methoxycinnamate. In contrast, ZnO is considered safe for marine environments and thus is often used without considering its photocatalytic and oxidative activities related to the generation of O2•- and HO•. Moreover, ZnO needs to be used in combination with other filters to reach higher protection factors. Thus, the study of its interaction with formulations and with organic filters is important in sunscreen technology for the development of safer by-design products. In this work, the photocatalytic activity of zinc oxides with different surface areas (30, 25 and 9 m2/g) and their interaction with selected organic sunscreen filters were investigated. In particular, the ZnO photocatalytic kinetics were studied following the photodegradation of Acid Blue 9 (AB9) observing a first-order reaction with a chemical regime. Our evaluations of the selective inhibitions by hvb+ and HO• demonstrated a substantial predominance of the hydroxide radicals in the expression of the photocatalysis, a trend that was also confirmed by the irradiation of ZnO in an ethanolic solution. Indeed, the formulations containing both ZnO and organic filters defined as "safe" for coral reefs (i.e., Diethylamino Hydroxybenzoyl Hexyl Benzoate, DHHB, and Ethylhexyl Triazone, EHT) showed a non-negligible photocatalytic oxidation and thus the combination was underlined as safe to use.

The effect of magnesium doping concentration on the structural and optical properties of zinc oxide nanoparticles

In this study, the optical and structural properties of Magnesium doped Zinc Oxide (Zn1-xMgxO) nanoparticles (x = 1%, 3%, and 5%) were examined. The synthesis was carried out at 300 oC by using a simple co-precipitation method. The structural samples were used to characterize the synthesized nanoparticles by using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). Energy Dispersive X-Ray spectroscopy (EDX) was used to determine the chemical composition of the samples. Furthermore, UV-Vis spectroscopy was conducted to study our samples’ optical characteristics. As per XRD analysis, both pure and Mg doped ZnO samples possess wurtzite structure. The particle size was revealed to decrease significantly with Mg concentration, from 36 nm for pure sample to 23.87 nm with 5% Mg. In comparison to ZnO, the XRD pattern of Mg-doped ZnO shows a peak shift towards lower 2θ values. As a result of deformation of crystal structure caused by integrated Mg+2 ions onto Zn+2 sites. SEM images of synthesized samples reveal that the nanoparticles possess sheet, spherical and rod like morphologies for different values of x. The EDX analysis verifies the purity of samples within the detection limits. According to optical absorption spectra obtained from UV-Visible spectroscopy in the 200nm to 1000nm range affirmed that as Mg concentration increased, the band gap increased from 3.37 eV for pure sample to 3.74 eV with 5% Mg. The UV-Visible spectra of pure ZnO and Mg-doped ZnO samples also exhibit distinct peaks in the UV region at 335 nm, 311 nm, 310.6 nm, and 310 nm. Across the spectra of pure and Mg-doped ZnO samples, the UV peak is attributed to free exciton transitions, whereas, in the spectra of Mg-doped ZnO UV absorbance peak in the visible region is attributed to the radiative transitions of electrons captured at oxygen vacant sites with holes trapped at singly ionized oxygen vacancies.

Ultraviolet Photodetector Based on Poly(3,4-Ethylenedioxyselenophene)/ZnO Core–Shell Nanorods p-n Heterojunction

In this work, we successfully assembled an organic–inorganic core–shell hybrid p-n heterojunction ultraviolet photodetector by the electropolymerization deposition of poly(3,4-ethylenedioxyselenophene) (PEDOS) on the surface of zinc oxide nanoarrays (ZnO NRs). The structures of composite were confirmed by FTIR, UV–Vis, XRD and XPS. Mott–Schottky analysis was used to study the p-n heterojunction structure. The photodetection properties of ZnO NRs/PEDOS heterojunction ultraviolet photodetector were systematically investigated current–voltage (I–V) and current–time (I–t) analysis under different bias voltages. The results showed that PEDOS films uniformly grew on ZnO NRs surface and core–shell structure was formed. The p-n heterojunction structure was formed with strong built-in electric field between ZnO NRs and PEDOS. Under the irradiation of UV light, the device showed a good rectification behavior. The responsivity, detection rate and the external quantum efficiency of the ultraviolet photodetector reached to 247.7 A/W, 3.41 × 1012 Jones and 84,000% at 2 V bias, respectively. The rise time (τr) and fall time (τf) of ZnO NRs/PEDOS UV photodetector were obviously shortened compared to ZnO UV photodetector. The results show that the introduction of PEDOS effectively improves the performance of the UV photodetector.

Continuous flow scale-up of biofunctionalized defective ZnO quantum dots: A safer inorganic ingredient for skin UV protection

The versatility of ZnO quantum dots (QDs) exhibiting size-tunable visible photoluminescence has propelled them to the forefront of leading-edge innovations in healthcare. At the nano-bio interface, enhancing the singly-ionized oxygen vacancy defects (VO•) through holistic, sustainable synthesis protocols driven by the synergistic influence of QDs’ nucleation-growth kinetics has implications on their bioactivity, physiochemical, and optical performance. Recently, robust continuous flow platforms have transcended the conventional batch reactors by alleviating the concerns of “hot-spot” formation due to inhomogeneous heat distribution, acute energy consumption, poor quality, and yield. However, complexities exist in translating batch chemistries into flow processes. Here, a unique, rationally designed continuous flow synthesis of luminescent defect-engineered ZnO QDs (E-QDs) via helical-reactor assembly that can adequately synthesize on a large scale is reported. The crux of this lies in the amalgamation of “green chemistry” and flow synthesis, which results in Lamer-mechanism mediated monodispersed E-QDs demonstrating high photoluminescence quantum yield (PLQY) of 89% under an accurately regulated synthesis environment. Process intensification corroborated that the bio-stable E-QDs manifested admirable photostability, broad-spectrum UV-shielding (400–250 nm), colloidal stability, in vitro biocompatibility against L929 and HaCaT cells, and antioxidant activity. These attributes were better compared to the commercial ZnO nanoparticles (ZnOC-NPs) used for skin UV protection. Delving deeper, the main drivers for the high density of intrinsic VO• formation (Iv/Io∼42.5) were revealed to be the reactor's hydrodynamic performance and the improvised heating rate (2.5°C/sec). Hence, these E-QDs have potential as a new, safe, and economical multifunctional active ingredient for skin UV protection and antioxidants for treating ROS-mediated disorders. Statement of significanceUV filters exhibiting questionable UV-attenuation efficacy and phototoxicity are significant impediments to the healthcare industry emphasizing skin cancer prevention. Although least explored, VO•-governed aberrant photoactive, biological, and surface-reactive qualities of engineered ZnO QDs (E-QDs) have created ample room to investigate these hallmarks for skin UV protection. However, the bottlenecks in stereotypical ZnO QDs production confined by inefficient process control are annihilated by continuous flow strategies. Herein, the high-throughput continuous flow helical reactor assembly was designed and fabricated to successfully showcase optimized transport properties, reproducibility, yield, and quality E-QDs. Anticipating a skyrocketing demand for E-QDs as bioactive-sunscreen components, the comprehensive investigation has demonstrated unprecedented biofunctionality and ROS-scavenging behaviour, even upon UVR exposure, contrary to the traditional nanoparticulate ZnO UV filters.

High performance ZnO quantum dot (QD)/ magnetron sputtered ZnO homojunction ultraviolet photodetectors

The performance of photodetectors can be simultaneously determined by the photoinduced carrier generation and transportation, and thereby a huge challenge still remains for the fabrication of ultra-sensitive ZnO UV due to the irreconcilable contradiction between high crystallinity and additional adsorption–desorption sites. Here, we demonstrate ZnO quantum dot (QD) / magnetron sputtered ZnO homojunction photodetectors with an excellent performance by systematically varying the thickness ratios between two ZnO layers. With the well-balanced ratio, ZnO QDs offers extra adsorption–desorption sites owing to the increased surface defects, and accelerated carrier transportation is concurrently achieved with the highly crystallized magnetron sputtered ZnO layers. As a consequence, the responsivity and external quantum efficiency of the ZnO homojunction photodetector fabricated at 250 ℃ radically increased to ∼ 551 mA/W and 195.4% under 350 nm light illumination (8.58 mW cm−2) at the bias of 10 V. Depending on the annealing temperature, the responsivity of the ZnO homojunction photodetector is further increased to ∼ 1.3 A/W at 450 ℃ even with an identical ratio on account of the improved crystallinity, which paves the path to overcome the hindrance for the ultra-sensitive UV photodetection.

Zno Uv Sensor Photoresponse Enhancement by Coating Method Optimization

Zno Uv Sensor Photoresponse Enhancement by Coating Method Optimization

Zno Uv Sensor Photoresponse Enhancement by Coating Method Optimization

Zno Uv Sensor Photoresponse Enhancement by Coating Method Optimization

ZnO Quantum Dot/MXene Nanoflake Hybrids for Ultraviolet Photodetectors

Efficacious utility of fugacious photons within a limited dimension of photoactive semiconductor thin films provides a facile approach to break through the obstacle for the sensitivity improvement of photodetection. Herein, we demonstrate a facile way to fabricate ZnO quantum dot (QD)/MXene nanoflake photodetectors by uniformly blending various ratios of two-dimensional (2D) Ti3C2Tx nanoflakes into ZnO QD thin films, which can establish a carrier transportation highway and light confinement centers within the photoactive layers. The light absorption of hybrid thin films is obviously enhanced because of the localized surface plasmon resonance effect of MXene nanoflakes, resulting in an expressively enhanced external quantum efficiency by 35 times for the device with 0.1 mg/mL 2D Ti3C2Tx nanoflakes (150.0%) in comparison with that of the pristine photodetector (4.3%). Under 350 nm light illumination (1.72 mW cm–2), the carrier transportation in ZnO thin films is significantly accelerated with the hot electron injection from the high-conductivity 2D Ti3C2Tx nanoflakes and thereby the optimal responsivity of 425 mA/W with an improved response speed at 10 V. Furthermore, ZnO QD/MXene nanoflake photodetectors also exhibit an excellent long-term stability. This work provides an efficient method to fabricate high-performance ZnO UV photoelectric devices in the military and civilian fields at low light intensities.

Comparative evaluation of ZnO nanorod material properties and UV photodetector performance with various transition metal dopings

Comparative evaluation of ZnO nanorod material properties and UV photodetector performance with various transition metal dopings

Biosynthesis of zinc oxide nanoparticles using Phoenix dactylifera and their effect on biomass and phytochemical compounds in Juniperus procera

Biosynthesized nanoparticles have played vital role recently, as suggested to be alternative to physical and chemical methods. In this study, biosynthesis of zinc oxide nanoparticles (ZnO NPs) were carried out using leaf extracts of Phoenix dactylifera L. and Zinc nitrate. The effect of ZnO nanoparticles on biomass and biochemical parameters was investigated. Biosynthesized ZnO nanostructure was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–visible spectrophotometer and Fourier transform infrared spectroscopy (FTIR). Which resulted in spherical shape with size ranging between 16 to 35 nm of Biosynthesized ZnO nanoparticles and UV absorption beak at 370.5 nm with clear peaks of functional groups. The impact of different concentrations (0.0 mg/L, 80 mg/L and 160 mg/L) of biosynthesized ZnO nanoparticles on biomass and bioactive compounds production of Juniperus procera in vitro was investigated. The results showed that, biosynthesized ZnO NPs (80 mg/L and 160 mg/L) concentrations were boosted the growth of J. Procera with significantly compared to non-treated plants in vitro. The highest concentration (160 mg/L) of ZnO NPs was enhanced the growth of plant at beginning period, one month later shoots became yellow and callus turned to be brownish. Moreover, the influence of ZnO NPs on phytochemical compounds in callus of Juniperus procera was examined using GC–MS analysis. The differences among treatments were recoded. Overall, zinc oxide nanoparticles substantially improved the growth of shoots and callus with increasing of biochemical parameters such as chlorophyll a, total phenolic and flavonoids contents, besides the total protein and, SOD, CAT and APX activity. ZnO NPs might be induced some phytochemical compounds as well as inhibit.

Comparative analysis of aeration and oscillation in a suspended catalyst photocatalytic membrane reactor

Comparative analysis of membrane oscillation and aeration in a photocatalytic membrane reactor is conducted. The investigation involved degradation of methylene blue dye as model pollutant using suspended ZnO photocatalyst and UV illumination. The effect of reactor hydrodynamics and design parameters on the system performance and its relation to the membrane-catalyst retention characteristics is evaluated using flat surface membranes roughed with transverse turbulence promoters (TP). The investigation showed that membrane oscillation is more energy efficient than aeration and can provide higher shear rates and better mixing which decreases both the catalyst agglomeration and deposition on the membrane surface. These, in turn, increase both the suspended catalyst concentration in solution and enhance the membrane flux. Compared to oscillation, achieving high shear rates through aeration is limited due to the adverse effects of high gas flow on photocatalytic reactions. Considering the above together with the small effect of aeration on ZnO photocatalytic kinetics, the need for aeration may be relaxed when using membrane oscillation in a ZnO photocatalytic reactor.

Research on piezo-phototronic effect in ZnO/AZO heterojunction flexible ultraviolet photodetectors

A novel Al-doped (3 wt%) ZnO (AZO) UV photodetector (PD) and ZnO/AZO heterojunction double-layer UV PD were prepared on a polyethylene terephthalate (PET) substrate by utilizing the radio frequency (RF) sputtering technology and conventional photolithography. Because the ZnO/AZO heterojunction possesses the ability to improve the separation of the photogenerated electron-hole pairs, the responsivity of the ZnO/AZO PD is higher than that of the pure AZO PD under the same bias voltage. Moreover, the responsivity of the obtained ZnO/AZO PD showed a 1.13 fold increase from 5.91 to 6.70 A/W when the tensile variable ɛ was 0.16. These findings also provide a new alternative for the preparation of flexible UV PDs with piezo-phototronic effect, which is low-cost and offers environmental sustainability.

One-pot synthesis of zinc oxide nanoparticles via chemical precipitation for bromophenol blue adsorption and the antifungal activity against filamentous fungi

In this research, zinc oxide nanoparticles (ZnONPs) were prepared via a facile one-pot chemical precipitation approach and applied in the adsorption of bromophenol blue (BRB) and as antifungal agents against the filamentous fungi and plant pathogens; Alternaria alternata CGJM3078, Alternaria alternata CGJM3006 and Fusarium verticilliodes CGJM3823. The ZnONPs were characterized by the UV–Vis, FTIR, XRD, TGA, BET, SEM, TEM, and EDX techniques, which showed efficient synthesis. The characteristics ZnO UV–Vis absorption band was observed at 375 nm, while the XRD showed an average ZnONPs crystalline size of 47.2 nm. The SEM and TEM images showed an irregular shaped and aggregated porous structure of 65.3 nm average-sized ZnONPs. The TGA showed 22.9% weight loss at 800 °C indicating the high thermal stability of ZnONPs, while BET analysis revealed a surface area, pore volume and pore diameter of 9.259 m2/g, 0.03745 cm3/g and 9.87 nm respectively. The Freundlich, pseudo-second-order, and intra-particle diffusion models showed R2 > 0.9494 and SSE < 0.7412, thus, exhibited the best fit to the isotherm and kinetics models. Thermodynamics revealed feasible, endothermic, random, and spontaneous adsorption of BRB onto the synthesized ZnONPs. The antifungal assay conducted depicts strong antifungal activities against all three tested fungi. Noticeably, ZnONPs (0.002–5 mg/mL) showed maximum activities with the largest zone of inhibition against A. alternata CGJM 3006 from 25.09 to 36.28 mm. This was followed by the strain F. verticilliodes CGJM 3823 (range from 23.77 to 34.77 mm) > A. alternata CGJM3078 (range from 22.73 to 30.63 mm) in comparison to Bleach 5% (positive control). Additionally a model was proposed based on the possible underlying mechanisms for the antifungal effect. This research demonstrated the potent use of ZnONPs for the adsorption of BRB and as effective antifungal agents.

Improved Responsivity of ZnO Nanowires Ultraviolet Photodetector by Light Trapping Effect

The absorbability of ZnO planar thin layer is weak because of the short transmission path of incident light. The light trapping effect of ZnO UV PDs has been established as a promising method to optimize the performance of optoelectronic devices. By measuring the optical transmission and photocurrent of the ZnO PDs, we demonstrate that the ordered ZnO NWs increases the optical responsivity. In addition, when the photodetector was connected to nanowires, the responsivity is increased by a factor of 102, accompanied by a large light dark current ratio (105). ZnO nanowires with light trapping effect provide a new perspective for the research of ultraviolet irradiation nanomaterials.

Investigation of calcium silicate as a natural clay-based sunblock: Formulation and characterization.

Sunlight exposure causes several types of health issues to humans, and in particular, it affects especially the skin. Among the most common harmful issues developed by UV exposure are erythema, pigmentation, and lesions in DNA, which may lead to cancer. These long-term effects can be minimized with the use of sunscreen. The use of commercial UV filters causes severe side effects such as skin allergy and whitening of the skin. Therefore, in this study the effectiveness of Ca2 SiO4 , a compound abundantly present in the soils of certain South Asian regions, has been the first time explored as UV filter. This compound leaves a low amount of white residue on the skin and is highly stable. The comparative study of a cosmetic formulation having 5% Ca2 SiO4 , and other formulations containing 5% TiO2 and 5% ZnO as inorganic UV filters, was performed to evaluate the physical and chemical stability. The zeta potential and chemical stability of formulations containing these different UV filters were investigated by using UV-Vis spectroscopy, FTIR-ATR, and X-ray diffraction. Results indicated Ca2 SiO4 as a promising innovative UV filter with an SPF value of 37.94. One of the reasons is its low interaction with organic filter, that is, PABA, as compared to commercial ZnO and TiO2 inorganic UV filters. Biological absorption in organs was studied by ICP-MS on model mice. It also has a low photocatalytic activity; thus, formation of radicals is minimum. Moreover, Ca2 SiO4 showed a recognized ability to leave a low amount of white residue on the skin combined with great stability.

DFT band alignment of polar and nonpolar GaN/MgGeN2, ZnO/MgGeN2 and GaN/ZnO heterostructures for optoelectronic device design

We calculated the band alignment among MgGeN2, ZnO and GaN compounds using density functional theory (DFT) calculations. The norm-conserving pseudopotentials approach was performed to determine the band gap of each compound. The band offsets at the interfaces of GaN/MgGeN2 and ZnO/MgGeN2 were calculated from the differences in the bulk band edges including the interfacial dipole-potentials. Moreover, the effect of strain was also investigated to govern the lattice mismatches between MgGeN2 and substrates (i.e. GaN and ZnO). We found that the band alignment of nonpolar heterojunctions is type-I for GaN/MgGeN2 and type-II for ZnO/MgGeN2 respectively. From these results, the band offsets of GaN/ZnO were extracted by using transitivity rule and confirmed with the direct calculation. Moreover, the polar band offsets shift from nonpolar ones and change the band alignment of ZnO/MgGeN2 with (Mg,Ge)-O interface to type-I. These calculated band alignments present the potential of using MgGeN2 in optoelectronic applications as an electron blocking layer for ZnO-based UV-LED and a quantum-well barrier for ZnO and GaN-based UV laser diode.