Band Gap Of Zinc Oxide Research Articles

Crystallographic, Spectroscopic and Electrical Study of ZnO:CdO Nanocomposite-Coated Films for Photovoltaic Applications

In this paper, we report structural, optical and electrical properties of wide band gap zinc oxide: cadmium oxide-coated films prepared by cost-effective screen printing technique on glass substrates. Characterizations of the samples were carried out with X-ray diffraction (XRD), UV–Vis spectroscopic analysis. Fourier transform infrared (FTIR) spectroscopy and two probes for electrical conductivity measurement. The XRD patterns show polycrystalline nature of the films. It was observed that ZnO belongs hexagonal and CdO cubic crystal structures for x = 0 and 1% with a preferred orientation along (101) and (111) direction. While the mixed hexagonal and cubic phases were observed at x = 30%, FTIR spectra show the vibrational bands pertaining to ( $$\upnu $$ Zn–O and $$\upnu $$ Cd–O) stretching modes. Absorption spectroscopy exhibits the direct band gap transition, and optical band gap is decreased from 3.21 to 2.41 eV in ZnO:CdO nanocomposite. The Arrhenius plot of DC conductivity shows semiconductor nature with decreasing of activation energy.

Structural and Optical Analysis of 1D Zinc Oxide Nanoparticles Synthesized Via Hydrothermal Method

Nano sized zinc oxide was synthesized by simple hydrothermal method using zinc acetate dihydrate as a transition metal precursor in the presence of NaOH. The synthesized nanoparticles were characterized by X-ray Diffraction (XRD), High resolution scanning electron microscope (HR-SEM), UV-Visible spectroscopy (UV-Vis) Fourier Transform Infrared Spectroscopy (FT-IR) and Dielectric studies. From the XRD analysis of ZnO the hexagonal crystalline structure was found based on which the crystal size and lattice parameters were calculated. The HR-SEM shows the morphology of ZnO nanoparticles. A UV-Visible spectrum helps to find the band gap of zinc oxide. The FT-IR studies show a prominent peak at 447 cm-1 which indicates the formation of ZnO bond. The dielectric loss and dielectric constant have high values at low frequency. The high ac resistance shows the presence of space charge polarization, which plays an important role in the electrical property of ZnO.

Potentials of Costus woodsonii leaf extract in producing narrow band gap ZnO nanoparticles

Narrow band gap zinc oxide (ZnO) nanoparticles (NPs) were synthesized using unboiled and boiled leaf extracts of Costus woodsonii. The as-synthesized NPs were characterized using a range of techniques. The as-synthesized ZnO NPs were crystalline with a hexagonal wurtzite structure similar to the commercial ZnO (ZnO-C). The maximum absorbance was observed at ~390 nm for ZnO-C and the as-synthesized ZnO NPs (ZnO-UL and ZnO-BL) showed a red shift, i.e. ~448 nm to ~462 nm, hence, a lower band gap of ~2.68–2.77 eV. The band gap energy of the as-synthesized ZnO NPs was lower than that of commercial ZnO. The surface of ZnO was coated/modified with the components of the leaf extract. The as-synthesized ZnO NPs showed similar particle sizes and were spherical in shape. These studies confirmed the green synthesis of ZnO NPs using Costus woodsonii and the significantly reduced band gap (Eg = ~2.68 eV to ~2.77 eV) of the as-synthesized ZnO NPs compared to the ZnO-C (Eg = 3.18 eV).

MOF-derived C-doped ZnO composites for enhanced photocatalytic performance under visible light

Carbon-doped zinc oxide (ZnO) with porous structure was synthesized by pyrolysis of a zinc-based metal organic framework (MOFs). Photocatalytic effect was measured by the photodegradation of Rhodamine B (RhB) under visible light irradiation. The morphology, structure, and porous properties of the as-synthesized composites were characterized by using field emission scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), the thermogravimetric and differential scanning calorimetry analysis (TG-DSC), diffuse reflectance UV–vis spectroscopy (UV–vis DRS), photoluminescence (PL) and N2 sorption-desorption isotherms (BET). Compared with other conventional C-doping methods, MOF sacrificial template method not only retains the porous structure with interconnected ZnO nanoparticles but also introduces carbon doping evenly in ZnO lattice which reduces the band gap of ZnO and thus improves the charge-separation efficiency. The trapping experiment results showed that superoxide radicals (O2−) and photoexcited hole (h+) are the main and minor oxidative species in the photodegradation of RhB respectively. And the enhanced photocatalytic mechanism was also proposed.

Effect of metal/metal oxide coupling on the photoluminescence properties of ZnO microrods

Despite its unique properties, zinc oxide (ZnO) particles have limited usage in optoelectronic devices and biochemical sensors due to its relatively poor ultraviolet (UV) emission. In this research, the localized surface plasmon resonance (LSPR) effect of metal nanoparticles such as silver (Ag), aluminium (Al), copper (Cu) and iron (Fe) that were coupled with ZnO microrods was studied. The metal coupled ZnO microrods were synthesized by solution impregnated method. The metal nanoparticles were clearly observed deposited onto the surface of ZnO microrods using transmission electron microscope (TEM) and energy dispersive X-ray (EDX) mapping. The room temperature photoluminescence (RTPL) analysis of ZnO microrods coupled with Al, Ag, Fe showed remarkable improvement of UV emission and quenching of defect related emission. The intensity ratio (Iuv/Ivis) of ZnO microrods was 1.6 but was enhanced to 26.1, 4.4, and 4.0 by coupling of Al, Ag and Fe, respectively. However, when Cu was embedded onto ZnO microrods, the Iuv/Ivis of ZnO microrods was suppressed to 0.1. The photoluminescent mechanism of Al, Ag and Fe–ZnO particles was attributed to LSPR effect. In contrary, deposition of Cu onto ZnO microrods induced energy level in bandgap of ZnO, producing the visible light emission.

Wide Bandgap Zinc Oxide Thin Films Prepared by RF Magnetron Sputtering at Room Temperature

Room temperature RF magnetron sputtering deposition of Zinc Oxide thin films on a glass substrate was carried out by varying deposition parameters such as sputtering pressure, target-to-substrate distance, and RF power. The as-deposited film at 75 W, sputtering pressure of 9.8 mbar and a target-to-substrate distance of 104 mm has showed a band gap of 3.31 eV and RMS surface roughness of 7.1 nm. Electrical characterization and UV–VIS results reveal its high resistivity (1.3 × 107 Ω-cm) and transparency >86% in a wide optical range (494–1100 nm). This film could be used as a buffer layer of CIS solar cells, SAW, and other similar thin film devices over a flexible substrate.

Synthesis and Characterization of ZnO Nanoparticles and Its Application to Dye Sensitized Solar Cell

In this paper, we have reported the synthesis of zinc oxide (ZnO) nanoparticles by aqueous route method and its characterization. By X-ray diffraction pattern (XRD) study it reveals that ZnO has hexagonal wurtzite structure with average particle size of 16.5 nm. From the results of scanning electron microscope (SEM) and Atomic force microscope (AFM) images, particles were spherical in nature with good aggregation. Stoichiometric ratio of Zinc and oxygen were almost close which was revealed from energy dispersive analysis of X-ray (EDAX). From infrared spectroscopy (FTIR), peak of Zn–O bond appears at 433.43 cm−1. Direct band gap of ZnO was found to be 3.36 eV estimated from UV-Vis absorption spectra. The Photovoltaic properties of DSSC sensitized by Di-tetrabutylammonium cis-bis (isothiocyanato) bis (2,2′ -bipyridyl-4,4′-dicarboxylato) ruthenium(II) (N-719 dye) were obtained in which photo anode is prepared by synthesized ZnO. Photocurrent (I) and photovoltage (V) was measured using designed automated load variable solar simulator and optimum solar energy to electricity conversion efficiency (η) of 2.35% under AM 1.5 irradiation (1000 W/m2) was observed.

High responsivity, self-powered carbon–zinc oxide hybrid thin film based photodetector

A self-powered n-Si/C–ZnO/SiO2/p-Si heterojunction photodetector (PD) which comprises of carbon (C) and zinc oxide (ZnO) nanostructures on a n-type silicon (n-Si) substrate was prepared via vapor phase transport method. Excellent photodetection under 468 nm light illumination for powers ranging from 2.78 to 2910 µW delivered a quick response of about 9.5 µs. A high photoresponsivity of 2.082/AW and external quantum efficiency about 551% were obtained. The mechanism involved for the generation of a photocurrent at a zero bias voltage was discussed for future energy efficient optoelectronics devices. The morphology and composition of C, Zn and O were confirmed by field emission scanning electron microscope, energy dispersive X-ray and Raman scattering analysis. The formation of ZnO nanowires range from 10 to 100 nm, aided by the photoconduction mechanism. The Raman E2high mode of 437/cm of ZnO and the presence of D and G bands show the formation of a hybrid C–ZnO thin film. The calculated rectifying ratio is found to shift as the direct current bias voltage and light power increased. The deposition of C particles on the ZnO surface creates point defects and sub-energy levels in the ZnO bandgap which favour fast responsivity in the PD.

Halide‐Modulated Functionality of Wide Band Gap Zinc Oxide Semiconductor Nanoparticle

AbstractSurface modification of inorganic nanomaterials using different ions is well‐known to induce significant modulation in functionality of the nanoparticles (NP), which improves tuning their relevant properties for suitable applications in the field of nanotechnology. Here, we report synthesis and surface modification of a model inorganic wide bandgap semiconductor ZnO NP by halide ions by simple precipitation method and demonstrate that proximity of various halide ions to the NP modifies their electronic properties. It is interesting to note that such surface modulation has little impact on its morphology, while significantly influencing their applications in photocatalytic activity or magnetism. Indeed, the halide attached ZnO NP displays a large reduction of defect state emission. Various microscopic and spectroscopic tools (including picosecond resolved technique) were used to characterize and understand the key role of the halide ions to modulate the light induced charge separation in ZnO NP. Picosecond resolved fluorescence spectra unveil a significant quenching, implying an electronic cross‐talking between the NP and the attached halide ions. Magnetic measurements indicate that attachment of a suitable halide ion introduces room temperature ferromagnetism in this system. Finally, the photocatalytic activity of the ZnO NP for the photodegradation of a model pollutant, methyl orange was evaluated under UV light irradiation. Halide ZnO is anticipated to be a very promising photocatalytic agent; hence it can be used to cleanup environmental pollution. First principles analysis has been performed to understand the modulation of electronic properties like photocatalysis and magnetism in halide attached nanosystem. The experimental behavior resembles nicely with theoretical results.

Influence of cobalt doping on residual stress in ZnO nanorods

Cobalt-doped (0%, 5%, 10%, 15%, and 20%) zinc oxide (ZnO) nanorods were deposited on silicon wafers by a chemical bath deposition technique. Variations in energy band gap and stress due to cobalt doping were analyzed by X-ray diffraction techniques, optical measurements and modeled by density functional theory calculations. Also, the direct residual stress in ZnO nanorods was investigated by measuring the difference in curvature across the doped ZnO thin films deposited on a silicon substrate using the Bow Optic wafer stress measurement system. The stress in doped ZnO films was found to be of compressive in nature. The residual stress in doped ZnO thin films was found in the range of 0.0427–1.0174 GPa. The residual stress was also found to scale with the cobalt doping concentration in ZnO thin film. Also, the crystalline structure of various cobalt doped ZnO nanorods films was confirmed by X-ray diffraction analysis to be of the wurtzite structure. The bandgap of cobalt-doped ZnO was red-shifted from 3.30 eV to 3.21 eV as the cobalt concentration in ZnO nanostructures varied from 0% to 20%. A linear relationship between stress and bandgap shifting in cobalt-doped ZnO nanorods was obtained based on x-ray diffraction and direct stress measurements.

Study of Undoped and Indium Doped ZnO Thin Films Deposited by Sol Gel Method

In this paper, we report the effects of Indium doping concentrations (from 0 to 10wt%) on the structural, morphological, and optical properties of deposited In doped ZnO (IZO) thin films prepared by the sol–gel method through the dip coating technique. X-ray diffraction (XRD) analysis indicates that all ZnO thin films have a polycrystalline nature with a hexagonal wurtzite phase with (002) as a preferential orientation. XRD results demonstrate that the particle size of ZnO decreased with the increase in Indium concentrations. Raman scattering spectra confirmed the wurtzite phase and the presence of intrinsic defects in our samples. Energy dispersive spectroscopy (EDS) and the X-ray photoelectron spectroscopy (XPS) measurements, confirmed the presence of zinc, oxygen and indium elements which is in agreement with XPS results. The photoluminescence (PL) spectra of the films exhibit defects-related visible emission peaks, with intensities differing owing to different concentrations of zinc vacancies. UV–Vis spectrometer measurements show that all the films are highly transparent in the visible wavelength region (≥ 70%) and presented two different absorption edges at about 3.21 eV and 3.7 eV, these may be correspond to the band gap of zinc oxide and indium oxide respectively.

Red/green/blue selective phototransistors with a hybrid structure of quantum-dots and an oxide semiconductor

Color-selective phototransistors have been developed using a hybrid film of quantum-dots (QDs) and an oxide semiconductor. The zinc oxide (ZnO) phototransistor with QDs with a 2.96 eV band gap showed a photocurrent when illuminated by 450 nm light. The device with QDs with a 2.28 eV band gap started to show a photocurrent under 520 nm light, and the device with QDs with a 1.95 eV band gap showed a photocurrent under light with a wavelength of 635 nm. The photocurrent with low-energy photons, such as visible light, originated when small band-gap QDs absorbed and converted visible light into photoelectrons, and the transparent wide band-gap ZnO supplied a conductive channel in the conduction band to allow the photocurrent to flow through the device. Based on those results, we developed a color-selective phototransistor that can separate red, green, and blue light using a hybrid structure of ZnO and multilayer QDs. The device showed photoresponsivity values of 0.032, 0.053, and 0.26 mA/W to red, green, and blue light, respectively, which are different enough to distinguish the color of the visible light. Therefore, we fabricated and characterized a photogating inverter to convert the color of visible light into an electrical voltage signal. Our results show that the hybrid film of ZnO and QDs could be a feasible way to develop a highly transparent, full-color image sensor.

Temperature dependence of bulk luminescence from ZnO.

X-Ray excited luminescence (radioluminescence, RL) spectra from nominally pure crystalline zinc oxide (ZnO) are reported. The temperature range is from 20 to 673K. Significant changes of emission band energies and intensities are observed across the temperature range. Photon energies of emission bands linked to the band gap decrease with increasing temperature in RL. This dependence fits the theoretical equations describing the temperature response of the ZnO band gap. Defect related luminescence includes a complex mixture of features at low temperature for RL. Thermoluminescence (TL) signals from 20 to 300K confirm the presence of an unresolved feature in the RL data. Comments on the possible origin of these bands are summarized. The data underline that it is essential to record the temperature dependence for the luminescence data in order to separate overlapping spectral features.

FESEM, XRD and DRS studies of electrochemically deposited boron doped ZnO films

AbstractIn this study, the effect of boron (B) incorporation into zinc oxide (ZnO) has been investigated. The undoped, 2 at.%. and 4 at.% B doped ZnO films were deposited on p-type silicon (Si) substrates by electrodeposition method using chronoamperometry technique. Electrochemical depositions were performed by applying a constant potentiostatic voltage of 1.1 V for 180 min at 90 °C bath temperature. To analyze the surface morphology, field emission scanning electron microscopy (FESEM) was used and the results revealed that while a small amount of boron resulted in smoother surface, a little more incorporation of boron changed the surface morphology to dandelion-like shaped rods on the whole surface. By using X-ray diffraction (XRD) analysis, the crystal structures of the films were detected and the preferred orientation of the ZnO, which exhibited polycrystalline and hexagonal wurtzite structure, changed with B doping. For the estimation of the optical band gap of obtained films, UV-Vis diffuse reflectance spectra (DRS) of the films were taken at room temperature and these data were applied to the Kubelka-Munk function. The optical band gap of ZnO narrowed due to incorporation of B, which was confirmed by red-shift.

Effect of Pre-Annealing on Thermal and Optical Properties of ZnO and Al–ZnO Thin Films

Zinc oxide (ZnO) nanoparticles were synthesized by a simple solution route method using zinc acetate as the precursor and ethanol as the solvent. At a temperature of 60[Formula: see text]C, a clear homogenous solution is heated to 100[Formula: see text]C for ethanol evaporation. Then the obtained precursor powder is annealed at 600[Formula: see text]C for the formation of ZnO nanocrystalline structure. Doped ZnO particle is also prepared by using aluminum nitrate nonahydrate to produce aluminum (Al)-doped nanoparticles using the same solution route method followed by annealing. Thin film fabrication is done by air evaporation method using the polymer polyvinyl alcohol (PVA). To analyze the optical and thermal properties for undoped and doped ZnO nanocrystalline thin film by precursor annealing, characterizations such as UV, FTIR, AFM, TGA/DTA, XRD, EDAX and Photoluminescence (PL) were also taken. It was evident that precursor annealing had great influence on thermal and optical properties of thin films while ZnO and AZO film showed low crystallinity and intensity than in the powder form. TGA/DTA suggests pre-annealing effect improves the thermal stability, which ensures that Al ZnO nanoparticle can withstand at high temperature too which is the crucial advantage in the semiconductor devices. UV spectroscopy confirmed the presence of ZnO nanoparticles in the thin film by an absorbance peak observed at 359[Formula: see text]nm with an energy bandgap of 3.4[Formula: see text]eV. A peak obtained at 301[Formula: see text]nm with an energy bandgap of 4.12[Formula: see text]eV shows a blue shift due to the presence of Al-doped ZnO nanoparticles. Both ZnO and AZO bandgap increased due to precursor annealing. In this research, PL spectrum is also studied in order to determine the optical property of the nanoparticle embedded thin film. From PL spectrum, it is observed that the intensity of the doped ZnO is much more enhanced as the dopant concentration is increased to 1[Formula: see text]wt.% and 2[Formula: see text]wt.% of Al in ZnO.

Synthesis of Zn1−xCdxO Nanoparticles by Co-Precipitation: Structural, Optical and Photodetection Analysis

Zinc oxide (ZnO) is a wide bandgap semiconductor with excellent photoresponse in ultra-violet (UV) regime. Tuning the bandgap of ZnO by alloying with cadmium can shift its absorption cutoff wavelength from UV to visible (Vis) region. Our work aims at synthesis of Zn[Formula: see text]CdxO nanoparticles by co-precipitation method for the fabrication of photodetector. The properties of nanoparticles were analyzed using X-ray diffractometer, UV–Vis spectrometer, scanning electron microscope and energy dispersive spectrometer. The incorporation of cadmium without altering the wurtzite structure resulted in the red shift in the absorption edge of ZnO. Further, the photoresponse characteristics of Zn[Formula: see text]CdxO nanopowders were investigated by fabricating photodetectors. It has been found that with Cd alloying the photosensitivity was increased in the UVA-violet as well in the blue region.

Photocatalytic degradation of roxarsone by using synthesized ZnO nanoplates

Abstract An efficient photodegradation of roxarsone (ROX) was achieved by using synthesized zinc oxide (ZnO) nanoplates under UV light irradiation. ZnO nanoplates were synthesized by facile wet chemical method. Characterization of ZnO nanoparticles was done by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, diffuse reflectance (DRS) UV–Visible absorption spectroscopy, BET analyzer, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The obtained results reveal that the synthesized sample is ZnO which has hexagonal structure and plate-like morphology. The band gap and specific surface area of ZnO was found to be 3.02 eV and 7 m2 g−1 respectively. ROX’s degradation by-products such as As(III), As(V) were analyzed by high performance liquid chromatography-hydride generation coupled with atomic absorption spectrometry (HPLC-HG-AAS). The photogenerated hydroxyl ( ) and carbon-centered radicals were detected by electron paramagnetic resonance (EPR) spectroscopy. According to experimental evidences a possible photocatalytic mechanism has also been proposed. Photocatalytic degradation of ROX leads to mineralization as CO2 and As(V). This can be considered as a promising method for removing ROX from contaminated waters.

Nanophotosensitive drugs for light-based cancer therapy: what does the future hold?

Nanophotosensitive drugs for light-based cancer therapy: what does the future hold?

Synthesis of nano-ZnO by wire explosion process and its photocatalytic activity

Zinc oxide (ZnO) nanoparticles were produced by wire explosion process and characterized through X-ray diffraction (XRD) studies and by TEM studies. The particle size analysis indicates that they follow log-normal distribution and the mean size of the ZnO nanoparticles formed is about 44nm. Optical band gap of ZnO is found to be 3.21eV by UV–vis diffuse reflectance spectroscopy (DRS). The synthesized ZnO nano particles were used as photo catalyst for degradation of methylene blue (MB) in aqueous solution. Nano zinc oxide of 100mg/L was found as the optimum quantity for UV photo degradation of 10mg/L MB. ZnO nanoparticles were verified for its reusability. The results of the study are compared with commercial ZnO nanoparticle and with Degussa P-25 TiO2. LC-MS studies were carried out to identify the intermediates and degradation pathway.

Impact of Post- Deposition Heat Treatment on the Morphology and Optical Properties of Zinc Oxide (ZnO) Thin Film Prepared by Spin-Coating Technique

This research work examines the structural and optical properties of ZnO thin films. Deposition were done by spin coating of solution of Zinc oxide onto pre-cleaned glass substrate at 4000 rpm for 30 sec using spin-coater under ambient condition at room temperature in order to form desired thickness of the film on the substrate. Post- deposition thermal annealing at different range of temperatures from 150°C to 600°C with steps of 50°C was carried out on the samples. The impact of thermal annealing on optical properties of the deposited thin film was investigated using UV-VIS spectrophotometer and scanning Electron Microscope for the morphology. The optical transmittance, reflectance, absorbance were recorded which was used to evaluate the optical band gap of Zinc oxide. Observation shows that band gap energy reduces as annealing temperature is increased from 150°C to 600°C. Observation made on the morphology using SEM model ASPEX 3020 showed that as the temperature increases the surface of the sample roughness increases. It was deduced that as the annealing temperature is increased the surface roughness increases. This may be due to increase in grain size with increase in annealing temperature. The band gap energy decreases as the annealing temperature increases.