Thin Zinc Oxide Research Articles

Heterogeneous photoelectro-Fenton using ZnO and TiO2 thin film as photocatalyst for photocatalytic degradation Malachite Green

Titanium dioxide (TiO2) and zinc oxide (ZnO) particles as photocatalysts are known to be effective in the degradation of various organic pollutants. Here we use a simple way of preparing an active TiO2 thin film for Malachite Green (MG) elimination from an aqueous solution based on a combination of advanced oxidation processes (electro Fenton and photocatalytic degradation) under UV wavelengths irradiation. The TiO2 and ZnO as nano-photocatalytic material as thin layers on the glass surface are applied. For the characterization of synthesized ZnO and TiO2 paste, SEM, TEM and XRD were used. The effects of operational variables on the degradation of MG were studied by central composite design (CCD). The results showed that MG was degraded by the TiO2 and ZnO pastes in photoelectro-Fenton system under UV irradiation at optimum conditions with 79.4 and 97.5% degradation efficiency, respectively, which reaction constant of thin film ZnO was 1.96 times as high as that of the TiO2 paste in the mentioned system. The optimum degradation conditions for thin film ZnO were as follows: pH of 3, 30 mg/L of initial MG concentration, 200 mA of electrical current, 0.4 mmol/L of FeCl3, and 16 min of contact time. In addition, the degradation rates of MG by both photocatalysts in the photoelectro-Fenton system could be explained in terms of the Langmuir-Hinshelwood pseudo-first-order kinetic equation.

Low-Temperature Growth of ZnO Nanowires from Gravure-Printed ZnO Nanoparticle Seed Layers for Flexible Piezoelectric Devices.

Zinc oxide (ZnO) nanowires (NWs) are excellent candidates for the fabrication of energy harvesters, mechanical sensors, and piezotronic and piezophototronic devices. In order to integrate ZnO NWs into flexible devices, low-temperature fabrication methods are required that do not damage the plastic substrate. To date, the deposition of patterned ceramic thin films on flexible substrates is a difficult task to perform under vacuum-free conditions. Printing methods to deposit functional thin films offer many advantages, such as a low cost, low temperature, high throughput, and patterning at the same stage of deposition. Among printing techniques, gravure-based techniques are among the most attractive due to their ability to produce high quality results at high speeds and perform deposition over a large area. In this paper, we explore gravure printing as a cost-effective high-quality method to deposit thin ZnO seed layers on flexible polymer substrates. For the first time, we show that by following a chemical bath deposition (CBD) process, ZnO nanowires may be grown over gravure-printed ZnO nanoparticle seed layers. Piezo-response force microscopy (PFM) reveals the presence of a homogeneous distribution of Zn-polar domains in the NWs, and, by use of the data, the piezoelectric coefficient is estimated to be close to 4 pm/V. The overall results demonstrate that gravure printing is an appropriate method to deposit seed layers at a low temperature and to undertake the direct fabrication of flexible piezoelectric transducers that are based on ZnO nanowires. This work opens the possibility of manufacturing completely vacuum-free solution-based flexible piezoelectric devices.

Optical and Electrophysical Properties of Thin Zinc Oxide Films Doped with Manganese Oxide and Obtained by Laser Deposition

Nanostructured thin films on a silicon substrate were obtained on a ceramic of zinc oxide doped with manganese oxide by high-frequency periodic pulsed laser action with f ~ 10–15 kHz, wavelength λ = 1.064 μm at power density q = 150 MW/cm2 in a vacuum chamber with p = 2.7 Pa. The surface morphology and the elemental composition of the obtained films were studied using atomic force microscopy, scanning electron microscopy, and X-ray spectral microanalysis. Features of the transmission spectra in the visible, near, and middle IR regions were determined. The electrophysical properties of the ZnO + 2% MnO2/Si heterostructure were analyzed.

Fabrication and Study of ZnO thin Films using Thermal Evaporation Technique

In this study, thin film Zinc oxide (ZnO) deposited by thermal evaporation techniques on unheated glass substrates. The findings of X-ray diffraction (XRD) show that the ZnO films are amorphous before annealing. The subsequent diffraction patterns demonstrate that the films crystalline into polycrystalline mixed Tetragonal α-ZnO compounds and Orthorhombic s-ZnO compounds. Atomic power microscope (AFM) shows that the ZnO films are of a large homogeneous surface. The median crystallite size is calculated from XRD data, which are increased for all thickness with an increasing ringing temperature and are less than the AFM data. The findings of the optical properties show that with rising annealing temperature for all thicknesses, the transmittance decreases. ZnO film shows transmittance that exceeds 95% in the IR radiation area of the spectrum at the lower thickness of 60 nm annealed at 523 K for 2 hr, but decreases to 87% percent with increasing annealing temperatures, although ZnO films with thicknesses of 130 nm annealed at 723 K for 2 hr have a transmittance of 94 % and 88 % in the IR region, but decreases High transmission in the IR area reveals that ZnO films are good materials for agricultural applications. All the prepared ZnO-thin films were n-type semiconductors and it is known that the concentration of the carriers (n) and the conductivity (σ) increased with an ever-greater annealing temperature, while their mobility (μ) and resistivity (ρ) is reduced with an increase in the annealing temperature.

Dual Laser Beam Processing of Semiconducting Thin Films by Excited State Absorption.

We present a unique dual laser beam processing approach based on excited state absorption by structuring 200 nm thin zinc oxide films sputtered on fused silica substrates. The combination of two pulsed nanosecond-laser beams with different photon energies—one below and one above the zinc oxide band gap energy—allows for a precise, efficient, and homogeneous ablation of the films without substrate damage. Based on structuring experiments in dependence on laser wavelength, pulse fluence, and pulse delay of both laser beams, a detailed concept of energy transfer and excitation processes during irradiation was developed. It provides a comprehensive understanding of the thermal and electronic processes during ablation. To quantify the efficiency improvements of the dual-beam process compared to single-beam ablation, a simple efficiency model was developed.

Quantum-Sized Objects in the Form of Exciton and Trion Traps: Their Role in Excitonic Partial Blocking of the Memristor Properties of Thin Zinc Oxide Films

Possible mechanisms of the emergence of exciton and trion traps at room temperature and the dynamics of relaxation processes occurring in them are discussed, based on an analysis of the results from experiments on photon echoes in thin films of zinc oxide and doped silicon. The current–voltage characteristics recorded for such films with traps displaying the memristor effect are studied, and the influence traps exert on the parameters of such characteristics is established.

High‐Performance Coplanar Dual‐Channel a‐InGaZnO/a‐InZnO Semiconductor Thin‐Film Transistors with High Field‐Effect Mobility

AbstractAn amorphous indium gallium zinc oxide (a‐IGZO) layer is deposited on very thin conductive amorphous indium zinc oxide (a‐IZO) thin film to demonstrate high‐performance, coplanar thin‐film transistors (TFTs) with dual‐channel oxide semiconductor architecture. Based on material properties, a conduction band offset (∆EC) of ≈0.28 eV between a‐IZO and a‐IGZO layers and a conduction band bending of ≈0.3 eV at a‐IGZO/gate insulator (GI) interface exist. Through the electrical characterization, high field‐effect mobility (μFE) of ≈50 cm2 V−1 s−1, a positive threshold voltage (VTh) of ≈2.3 V, and low off‐current (IOFF) of <1 pA in coplanar a‐IZO/a‐IGZO TFT are demonstrated. The electron accumulation (>5 × 1018 cm−3) at both the a‐IZO/a‐IGZO and a‐IGZO/GI interfaces confirm the dual‐channel conduction. The bottom a‐IZO channel significantly contributes to increasing drain current (ID) due to large electron density (≈1019 cm−3). The dual‐channel coplanar TFT with a‐IGZO/IZO provides a guideline for overcoming the trade‐off between high μFE and positive VTh control for stable enhancement mode operation with increased ID.

Modeling, fabrication, and structural characterization of thin film ZnO based film bulk acoustic resonator

This work reports the finite element modeling, fabrication and structural characterization a film bulk acoustic resonator (FBAR) devices using shadow mask technique. For the performance analysis of the FBAR device, simulations were performed on COMSOL Multiphysics platform. RF sputtering technique is used to deposit c-axis oriented zinc oxide (ZnO) thin film on Aluminum electrodes. The Aluminum electrodes were deposited using e-beam evaporation technique. The X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) techniques were used to examine the surface morphologies of the deposited piezoelectric film (ZnO). The quality of the deposited piezoelectric material film was measured with the help of XRD spectra and AFM is used to measure surface roughness of the deposited ZnO film and its measured value is 6.94 nm. The resonant characteristics of fabricated FBAR device are evaluated with the help of COMSOL Multiphysics simulations and the obtained values of effective electromechanical coupling constant (k2eff), quality factors (Qs and Qp) and Figure of merit are 3.0025%, 1811.3, 1711.4 and 54 (approximately), respectively.

МОБІЛЬНИЙ СЕНСОР АЦЕТОНУ

The aim of this work is to develop mobile sensors for acetone based on metal oxide for their subsequent use in the development of devices for monitoring health status. The following research methods were used in the work: measuring the sensitivity of sensor samples on the film thickness and annealing temperature; removal of dependences of sensitivity, selectivity and detection limits on operating temperature; studying the morphology of sensor samples using X-ray diffractometry and field emission scanning electron microscopy. An acetone sensor was developed on the basis of nanostructured thin zinc oxide films, its sensitivity was determined at various temperatures, as a result of which the optimal operating temperature of the sensor was about 400 ° C. The sensitivity value of the ZnO gas sensor was more than 26.5% at 1000 ppm, 65% at 500 ppm and 5% at 300 ppm acetone. Possible future directions of development are the development of multisensor VOC sensor systems for implementation in wireless intelligent systems for monitoring the health of the population.

Cathodoluminescence of ZnO Films on a Rhombohedral Plane of Sapphire with a Gold Buffer Layer

We have studied the luminescent properties of zinc oxide (ZnO) films on a rhombohedral plane of sapphire with a buffer layer of gold nanoislands. The luminescence spectrum revealed a set of oscillations caused by the classical interference in the thin ZnO film. This set can be represented by a bar code in which every bar corresponds to the oscillation line wavelength and the bar width corresponds to the line intensity. The high reproducibility and simplicity of manufacturing these thin-film ZnO structures and the high sensitivity of interference phenomena in these structures with respect to environment imply that their application as elements in various chemo- and biosensors holds promise.

The Technique of thin Zinc Oxide Films Synthesis by ALD Method

Article shows experimental results of thin ZnO films synthesis with required structure and thickness produced by different atomic layer deposition methods (normal temperature, thermal and photo-assisted deposition). The influence of the synthesis temperature and UV-irradiation on the characteristics of ZnO films was analyzed. Both amorphous and polycrystalline films were synthesized by changing the deposition parameters. Film optical properties were examined in UV, visible and IR range. The bandgap was determined using absorption spectra. Morphological parameters of the films were valued using the atomic force microscopy. Suppositions on film growth mechanisms were made, preliminary results of friction wear tests are quoted.

Development and characterization of confocal sputtered piezoelectric zinc oxide thin film

Thin film zinc oxide (ZnO) is often used as a piezoelectric material, but its material properties are dependent on the deposition method and parameters. Direct sputtering using reactive DC or RF sputtering are the most common deposition methods for thin film piezoelectric ZnO. This paper investigates the influence of varying sputtering parameters on piezoelectric and mechanical properties of ZnO deposited by confocal sputtering using pulsed DC on a silicon substrate. Parameters such as varying power, duty cycle and temperature were examined. Crystallinity of the films were investigated systematically by X-ray Diffraction. Mechanical properties such as hardness and Youngs Modulus of thin films were measured via nanoindentation. Piezoelectric coefficient d33 was also measured for the films. Results demonstrated that the ZnO thin film exhibited high c-axis (002) textured films with rocking curve full width half maximum values of 1.69°. It was observed that power, duty cycle and temperature significantly affected the crystallinity, mechanical properties and d33 values of the ZnO thin film. This paper demonstrates that pulsed DC confocal sputtering can be utilized to deposit piezoelectric ZnO films and demonstrates key sputtering parameters that influence the piezoelectric, mechanical and morphology properties of the film.

Optical and Electrophysical Properties of Thin Zinc Oxide Films Doped with Scandium and Obtained by Laser Deposition

Nanostructured thin films on a silicon substrate were obtained by high-frequency pulse-periodic laser action (f ~ 10–15 kHz) with wavelength λ = 1.064 μm and power density q = 85 MW/cm2 on zinc oxide ceramic doped with scandium oxide in a vacuum chamber with pressure p = 2·10–2 mm Hg. The morphology of the obtained films was studied by atomic-force microscopy. Features of the transmission spectra in the visible and near and middle infrared regions were shown. The luminescence spectra obtained by excitation at various wavelengths were practically unchanged. The electrophysical properties of the ZnO + 0.9% Sc2O3/Si heterostructure were analyzed. It was established that the main conduction mechanism is current limited by space charge in an oxide film with deep traps.

Application of X-rays Diffraction for Identifying Thin Oxide Surface Layers on Zinc Coatings

Structural characterization of compound material coatings is usually achieved using time-consuming and destructive techniques such as optical and electrical microscopy, which require the use of grinding processes not always compatible with the material. This paper reports on the effective use of a theoretical model based on X-ray diffraction to calculate the thickness and composition of thin oxide films formed on the surface of zinc coatings. Zinc coatings are widely used in industrial application as protective layers against the atmospheric corrosion of steel substrates. The thickness of single- and multi-layer coatings is estimated using grazing incidence X-ray diffraction and various incidence angles. The coatings were grown using hot-dip, pack cementation and thermal spray techniques, and their experimental characteristics were compared to the theoretically predicted values of thickness and composition. The results indicate the formation of a thin zinc oxide film on top of each coating, which acts as an isolation layer and protects the surface of the sample against the environmental corrosion. Finally, the penetration depth of the X-rays into the zinc-based coatings for grazing incidence and Bragg–Brentano X-ray diffraction geometries were calculated using theoretical equations and experimentally confirmed.

Tailored β-diketones as effective surface passivation for solution processed zinc oxide thin film transistors

Diketone passivation of defect states at the surface of solution-processed zinc oxide thin film transistors is investigated. Trifluoroacetylacetophenone is used as the basis for passivating molecules due to its easy chemical variability on the phenyl ring. Electron withdrawing or donating substituents can be introduced at the phenyl ring to vary the electron density at the ketone anchoring positions of the passivating molecule. The relative change of electron density is quantified by DFT calculations for different substituents. Experimentally thin zinc oxide films are prepared by aqueous spray pyrolysis, while passivating diketones are deposited in vacuum on the ZnO surface. XPS and AFM measurements confirm the successful deposition of passivating molecules at the zinc oxide surface. Electrical characterization of passivated zinc oxide transistors is carried out for different exposure times. All diketones improve transistor stability for positive and negative bias stress. The passivated transistors show improved electrical properties with increased electron mobility and decreased disorder parameter. Finally, threshold voltages shift systematically to negative values and hysteresis clearly reduces. The experimentally determined electrical properties of passivated zinc oxide transistors show a systematic correlation to the effective electron density at the oxygen anchor atoms of diketones and higher charge results in a better performance. • 1,3-diketone molecules as passivation with adjustable effective charge at oxygen. • Chemical passivation of zinc oxide surface defects. • High electron density at oxygen anchor atoms improves transistor performance best.

Tribological study of hafnium dioxide and aluminium oxide films grown by atomic layer deposition on glass substrate

In the present work we studied the mechanical properties of hafnium dioxide (HfO2) and aluminium oxide (Al2O3) thin films deposited on glass at low temperature by means of atomic layer deposition method. The scratch resistance and tribological properties of HfO2 and Al2O3 were investigated. During scratch tests the first small cracks in the films were detected with a relatively low load of 3.4–4.9 N. However, up to a load of 30 N, crushing, cracking, and delamination of the Al2O3/glass system not occurs. The tribological experiments revealed a significant difference in the wear between the HfO2 and Al2O3 films. The microcrystalline structure observed for HfO2 resulted in better tribological properties than the Al2O3 film. The addition of a thin zinc oxide interlayer significantly improved the mechanical properties of the system with HfO2 film.

Comparison of ALD-grown thin ZnO films with various thicknesses for NO2 sensing

Thin zinc oxide (ZnO) films of various thicknesses were characterized and compared in terms of their suitability to gas sensor applications. Applying atomic layer deposition (ALD), very thin ZnO films were deposited on quartz resonators, and their gas sensing properties were studied using a quartz crystal microbalance (QCM). The ZnO thin films were prepared using diethyl zinc and water as precursors. The crystal structure of the films was studied by X-ray diffraction (XRD), and their surface was observed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX) used to study the films’ composition. Films of thickness of ~10 – 80 nm were deposited on quartz resonators with Au electrodes and the QCM method was used to build highly sensitive gas sensors. These were tested for sensitivity to various concentrations of NO2. Although some of the films were very thin, they were sensitive to NO2 already at room temperature and could register reliably as low concentrations as 50 ppm, while the sorption was fully reversible and the sensors could be fully recovered. With the technology presented, manufacturing of QCM gas sensors is simple, fast and cost-effective, and suitable for application in energy-effective portable equipment for real-time monitoring of NO2 in the automotive industry or environmental protection.

Solution-Processed Amorphous Zinc Oxide Thin Film Transistor Based NAND Gate

Herein, we discuss the synthesis and deposition of thin films amorphous zinc oxide (a: ZnO) by custom-designed spray pyrolysis unit for Thin Film Transistor (TFT) application towards NAND gate fabrication. Top gate top contact TFT was fabricated on a glass substrate, a: ZnO as the channel layer, PVA as gate dielectrics material and Al as electrodes. Electrical properties of a: ZnO TFT (W/L = 500/200μm) were probed. The individual transistor with a threshold voltage (Vth = 2.1 V), off and on current (Ioff = order of 10-8A; Ion = 10-3) and Ion / Ioff ratio (order of 105). The linear mobility is calculated and obtained as 3 cm-2/Vs. NAND gate is one of the universal and basic building blocks of a digital circuit. The fabricated NAND gate is subjected to the logic operation in the range of 0 to 10 V was tested. The result implies that it can be utilized for logical circuit operation.

Mathematical model development for thin zinc oxide film formation with assigned dielectric constant values

This article deals with the problem of the mathematical model development linking the magnetron sputtering technological parameters with the complex dielectric constant of thin zinc oxide films. Computational procedures to calculate the regression equation coefficients are given. The equipment to obtain zinc oxide thin films using the method of reactive magnetron sputtering is described.

Optical properties of ZnO nanorods derived from chemical bath deposition process with different seeds solution concentration

Owing to their high surface to volume ratio and fast electron transfer, zinc oxide (ZnO) nanorods have been well-known as potential nanostructured material for various applications including sensors, dye sensitized solar cells, optoelectronic, transparent heater and biomedical devices. Among other synthesizing techniques for obtaining ZnO nanorods, chemical bath deposition (CBD) has been thought as a simple and low-cost method. However, there are several processing parameters that need to be investigated for the above-mentioned applications where the highly optical transparency of thin film ZnO nanorods grown on glass substrates is one of important targets to be achieved. In this work, ZnO nanorods were synthesized through CBD process at low temperature (0°C) by using seed solution prepared by dissolving 1: 1 equimolar zinc nitrate tetrahydrate and hexamethylene tetraamine. For investigation purposes, three different concentration of seed solutions i.e. 0.005, 0.025 and 0.05 M were used. Thin films containing ZnO nanoseeds were formed by spin coating the precursors on the glass substrates, followed with annealing at 2000C for 5 minutes. Finally, the ZnO nanorods were further grown at 90ºC for 3 hours in the beaker glass using the same solution. Xray diffraction (XRD) analysis showed that all ZnO nanorods demonstrated a strong (002) peak belong to wurtzite phase. It was found that the estimated crystallite size and band gap energy (Eg) for ZnO nanorods derived from the seed solutions of 0.005, 0.025 and 0.05 M were 21.42, 137.11, 171.39 nm, and 3.60, 3.20, 3.18 eV, respectively. However, the optical transparency was adversely lowered from about 75 to 40 % as a result of increased coverage of ZnO nanorods on the glass substrate. For transparent heater application where, a desired combination of high optical transparency and suitable electronic properties is needed, the current results were considered to be promising.