Deposition Of ZnO Research Articles

Area‐Selective Atomic Layer Deposition on Functionalized Graphene Prepared by Reversible Laser Oxidation

AbstractArea‐selective atomic layer deposition (ALD) is a promising “bottom‐up” alternative to current nanopatterning techniques. While it has been successfully implemented in traditional microelectronic processes, selective nucleation of ALD on 2D materials has so far remained an unsolved challenge. In this article, a precise control of the selective deposition of ZnO on graphene at low temperatures (<250 °C) is demonstrated. Maskless femtosecond laser writing is used to locally activate predefined surface areas (down to 300 nm) by functionalizing graphene to achieve excellent ALD selectivity (up to 100%) in these regions for 6‐nm‐thick ZnO films. The intrinsic conductive properties of graphene can be restored by thermal annealing at low temperature (300 °C) without destroying the deposited ZnO patterns. As the graphene layer can be transferred onto other material surfaces, the present patterning technique opens new attractive ways for various applications in which the functionalized graphene is utilized as a template layer for selective deposition of desired materials.

Synthesis and applications of TiO2/ZnO hybrid nanostructures by ZnO deposition on TiO2 nanotubes using electrochemical processes

Abstract In recent years, TiO2/ZnO hybrid nanostructures have been attracting the interest of the scientific community due to their excellent photoelectrochemical properties. The main advantage of TiO2/ZnO hybrid nanostructures over other photocatalysts based on semiconductor materials lies in their ability to form heterojunctions in which the valence and conduction bands of both semiconductors are intercalated. This factor produces a decrease in the band gap and the recombination rate and an increase in the light absorption range. The aim of this review is to perform a revision of the main methods to synthesise TiO2/ZnO hybrid nanostructures by ZnO deposition on TiO2 nanotubes using electrochemical processes. Electrochemical synthesis methods provide an easy, fast, and highly efficient route to carry out the synthesis of nanostructures such as nanowires, nanorods, nanotubes, etc. They allow us to control the stoichiometry, thickness and structure mainly by controlling the voltage, time, temperature, composition of the electrolyte, and concentration of monomers. In addition, a study of the most promising applications for TiO2/ZnO hybrid nanostructures has been carried out. In this review, the applications of dye-sensitised solar cell, photoelectrocatalytic degradation of organic compounds, photoelectrochemical water splitting, gas sensors, and lithium-ion batteries have been highlighted.

Pulsed laser deposition of ZnO and MoO3 as reflection prohibitors on photovoltaic cell substrate to enhance the efficiency

With the ever-growing demand for conventional fuels, the improvement in the efficiency of the photovoltaic system is the need of the hour. Antireflection coatings enhance the availability of solar power by reducing the percentage of light reflected. A new coating has been developed to improve the solar cell's overall efficiency. This study focuses on enhancing the efficiency of the monocrystalline solar cell when a coating of ZnO-MoO3 is applied at a certain thickness. A layer of ZnO followed by MoO3 is deposited on a Silicon solar cell substrate using a Pulsed Laser Deposition process. Due to the transmissivity d between the two materials, they act as excellent antireflection coating. The layer thickness has been engineered to lie in the maximum absorption spectrum of monocrystalline silicon solar cells, which is between 400 and 800 nanometers. Based on the calculation of transmissivities for a given layer thickness of coating material, the coating has been done, and the efficiencies of the coated specimen were compared with the uncoated solar cell. The percentage improvement in the electrical efficiency of a single crystalline silicon solar cell with an anti-reflection coating at 1059 W/m2 is about 35.7%. Among the available antireflection coating materials, the combination that provides better efficiency when coated on top of a solar cell is hard to find. This anti-reflection coating could be a better solution to enhance the overall efficiency of the single crystalline silicon solar cell. Although ZnO and MoO3 coatings have been investigated separately for improvement in solar cell efficiency with varying levels of success, the hybrid coating of ZnO/MoO3 with a performance enhancement of 35.7% is a great leap.

Nondestructive Direct Photolithography for Patterning Quantum Dot Films by Atomic Layer Deposition of ZnO

AbstractColloidal quantum dot‐based light‐emitting diodes (QD‐LEDs) are one of the potential future self‐emissive displays owing to their large‐scale solution‐processibility and high color purity. For the industrial application of QD‐LEDs, high‐performance QD‐LED and high‐resolution patterning of quantum dot (QD) films are required. Photolithography is an ideal tool for patterning QD films. Previously, the high‐resolution patterning of QD films using direct photolithography by ultra‐thin atomic layer deposition of ZnO on the QD surface is reported. The patterning process is acceptable for Cd‐based QD films, but the photoresist severely deteriorates the photoluminescence (PL) intensity of InP‐based QD films owing to the presence of sulfonic groups in the photoactive compound. Herein, a non‐destructive direct photolithography process for QD film patterning using a negative photoresist that does not affect the PL intensities of Cd‐ and InP‐based QD films is reported. The effect of the photoresist is also verified by a PL lifetime study. Extremely bright Cd‐ and InP‐based QD films are successfully patterned using a softer photoresist, and micropatterning of InP‐based QD films is reported for the first time in this work using photolithography. A QD electroluminescence device is also successfully fabricated using the patterning method.

Spectral tuning of biotemplated ZnO photonic nanoarchitectures for photocatalytic applications.

The photocatalytic activity of a flat surface can be increased by micro- and nanostructuring the interface to increase the area of the contact surface between the photocatalyst and the solute, and moreover, to optimize charge carrier transfer. Further enhancement can be achieved by using photonic nanostructures, which exhibit photonic band gap (PBG). Structurally coloured butterfly wings offer a rich ‘library’ of PBGs in the visible spectral range which can be used as naturally tuned sample sets for biotemplating. We used conformal atomic layer deposition of ZnO on the wings of various butterfly species (Arhopala asopia, Hypochrysops polycletus, Morpho sulkowskyi, Polyommatus icarus) possessing structural colour extending from the near UV to the blue wavelength range, to test the effects arising from the nanostructured surfaces and from the presence of different types of PBGs. Aqueous solutions of rhodamine B were used to test the enhancement of photocatalytic activity that was found for all ZnO-coated butterfly wings. The best reaction rate of decomposing rhodamine B when illuminated with visible light was found in 15 nm ZnO coated M. sulkowskyi wing, the reflectance of which had the highest overlap with the absorption band of the dye and had the highest reflectance intensity.

Study of zinc salt concentration effect on the growth of zno nanostructured oxides obtained by direct electrodeposition

"Effect of zinc salt concentration on the growth of electrodeposited zinc oxide phases was investigated. ZnO thin films were elaborated via chronoamperometry on fluorine doped tin oxide (FTO) substrates from aqueous mixed bath of zinc nitrate and chlorate at 70°C. X ray diffraction patterns showed nanocrystalline films of hexagonal wurtzite phase with (101) preferential orientation for ZnO as grown in low concentration of Zn2+ salt. High concentration of Zn2+ favor the formation of Zn5(OH)8Cl2H2O simonkolleite phase. After heat treatment at 400 °C for 1h this later decomposes to ZnO oxide which presents no preferential orientation. The route mean square RMS roughness of surfaces estimated from AFM technique shows that ZnO generated from heat treated Zn5(OH)8Cl2H2O present more increasing roughness than ZnO deposits obtained at lower salt concentration. The photoelectrochemical answer indicated important generated photocurrents for both films which present n-type electrical conductivity"

High‐Resistance Metal Oxide Window Layers for Optimal Front Contact Interfaces in Sb2Se3 Solar Cells

Herein, an in‐depth experimental investigation into the effect of employing different high resistance metal oxide (HRMO) layers on the quality of the front contact in solar cells with an fluorine‐doped tin oxide (FTO)/(HRMO)/CdS/Sb2Se3/Au device architecture is presented. The application of ZnO or TiO2 HRMO layers between FTO substrates and CdS improves the overall device performance. Short‐circuit current gains of ≈20%, orders of magnitude higher shunt resistances (≈104 Ω cm2), and greatly improved device stabilities—maintaining over 95% of their initial efficiency over 137 days are observed. A suppression of the unfavorable (120) orientation of the photoactive Sb2Se3 layer is observed in devices with HRMO interlayers. The application of HRMO layers is crucial to prevent both ohmic and non‐ohmic current leaks and maintain device stability over time. Cross‐over in the current‐voltage (JV) curves observed in the case of TiO2 indicates the presence of a high barrier for the diode current in these devices. Wavelength‐dependent JV curves coupled with capacitance measurements and simulations show that this barrier can be attributed to a high density of interfacial acceptor states. In contrast, ZnO deposition is found to reduce interface defects and enhance the quality of the front contact, while boosting performance and increasing device longevity.

Spatial ALD of Al2O3 and ZnO using heavy water

Al2O3 and ZnO thin films were deposited from trimethylaluminium (TMA) and diethylzinc (DEZ) in combination with water using cylindrical rotating substrate spatial atomic layer deposition (SALD). The depositions were done between 67 and 140 °C. The growth per cycle for Al2O3 varied between 0.75 and 2.0 × 1015 at./cm2 per cycle and for ZnO between 0.52 and 1.07 × 1015 at./cm2 per cycle. The hydrogen incorporation was studied by varying the deposition temperature and substrate rotation speed. The rotation speed affects the precursor exposure time (46–458 ms) and inert gas purging time (111–1120 ms). The results show that Al2O3 films can contain up to 25 at.% of hydrogen when the deposition temperature is 67 °C or the deposition exposure/purging times are short. The deposition of ZnO in similar conditions produces films with hydrogen concentrations up to 15 at.%. The source of impurity hydrogen was investigated by using heavy water, 2H2O, as an oxygen source. The main hydrogen isotope in the Al2O3 films at low temperatures and fast deposition speed was found to be 1H, while at higher temperatures and lower deposition speeds 2H isotope was dominant. For ZnO, 1H was the majority hydrogen isotope in the films in all the studied deposition conditions except at the lowest rotation speed.

Functionalization of the hydroxyapatite surface with ZnO for alizarin immobilization

The surface of hydroxyapatite (HAp) was functionalized by the deposition of ZnO using microwave-assisted co-precipitation and hydrothermal synthesis with sucrose as a template. X-ray diffraction indicated the formation of ZnO/Zn-HAps without a significant change in the crystallinity of HAp. X-ray photoelectron spectroscopy indicated the substitution of Ca2+ by Zn2+ in the HAp structure and the formation of ZnO/Zn-HAp-type compounds, corroborating the refinement data. The morphology of the prepared particles was investigated through field emission gun-scanning electron microscopy and transmission electron microscopy, which revealed that nanoflowers of ZnO were deposited on the HAp surface. ZnO/Zn-doped HAps was impregnated with alizarin (AZ) at pH 4 and 8.5, resulting in hybrid pigments with varying hues of red. Attenuated total reflectance-Fourier transform infrared spectroscopy, UV–vis spectroscopy, and X-ray photoelectron spectroscopy suggested that better solids@dye interactions occurred at pH 8.5, and as indicated by C1s spectra, the appearance of the peak at 286.5 eV (C = O) and an increase in the peak intensity at 284.6 eV (C–C/H) confirmed the adsorption of the dye on the surface. Photodegradation tests revealed that the prepared pigments were highly stable after exposure to light.

A Simple Method to Obtain Protective Film against Acid Rain

Acid rain is a major problem for animals, plants, buildings, and also for the top glass of photovoltaic (PV) solar panels and greenhouses. Air pollutants such as NOx, NH3, and H2S can mix with water in the atmosphere to form acid rain. It was discovered that atmospheric water vapor adsorbed on the surface of glass can also lead to corrosion of the glass surface. The purpose of this work is to obtain a protective film for glasses used in different domains such as solar cells, windows, stained glass windows from historical buildings, etc. Thin film deposited on glass must be protective against acid rain, transparent in the visible domain with a band gap up to 3.2 eV, and have a vitreous structure (glass). Electron beam (e-gun) technology is a deposition technique for producing high-purity and dense coatings in a short time. It is well known that Ta2O5 is an oxide with anticorrosive properties, but it is expensive and cannot form glass by itself. ZnO is an oxide known as a glass former, exhibiting good optical properties. In this paper, a thin film obtained by the deposition of ZnO and Ta2O5 on a glass substrate using e-gun technology are studied. The simulated acid rain effect on the structure, morphology, and optical properties of thin films are studied after a 65% nitric acid attack on the surface. The X-ray diffraction (XRD) pattern shows the vitreous state of the thin film with a composition 50%ZnO 50%Ta2O5 before and after the acid attack. The morphology, composition, and thickness of the film are investigated using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) and profilometry.

Fabrication and Characterization of ZnO Nanosheet on a Silver-metalized Polyimide Substrate

ZnO nanosheets were fabricated on a silver-metalized polyimide (PI/Ag) substrate using electrochemical deposition. For a comparison, PI/Ag film was also obtained by electroless deposition. FE-SEM, XRD, UV–Vis absorption, and I-V measurements were employed to examine the structural, optical and electrical properties of silver-metalized PI film and ZnO deposited PI/Ag film. FE-SEM analysis indicated that a continuous silver film layer, consisted of spherical Ag nanoparticles, and the ZnO nanosheets were synthesized on PI substrate by electroless and electrochemical deposition, respectively. Moreover, the growth mechanism of the Ag film and ZnO nanosheets was also discussed. The characterization of X-ray diffraction verified that the ZnO nanosheets had a hexagonal phase and grew along the [002] direction. The optical absorbance spectra of bare PI, PI/Ag, and PI/Ag/ZnO showed a broad absorption peak around 300 nm. The electrical properties of the PI/Ag and PI/Ag/ZnO samples were studied by current-voltage (I-V) measurements in the dark environment at room temperature (300 K). The I-V measurements suggested that the samples presented ohmic characteristics. The results revealed that the deposition of ZnO on PI/Ag substrate improved the electrical conductivity compare with bare PI/Ag.

Broadband wavelength-selective isotype heterojunction n+-ZnO/n-Si photodetector with variable polarity

Αn isotype heterojunction n+-ZnO/n-Si photodetector is developed, demonstrating wavelength-selective or broadband operation, depending on the applied bias voltage. Additionally, at self-powered (zero bias) operation, it distinguishes between UV, visible, and near IR (NIR) photons by polarity control of the photocurrent. The photodetector is developed by atomic layer deposition (ALD) of ZnO on n-Si, followed by electric contact deposition and annealing. Photoluminescence measurements reveal high optical quality and improved crystallinity of annealed ZnO on silicon. Photocurrent measurements as a function of illumination wavelength and bias voltage show small negative values in the UV–visible spectral range at zero and positive bias voltage and high positive values in the NIR spectral range. For these measurements, we consider the electric contact to ZnO as the anode and the electric contact to silicon as the cathode. At negative bias voltage, the device shows broadband operation with high photocurrent values across the UV–vis-NIR.

TiO2–ZnO/Au ternary heterojunction nanocomposite: Excellent antibacterial property and visible-light photocatalytic hydrogen production efficiency

TiO 2 –ZnO/Au ternary heterojunction nanocomposite was fabricated by producing TiO 2 nanosheets first using solvent-thermal method followed by Au deposition and ZnO deposition respectively. The TiO 2 nanosheets provide a relatively large surface area for the good dispersion of ZnO nanoparticles and Au particles and sufficient contact with the medium, which contribute to the excellent photocatalytic performances of TiO 2 –ZnO/Au heterojunction composite. The phases and structures, morphologies, surface and optical properties of the ternary heterojunction composite are well-characterized. Subsequently, the photocatalytic hydrogen generation of TiO 2 –ZnO/Au is evaluated under visible light irradiation. TiO 2 –ZnO/Au ternary heterojunction composite has efficient light absorption ability and excellent performances in photocatalytic hydrogen generation (1068 μmol/g under the irradiation of visible light for 4 h) and antibacterial properties (reaching 98.2%). TiO 2 –ZnO/Au ternary heterojunction nanocomposite has a large potential to be used in areas such as interior wall coating.

A comparative study of the structure and corrosion resistance of ZnAl hydrotalcite conversion layers at different Al3+/Zn2+ ratios on electrogalvanized steel

The dissimilarities of the composition, crystal structure, and corrosion resistance of ZnAl hydrotalcite (ZnAl-HT) conversion films grown “in situ” on electrogalvanized (EG) steel substrate were investigated for different Al3+/Zn2+ ratios at pH 12. The corrosion behavior of all conversion films in 0.1 M NaCl was compared through electrochemical techniques. The composition, morphology, structure, and thickness of conversion films with different Al3+/Zn2+ ratios were characterized by Fourier-transform infrared spectroscopy (FT-IR), scanning electronic microscopy (SEM), and electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), and X-ray diffraction (XRD). The polarization curves indicated that the ZnAl-HT films provided anodic inhibition for EG steel and the inhibition efficiency of the ZnAl-HT conversion films increases sharply with decreasing the Al3+/Zn2+ ratios from 5/1 to 5/3, while, for the 5/4 and 5/5 ratios, the corrosion resistance of ZnAl-HT conversion films showed a downward trend after two immersion hours. However, the corrosion behavior of HT conversion films with the Al3+/Zn2+ ratios from 5/3 to 5/5 remained stable for a longer immersion time. The protection performance of the ZnAl-HT films can be attributed to the barrier effects, ion-exchange competitive adsorption of chloride ions, and protective deposition of ZnO on the EG steel surface.

Machine learning approach to thickness prediction fromin situspectroscopic ellipsometry data for atomic layer deposition processes

A machine learning approach is applied to estimate film thickness from in situ spectroscopic ellipsometry data. Using the atomic layer deposition of ZnO as a model process, the ellipsometry spectra obtained contains polarization data (Ψ, Δ) as a function of wavelength. Within this dataset, 95% is used for training the machine learning algorithm, and 5% is used for thickness prediction. Five algorithms—logistic regression, support vector machine, decision tree, random forest, and k-nearest neighbors—are tested. Out of these, the k-nearest neighbor performs the best with an average thickness prediction accuracy of 88.7% to within ±1.5 nm. The prediction accuracy is found to be a function of ZnO thickness and degrades as the thickness increases. The average prediction accuracy to within ±1.5 nm remains remarkably robust even after 90% of the (Ψ, Δ) are randomly eliminated. Finally, by considering (Ψ, Δ) in a limited spectral range (271–741 nm), prediction accuracies approaching that obtained from the analysis of full spectra (271–1688 nm) can be realized. These results highlight the ability of machine learning algorithms, specifically the k-nearest neighbor, to successfully train and predict thickness from spectroscopic ellipsometry data.

Architecture lattice‐matched cauliflower‐like CuO/ZnO p–n heterojunction toward efficient water splitting

AbstractBACKGROUNDIn photoelectrochemical (PEC) water splitting, hydrogen and oxygen can be dissociated from water molecules on semiconductors by directly utilizing clean renewable solar energy. The key bottleneck of PEC water splitting is to design new types of photoelectrodes with long‐term stability and high PEC performance.RESULTSHere, cauliflower‐shaped p–n CuO/ZnO heterojunction photocathodes with lattice matching were synthesized using one‐step electrodeposition and heat treatment. The results showed that the deposition of CuO and ZnO took place simultaneously. The proportion of CuO and ZnO varied with the electrodeposition time and calcination temperature and duration. The parallel lattice‐matched CuO/ZnO heterojunction enhanced the separation and migration of photogenerated charge carriers, which accomplished a photocurrent density value of approximately −1.8 mA cm−2 at a bias of 0 VRHE in 0.5 mol L−1 Na2SO4 solution.CONCLUSIONSThis work could provide a simplified strategy for the synthesis of p–n copper‐based heterogeneous photocathodes for application in PEC water splitting. © 2021 Society of Chemical Industry (SCI).

One-Step Hydrothermal Deposition of ZnO–TiO2 Heterojunction Nanostructures as Photoelectrochemical Performance for Sb2S3 Quantum-Dot-Sensitized Solar Cells by High-Efficiency Enhancement

One-Step Hydrothermal Deposition of ZnO–TiO2 Heterojunction Nanostructures as Photoelectrochemical Performance for Sb2S3 Quantum-Dot-Sensitized Solar Cells by High-Efficiency Enhancement

Acoustofluidic multimodal diagnostic system for Alzheimer's disease

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative brain disorder that affects tens of millions of older adults worldwide and has significant economic and societal impacts. Despite its prevalence and severity, early diagnosis of AD remains a considerable challenge. Here we report an integrated acoustofluidics-based diagnostic system (ADx), which combines triple functions of acoustics, microfluidics, and orthogonal biosensors for clinically accurate, sensitive, and rapid detection of AD biomarkers from human plasma. We design and fabricate a surface acoustic wave-based acoustofluidic separation device to isolate and purify AD biomarkers to increase the signal-to-noise ratio. Multimodal biosensors within the integrated ADx are fabricated by in-situ patterning of the ZnO nanorod array and deposition of Ag nanoparticles onto the ZnO nanorods for surface-enhanced Raman scattering (SERS) and electrochemical immunosensors. We obtain the label-free detections of SERS and electrochemical immunoassay of clinical plasma samples from AD patients and healthy controls with high sensitivity and specificity. We believe that this efficient integration provides promising solutions for the early diagnosis of AD.

Enhanced microwave absorption of flaky FeSiAl/ZnO composites fabricated via precipitation

In this study, we investigated the effects of ZnO loading on flaky FeSiAl alloys and assessed their material structure, morphology, magnetism, and microwave absorption characteristics. The structure and morphology indicated a ZnO precipitation limit on the flaky FeSiAl alloy surfaces, and the surface precipitation and mixture were tunable via precipitation technology. The results also indicated that the surface deposition weight ratio of ZnO to FeSiAl should not exceed 2:5, as excessive ZnO deposition resulted in the formation of large ZnO nanoparticles. In addition, nonmagnetic ZnO caused a steady decrease in saturation magnetization from 89.3 to 48.2 emu/g. Following the ideal impedance matching and high dielectric loss, we obtained a minimum reflection loss of −47.85 dB and bandwidth of 3.24 GHz. Compared to conventional oxides coated with flaky FeSiAl, the low density and semiconductor ZnO composites exhibited greatly improved microwave absorption performance for future lightweight and microwave absorption applications.

Substrate temperature-dependent diffusion from CdS/ZnO:Al layer into the absorber layer in Cu(In, Ga)Se2 solar cell during the deposition of ZnO:Al window layer

Substrate temperature-dependent diffusion from CdS/ZnO:Al layer into the absorber layer in Cu(In, Ga)Se2 solar cell during the deposition of ZnO:Al window layer