Nanostructured ZnO Thin Films Research Articles

Effect of Picosecond Laser Irradiation on the Properties of Nanostructured Zinc Oxide Thin Films

In this article, a picosecond laser source was employed to irradiate the nanostructured ZnO thin film prepared by the sol-gel method. The impact of laser irradiation on the characteristics of a nanostructured ZnO thin film was investigated. Analysis using X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy confirmed a significant influence on the structure of the ZnO thin film. As the duration of laser irradiation (the number of laser pulses) increased, there was a remarkable decrease in both the electronic and photoluminescence intensities of the nanostructured film. Tauc's plot indicates a noticeable change in the optical band gaps of the thin film with the increase in irradiation time. The morphological image suggests that the laser irradiation energy induces both degradation and modification of the film surface, consequently causing changes in the structural, absorption, and photoluminescence properties of nanostructured ZnO. The observed effects are attributed to alterations in the crystal structure and size of the nanostructured ZnO film, as confirmed by XRD. The reduction in photoluminescence intensity observed over the laser irradiation times may be a result of potential degradation in the crystalline structure of the nanostructured ZnO film.

Enhancement capacitance of FTO electrodes via the electrospun ZnO thin film coating for supercapacitor applications; the role of dopants

The present study aimed to investigate the electrochemical performance of nanostructured ZnO thin films (TFs) on the fluorine-doped tin oxide (FTO) substrate. The pure ZnO TFs, Al-doped ZnO TFs, and Cu-doped ZnO TFs were fabricated using electrospinning and post calcination at 400 °C. The electron microscopy studies revealed that electrospun nanofiber masks changed to dense TFs with an average thickness of 250–290 nm constructed by 10–20 nm connected nanoparticles (NPs). The doping of Al and Cu into ZnO TFs increased the hydrophilicity. Cyclic voltammetry (CV), electrochemical impedance (EIS), charge-discharge profiles, and Mott-Schottky (M − S) analysis were performed on the samples to evaluate the capacitance performance of pure and doped ZnO TFs. The semiconductor of TFs was n-type. The results confirm that all films can be used as a supercapacitor. Also, our results suggest that Cu-doped ZnO (CZO) TFs are the best choice for a supercapacitor electrode due to their 1.14 F cm−2 areal capacitance at 1 mA cm−2 applied current.

Improved humidity sensing performances of boron doped ZnO nanostructured thin films depending on boron concentration

Abstract This study details the production and analysis of undoped zinc oxide (uZnO) and boron (B) doped zinc oxide nanostructured thin films, with a specific focus on assessing the influence of varying B doping concentrations on humidity sensing performance. The synthesis of undoped ZnO and B doped ZnO nanoparticles was carried out using sol–gel method. B doping concentrations within the ZnO lattice were adjusted to 1, 3, 4, 5, and 10 mol%. Subsequently, nanostructured thin films were obtained through the spin coating technique on glass substrates. X-ray diffraction analysis revealed a hexagonal wurtzite structure for all nanostructured thin films. Notably, a change in preferential orientation from the (002) plane to the (100) plane occurred when B doping concentration exceeded 5 mol%. Scanning electron microscopy showcased nano-sized grains and capillary nanopores on the surface of each thin film. Energy dispersive X-ray spectra confirmed the presence of zinc, oxygen, and boron elements in the nanostructured thin films. Humidity sensing performance was assessed through electrical resistance measurements in the range of 45%–90% relative humidity at room temperature. All fabricated sensors exhibited sensitivity to humidity. Remarkably, the sensor with a 5 mol% B doping concentration demonstrated the highest humidity sensitivity (438.44 times) and the fastest response (2.0 s) and recovery times (14.2 s). The study concluded that the optimal B doping concentration for designing a highly efficient humidity sensor was determined to be 5 mol%. Overall, the study underscores the potential of B doped ZnO nanostructures for humidity sensor applications, given their exceptional sensor performance.

Impact of annealing temperature on the structural, morphological and optical properties of Ni doped ZnO nanostructured thin films synthesized by sol–gel methodology

Abstract Nickel doped zinc oxide (NZO) nanostructured thin films were prepared by hydrolysis and poly condensation reaction based on the sol–gel methodology. Nanostructured thin films were prepared over the glass substrate by dip coating. Prepared samples were annealed at 350 °C and 450 °C respectively to tune the desired characteristics. The XRD studies endorses the prepared films were polycrystalline in nature and high intensity sharp peaks were exhibited in (101) direction. EDAX results confirms the presence of Ni, Zn and O elements. FESEM results exhibits the spherical like morphology throughout the sample. The typical grain size of prepared samples are vary from 35 nm to 105 nm. Results of the FTIR divulges the different composition of prepared NZO samples. UV–vis spectrophotometer results reveals that the fabricated 1 at.% NZO thin films annealed at 450 °C were guaranteed to have the lowest absorbance of less than 10 %, while the 0.5 at.% NZO thin films have an energy band gap of roughly 3.08 eV. The obtained results of the prepared films are useful for devices like solar cells, optoelectronic devices, flat panel displays, anticorrosion and surface protection applicant against stainless steel etc.

Synergistically enhanced NH3 gas sensing of graphene oxide-decorated Nano-ZnO thin films

This study focuses on enhancing nanostructured ZnO thin films ammonia (NH3) sensing capabilities at room temperature by integrating graphene-oxide (GO) via the drop-casting technique, thereby exploring the possibilities of tailoring NH3 sensing measurements. Structural investigations indicated the hexagonal-wurtzite structure of the sputtered ZnO and GO-decorated thin films. The Raman spectroscopy results validate the electrochemically exfoliated GO, and the X-ray photoelectron spectroscopy characterization revealed the Zn2+ state and oxygen vacancies. The NH3 gas sensing measurements for GO/ZnO revealed a remarkable increase in sensitivity, with a limit of detection (LOD) of 0.1 ppm. This exhibited a response 50 times superior to bare ZnO for 5 ppm of NH3 at room temperature (RT). As a result of decorating GO increased active sites and surface area. This significant enhancement in sensor response underscores the synergistic effect of GO-decoration, and ZnO leading to substantially improved gas-detecting capabilities.

Design of a new ZnO photocatalytic Fenton-like system for enhancing the removal of methylene blue at neutral pH

Although doping, nanostructuration, metallization, and binary/ternary oxide systems are widely used to improve the degradation kinetics in photocatalytic processes, rapid electron _ hole recombination remains one of its major limitations. On the other hand, homogeneous photo-Fenton-like processes suffer from the slow regeneration of Fe3+/Fe2+ catalysts and the formation of iron sludge at pH > 3. In this work, a new catalytic system is designed based on the coupling of nanostructured ZnO thin films photocatalysts with Fe3+/H2O2 (Fenton-Like) for the degradation of methylene blue (MB) molecules under UVA irradiation, at near-neutral pH (7.5). This coupled process promotes the formation of additional reactive oxygen species and reduces the formation of sludge by accelerating the regeneration of the iron catalysts in the medium. Furthermore, it exhibits a single kinetic regime of degradation with a rate constant of 0.0049 min−1 exceeding the sum of both individual processes and allowing therefore the removal of 94 % of MB after 480 min.

Sol–Gel Synthesis of ZnO:Li Thin Films: Impact of Annealing on Structural and Optical Properties

A sol–gel deposition approach was applied for obtaining nanostructured Li-doped ZnO thin films. ZnO:Li films were successfully spin-coated on quartz and silicon substrates. The evolution of their structural, vibrational, and optical properties with annealing temperature (300–600 °C) was studied by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), UV-VIS spectroscopic, and field emission scanning electron microscopic (FESEM) characterization techniques. It was found that lithium doping maintains the wurtzite arrangement of ZnO, with increasing crystallite sizes when increasing the annealing temperature. Analysis of the FTIR spectra revealed a broad main absorption band (around 404 cm−1) for Li-doped films, implying the inclusion of Li into the ZnO lattice. The ZnO:Li films were transparent, with slightly decreased transmittance after the use of higher annealing temperatures. The porous network of undoped ZnO films was transformed to a denser, grained, packed structure, induced by lithium doping.

Tailoring of physical properties and photo-catalytic activity of nanostructured ZnO thin films: The role of cobalt doping

ZnO nanostructured thin layers doped with cobalt (0 %, 2 %, 4 %, and 6 %) were successfully deposited on glass substrates via nebulized spray pyrolysis. The XRD and FE-SEM analyses indicated that all samples exhibited a hexagonal wurtzite structure and a densely flaked microstructure in petal-like shapes. The EDX investigations confirmed Zn and O elements in all films and Co in doped samples. The Photoluminescence (PL) spectra showed Co-doping's impact on emission. In addition, ZnO thin film transparency decreased by an average of 26 % in the visible range after doping. With increased Co-doping, the band gap (Eg) slightly decreased while ferromagnetic behavior increased. Furthermore, with an increase in the Co doping level, the material's electrical resistivity increased significantly from 2.5 × 10³ to 5.3 × 105 Ω cm. We found that doping with Co enhances the photo-catalytic efficiency of ZnO under sunlight. The sample doped at 2 % Co shows the highest photo-degradation efficiency of methylene blue (MB), about 93 %.

Synthesis and ultrafast humidity sensing performance of Sr doped ZnO nanostructured thin films: the effect of Sr concentration

Synthesis and ultrafast humidity sensing performance of Sr doped ZnO nanostructured thin films: the effect of Sr concentration

Comparative study of structural, optical and electrical properties variation of pure, (Ag, Mg) doped and co-doped ZnO nanostructured thin films

Abstract Nanostructured thin films are one of the most valuable types of industrial semiconductors for a variety of optoelectronics and optical device applications, having recently been used as a transparent conductive oxide in solar cells. In this work, nanostructured thin films of pure ZnO, Ag doped ZnO, Mg doped ZnO and Ag–Mg co-doped ZnO were successfully synthesized on silicon and glass substrates, using rapid thermal evaporation. The impact of the doping elements on the surface morphology, structural, electrical, and optical properties of the deposited films were investigated. It was found that all films have polycrystalline hexagonal wurtzite structure using X-ray diffraction. Images obtained by scanning electron microscopy (SEM) revealed compact and smooth surfaces, with uniform coverage of all substrate regions. SEM images confirm the nanostructured nature of the surfaces with particle size varying as a function of doping. Raman spectroscopy showed A1(LO), E2(high) and LVM modes for all samples. The developed films’ optical transmission ranged from 74 % to 87 %, with an optical bandgap ranging from 3.09 for Mg:ZnO films to 3.8 eV for Ag:ZnO samples. Depending on the doping nature modification, these alterations were associated to structural and morphological changes in the films. All films were electrically conductive, while Ag:ZnO films exhibited the lowest resistivity value reaching 0.56 Ω cm.

Fabrication of n-CeZnO/p-Si heterojunction diodes for enhanced solar energy conversion

Doping in semiconductor nanostructures greatly influences in their fundamental properties and greatly enhances the finale efficiencies in various applications. Here, we report the formation of n-type Ce3+ doped ZnO nanostructured thin films on p-Si wafers via a facile phytochemical assisted hydrothermal technique. The heterostructure diodes were examined for their structural, morphological, optical, electrical and photocatalytic properties. Ce3+ ions doping in the ZnO lattices were confirmed with the change in peak position shift and the decreased crystalline size from 34 nm (pristine ZnO) to 18 nm (5% Ce3+ doped ZnO). The Ce3+ induced flake like morphology was also identified in our experiment. Further the optical bandgap values have got decreased from 3.3 eV to 2.9 eV for cerium ions doping. Measured diode parameters were sensitive to the cerium ions doping concentration besides with good rectification behaviour. Upon the light illumination enhanced current of 75% over the dark current is realized. In sunlight methylene blue dye degradation photocatalysis the n-ZnO/p-Si exhibited 45% efficiency whereas the n-CeZnO/p-Si exhibited 77%.

Tailored Zn content in reactive gas-timing sputtered ZnO nanostructure thin film deposited on Ti implant for enhanced antimicrobial activity

The modification of a titanium surface using tailored Zn content in ZnO nanostructure thin films was fabricated using DC magnetron sputtering which was incorporated with a reactive gas-timing (RGT) technique where the on-off sequence of the gas was controlled. The RGT with optimal O2 timing provided a grainy nanoporous structure of ZnO thin films, whereas the conventional films demonstrated a nanocolumnar structure along with a uniform surface. In addition, atomic concentration analysis confirmed that the Zn content in thin films depended on the oxygen flow during the deposition. These specific properties of RGT-ZnO thin films could improve the antifungal activity of titanium. We found that the antifungal activity against C. albicans of the RGT-ZnO thin film was more than 99.99% compared to uncoated Ti (p-value < 0.01). It was also greatly higher than those prepared by a conventional technique which had approximately 70%. Therefore, these findings demonstrated that ZnO thin films with tunable morphology and Zn composition could significantly enhance the antifungal property. This could be an alternative strategy to enhance the biological performance of titanium-based materials and reduce infections in dental implants as well.

A study on morphology dependent nanostructured ZnO thin films: An efficient gas sensing response for acetaldehyde

In this work, kinematically grown highly oriented hexagonal ZnO nanorods and nanograined films were fabricated on silicon substrates via pulsed laser deposition method. The structural, morphological, optical properties and the gas sensing studies of ZnO nanostructured thin film were systematically studied. Structural study shows high crystalline films with preferred c-axis orientated nanorods, which are grown over (002) plane nanograined films. Morphological study shows spherical-shaped nanograins and hexagonal vertical rod like structures due to kinematic growth parameters. The optical band gaps of ZnO-NR film at Eg ∼ 3.18 eV and 3.46 eV, depicts greater grain boundary resistance to nanorod resistance. The artificial olfaction effect of ZnO nanorods in detecting acetaldehyde (CH3CHO) is found to be 40% more sensitive than ZnO nanograined films. The ZnO nanorods displays a greater sensitivity response for CH3CHO than other target gases. Transient gas Responsive Resistance (TRR) of ZnO nanorods and nanograined films shows increased sensitivity with higher concentration CH3CHO (10 to 100 ppm) at ambient temperature. The study indicates that ZnO nanorods could be a potential material for the detection of CH3CHO gas at room temperature.

Photocatalytic degradation of methylene blue at nanostructured ZnO thin films

The photocatalytic degradation of the wastewater dye pollutant methylene blue (MB) at ZnO nanostructured porous thin films, deposited by direct current reactive magnetron sputtering on Si substrates, was studied. It was observed that over 4 photocatalytic cycles (0.3 mg · l−1 MB solution, 540 minUV irradiation), the rate constant k of MB degradation decreased by ∼50%, varying in the range (1.54 ÷ 0.78) · 10–9 (mol·l−1·min−1). For a deeper analysis of the photodegradation mechanism, detailed information on the nanostructured ZnO surface morphology and local surface and subsurface chemistry (nonstoichiometry) were obtained by using scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS) as complementary analytical methods. The SEM studies revealed that at the surface of the nanostructured ZnO thin films a coral reef structure containing polycrystalline coral dendrites is present, and that, after the photocatalytic experiments, the sizes of individual crystallites increased, varying in the range 43 ÷ 76 nm for the longer axis, and in the range 28 ÷ 58 nm for the shorter axis. In turn, the XPS studies showed a slight non-stoichiometry, mainly defined by the relative [O]/[Zn] concentration of ca. 1.4, whereas [C]/[Zn] was ca. 1.2, both before and after the photocatalytic experiments. This phenomenon was directly related to the presence of superficial ZnO lattice oxygen atoms that can participate in the oxidation of the adsorbed MB molecules, as well as to the presence of surface hydroxyl groups acting as hole-acceptors to produce OH· radicals, which can be responsible for the generation of superoxide ions. In addition, after experiments, the XPS measurements revealed the presence of carboxyl and carbonyl functional groups, ascribable to the oxidation by-products formed during the photodegradation of MB.

Tailoring Sb doping concentration to achieve p-type nanostructured ZnO thin film grown by sol–gel method

Tailoring Sb doping concentration to achieve p-type nanostructured ZnO thin film grown by sol–gel method

Spray deposition of the nanostructured ZnO thin films for non-volatile resistive switching memory applications

Spray deposition of the nanostructured ZnO thin films for non-volatile resistive switching memory applications

Substrate dependent structural variations of biomimetic carbonated hydroxyapatite deposited on glass, Ti and sputtered ZnO thin films

The formation of hydroxyapatite films on glass, titanium (Ti), and sputtered ZnO is attempted to understand the crystal growth and its manipulation by substrates of a different kind. The substrates used are commercially available glass and polished Ti (99.9% purity), as-deposited, and annealed nanostructured ZnO thin films developed by pulsed DC magnetron sputtering, which are immersed in the calcifying solution for the nucleation and growth of the hydroxyapatite. The calcifying solution is obtained by mixing equal volumes of aqueous calcium (5 mM) and carbonate-containing phosphate (3 mM) solutions prepared at 37 °C and with a pH of ~7.4. X-ray diffraction, Raman spectroscopy, and Field Emission Scanning & Transmission Electron Microscopy (FESEM & FETEM) analyses reveal that the structure and morphology of the hydroxyapatite films are dependent on the growth duration, substrate type, and even on the post-deposition annealing of the sputtered ZnO substrates. The Ti substrate induces greater crystallinity in hydroxyapatite, whereas sputtered ZnO thin films cause a significantly reduced crystallinity. Moreover, the thicknesses of HAp are exacerbated by increasing deposition time irrespective of the substrate. FETEM analyses reveal the formation of needle-shaped hydroxyapatite nanocrystals grown on Ti and ZnO thin films. Thicker needle-shaped hydroxyapatite nanocrystals are observed when grown on Ti (~6–12 nm) than ZnO thin films (~4–6 nm). Further, the amorphous calcium phosphate phase coexists with nanocrystalline hydroxyapatite when ZnO thin films deposited at 50 and 70 W sputtering powers are used as the substrates. Both charged surfaces and the supersaturation of the calcifying solution impact the nucleation of hydroxyapatite onto substrates.

SYNTHESIS OF Mg-DOPED n(ZnO) THIN FILMS USING SOL-GEL 6 DIP-COATING METHOD AND CHARACTERIZATION OF ITS STRUCTURAL AND OPTICAL PROPERTIES

Mg-doped ZnO alloy thin films having hexagonal Wurtzite structures were prepared using the Sol-Gel method. The doping results into, increased surface roughness and reduced grain size. Photonic applications are made easier by altering the optical bandgap of ZnO nano-structured thin films doped with various components. Mg metal atom doped ZnO films are an excellent example for study. In this work, the thin film of Mg-doped ZnO is formed on glass substrate via dip coating method with varied concentration of dopant. Dip-coating method is one of the cheapest methods. SEM, Raman spectroscopy and UV-vis spectroscopy are used to characterize the thin films. The spectroscopic analysis revealed a more uniformed crystalline nano-structured surface with fewer structural deffects. As the Mg atom concentration is increased, the results show a linear increment in the band gap of Mg-doped ZnO thin film in comparsion to the pure ZnO nanostructured thin film, as well as there occurs an improvement in crystalline character. The reduction in intensity of visible radiation (enhancement in radiation in UV region) with increase in Mg concentration indicates for a decrease in intrinsic defects. The changing trends in optical and structural parameters as with increased Mg content reveal a nonlinear and non-monotonic relations. The work provides insights to analyse the dependence of optical bandgap on crystal structure and defects.

Optical properties of hydrothermally deposited Ni and Co doped nanostructured ZnO thin films as scintillating coatings for beta-particles detection

The optical properties of ZnO films doped with the Ni and Co transition metals that were hydrothermally deposited on a silicon substrate are discussed. The SEM, EDX, XRD and Raman spectroscopy studies showed that the films deposited have a compact crystalline structure and can be considered as nanostructured polycrystalline ZnO films doped with Ni and Co and designated as ZnO:Ni and ZnO:Co, respectively. Under optical and electronic excitation, the films demonstrated both near-band-edge ultraviolet and visible range luminescence due to crystal lattice defects. The highest intensity of the ultraviolet luminescence with a fast decay was achieved for the ZnO:Ni and ZnO:Co samples deposited in the 0.05 M solutions of Ni or Co nitrate salts. Wide luminescence spectra make the films obtained promising as luminophore or scintillating coatings for the beta-particles detection including structures integrated with silicon circuits, for example, solid state silicon-based radiation counters.

Tailoring the optical properties and the UV detection performance of sol-gel deposited ZnO nanostructured thin films via Cd and Na co-doping

Cd and Na co-doped ZnO nanostructured thin films with different doping concentrations were prepared using a sol-gel spin coating technique on glass substrates. The effect of doping with Cd and 1, 2 and 3 wt % Na on the structural, morphological, optical and UV detection properties of the nanostructured ZnO thin films was investigated. The grown co-doped nanostructured thin films exhibit wurtzite structure with preferential growth along the (002) plane. The change in the doping concentration was found to have a considerable effect on the grain size of the prepared films as well as their morphology. A variation in the band gap of the co-doped nanostructured thin films was also observed with changing the doping concentration. The band gap was found to vary in the range from 3.27 to 3.24 eV with increasing Na concentrations. The UV detection performance of the co-doped ZnO nanostructured thin films based UV detector was also investigated and found to strongly depend on the dopants concentrations with an obvious correlation with the variation in the films band gap. The findings of the current study show that a good control of the optical properties and the UV detection performance of the ZnO nanostructured thin films can be achieved through co-doing with Cd and Na with increased potential for their uses in high performance opto-electronic devices.