Sol–gel spin coated Ag and Rb co-doped ZnO thin films: structural, morphological, and optical insights for enhanced photocatalysis

Room temperature photoluminescence and spectroscopic ellipsometry of reactive co-sputtered Cu-doped ZnO thin films

ZnO thin films are deposited on glass substrate using sol–gel spin coating methods with various annealing temperatures. The structural, morphological, and optical properties are studied by XRD, FE-SEM, UV–Vis, and photoluminescence spectrophotometer. The photocatalytic activity was assessed by examining the decomposition of Rhodamine-B (Rh-B) dye under UV illumination. The result shows that the ZnO films have a hexagonal wurtzite structure with highly preferred c-axis orientation. The (101) crystallographic plane appears at higher annealing temperatures. The transmittance of ZnO films is more than 80%, with a slight red shift in absorption and decrease in the optical band gaps as the annealing temperature increases to some extent. The photoluminescence spectra of the ZnO films at room temperature demonstrated the ultra-violet (UV) emission with a peak emission at 410 nm (3.03 eV). According to the photocatalytic activity examination, the presence of (101) plane in the c-axis oriented ZnO films enhances the photocatalytic performance by a factor of 5. The result revealed that ZnO films with multi-orientation structure possess better photocatalytic performance than that of the single-orientation ones. In particular, the photocatalytic performance is highly contributed by the polar crystal plane and slightly improved by the crystallinity and surface morphology.

In this work, Ce-doped ZnO thin films at various contents of cerium were deposited on glass substrates by thermal vacuum evaporation to study the influence of Ce concentration on their optical, structural, morphological, and photocatalytic behavior. Pure ZnO and Ce-doped ZnO films doped with 2% and 5% Ce were characterized by SEM, XRD, AFM, UV–VIS spectroscopy, and ellipsometry. The XRD analysis confirmed that all the films retained the hexagonal wurtzite structure, while Ce incorporation induced lattice strain and reduced crystallite size, particularly at higher doping levels. SEM and AFM studies showed that films with 2% Ce exhibited smaller grain size and lower roughness, whereas 5% Ce-doped films showed grain growth and increased roughness. Pure ZnO films displayed high transparency (>90%), whereas Ce incorporation caused a red shift in the absorption edge and narrowing of the optical band gap due to defect-related states and lattice distortion. Photocatalytic experiments revealed that Ce doping improved charge carrier separation and increased the number of oxygen vacancies. Among all samples, the 2% Ce-doped ZnO film demonstrated the highest photocatalytic efficiency. These findings highlight the importance of controlled Ce doping in tuning the microstructure, optical properties, and photocatalytic performance of ZnO thin films, making them suitable for environmental remediation and optoelectronic applications.

NiO-ZnO nanocomposite thin film was prepared via spray pyrolysis method at a temperature of 350 °C and concentration of 0.1M on glass substrate. Structural and optical propertis of the nanocomposite thin film have compared with the properties of both NiO and ZnO Thin films. XRD results reveals that the nanocomposite thin films are polycrystalline with ZnO hexagonal wurtzite and NiO cubic structures and no secondary phases observed. The grain size for the nanocomposite thin film as determined by SEM show a smaller grain in comparison with the grains of the pure ZnO thin films, which suggest that the nickel oxide act as grain growth inhibitor. It was also found that the highest value of the energy gap was (3.6 eV) for the NiO-ZnO films and decreased for pure ZnO and NiO thin films.

Pure ZnO has excellent conductivity as it contains high concentration of native defect (oxygen vacancy or zinc interstitials). At high temperature, pure ZnO thin films are not stable chemically and electrically. The performance of ZnO thin films can be greatly modified and improved by appropriate impurity doping. Modification of ZnO with transient metals (Al, In, Ga, Ti) provides a successful and cost effective alternative. In order to create free electrons and enhance n-type conductivity, two criteria should be satisfied: (i) the doping ion should be smaller than, or equal to, the diameter of the host ion; (ii) the ion of the dopant should have higher valency than that of the host atom. The ionic radius of Ti4+ (0.068 nm) should be smaller than that of Zn2+ (0.074 nm), and hence Ti4+ ions can replace Zn2+ ions at substitutional sites. In the present study, ZnO films doped with small Ti concentration were deposited on glass substrate by spray pyrolysis.Both un-doped and Ti-doped ZnO films were deposited on microscopic glass substrates using spray pyrolysis technique systematically by controlling the deposition parameters. For deposition, 0.1 M of zinc acetylacetonate Zn(AcAc) was dissolved in ethanol and sprayed onto microscopic glass substrates with dimensions of 75 x 25 mm2 at fixed substrate temperature; Ts = 400°C. In order to dope ZnO with Ti, titanyl acetylacetonate Ti(AcAc) solution was added to the starting solution. The solution was sprayed using different doping concentrations ranging from 0.1% to 0.9%.The strongest lines in the entire pattern are the principle lines (100), (002) and (101) of the hexagonal wurzite ZnO, in agreement with JCPDS standard card No. 75-0576. On doping with Ti up to 0.7%, no additional peaks are observed. This is attributed to the fact that the concentration of the dopant Ti is low. When the doping concentration is further increased above 0.7%, it is observed that the crystallinity becomes lower. The crystallite size determined using Scherrer’s relation decreased from 39 nm to 12 nm after doping with Ti. Parameters like dislocation density and strain were also estimated.Composition of the films was studied by EDAX. Peaks corresponding to Ti, Zn and O elements were presented along with Si peaks coming from the glass substrate.The value of the band gap of the films is obtained from Tauc’s plot indicate that the band gap gradually increases with increasing Ti concentration. Similar result is reported in the literature. The band gap value decreases from 3.20 eV to 3.32 eV.Room temperature electrical resistivity of the films doped with different concentrations of Ti was studied. As deposited undoped films exhibited resistivity around 105 ohm cm. After annealing in vacuum, the resistivity decreased by three orders to 100 ohm cm. As the doping concentration increased, the resistivtiy decreases further to 8 ohm cm for 0.9 % Ti doping. Ti4+ ions substituted Zn2+ ions within the crystal lattice induce positive TiZn charges in the material. In order to maintain electrical neutrality, two negative electrons are induced to compensate the excess positive charges. Hence, the resistivity slightly decreases due to the increase of the free electrons in the film. The mobility of the films increases from 10 cm2V-1s-1 to 22 cm2V-1s-1 with increase of Ti concentration. The carrier density increases from 6.24 x 1015 cm-3 to 3.54 x 1016 cm-3. The decrease of resistivity can be attributed to the increase of carrier concentration.Preliminary studies on Dye sensitized solar cells (DSSC), indicated that Ti doped ZnO films exhibited higher photo output compared to undoped ZnO. The results show that the films can be used in DSSC.

In this work, the ZnO thin film, the Al-doped ZnO (AZO) thin film (0.98M ZnO, 0.02M Al) and the (Al,Co) co-doped ZnO thin film (AZO:Co) (0.95M ZnO, 0.02M Al, 0.03M Co) were deposited on the glass substrate by the Sol–Gel method. We fabricated a sample of the ZnO thin film, a sample of the AZO thin film and three samples of AZO:Co thin films. The spin-coating was used to deposit thin film on the glass substrate. The ZnO and the AZO thin films were annealed at 450[Formula: see text]C while three samples of the AZO:Co thin films were annealed at 300[Formula: see text]C, 450[Formula: see text]C and 600[Formula: see text]C in air for 60 min, respectively. In order to prepare three samples of the AZO:Co thin films, we deposited the (Al,Co) co-doped ZnO on the glass substrate for 20 s then all samples were per-heated at 80[Formula: see text]C for 10 min. we repeated this deposition process five times for each sample. Finally, three samples were annealed at 300[Formula: see text]C, 450[Formula: see text]C and 600[Formula: see text]C in air for 60 min, respectively. The procedure to prepare of the ZnO and AZO thin films was like the AZO:Co thin films except that the annealing temperature was 450[Formula: see text]C. The structural and optical properties of the thin films were investigated by X-ray diffraction technique, UV-Vis spectrophotometer and Field Emission Scanning Electron Microscopy (FESEM). Results indicated that (Al,Co) co-doping in the ZnO thin film improve the optical transmission while changes in the lattice structure is small with respect to the AZO thin film. Also, the AZO:Co thin film which was annealed at 450[Formula: see text]C exhibited simultaneously the high thickness and high optical transmission.

In this study, a detailed investigation on the transparent conducting oxide (TCO) and dielectric properties of undoped ZnO and Hf-doped ZnO (HZO) thin films has ben presented. ZnO-based TCOs are highly valued in optoelectronic and photovoltaic applications due to their unique combination of high optical transparency and electrical conductivity. Hafnium doping introduces an additional degree of tunability, enabling ZnO films to demonstrate both conducting and dielectric characteristics depending on stoichiometry as well as the doping concentration. This dual behaviour enhances the versatility of HZO for a wide range of technological applications, including solar cells, sensors and capacitive devices.Atomic layer deposition (ALD) method was used to deposit ZnO and HZO films, because ALD offers precise control over film thickness, doping concentration and uniformity at the atomic scale. ALD's self-limiting reaction mechanism ensures conformal growth on complex surfaces, enabling the production of high-quality, reproducible TCO and dielectric films. The deposition was performed on cleaned glass and p-Si substrates, maintaining a consistent film thickness of approximately 50 nm, which was confirmed through spectroscopic ellipsometry. Prior to the deposition, the substrates were cleaned using standard cleaning procedures. ZnO and HZO films with varying Hf doping concentrations were deposited at 250 °C using diethylzinc (DEZ), deionized water (DI), and tetrakis(ethylmethylamino)hafnium (TEMAHf) as the zinc, oxidant and hafnium precursors, respectively. The doping concentration was varied using the super-cycle approach. For low Hf doping (3 %), the HZO films were deposited at a 10:1 super-cycle ratio, ten cycles of DEZ-DI precursors followed by one cycle of TEMAHf and water precursors. For higher Hf doping concentrations (9 %), a 1:1 super-cycle ratio was employed. The structural properties of the films were analysed using grazing incidence X-ray diffraction (GIXRD), confirming that ZnO and HZO films with low Hf doping (10:1) exhibit a polycrystalline hexagonal wurtzite structure. However, higher Hf doping concentrations (1:1) led to a reduced crystallinity and conductivity of the films, which are due to the limited solubility of Hf in the ZnO matrix, as confirmed by elemental analysis. Surface morphology and topography were analyzed using field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM), revealing smooth and uniform film surfaces. Optical measurements performed using UV–Vis-NIR spectroscopy demonstrated an optical transmittance > 80% across the visible spectrum for all films, highlighting their suitability for optoelectronic applications. Electrical measurement results showed that undoped ZnO and Hf-doped ZnO films with higher doping concentrations exhibited high resistivity, whereas low Hf-doped ZnO films displayed enhanced conductivity with a minimum resistivity of 1.5 mΩ-cm. For electrical characterization, Al contacts were thermally evaporated onto both sides of ZnO/p-Si and HZO/p-Si heterojunctions. Current-voltage (I-V) measurements revealed a transition from rectifying to Ohmic behaviour with decreasing Hf concentration, which was attributed to variations in the work function of HZO film. Kelvin probe measurements further validated these findings by confirming changes in the work function of HZO films with the doping concentration. The interface properties of these heterostructures were studied using capacitance-voltage (C-V) measurements at different frequencies and impedance spectroscopy.Overall, this study demonstrates that ALD-grown Hf-doped ZnO films at lower doping concentrations are promising TCO materials for photovoltaic and optoelectronic devices due to their superior conductivity and optical transparency. Conversely, highly Hf-doped ZnO films exhibit enhanced dielectric properties, making them suitable for advanced electronic applications such as capacitors and memristors. These findings provide valuable insights into the tunability of ZnO-based materials for multifunctional applications. Detailed results and analyses will be presented at the conference. Figure 1

Antibacterial activity of the thin ZnO film formed by atomic layer deposition under UV-A light

Development of transparent conductive Mg and Ga co-doped ZnO thin films: Effect of Mg concentration

Achieving thermoelectric devices with high performance based on low-cost and nontoxic materials is extremely challenging. Moreover, as we move toward an Internet-of-Things society, a miniaturized local power source such as a thermoelectric generator (TEG) is desired to power increasing numbers of wireless sensors. Therefore, in this work, an all-oxide p-n junction TEG composed of low-cost, abundant, and nontoxic materials, such as n-type ZnO and p-type SnOx thin films, deposited on borosilicate glass substrate is proposed. A type II heterojunction between SnOx and ZnO films was predicted by density functional theory (DFT) calculations and confirmed experimentally by X-ray photoelectron spectroscopy (XPS). Moreover, scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDS) show a sharp interface between the SnOx and ZnO layers, confirming the high quality of the p-n junction even after annealing at 523 K. ZnO and SnOx thin films exhibit Seebeck coefficients (α) of ∼121 and ∼258 μV/K, respectively, at 298 K, resulting in power factors (PF) of 180 μW/m K2 (for ZnO) and 37 μW/m K2 (for SnOx). Moreover, the thermal conductivities of ZnO and SnOx films are 8.7 and 1.24 W/m K, respectively, at 298 K, with no significant changes until 575 K. The four pairs all-oxide TEG generated a maximum power output (Pout) of 1.8 nW (≈126 μW/cm2) at a temperature difference of 160 K. The output voltage (Vout) and output current (Iout) at the maximum power output of the TEG are 124 mV and 0.0146 μA, respectively. This work paves the way for achieving a high-performance TEG device based on oxide thin films.

Effect of substrate temperature on the structural and optical properties of ZnO and Al-doped ZnO thin films prepared by dc magnetron sputtering

Producing CuO and ZnO composite thin films using the spin coating method on microscope glasses

ZnO thin films have emerged as an interesting research area owing to its useful properties. Recently, lots of attention have been given to doped ZnO with Cu atom due to its favourable potential in semiconductor devices. Pure and Cu-doped ZnO (CZO) thin films were deposited on the glass, p-GaN/Al2O3 and n-GaN/Al2O3 substrates using radio frequency magnetron sputtering of Cu/ZnO alloy target with a ratio of 10/90 at 200 °C. The crystal structure, optical properties, surface morphology and electrical properties were investigated by using X-ray diffraction (XRD), ultraviolet-visible (UV-VIS) spectrophotometer, atomic force microscopy (AFM) and Hall measurement with four-point Van der Pauw configuration respectively. XRD analysis showed that single phase ZnO with hexagonal wurtzite structure and c-axis orientation was fabricated. The transmittance of all films deposited on glass in the visible region were more than 85%. The optical band gap of the films were calculated by using transmittance data obtained from UV-VIS spectrophotometer. Optical band gap reduction occurred when Cu is introduced into ZnO. Deposited CZO films showed smoother surface compare with ZnO films. Hall measurement results revealed that CZO film deposited on n-GaN/Al2O3 had higher mobility and conductivity than pure ZnO films.

Effect of Er doping on the ammonia sensing properties of ZnO thin films prepared by a nebulizer spray technique

Root like structured Ni-doped zinc oxide [Zn(1-x)NixO (x = 0.09)] thin films were deposited on a non-conducting glass substrate by indigenously developed spray pyrolysis system at optimized substrate hotness of 573±5 K. Thus obtained Ni-doped ZnO thin films were characterized by UV-visible spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Atomic Force Microscopy (AFM). XRD result revealed that Ni-doped ZnO has a polycrystalline nature with a hexagonal wurtzite structure. For pure ZnO and Ni-doped ZnO thin films, the particle sizes were 60.9 and 53.3 nm while lattice strain values were 1.56×10-3 and 1.14×10-3, respectively. The film surface showed characteristic root-like structure as observed by the SEM. It was observed that the Ni-doped ZnO thin films were grown in high density along with more extent of branching as compared to pure ZnO thin films but retained the root-like morphologies, however, the branches were more-thinner and of shorter lengths. AFM analysis showed that the surface grains of the Ni-doped samples are homogeneous with less RMS roughness values compared with the undoped ZnO samples. The photocatalytic activity of the prepared thin films was evaluated by the degradation of methyl orange (MO) dye under UV light irradiation. Pure ZnO and Ni-doped ZnO thin films took 150 min and 100 min to degrade about 60% MO dye, respectively.