Sol–Gel Synthesis and Characterization of Na0.5Bi0.5TiO3–NaTaO3Thin Films

Thin films with the composition 70 mol% Na_0.5Bi_0.5TiO₃ + 30 mol% NaTaO₃ were prepared by sol–gel synthesis and spin coating. The influence of the annealing temperature on the microstructural development and its further influence on the dielectric properties in the low‐ (kHz–MHz) and microwave‐frequency (15 GHz) ranges were investigated. In the low‐frequency range we observed that with an increasing annealing temperature from 550°C to 650°C the average grain size increased from 90 to 170 nm, which led to an increase in the dielectric permittivity from 130 to 240. The temperature‐stable dielectric properties were measured for thin films annealed at 650°C in the temperature range between ?25°C and 150°C. The thin films deposited on corundum substrates had a lower average grain size than those on Si/SiO₂/TiO₂/Pt substrates. The highest average grain size of 130 nm was obtained for a thin film annealed at 600°C, which displayed a dielectric permittivity of 130, measured at 15 GHz.     

Effect of annealing on grain growth and Y segregation behavior in tetragonal ZrO2 thin film

In order to fabricate tetragonal yttria stabilized zirconia samples with large grain size, 3 mol% Y₂O₃ doped zirconia thin films were grown on (0001) α-Al₂O₃ substrate by pulsed laser deposition (PLD) followed by subsequent high temperature annealing. The thin film samples were annealed at 1200°C, 1250°C, 1300°C, and 1350°C in order to obtain larger grain size without Y segregation. The microstructure and chemical composition of these annealed films were analyzed using atomic force microscopy, scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy. The as-grown thin film was found to be composed of [111]-oriented grains of ∼100 nm connected with small-angle tilt boundaries. Based on analysis of annealed thin films, it was revealed that grain growth of tetragonal zirconia occurred anisotropically. Cross section scanning transmission electron microscopy observations revealed that such grain growth behavior is affected by the step-terrace structures of the sapphire substrate. Energy-dispersive X-ray spectroscopy showed that Y was found to distribute almost uniformly below 1300°C but to segregate at the grain boundaries at 1350°C. As a conclusion, the 1300°C-annealed sample shows the largest grain size with homogeneous Y distributions.     

Structural and optoelectronic properties of transparent conductive c-axis-oriented ZnO based multilayer thin films with Ru interlayer

ZnO and Ru multilayer thin films are deposited using the sputtering deposition technique at room temperature. The effects of the Ru interlayer thickness and annealing temperature on the properties of multilayer thin films have been studied. An X-ray diffraction study reveals that ZnO layers are highly c-axis-oriented. The use of an Ru interlayer improves the crystalline quality of the subsequently deposited ZnO layers. Moreover, the crystalline quality of the entire structure is further enhanced through thermal annealing in a vacuum. Atomic force microscopy images show that the surface roughness of the multilayer thin films increases with a Ru interlayer thickness greater than 6 nm. The roughness of the film surface increases in correlation with annealing temperatures. This accounts for the decreased optical transmittance of the multilayer thin films annealed at temperatures higher than 450 °C. The electrical resistivity of multilayer thin films decreases with an increase in the metallic interlayer thickness. Thermal annealing at 450 °C causes low resistivity in multilayer thin films. The lowest resistivity reached ～5.4 × 10^?4 Ω cm for multilayer films with a 10-nm-thick Ru interlayer annealed at 450 °C.     

Structural and optical studies on sol–gel derived ZnO thin films by excimer laser annealing

High-quality polycrystalline ZnO thin films were deposited onto alkali-free glasses at a temperature of 300°C in air ambience by combining sol–gel spin coating and KrF excimer laser annealing. The effects of laser irradiation energy density on the crystallization, microstructure, surface morphology, and optical transmittance of as-prepared ZnO thin films were investigated and compared to the results of thermally annealed ZnO thin films. The crystallinity level and average crystallite size of laser annealed ZnO thin films increased as laser energy density increased. The crystallinity levels and average crystallite size of excimer laser annealed (ELA) thin films were greater than those of the thermally annealed (TA) thin films. However, laser annealed thin films had abnormal grain growth when irradiation energy density was 175 mJ/cm². Experimental results indicated that the optimum irradiation energy density for excimer laser annealing of ZnO sol–gel films was 150 mJ/cm². The ELA 150 thin films had a dense microstructure, an RMS roughness value of 5.30 nm, and an optical band gap of 3.38 eV, close to the band gap of a ZnO crystal (3.4 eV).     

Microstructure-related piezoelectric properties of a ZnO film grown on a Si substrate

We investigated the effect of grain size on the piezoelectric properties of ZnO using films of different grain sizes and a fixed thickness of 800 nm deposited on a Si substrate by pulsed laser ablation in the temperature range of 300–700 °C. All of the deposited films have a crystal structure with a c-axis orientation. The grain size of the grown films, characterized by transmission electron microscopy (TEM), increases with the deposition temperature. In contrast, their piezoelectric efficiency (PE, d₃₃), characterized by piezoelectric force microscopy (PFM), was found to initially increase with the deposition temperature up to 500 °C, after which it decreased with further increases in temperature. The maximum PE value is observed for the film deposited at 500 °C with a grain size of approximately 60 nm. The peculiar PE behavior observed was theoretically explained by a competition between the contribution of the c-axis orientation favoring a larger d₃₃ value due to the enhanced static asymmetry and the strong grain size effect that influences the piezoelectric polarization as a result of domain motion.     

Sandwich-structured ZnO-MnO2-ZnO thin film varistors prepared via magnetron sputtering

ZnO varistors are widely used to protect electronic circuits form transient voltages. However, it is difficult to prepare varistors with voltage less than 10 V using ZnO ceramics. Here we prepared a ZnO-MnO₂-ZnO (ZMZ) sandwich thin film via magnetron sputtering and subsequent annealing at 200-500 °C. With the increase of annealing temperature, the manganese oxide sandwich layer reacts with the upper and lower ZnO layer and becomes thinner. After annealed at 500 °C, because of ZnO grain growth, the upper and lower ZnO layers joined together. The electrical properties of ZMZ films annealed at 400 °C show strong nonlinear I-V characteristics. A ZMZ low voltage thin film varistor with planar boundary potential barrier was obtained whose nonlinear coefficient α and varistor voltage V1 mA are about 30 and 6.0 V, respectively. The stable and excellent nonlinear characteristics make it a promising candidate for overvoltage protection in low operating voltage circuits.     

Effects of annealing temperature on the phase formation,optical, photoluminescence and magnetic properties of sol-gel YFeO3 films

YFeO₃ (YFO) thin films were deposited onto quartz substrates via sol-gel spin-coating technique and annealed at different temperature ranged between 650 and 900 °C. The impact of annealing temperature on the phase formation, microstructural, optical, photoluminescence (PL) and magnetic properties of the films were systematically investigated. X-ray diffraction analysis revealed an amorphous structure in film annealed at 650 °C and formation of hexagonal-YFO (h-YFO) phase in films annealed at 750–800 °C. The films annealed at 850–900 °C exhibited an orthorhombic-YFO (o-YFO) structure. Atomic force microscopy images of h-YFO films showed homogeneous surface with uniform particles size and shape. The particle size increased and had irregular shape in o-YFO films. The average particle size was 44 and 117 nm, while the root square roughness was 1.38 and 2.55 nm for h- and o-YFO films annealed at 750 and 850 °C, respectively. The optical band gap (E_g) was 2.53 and 2.86 eV for h- and o-YFO films annealed at 750 and 850 °C, respectively. The PL spectra of h-YFO films were red-shifted compared with that of o-YFO films. The PL emission related to near band edge was observed at 459.0 and 441.9 nm for h- and o-YFO films annealed at 750 and 850 °C, respectively. The magnetization was enhanced with the increasing of annealing temperature and has the value of 4.8 and 12.5 emu/cm³ at 5000 Oe for h- and o-YFO films annealed at 750 and 850 °C, respectively.     

Effects of atomic layer deposition conditions on the formation of thin ZnO films and their photocatalytic characteristics

The use of photocatalysts in water treatment systems is regarded as an advanced technology. To ensure efficiency and stability, the optimization of photocatalyst immobilization is essential for application in water treatment processes. In this study, we investigated the effect of atomic layer deposition (ALD) conditions on the development of highly photocatalytically active thin ZnO films. Three different temperatures and three ALD cycles were employed to evaluate the photocatalytic activity of thin ZnO films (represented by the production rate of reactive oxygen species and the degradation rate of methylene blue). We found that the surface properties of the thin ZnO films, such as grain size and homogeneity, exerted a dominant influence on the photocatalytic activity. At a low temperature (50 °C), nanograins were not formed properly, while various nanograin shapes were obtained at a high temperature (250 °C). The optimized grain had a grain size of 20 nm and a (002)/(101) crystalline orientation ratio of 2.2. The UV light absorption increased in proportion to the film thickness, and a minimum film thickness (50 nm) was necessary to ensure high photocatalytic activity at the film surface. In addition, the increase in the photocatalytic activity was not significant as the thickness increased beyond the optimum thickness. These results will provide useful guidelines for the fabrication of thin ZnO films with excellent photocatalytic activity for water treatment.     

Effects of power and temperature on the structural,anti-icing,wettability, and optical properties of zinc oxide thin films

Zinc oxide semiconductors have received significant research attention over the past decade owing to their diverse applications. In this paper, we report the development and characterisation of ZnO thin films prepared by radio-frequency (RF) magnetron sputtering. The optical, anti-icing, wettability, and structural properties of the films were investigated at various sputtering power levels and temperatures. With an increase in the power from 175 to 250 W, the ZnO thin films showed fine (002) structures. X-ray diffraction analysis of the coated thin films revealed a considerable increase in the (002) peak intensity along the c-axis with increasing power and temperature. Increasing the sputtering power from 175 to 250 W and the deposition temperature from 150 to 300 °C led to an increase in the average size of the grains from 10.548 to 13.151 nm and from 9.97 to 13.151 nm, respectively. The water contact angle possibly depends on the RF power and temperature employed for material deposition. Within the 350–800 nm range, the prepared films achieved optical transmissions of 92%–88%, refractive indices of 1.52–1.50, and band gaps of 3.28–3.24 eV. The anti-icing properties were also improved by adjusting the sputtering power and temperature during material deposition.     

The ultraviolet emission mechanism of ZnO thin film fabricated by sol–gel technology

ZnO thin films were successfully deposited on SiO₂/Si substrate by sol–gel technology. The as-grown ZnO thin films were annealed under an ambient atmosphere from 600 to 900 °C by rapid thermal annealing (RTA) process. X-ray diffraction and scanning electron microscopy analyses reveal the physical structures of ZnO thin films. From PL measurement, two ultraviolet (UV) luminescence bands were obtained at 375 and 380 nm, and the intensity became stronger when the annealing temperature was increased. The strongest UV light emission appeared at annealing temperature of 900 °C. The chemical bonding state in ZnO films was investigated by using X-ray photoelectron spectrum. The mechanism of UV emission was also discussed.     

Effect of rapid thermal annealing on the properties of zinc tin oxide films prepared by plasma-enhanced atomic layer deposition

The effect of rapid thermal annealing treatments on the microstructure, surface morphology, and optical characteristics of zinc tin oxide (ZTO) films produced by plasma-enhanced atomic layer deposition was investigated. The ZTO films were annealed in oxygen atmosphere for 2 min at four selected temperatures from 500 to 800 °C. The X-ray diffraction showed that the annealing temperature has a great influence on the crystalline characteristics of ZTO films. The film shows complete amorphous structure for as-deposited ZTO film. Meanwhile, the spinel zinc stannate Zn₂SnO₄ was obtained for the samples annealed from 500 to 800 °C, which shows polycrystalline nature. The X-ray photoelectron spectroscopy proved that the annealing process in oxygen gas can effectively can reduce the oxygen vacancy defects in the films. In addition, the photoluminescence spectroscopy manifests an ultraviolet emission with a broad peak range from 345 to 385 nm. Moreover, the ultraviolet luminescence intensity increases continuously with the increase of annealing temperature. Spectroscopic ellipsometry analyses demonstrate that the refractive index of annealed films increases as the increase of annealing temperature, while the extinction coefficient decreases gradually with the increase of annealing temperature in the visible light range.     

Impact on nonlinear/linear optical and structural parameters in quaternary In15Ag10S15Se60 thin films upon annealing at different temperatures

In the present study, the effect of thermal annealing on structural, linear, and nonlinear optical properties of quaternary chalcogenide In₁₅Ag₁₀S₁₅Se₆₀ thin film has been reported. The bulk sample synthesized by the melt quenching technique was used for the thin film preparation by the thermal evaporation method. Post deposition, the thin films were annealed at different temperatures like 100 °C, 150 °C, 200 °C, and 250 °C for 2 hs. X-ray diffraction (XRD) and Raman spectroscopy were used for structural studies, which showed the increase in crystalline phases with the increase of annealing temperature. The morphological images taken by field emission scanning electron microscope (FESEM) showed the densification and enlargement of scattered grains for annealed films. Furthermore, the constituent elements and their percentage in the sample were confirmed by Energy dispersive X-ray analysis (EDX). The linear and nonlinear optical parameters were calculated from the transmittance data obtained from UV–Vis spectroscopy in the wavelength range of 600–1100 nm. There is a large reduction in third-order nonlinear susceptibility at the higher annealing temperature. Subsequently, the transmission increased, whereas the absorption decreased with the annealing temperature. The extinction coefficient decreased while there was an increase in optical bandgap for the annealed films due to the decrease in surface defects and disorder, which forms the localized states in the bandgap. The oscillator energy, dispersion energy, dielectric constant, optical conductivity were calculated and discussed in detail. The change in both linear and nonlinear parameters by thermal annealing could be useful for controlling the optical properties of In₁₅Ag₁₀S₁₅Se₆₀ thin film, which could be the preferable candidate for numerous photonic applications.     

Enhanced electrical properties of In-Ga-Sn-O thin films at low-temperature annealing

Electrical and optical properties of In-Ga-Sn-O (IGTO) thin films deposited by radio-frequency magnetron sputtering were investigated according to annealing temperatures. While IGTO films remained an amorphous phase even after a heat treatment at temperature up to 500 °C, Hall measurements showed that annealing temperature had a significant impact on electrical properties of IGTO thin films. After investigating a wide range of annealing temperatures for samples from as-deposited state to 500 °C, IGTO film annealed at 200 °C exhibited the best electrical performance with a conductivity of 229.31 Ω^?1cm^?1, a Hall mobility of 36.89 cm²V^?1s^?1, and a carrier concentration of 3.85 × 10¹⁹ cm^?3. Changes in proportions of oxygen-related defects and percentages of Sn²⁺ and Sn⁴⁺ ions within IGTO films according to annealing temperatures were analyzed with X-ray photoelectron spectroscopy to determine the cause of the superb performance of IGTO at a low temperature. In IGTO films annealed at 200 °C, Sn⁴⁺ ions acting as donor defects accounted for a high percentage, whereas hydroxyl groups working as electron traps showed a significantly reduced percentage compared to the as-deposited film. Optical band gaps of IGTO films obtained from UV–visible spectrum were 3.38–3.47 eV. The largest band gap value of 3.47 eV for the IGTO film annealed at 200 °C could be attributed to an increase in Fermi-level due to an increase of carrier concentration in the conduction band. These spectroscopic results well matched with electrical properties of IGTO films according to annealing temperatures. Excellent electrical properties of IGTO thin films annealed at 200 °C could be largely due to Sn donors besides oxygen vacancies, resulting in a significant increase in free carriers despite a low annealing. temperature.     

Aqueous chemical route deposition of nanocrystalline ZnO thin films as acetone sensor: Effect of molarity

Nanocrystalline ZnO thin films were deposited onto glass substrate using a simple and inexpensive aqueous chemical method at low temperature (90 °C). The concentration of precursor solution was varied in order to study its effect on structural, morphological, and gas response properties. Field-emission scanning electron microscopy (FESEM) images indicate the growth of ZnO with hexagonal shaped nanostructure. Further these films were used to explore gas response properties towards acetone, propanol and ethanol vapors. The sensor response was found to be decreased with increase in precursor concentration. The highest sensor response of 92% was observed towards acetone for the film deposited at 0.05 M at an operating temperature of 350 °C. The higher vapor response towards acetone is attributed to size and surface morphology of the film deposited at 0.05 M.     

Solvothermally grown WO3·H2O film and annealed WO3 film for wide-spectrum tunable electrochromic applications

Tungsten trioxide (WO₃) is a classical electrochromic (EC) material with advantages of abundant reserves, high coloration efficiency and cyclic stability. However, WO₃ films are often accompanied by a narrow spectrum of modulation due to a single-color change from transparent to blue. In this work, we report a wide-spectrum tunable WO₃·H₂O nanosheets EC film solvothermally grown on fluorine-doped tin oxide (FTO) glass. Interestingly, the crystalline WO₃·H₂O nanosheets film is transformed into amorphous WO₃ after annealing at 250 °C for 1 h. The amorphous film can be transformed into crystalline WO₃ film by increasing the annealing temperature to 450 °C. After annealing at 250 °C, the WO₃ film exhibits an optical modulation of 75.8% in a broad solar spectrum range of 380–1400 nm and blocks 88.9% of solar irradiance. Fast switching responses of 4.9 s for coloration and 6.0 s for bleaching, and a coloration efficiency of 86.4 cm² C⁻¹ are also achieved. Additionally, the WO₃ film annealed at 250 °C also demonstrates an excellent cyclic stability, where 99.6% of the initial optical modulation can be retained after 1500 cycles. This simple and mild solvothermal method used in this work provides a new idea for the preparation of wide-spectrum tunable WO₃ EC films.     

Schottky barrier effect of ZnO modified methyl glycol thin films for detection of hydrogen sulfide gas

Highly nanocrystalline ZnO modified methyl glycol thin films have been deposited on a p-type silicon substrate via the sol–gel spin coating manner. The morphology of the as-deposited film was scrutinized using scanning electron microscopy. I–V characteristics of the as-prepared ZnO film under vacuum and in open air were monitored. The results showed that the ZnO films have a barrier height of 0.38 eV under vacuum and 0.62 eV in open air. The Schottky barrier height between ZnO grains was determined for different reducing gases. The ZnO film showed high sensitivity to H₂S gas compared with other reducing gases due to the reduction of barrier height between ZnO grains. The as-prepared ZnO film was annealed at four different temperatures. X-ray diffraction manifested that the wurtzite hexagonal structure of ZnO deviated from ideality at annealing temperature greater than 650 °C. The barrier height of ZnO film decreased due to the increase of annealing temperature up to 650 °C and then decreased. The results also confirmed that the change of barrier height strongly affected the sensitivity of ZnO film.     

The effects of deposition temperature on structure and dielectric properties of Ba0.6Sr0.4TiO3 thin films produced by pulsed laser deposition

The effects of deposition temperature on orientation, surface morphology and dielectric properties of the thin films for Ba_0.6Sr_0.4TiO₃ thin films deposited on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition were investigated. X-ray diffraction patterns revealed a (2 1 0) preferred orientation for all the films. With rising substrate temperature from 650 °C to 700 °C, the crystallinity and crystal grain size of the films increase, the relative dielectric constant increases, but the dielectric losses have not obvious difference. The film deposited at 350 °C and annealed at 700 °C has strongly improved roughness and dielectric permittivity compared with the film only deposited directly at 700 °C. Three distinct relaxation processes within tan(δ) were found for the Ba_xSr_1?xTiO₃ film: a broadened process of the film relaxation, an intermediate peak which originates from Maxwell–Wagner–Sillars polarization, and an extremely slow process ascribed to leak current. The complex dielectric permittivity and loss can be fitted by an improved Cole–Cole model corresponding to a stretched relaxation function.     

Effects of annealing temperature on the microstructure,optical, ferroelectric and photovoltaic properties of BiFeO3 thin films prepared by sol–gel method

Bismuth ferrite thin films were prepared via sol–gel spin-coating method and the effects of annealing temperature on microstructure, optical, ferroelectric and photovoltaic properties have been investigated. The results show that the bismuth ferrite thin films annealed at 550 °C is single phase and the grain size increases with the rise of annealing temperature. The band gap of bismuth ferrite thin films annealed at 550–650 °C is between 2.306 eV and 2.453 eV. With the rise of the annealing temperature, the remnant polarization gradually decreases and the coercive electric field increases. The short circuit photocurrent density decreases with the rise of annealing temperature, and the open circuit photovoltage and the power conversion efficiency of bismuth ferrite thin films annealed at 550 °C are higher than the thin films annealed at higher temperature.     

Polymeric semiconducting carbon from fullerene by pulsed laser ablation

The polymeric semiconducting carbon films are grown on silicon and quartz substrates by excimer (XeCl) pulsed laser deposition (PLD) technique using fullerene C₆₀ precursor. The substrate temperature is varied up to 300 °C. The structure and optical properties of the films strongly depend on the substrate temperature. The grain size is increased and uniform polymeric film with improved morphology at higher temperature is observed. The Tauc gap is about 1.35 eV for the film deposited at 100°C and with temperature the gap is decreased upto 1.1 eV for the film deposited at 250 °C and increased to about 1.4 eV for the film deposited at 300 °C. The optical absorption properties are improved with substrate temperature. Raman spectra show the presence of both G peak and D peak and are peaked at about 1590 cm^− 1 and 1360 cm^− 1, respectively for the film deposited at 100 °C. The G peak position remains almost unchanged while D peak has changed only a little with temperature might be due to its better crystalline structure compared to the typical amorphous carbon films and might show interesting in device such as, optoelectronic applications.     

Temperature and processing effects on lithium ion conductivity of solution-deposited lithium zirconium phosphate (LiZr2P3O12) thin films

Lithium zirconium phosphate (LiZr₂P₃O₁₂) thin films have been prepared on platinized silicon substrates via a chemical solution deposition approach with processing temperatures between 700°C and 775°C. Films that were subject to a single high-temperature anneal were found to crystallize at temperatures above 725°C. Crystallization was observed in films annealed after each deposited layer at 700°C and above. In both cases, grain size was found to increase with annealing temperature. Ion conductivity was found to increase with annealing temperature in singly annealed films. In per-layer annealed films ion conductivity was found to initially increase then decrease with increasing annealing temperature. A maximum ion conductivity of 1.6 × 10⁻⁶ S/cm was observed for the singly annealed 775°C condition, while a maximum ion conductivity of 5.8 × 10⁻⁷ S/cm was observed for the 725°C per-layer annealed condition. These results are consistent with an increasing influence of cross-plane, internal interface resistance and vapor phase carrier loss in the per-layer annealed samples. This work demonstrates that post-deposition processing methods can strongly affect the ion conducting properties of LiZr₂P₃O₁₂ thin films.