Papers by Keyword: ZnO Thin Film

Abstract: Multilayers zinc oxide thin films were synthesized by the sol–gel spin coating process to fabricate sensing membranes in an electrolyte-insulator-semiconductor (EIS) sensor for pH detection. The effect of various layers (single, three and five layers) on the crystallinity, morphological and optical properties of ZnO films were investigated by XRD, FE-SEM, and Photoluminescence respectively. The ZnO thin films grown were polycrystalline with hexagonal wurtzite structure. The films were not smooth, with grains and porosity in between them, and become denser as film thickness increased. The PL spectra exhibit two main emission peaks at near band edge 360-380 nm region (strong and sharp UV radiation) and 450–600 nm region (broad blue, green, and yellow radiation). Sensitivity, linearity was measured to determine the sensing and reliability performance of fabricated devices. The result confirmed that, the sensitivity for the three samples increased with increased layer from 48.3 mV/pH to 82.58 mV/pH. Compared to single and three layers of the ZnO electrolyte-insulator-semiconductor (EIS), ZnO grown with five layers exhibits a higher sensitivity of 82.58 mV/pH in solutions from pH 2–12 and linearity of 99.015 %. This is due to the increased of ZnO thickness, which produces dense surface and a well-crystallized grain structure.

Abstract: This research deals with ambient energy harvesting by using zinc oxide thin film. The objectives of this thesis are to prove the ZnO film as a piezoelectric material can produce electric when vibration is applied and determine its optimal voltage. The thesis describes the sol gel spin coating technique to fabricate zinc oxide thin film. Zinc acetate dehydrate, absolute ethanol and diethanolamine were used in this thesis to act as sol gel precursor. Sol gel was coated on glass slide which wrapped by aluminum foil. The thin film was formed after preheating and annealing. The thin film was characterized by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Photoluminescence spectroscopy (PL) and Ultraviolet-visible spectroscopy (UV-Vis) as well as analyzed using vibration technique. From XRD results, the films were preferentially diffracted at around 65° which corresponding to (1 1 2) diffraction phase. From FESEM results, it was observed that when the spin speed was increased at same annealing temperature, the thickness was also decreased. When the annealing temperature was increased at same spin speed, both grain size and thickness were increased. From the PL results, there was only film with spin speed of 2000 rpm and annealing temperature of 300 °C had slightly left wavelength which was 380 nm. Annealing temperature would affect only the intensity of PL wavelength. From the results of UV-Vis, it was observed that when the spin speed was increased at same annealing temperature, the band gap was decreased. When the annealing temperature was increased at same spin speed, the band gap was decreased. Piezoelectric test had proven the ZnO film could produce electricity. The maximum voltage (20.7 mV) was produced by the ZnO film with spin speed of 2000 rpm and annealing temperature of 300 °C.

Abstract: Zinc Oxide (ZnO) thin films were produced by the sol gel dip coating process on the p-type silicon substrate with various withdrawal speeds changing from 1 to 4 cm/min, respectively. The films were annealed at a temperature of 500 ^°C for an hour in air ambient. The thin film thickness was found to be raised with the rise in withdrawal speed. The uniform distribution of the grains was appeared for all the films. The evolution of c-axis oriented (002) peak was revealed from X-ray diffraction (XRD) studies. The microstructural and optical properties of ZnO films were investigated by Raman, FTIR and photoluminescence spectroscopy (PL). The resistive switching properties of ZnO based memristors were studied by performing the current-voltage (I-V) measurements, where the thin films coated with lower withdrawal speed, have shown better switching property with rapid rise and fall of current during SET and RESET process, respectively.

Abstract: Zinc Oxide thin films were prepared for different precursor solution molarities from 0.025M to 0.1M by spray pyrolysis deposition technique. A comprehensive study was carried out to realize the effect of concentration of precursor on ZnO thin films. The optimized temperature of the glass substrate was 300°C. From the XRD data it is inferred that the films are polycrystalline and hexagonal wurtzite structure . The degree of preferred orientation were along diffraction planes (100), (002) and (101) for all the ZnO films. The intensity of the diffraction peak prepared with 0.1M concentration is higher than those prepared at lower concentrations. The grain size (D) was calculated using Debye-Scherrer formula. It was found that the average grain size increases, when the molar concentration increases. As the solution concentration increases, the band gap decreases. The films are transparent in the visible region (85%), and the transmittance decreases as the molar concentration increases, which is caused by optical scattering at grain boundaries.

Abstract: ZnO thin films is a kind of very potential semiconductor materials, due to their excellent chemical, electrical and optical properties. The effects of annealing temperature and coating layers on properties of ZnO thin films prepared by sol-gel immerse technique is studied in this work. The structure properties and optical properties were investigated by XRD, SEM and UV-Vis spectrophotometry respectively. It is found that the thin films were composed of better hexagonal wurtzite crystals with the c-axis preferred orientation by thermal annealing 550°C. With coating layers increasing from 2 layers to 8 layers, the intensity for all diffraction peaks were increased gradually, and the crystallite size of ZnO thin films is slightly increased. The transmittance of prepared thin films is over 80% in the visible-near IR region from 460 nm - 800 nm.

Abstract: ZnO thin films have attractive applications in photoelectric device, due to their excellent chemical, electrical and optical properties. In this paper, ZnO thin films with good c-axis preferred orientation and high transmittance are prepared on glass sheets by sol-gel immerse technique. The effects of withdrawal speeds on the growth process of thin film crystal, film crystal orientation and the crystallinity, the optical performance were investigated by XRD, SEM and UV-Vis spectrophotometry. The results show that the thin films were composed of better hexagonal wurtzite crystals with the c-axis prepared orientation. The transmittance of prepared thin films is over 80% in the visible-near IR region from 600 nm - 800 nm. ZnO films have sharp and narrow diffraction peaks, which indicates that the materials exhibit high crystallinity. With the withdrawal speeds increasing, the grain size of ZnO thin films and the intensity for all diffraction peaks were increased gradually. The growth model is changed from the stratified structure into the island structure in the growth process. The transmittance of the thin films decrease in the visible wavelength region, with the withdrawal speeds increasing.

Abstract: We examined structural properties of nitrogen doped (ZnO:N) thin films prepared by reactive RF magnetron sputtering technique in conjunction with gas timing method. The deposited films were polycrystalline ZnO in wurtzite structure. Morphology of the ZnO:N films could be modified by adjusting gas timing conditions. The x-ray photoelectron spectroscopy (XPS) and extended x-ray absorption fine structure (EXAFS) analysis showed that incorporation of nitrogen may cause structural distortion in the ZnO:N crystal.

Abstract: Thin film piezoelectric material plays a vital role in micro-electromechanical systems (MEMS), due to its low power requirements and the availability of high energy harvesting. Zinc oxide is selected for piezoelectric material because of its high piezoelectric coupling coefficient, easy to deposit on silicon substrate and excellent adhesion. Deposited ZnO and Al improve the electrical properties, electrical conductivity and thermal stability. The design, fabrication and experimental test of fabricated MEMS piezoelectric cantilever beams operating in d33 mode were presented in this paper. PVD (Physical Vapor Deposition) was selected as the deposition method for aluminium while spincoating was chosen to deposit ZnO thin film. The piezoelectric cantilever beam is arranged with self-developed experimental setup consisting of DC motor and oscilloscope. Based on experimental result, the longer length of piezoelectric cantilever beam produce higher output voltage at oscilloscope. The piezoelectric cantilevers generated output voltages which were from 2.2 mV to 8.8 mV at 50 Hz operation frequency. One of four samples achieved in range of desired output voltage, 1-3 mV and the rest samples produced a higher output voltage. The output voltage is adequate for a very low power wireless sensing nodes as a substitute energy source to classic batteries.

Abstract: Mesoporous ZnO thin film is an important part of dye-sensitized solar cells (DSSCs) due to it determines the amount of adsorbed dyes. However, small specific surface area of ZnO thin film prepared by ordinary methods restricts the increase of conversion efficiency of DSSCs. In this work we adopted two-step electrodeposition method to fabricate ZnO thin film, which increase the roughness and dyes adsorption. ZnO nanosheets with many adsorbing nanoparticles were observed by scanning electron microscope (SEM). It is noteworthy that DSSC based on two-step electrodeposition method exhibit more outstanding photoelectric performance than those based on one-step electrodeposition method, which demonstrates that two-step electrodeposition method is in favor of increasing specific surface area and adding dyes adsorption, which eventually contributes to improvement the conversion efficiency of DSSCs.

Abstract: ZnO will become a new pattern optoelectronic material because of its many excellent properties. But the defects in ZnO crystal are the key factors for restricting the luminescence properties of the material. In this paper, we summarized the defect types that exist in ZnO thin films and reviewed on the relationship between the luminescence mechanism and the structure defects of ZnO thin films reported in recent years.