Structural,Optical and Electrical Properties of ZnO Thin Films Prepared by Spray Pyrolysis: Effect of Precursor Concentration

ZnO thin films have been prepared using zinc acetate precursor by spray pyrolytic decomposition of zinc acetate on glass substrates at 450 °C. Effect of precursor concentration on structural and optical properties has been investigated. ZnO films are polycrystalline with (002) plane as preferential orientation. The optical transmission spectrum shows that transmission increases with decrease in the concentration and the maximum transmission in visible region is about 95% for ZnO films prepared with 0·1 M. The direct bandgap value decreases from 3·37 to 3·19 eV, when the precursor concentration increases from 0·1 to 0·4 M. Photoluminescence spectra at room temperature show an ultraviolet (UV) emission at 3·26 eV and two visible emissions at 2·82 and 2·38 eV. Lowest resistivity is obtained at 2·09 Ω cm for 0·3 M. The current– voltage characteristic of the ZnO thin films were measured in dark and under UV illumination. The values of photocurrent and photoresponsivity at 5 V are increased with increase in precursor concentration and reaches to maximum value of 1148 μA and 0·287 A/W, respectively which is correlated to structural properties of ZnO thin films.     

Investigation of dimpled fins for heat transfer enhancement in compact heat exchangers

Direct and Large-Eddy simulations are conducted in a fin bank with dimples and protrusions over a Reynolds number range of Re_H = 200 to 15,000, encompassing laminar, transitional and fully turbulent regimes. Two dimple-protrusion geometries are studied in which the same imprint pattern is investigated for two different channel heights or fin pitches, Case 1 with twice the fin pitch of Case 2. The smaller fin pitch configuration (Case 2) develops flow instabilities at Re_H = 450, whereas Case 1 undergoes transition at Re_H = 900. Case 2, exhibits higher Nusselt numbers and friction coefficients in the low Reynolds number regime before Case 1 transitions to turbulence, after which, the differences between the two decreases considerably in the fully turbulent regime. Vorticity generated within the dimple cavity and at the dimple rim contribute substantially to heat transfer augmentation on the dimple side, whereas flow impingement and acceleration between protrusions contribute substantially on the protrusion side. While friction drag dominates losses in Case 1 at low Reynolds numbers, both form and friction drag contributed equally in Case 2. As the Reynolds number increases to fully turbulent flow, form drag dominates in both cases, contributing about 80% to the total losses. While both geometries are viable and competitive with other augmentation surfaces in the turbulent regime, Case 2 with larger feature sizes with respect to the fin pitch is more appropriate in the low Reynolds number regime Re_H < 2000, which makes up most of the operating range of typical compact heat exchangers.     

Electrical, structural and optical properties of fluorine-doped zinc oxide thin films: Effect of the solution aging time

In this paper ageing effects of the solution used to prepare fluorine-doped ZnO films by the spray pyrolysis technique were investigated, concerning its role on the structure, the electrical and optical properties of films produced. The data reveal that the sheet resistance of the ZnO:F thin film decreases with the age of the solution used, reaching a minimum of 24 Ω/□, after 15 days. On the other hand the optical transmittance increases for films deposited using 6 days aging solution, decreasing afterwards as the aging time increases, being the optical transmittance in the visible range below 55%, for films deposited from solutions 36 days in age. The X-ray diffraction spectra show that the aged films are polycrystalline in nature with a [100] predominant orientation. The data also show that the intensity of (100) peak increases as the time of solution age increases, which is related to an improvement of the film crystallinity.     

Effect of substrate temperature on the properties of ZnO thin films prepared by spray pyrolysis

Sprayed ZnO films were grown on glass at different substrate temperatures from 200 °C to 500 °C and their structural, optical and electrical properties were investigated. All films are polycrystalline with hexagonal wurtzite structure. ZnO films at substrate temperatures above 400 °C appear to be better crystalized with (002) plane as preferential orientation. Optical transmission spectrum shows that ZnO films have high transmission (above 80%) in visible region for substrate temperatures above 400 °C. Photoluminescence spectra at room temperature show an ultraviolet emission and two visible emissions at 2.82 eV and 2.37 eV. The resistivity of ZnO films increases with increasing substrate temperatures (above 400 °C). The ZnO film deposited at 400 °C shows highest figure of merit.     

Influence of different process parameters on physical properties of fluorine dopes indium oxide thin films

Fluorine-doped indium oxide films were prepared by the spray pyrolysis technique. The physical properties of these films were investigated with respect to various process parameters, namely variation of dopant concentration (in the solution), deposition temperature (T _s), carrier gas (air) flow rate and the thickness of the film. The best films had a Hall mobility of the order of 28 cm²V^–1 s^–1 and a carrier density of 2.7 × 10²⁰ cm^–3. These films were deposited at T _s=425 °C at an air flow rate of 71 min^–1 for an atomic ratio of fluorine to indium of 72%. The electrical resistivity of these films was of the order of 10^–4 cm and the average transmission in the visible range was found to be 80–90%. The films were polycrystalline, n-type semiconductors with [400] as a preferred orientation. The preferred orientation changes from [400] to [222] depending upon the process parameters.     

Preparation of In2O3:F thin films grown by spray pyrolysis technique

Transparent conducting fluorine doped indium oxide (In₂O₃:F) thin films have been deposited on Corning 7059 glass substrates by the spray pyrolysis technique. The structural, electrical, and optical properties of these films were investigated as a function of substrate temperature. The X-ray diffraction pattern of the films deposited at lower substrate temperature (T_s=300 °C) showed no peaks of In₂O₃:F. In the useful range for deposition (i.e. 425–600 °C), the orientation of the films was predominantly [400]. For the 4500 Å thick In₂O₃:F deposited with an F content of 10-wt%, the minimum sheet resistance was 120 Ω and average transmission in the visible wavelength rang (400–700 nm) was 88%.     

Enhanced Li-storage performance of In-doped Li1.21[Mn0.54Ni0.125Co0.125]O2 as Li- and Mn-rich cathode materials for lithium-ion batteries

Journal of Applied Electrochemistry - Lithium manganese-rich nickel–manganese–cobalt oxides (LMR-NMCs) are promising candidates for cathodes in Li-ion batteries (LIBs) due to their high...     

Transparent conductive Sn-doped indium oxide thin films deposited by spray pyrolysis technique

Films of indium oxide doped with tin (ITO) are prepared using the low cost spray pyrolysis technique. The effect of tin doping on the physical properties of In2O3 are studied. In this study the polycrystalline ITO films with the different Sn concentration of 1 to 100-wt% SnCl₂ were prepared on Corning 7059 glass substrate. These films were confirmed to show the high crystallinity by X-ray diffraction technique. Low sheet resistance (25Ω/▪) and high visible transmission (˜82%) were obtained when the films were deposited at the tin concentration of 2-wt%.     

Spray Pyrolysis Deposition of ZnO Thin Films from Zinc Chloride Precursor Solution at Different Substrate Temperatures

ZnO films were prepared at different substrate temperatures through spraying pyrolysis deposition of zinc chloride precursor onto glass substrate. Substrate temperature affects surface morphology of films and therefore their optical and electrical properties. All films are polycrystalline with Wurtzite crystal structure and preferentially grow along c-axis direction. Formation of ZnO rods start at about 500 °C. The diameter and length of rods deposited at 500 °C are350–500 and 550–700 nm, respectively. By increasing substrate temperature, film becomes more coverage and diameter of the rods reduces to 250–300 nm but their length increases to 1,000–1,200 nm, respectively. Optical transmission in visible region decreases with increasing substrate temperature. An ultraviolet emission and two visible emissions at 2.82 and2.37 eV are observed for photoluminescence spectra at room temperature. The resistivity of ZnO films increases with increasing substrate temperature due to surface morphology.