Electron beam induced nanostructures and band gap tuning of ZnO thin films (original) (raw)
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Effects of laser irradiation on the structure and optical properties of ZnO thin films
The effects of laser irradiation on the surface microstructure and optical properties of ZnO films deposited on glass substrates were investigated experimentally and compared with those of thermal annealing. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements showed that the irradiation treatment with an Ar + laser of 514 nm for 5 min improves the crystalline quality of ZnO thin films through increasing the grain size and enhancing the c-axis orientation, with the effects similar to those of the thermal annealing at 500°C for 1 h. Laser irradiation was found to be more effective both for the relaxation of the residual compressive stress in the as-grown films and for the modification of the surface morphology. A significant increase in the UV absorption and a widening in the optical band-gap of the films were also observed after laser irradiation.
Ceramics International, 2018
In the present work, ZnO thin films were irradiated with 700 keV Au + ions at different fluence (1 × 10 13 , 1 × 10 14 , 2 × 10 14 , 5 × 10 14 ions/cm 2). The structural, morphological, optical and electrical properties of pristine and irradiated ZnO thin films were characterized by X-ray 2 diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), scanning electron microscope (SEM), spectroscopy ellipsometry (SE) and four point probe technique respectively. XRD results showed that the crystallite size decreased from pristine value at the fluence 1 × 10 13 ions/cm 2 , with further increase of ion fluence the crystallite size also increased due to which the crystallinity of thin films improved. SEM micrographs showed acicular structures appeared on the ZnO thin film surface at high fluence of 5 × 10 14 ions/cm 2. FTIR showed absorption band splitting due to the growth of ZnO nanostructures. The optical study revealed that the optical band gap of ZnO thin films changed from 3.08 eV (pristine) to 2.94 eV at the high fluence (5 × 10 14 ions/cm 2). The electrical resistivity of ZnO thin film decreases with increasing ion fluence. All the results can be attributed to localized heating effect by ions irradiation of thin films and well correlated with each other.
International Journal of Thin Films Science and Technology, 2014
Recently, nanocrystalline thin films with a uniform size and shape have shown interesting properties particularly nanocrystalline of metal oxides, due to its numerously important properties such as catalytic, electrical and optical properties [1, 2]. In materials science, ZnO is often called a II-VI semiconductor because zinc and oxygen belong to the 2nd and 6 th groups of the periodic table, respectively. This semiconductor has several favorable properties: good transparency, high electron mobility, wide band gap, strong room temperature luminescence, etc. Those
Effect of 8MeV Si ions irradiation and thermal annealing in ZnO thin films
Journal of Crystal Growth, 2012
ZnO thin films deposited by RF magnetron sputtering on silicon (100) wafers were irradiated by 8 MeV Si ions and thermal annealed in order to study optical properties. The presence of defects inside thin films as well as their implications was discussed by Photoluminescence and Spectroscopic Ellipsometry. Photoluminescence confirmed presence of energy states in forbidden band-gap associates with ultraviolet emission and Zn i , O i and O Zn defects according to the treatment received. Spectroscopic Ellipsometry using the Tauc-Lorentz model plus a Lorentz oscillator was found to be the best model to describe the properties of irradiated samples that did not receive a second thermal annealing treatment. Through this model, it was possible to obtain optical band-gap in the range of 3.1-3.3 eV and excellent approximation of position in energy of the oscillator.
Epitaxial ZnO thin films grown by pulsed electron beam deposition
Surface Science, 2010
In this work, the pulsed electron beam deposition method (PED) is evaluated by studying the properties of ZnO thin films grown on c-cut sapphire substrates. The film composition, structure and surface morphology were investigated by means of Rutherford backscattering spectrometry, X-ray diffraction and atomic force microscopy. Optical absorption, resistivity and Hall effect measurements were performed in order to obtain the optical and electronic properties of the ZnO films. By a fine tuning of the deposition conditions, smooth, dense, stoichiometric and textured hexagonal ZnO films were epitaxially grown on (0001) sapphire at 700°C with a 30°rotation of the ZnO basal plane with respect to the sapphire substrate. The average transmittance of the films reaches 90% in the visible range with an optical band gap of 3.28 eV. Electrical characterization reveals a high density of charge carrier of 3.4 × 10 19 cm −3 along with a mobility of 11.53 cm²/Vs. The electrical and optical properties are discussed and compared to ZnO thin films prepared by the similar and most well-known pulsed laser deposition method.
Characterization on pulsed laser deposited nanocrystalline ZnO thin films
Vacuum, 2010
Nanocrystalline zinc oxide thin films were deposited on glass and silicon substrates by using pulsed laser deposition at different laser energy densities (1.5, 2, and 3 J/cm 2 ). The film thickness, surface roughness, composition, optical and structural properties of the deposited films were studied using an a-step surface profilometer, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), optical transmittance, and X-ray diffraction (XRD), respectively. The film thickness was calculated as 244 nm. AFM analysis shows that the root-mean-square roughness increases with increasing laser energy density. XPS analysis shows that the interaction of zinc with oxygen atoms is greatly increased at high laser energy density. In the optical transmittance spectra, a shift of the absorption edge towards higher wavelength region confirms that the optical band gap increases with an increase in laser energy density. The particle size of the deposited films was measured by XRD, it is found to be in the range from 7.87 to 11.81 nm. It reveals that the particle size increases with an increase in laser energy density.
Nanostructure formation on zinc oxide film by ion bombardment
2006
Formation of regular nanostructures of zinc oxide (ZnO) by bombardment of 15keV Ar+ ions on 400nm thick ZnO film deposited on Si〈 100〉 is accomplished. Roughness of the bombarded films was reduced and bigger structures disintegrated into smaller ones. This reduction in roughness and grain size has been attributed to the elastic collisions induced rearrangement of surface atoms along with sputtering from the surface.
Influence of annealing on optical properties and surface structure of ZnO thin films
Journal of Crystal Growth, 2006
Thermal annealing effects on optical properties and surface structure of zinc oxide (ZnO) thin films prepared by filtered cathodic vacuum arc technique were investigated by spectroscopic ellipsometry (SE) and atomic force microscopy (AFM). In the SE study, Cauchy model was used to extract the optical constants of ZnO thin films for photon energies below the band gap while point-by-point fitting was used to determine the optical constants of the films for photon energies above the band gap. The influence of annealing on the optical properties, in the photon energy ranging from 1.1 to 5 eV, has been demonstrated. It was found that the values of the refractive index, the reflectance and the real part of the complex dielectric function decrease with increasing annealing time. On the other hand, tapping mode AFM was used to study the surface structure and topography of ZnO thin films. AFM study revealed that annealing roughened the surface of the films and increased the size of grains on the surface. It was observed that the changes in the optical properties were correlated to the changes in the surface structure as a result of annealing.
Journal of Luminescence, 2018
In this article we have explored an effect of electron beam irradiation (EBI) on physical and nonlinear optical properties ZnO thin nano films. Nanostructured ZnO thin films were grown by low cost spray pyrolysis technique. The irradiation dosage has been fixed at 5kGy, 10kGY, 15kGy and 20kGy. The structural investigation by Glancing angle X-Ray Diffractometer (GAXRD) confirms a polycrystalline phase of ZnO with wurtzite structure. The variation in the surface morphology upon EBI has been demonstrated using 2D and 3D Atomic force microscopy (AFM) images. Nanoscope software analysis quantifies the variation in surface roughness and average particle height upon EBI. The defect states created in the films upon irradiation experiments were investigated using UV-visible spectrophotometer, Room temperature Photoluminescence (RTPL), Raman and X-ray photoelectron spectroscopy (XPS). The increase in urbach tail validates the creation of localized defect states in the films The Gaussian fitting on RTPL spectra shows the quenching in the luminescent centers upon irradiation arised as result of recombination of vacancy defects. Phonon confinement model fitting on Raman spectra endorses that shift in the phonon modes observed on irradiation is due to spatial confinement of phonons. The elemental composition and impurity states of the EBI ZnO thin films were studied using XPS spectra. The shift in the binding energy of Zn and O elements infers the electron beam induced changes in the films. The electron beam irradiation has resulted in the increment of third order optical susceptibility χ(3) 3.5×10-4 esu to 8.13×10-3 esu due to the enhancement of electronic transition to different defect levels formed in the films and through local heating effects arising due to continuous wave (CW) laser illumination. The enhanced THG signal investigated using Nd:YAG laser at 1064nm and 8 ns pulse width shows the promising features of EBI ZnO films for frequency tripling applications.