Electronic excitation induced modifications in surface morphological, optical and physico-chemical properties of ALD grown nanocrystalline Al_2O_3 thin films

摘要

In this present communication, we report the possible outcomes on the investigation of structural, optical and morphological properties of unirradiated and swift heavy ions irradiated Al_2O_3 thin films (120 nm) grown on silicon and glass substrate using atomic layer deposition (ALD) technique. Al_2O_3 thin films were irradiated using 120 MeV S~(9+) swift heavy ions (SHI) with a range of fluence 5E11 to 1 E13 ion/cm~2. The surface characteristics and increase in grain size (38-45 run) in relation to pre and post high energy ions irradiation were examined by atomic force microscope (AFM). A quantitative detailed analysis of surface roughness along with vertical and lateral directions and surface morphology is provided by power spectral density (PSD). Moreover, the crystallite size (12-49 nm) of the unirradiated and irradiated samples was determined using the Debye Scherrer's method. It was observed that δ-Al_2O_3 tetragonal phase vanished after SHI irradiation. For a better understanding of the influence of high energy ion irradiation on structural properties, various parameters such as stress, strain, dislocation density and preferred orientation to be textured along the (953) plane using texture coefficient were determined by X-Ray Diffraction (XRD). The absorption coefficient was used to determine the variation in optical band gap (E_g) and Urbach energy (E_u) with the range of ion fluence. Photoluminescence (PL) spectroscopy at room temperature was carried out to understand the mechanism of significant variation in intensity and peak shifting of strong and broad photoluminescence emission spectra recorded at 250 nm and 240 nm excitation wavelengths. Further, the survey spectrum and chemical binding energy (B.E) of Al 2p and O 1s core levels at 74.2 eV and 553.45 eV in aluminium oxide unirradiated and irradiated thin films were provided by X-ray photoelectron spectroscopy (XPS) analysis. To estimate the quantitative elemental composition (2∶3), the crystalline quality of the samples and thickness (120 nm), Rutherford Backscattering Spectrom-etry (RBS) spectra were recorded using the backscattering of high energy He~(2+) ions.