Phase transformation and modifications in high-k ZrO2 nanocrystalline thin films by low energy Kr5+ ion beam irradiation

Abstract

In present communication, zirconium oxide (ZrO2) thin films of thickness (155 nm) were grown by using RF sputtering technique. To address and systematically understand the effects of low energy (800 keV) irradiation, high-k ZrO2 thin films were irradiated at room temperature by Kr ions with a range of fluence 1E15 to 1E17 ions. cm−2. The polymorphous zirconia pristine and irradiated thin films were characterized through X-ray diffraction (XRD) technique which confirms the coexistence of monoclinic and tetragonal phases. Monoclinic to tetragonal structural phase transformation was observed for Kr5+ ions irradiated samples at a fluence of 5E15, 1E16, 1E17 ions. cm−2. All samples were characterized by UV–Vis spectroscopy to study the mechanism of variation in optical energy band gap (4.42–4.52 eV), Urbach energy (402–449 meV) and refractive index (1.518–1.523) with increasing ion fluence. Photoluminescence (PL) spectroscopy was done at room temperature to record the significant PL broad prominent emission peaks at 350 nm and 430 nm and the peak intensity of these peaks significantly varies due to the annihilation of primary defects or generation of new defects centres by the influence of Kr ion irradiation. To determine the significant variation in grain size (50–85 nm) and RMS surface roughness (0.54–1.04 nm), pristine and irradiated sample were characterized by atomic force microscopy (AFM). A complete mechanism of the evolution of surface roughness was analyzed by determining the power spectral density (PSD). Further surface roughness component in the range of 0.4–1.7 was calculated using the slope of the tail of PSD. The FTIR spectra of pristine and low energy ion irradiated ZrO2 thin films were recorded in the range of 1250–3200 cm−1. The Rutherford backscattering spectrometry (RBS) was carried out in channeling condition and the experimental results were simulated to evaluate the elemental composition of Zr and O (⁓1:2) and film thickness (155 nm) of the samples. The changes of the chemical binding energy of ZrO2 thin films of Zr 3d and O 1s region before and after ion irradiation were investigated by x-ray photoelectron spectroscopy (XPS).