Analysis of Crystalline Quality and Ion Beam-Induced Damage Recovery in Epitaxially Grown Rare Earth Oxide Thin Films via Rutherford Backscattering Spectrometry and Ion Channeling

Rare earth functional oxide (REFO) materials, such as CeO₂, are employed in a diverse range of applications today, including catalysis, gas sensing, photovoltaics, capacitors, and silicon-on-insulator (SOI) structures. Recently, their importance as quantum host has been highlighted due to the anticipated long coherence times in this system due to the lack of any nuclear interference. There are various methods for epitaxial growth of high quality REFO thin films such as molecular beam epitaxy (MBE) and pulsed laser deposition (PLD). However, to use these films effectively, precise knowledge of their composition and stoichiometry is essential. Rutherford Backscattering Spectrometry (RBS) provides a valuable non-destructive method for examining the elemental depth profile, diffusion of species in heterostructures, and estimating the stoichiometry of the films. For applications in quantum computing platforms, it is crucial that the deposited films are highly crystalline and epitaxial with the substrate. Thus, identifying the nature and inherent defects, whether interstitial or substitutional, is vital. This can be achieved through ion channeling via RBS (RBS/C), which involves directing a beam of incident probing ions (typically 1-3 MeV He⁺) at a crystalline sample along specific crystallographic directions to quantitatively analyze substitutional and interstitial add-atoms.<br/>In this study, we have investigated the elemental composition and lattice match of CeO₂, Tm_xCe_1-xO₂, and Tb_xCe_1-xO₂ films deposited via pulsed laser deposition (PLD) at various growth conditions on Si (111), and YSZ (100) substrates. Based on the observed RBS/C results, the films were more lattice-matched when deposited on YSZ (100) substrates as compared to Si (111). The best results were for Tm_0.1Ce_0.9O₂/YSZ (100) which showed the minimum backscattering yield (Χ_min) as 16.67%, 22.59%, and 16.21% for Ce, Tm, and YSZ, respectively, indicating a good match between Ce and YSZ lattice. The slightly higher Χ_min value for Tm may be due to the overlap between the surface peak of Ce and Tm. In the latter part of this study, we will assess the feasibility of ion irradiation and its role in ionization energy loss (IEL) induced damage recovery in annealing the pre-existing defects in the PLD deposited film to improve its lattice match with the substrate. The results from this study aim to provide insights into the structural characterization of thin films with higher accuracy. Additionally, the novel use of ion irradiation to induce damage recovery in epitaxial films will open a new path for researchers to utilize IEL damage recovery across a wide range of materials and applications. We will also explore ion channeling to measure damage regrowth subsequent to anneals to measure solid phase regrowth in these crystalline oxide systems.<br/><br/><i>Keywords: </i>Rutherford backscattering spectrometry (RBS), ion channeling, rare earth oxides, ionization energy loss (IEL), epitaxial growth