Abstract
Imaging micro-Raman spectroscopy is used to investigate the materials physics of radiation damage in congruent LiNbO3 as a result of high-energy (~MeV) He+ irradiation. This study uses a scanning confocal microscope for high-resolution three-dimensional micro-Raman imaging along with reflection optical microscopy (OM), and scanning electron microscopy (SEM). The tight optical excitation beam in the Raman system allows spatial mapping of the Raman spectra both laterally and normal to the irradiation axis with ≤1 μm resolution. Point defects and compositional changes after irradiation and surface deformation including blistering and microstress are observed in the stopping region. We demonstrate that the probed area of the damaged region is effectively “expanded” by a beveled geometry, formed through off-angle polishing of a crystal facet; this technique enables higher-resolution probing of the ion-induced changes in the Raman spectra and imaging of dislocation line defects that are otherwise inaccessible by conventional probing (depth and edge scan). Two-dimensional (2D) Raman imaging is also used to determine the defect uniformity across an irradiated sample and to examine the damage on a sample with patterned implantation. The effects of different He+ doses and energies, together with post-irradiation treatments such as annealing, are also discussed.
Highlights
Complex oxide crystals and epitaxial thin films, with their remarkable physical properties [1], are of interest both for studies in basic condensed matter physics and for advanced microdevices such as high-performance acoustic and photonic applications
Confocal micro-Raman spectroscopy can provide an alternate approach to probing energetic ion damage and material changes; it provides a direct approach for sampling over the set of crystal vibrational normal modes and is sensitive to crystallinity and composition
Our experiments presented below used micro-Raman spectroscopy following irradiation of crystalline LiNbO3 with ~MeV He+ ions to probe the location of structural and chemical changes
Summary
Complex oxide crystals and epitaxial thin films, with their remarkable physical properties [1], are of interest both for studies in basic condensed matter physics and for advanced microdevices such as high-performance acoustic and photonic applications. Damage due to high-energy-ion exposure can be analyzed using well-developed ionbeam-probing instrumentation This includes Rutherford backscattering spectrometry (RBS) [4], nuclear reaction analysis (NRA) [5], and particle induced X-ray emission (PIXE) [6]. Confocal micro-Raman spectroscopy can provide an alternate approach to probing energetic ion damage and material changes; it provides a direct approach for sampling over the set of crystal vibrational normal modes and is sensitive to crystallinity and composition. This technique is laboratory based and can be operated at ambient atmospheric conditions with different sample configurations. The utility of Raman scattering to optimize post-irradiation processes, such as annealing, is shown
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