Ion-beam-induced epitaxial crystallization and amorphization in silicon

Disorder-Induced Ordering in Gallium Oxide Polymorphs

Polymorphs are common in nature and can be stabilized by applying external pressure in materials. The pressure and strain can also be induced by the gradually accumulated radiation disorder. However, in semiconductors, the radiation disorder accumulation typically results in the amorphization instead of engaging polymorphism. By studying these phenomena in gallium oxide we found that the amorphization may be prominently suppressed by the monoclinic to orthorhombic phase transition. Utilizing this discovery, a highly oriented single-phase orthorhombic film on the top of the monoclinic gallium oxide substrate was fabricated. Exploring this system, a novel mode of the lateral polymorphic regrowth, not previously observed in solids, was detected. In combination, these data envisage a new direction of research on polymorphs in Ga_{2}O_{3} and, potentially, for similar polymorphic families in other materials.

Extension of hydrophilicity stability by reactive plasma treatment and wet storage on TiO2 nanotube surfaces for biomedical implant applications

Micro and nanoscale changes allow the optimization of physico-chemical properties of titanium implant surfaces. Recently UV and plasma treatments have allowed surface hydrophilicity to take increased prominence; however, this beneficial effect is short-lived. The aim of this study is to investigate methodologies post-anodizing treatment to generate and maintain high surface hydrophilicity along with high biocompatibility. Anodized surfaces were characterized regarding physical-chemical properties. Then, surface wettability with nanomorphology was evaluated at different times and with distinct post-treatments: as deposited, with a reactive plasma and UV-light post-treatment, stored in air or deionized (DI) water. Adhesion, alkaline phosphatase (ALP) activity and bone cell viability tests were executed after the incremental treatments. The anodizing process generated a surface with TiO2 nanotubes morphology and micro-roughness. Plasma-treated surfaces resulted in the most hydrophilic samples and this property was maintained for a longer period when those were stored in DI water (angle variation of 7° to 12° in 21 days). Furthermore, plasma post-treatment changed the titanium surface crystalline phase from amorphous to anatase. Anodized surfaces modified by reactive plasma and stored in DI water suggest better hydrophilicity stability, biocompatibility, ALP activity and achievement of crystalline phase alteration, indicating future potential use on biomedical implants.

Ion-Beam-Induced Atomic Mixing in Ge, Si, and SiGe, Studied by Means of Isotope Multilayer Structures

Crystalline and preamorphized isotope multilayers are utilized to investigate the dependence of ion beam mixing in silicon (Si), germanium (Ge), and silicon germanium (SiGe) on the atomic structure of the sample, temperature, ion flux, and electrical doping by the implanted ions. The magnitude of mixing is determined by secondary ion mass spectrometry. Rutherford backscattering spectrometry in channeling geometry, Raman spectroscopy, and transmission electron microscopy provide information about the structural state after ion irradiation. Different temperature regimes with characteristic mixing properties are identified. A disparity in atomic mixing of Si and Ge becomes evident while SiGe shows an intermediate behavior. Overall, atomic mixing increases with temperature, and it is stronger in the amorphous than in the crystalline state. Ion-beam-induced mixing in Ge shows no dependence on doping by the implanted ions. In contrast, a doping effect is found in Si at higher temperature. Molecular dynamics simulations clearly show that ion beam mixing in Ge is mainly determined by the thermal spike mechanism. In the case of Si thermal spike, mixing prevails at low temperature whereas ion beam-induced enhanced self-diffusion dominates the atomic mixing at high temperature. The latter process is attributed to highly mobile Si di-interstitials formed under irradiation and during damage annealing.

Electron beam induced epitaxial crystallization in a conducting and insulating a-LaAlO3/SrTiO3system

We report the effect of the interfacial conductivity on the e-beam-induced crystallization of an oxide a-LaAlO₃thin film on the SrTiO₃substrate and the kinetics can be controlled by the electrical conductivity of the interface and the dose rate.