Doctor of Philosophy
Dr. Lyudmila Goncharova
The unique behaviour of thin films, and their surfaces and interfaces, significantly impact material and device properties. Probing these structures with ion beams (IB) provides quantitative composition and thicknesses measurements. In this dissertation, the IB techniques of medium energy ion scattering (MEIS), nuclear reaction profiling (NRP) and Rutherford backscattering spectrometry (RBS) are used to analyze energy losses in ultra-thin films, as well as elucidate the mechanisms of anodic film growth.
Accurate stopping cross sections of protons, ε, in the medium energy range (50-170 kV) often show deviations from Bragg’s rule. Here, εTi, εSi, and εTiO2, where derived from MEIS spectra. Thickness and composition of Ti, Si, and TiO2 films were determined using RBS, MEIS, and X-ray photoelectron spectroscopy. εTiO2 are systematically lower (≈14%) and the stopping maximum occurs at higher energies, compared to SRIM2013. Our experimental εTi and εTiO2 values allowed estimates of εO, which better predict the stopping maximum of previously reported εSrTiO3. This suggests that the effect of different electronic environments on the ε of O should not be neglected when applied to metal oxides.
Depth-profiling with MEIS and NRP, and 16O/18O isotopic labeling, can elucidate anodization growth models. Thin Ti films on Si(001) were exposed to H218O, and anodized in D216O potentostatically. Adonization at 0 - 10 V results in a bi-layer structure: Ti16O2/Ti18O2/Ti. The Ti16O2 region is on the oxide surface and the Ti18O2 region at the oxide/metal interface (composed of the original 18O atoms). The O depth profiles are consistent with the point defect model (PDM), in which anodic oxide growth is due to ionic transport via the continual generation and annihilation of point defects in the oxide.
A new in situ electrochemical cell was designed, constructed, and used to collect RBS data under potentiostatic control. Features of Ti anodization were observed by in situ RBS, for Ti thin films sputter-deposited onto 100 nm thick SiN windows. The evolution of the elemental depth profiles for Ti and O spectra were consistent with the PDM, while Cl incorporation, likely happens during the formation of oxide monolayers from Ti4+ precipitation. Compositional differences between in situ and ex situ measurements are emphasised.
Brocklebank, Mitchell A., "High Resolution Ion Beam Investigations of the Mechanisms of Titanium Anodization" (2018). Electronic Thesis and Dissertation Repository. 5768.