Optimisation of the synthesis of CuCrO₂ using molecular beam epitaxy

Abstract

Since the first discovery of delafossite oxides, numerous combinations of elements have been investigated for the unique properties found within these oxides. In particular, the Cu-based delafossites, of which CuCrO₂ is one, has shown the potential as a p-type transparent conducting oxide. Currently, only a few p-type transparent conducting oxides are commercially used due to the requirement of having a bandgap energy outside the range of visible light. Optical transparency can also be increased by reducing the overall thickness to the nanometre range limiting the amount of light attenuation. Through a combination of these two factors, thin film CuCrO₂, along with its doped varieties, is an ideal candidate for commercial applications. In this thesis, a method was developed for thin film synthesis using molecular beam epitaxy. Single phase, c-axis orientated thin films were synthesised on aluminium oxide (Al₂O₃) substrates. Through the exploration of growth parameters such as substrate temperature, oxidation source, flux ratios and growth modes, the optimal conditions required for epitaxial CuCrO₂ thin film growth were determined. In-situ measurements using reflective, high-energy electron diffraction (RHEED) allowed for visualisation of sample changes throughout the growth. Ex-situ measurements, using X-ray diffraction and atomic force microscopy (AFM), were used to determine sample composition and surface morphology, in an effort to determine the overall quality of samples produced. The changes in oxidation source, flux ratio, temperature and stoichiometric ratio parameters were investigated. In this work, growth conditions were identified for the creation of c-axis orientated thin films of CuCrO₂, without the requirements of additional steps, on aluminium oxide substrates.

Date of Award	30 Jun 2025
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Phil King (Supervisor)