Leake, S.J.; (2010) Coherent X-ray di�ffraction imaging of zinc oxide crystals. Doctoral thesis , UCL (University College London).

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Abstract

Zinc Oxide (ZnO) exhibits a plethora of physical properties potentially advantageous in many roles and is why it one of the most studied semiconductor compounds. When doped or in its intrinsic state ZnO demonstrates a multitude of electronic, optical and magnetic properties in a large variety of manufacturable morphologies. Thus it is inherently important to understand why these properties arise and the impact potentially invasive sample preparation methods have for both the function and durability of the material and its devices. Coherent X-ray Diff�raction Imaging (CXDI) is a recently established non-destructive technique which can probe the whole three dimensional structure of small crystalline materials and has the potential for sub angstrom strain resolution. The iterative methods employed to overcome the `phase problem' are described fully. CXDI studies of wurtzite ZnO crystals in the rod morphology with high aspect ratio are presented. ZnO rods synthesised via Chemical Vapour Transport Deposition were studied in post growth state and during in-situ modifi�cation via metal evaporation processing and annealing. Small variations in post growth state were observed, the physical origin of which remains unidentifi�ed. The doping of a ZnO crystal with Iron, Nickel and Cobalt by thermal evaporation and subsequent annealing was studied. The evolution of diff�using ions into the crystal lattice from was not observed, decomposition was found to be the dominant process. Improvements in experimental technique allowed multiple Bragg reflections from a single ZnO crystal to be measured for the fi�rst time. Large aspect ratio ZnO rods were used to probe the coherence properties of the incident beam. The longitudinal coherence function of the illuminating radiation was mapped using the visibility of the interference pattern at each bragg reflection and an accurate estimate of the longitudinal coherence length obtained, \xi(L) = 0.66\pm 0.02 \mu m. The consequences for data analysis are discussed. The combination of multiple Bragg reflections to realise three dimensional displacement �fields was also approached.

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