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Abstract:
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Transition metal oxides (TMOs ) exhibit a rich collection of interesting and intriguing properties which can be used for wide variety of applications . In this dissertation , I will discuss the first PAES measurements on vacuum anneal induced changes in the surface layers of Cu2O / Ta , Cu2O /TCO and oxidized Cu (100 ) prepared by spray coated , electrochemically deposition and thermal oxidation techniques respectively . PAES measurements on Cu <sub >2 < /sub >O /TCO shows that the a very large increase in the intensity of the Cu (M <sub >2 ,3 < /sub >VV ) Auger peak after annealing at 250 <sup >0 < /sup >C . Similar but significantly smaller changes were observed in the EAES spectra consistent with the fact that PAES is primarily sensitive to the top -most atomic layer due to the fact that the positrons are trapped just outside the surface prior to annihilation while EAES samples several atomic layers . While PAES measurements on oxidized Cu (100 ) show a large monotonic increase in the intensity of the annihilation induced Cu (M <sub >2 ,3 < /sub >VV ) Auger peak as the sample is subjected to a series of isochronal anneals in vacuum up to annealing temperature 300 <sup >0 < /sup >C . The intensity then decreases monotonically as the annealing temperature is increase to ~600 <sup >0 < /sup >C . These results provide a clear demonstration of the thermal reduction of the copper oxide surface after annealing at 300 <sup >0 < /sup >C followed by re -oxidation of the copper surface at the higher annealing temperatures presumably due to the diffusion of subsurface oxygen to the surface . |