The aim of this work was to investigate the structural properties of (Zn,M)O layers obtained by diffusion of thin films (~ 1nm) of M (M = Mn or Co) into ZnO by annealing. The samples were characterised in-situ by scanning tunnelling microscopy (STM), Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and ex-situ by time of flight secondary ion mass spectroscopy (ToF-SIMS) and X-ray diffraction (XRD).
From the evolution of the intensity of M, Zn and O Auger lines upon annealing and thanks to modelling of the attenuation of Auger lines by matter we could estimate the diffusion depth of M into ZnO under various conditions. The results of the model were then compared to ToF-SIMS depth profiles.
In the case of Co/ZnO, annealing at a temperature higher than 945 K leads to the diffusion of Co into ZnO and to the substitution of Zn by Co. According to our results a ~3nm thick (Zn0,5Co0,5)O layer forms upon annealing. In addition ToF-SIMS depth profiles show that minute amount of Co may diffuse to a depth of 25 nm after prolonged annealing. Finally although surface reconstructions were observed by LEED, no binary phase could be evidenced by XRD.
In the case of Mn/ZnO, from 800 K, the substitution of Zn by Mn is observed and a thin ZnMnO layer forms. Diffusion of minute amount of Mn is observed 10 nm below the surface. In addition, LEED patterns show Moiré structures.
|Date of Award||2007|
|Supervisor||ROBERT SPORKEN (Supervisor)|