The structural and chemical properties of Co growth on ZnO (10-10) surface

• Main Authors: Shu HsuanSu, 蘇書玄
• Other Authors: J.C.A Huang
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/97252519368965848970

博士 === 國立成功大學 === 物理學系碩博士班 === 101 === This study elucidates the epitaxial growth structure and chemical state of Co on ZnO (10-10) surface by using scanning tunneling microscopy (STM), reflection high-energy electron diffraction (RHEED), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS). In the growth behavior, the well-ordered cobalt oxide (CoOx) (2×1) structure is formed at 0.5 ML Co coverage. Increasing the Co coverage from 0.7 ML to 1 ML allows for the surface characterization by Co stripe structure, while the Co metallic clusters are clearly developed above 3 ML Co coverage. Coverage-dependent measurements of the Co chemical state indicate that the initial Co mixed oxidation and metallic state at submonolayer and gradually transfers to a metallic Co dominated state. The results also suggest that initial growth mode is two dimensional (2D) like and bridged to three dimensional (3D) at higher Co coverages. Furthermore, the nucleation and sintering characteristics of Co on ZnO (10-10) during annealing were investigated. The extent of coverage and annealing temperature were varied to modify the size of the Co nanoclusters. The Ostwald ripening process induces the observed sintering behavior of Co adatoms, which depend on the Co coverage. Temperature-dependent X-ray photoemission spectra of the Co chemical state reveal that metallic Co dominates the annealing procedure on ZnO (10-10), and is more thermally stable than Co on both ZnO (0001) and ZnO (000-1). The effects of annealing time and the distribution of Co adatoms were elucidated by STM. Therefore, the results have potential implications for the thermal stability of Co/ZnO (10-10) in real catalytic processes.