Center for Functional Nanomaterials Seminar

Abstract
Zinc oxide is a one of the most investigated binary metal oxide system, sharing applications in optoelectronic devices, gas sensors and heterogeneous catalysts, e.g. for methanol synthesis.1,2 The great interested on its electrical and optical properties such as near-band-edge photoluminescence, work function, photoconductivity, and Schottky contact barrier height is mostly related to its crystallographic structure and resulting surface polarity.3 These properties are linked to its crystal wurtzite structure, where Zn and O atomic planes are intercalated, which results on a non-zero electric dipole. The surface preparation conditions results on different surface terminations hence surface electronic structure and later on its unique chemical properties. These properties changes are partially associated to polarity compensation mechanisms and are expected to influence the distribution of free carriers and also affect the near-surface band bending. In previous studies we have systematically investigated the luminescence of well-characterized ZnO(0001) thin films by means of Scanning Tunneling Microscopy and Spectroscopy combined to Cathodo-luminescence, however, electron spectroscopy of such well-defined system remains hardly explored.4 In this talk, we will discuss these findings and correlate them with recent Ultraviolet Photoelectron Spectroscopy experiments.


[1] Wöll, C., The Chemistry and Physics of Zinc Oxide Surfaces, Prog. Surf. Sci. 2007, 82, 55-120.
[2] Dulub, O.; Boatner, L. A.; Diebold, U., STM study of the geometric and electronic structure of
ZnO(0001)-Zn, (000-1)-O, (10-10), and (11-20) surfaces, Surf. Sci. 2002, 519, 201-217.
[3] H. Moormann,; D. Kohl,; G. Heiland, Work function and band bending on clean cleaved zinc oxide
surfaces, Surf. Sci. 80, 261 (1979).
[4] F. Stavale, L. Pascua, N. Nilius, H-J. Freund, Morphology and Luminescence of ZnO Films Grown
on an Au(111) Support. Journal of Physical Chemistry. C, 117, 1055