Reactivity, Electronic Structure and Geometry of Nonpolar Zincoxide Surfaces

ZnO(1010)/O 2 was chosen as a model system to study characteristic interaction mechanisms of reactive gases with surfaces of compound semiconductors. Reactions between 120 and 1000 K depend on thermodynamically controlled surface structures. – Reconstruction and point defects characterize the geometric and electronic structure of clean surfaces. – Reversible physisorption data car be determined at 120 ≤ T ≤ 250 K (coverages θ < 10 −10 for P < 10 −4 Pa) characterized by adsorption isotherms and isosteric heats of adsorption. – Chemisorption of O 2 is found in the range of 300 to 650 K (θ<2.5 · 10 −4 ) on crystals with negligible amount of point defeats at the surface. The energy of chemisorption and reaction rates can be described quantitatively by electron transfer models. – From crystal sublimation measurements at T > 700 K desorption rates for zinc and oxygen are derived. The latter depend strongly on the concentration of point defects (most probably oxygen vacancies) at the surface, which can be determined quantitatively as a function of pressure and temperature and may be removed during reactions at lower temperatures ( T < 700 K). Under these conditions a strong influence of oxygen vacancies on sticking coefficients and rates of electron transfer during oxygen exposure is found. – Investigations with various independent techniques (such as AES, LEED, EPR, thermal desorption spectroscopy, isotopic exchange as well as changes in the surface conductivity and work function) are shown to be necessary for a unique interpretation of experimental results. This enables the separation of chemisorption processes and reactions with point defects during oxygen interaction which is of importance to understand the elementary steps during oxidation catalysis on ZnO.