OXYGEN-ADSORPTION PROCESS ON ZNO SINGLE-CRYSTAL

The adsorption of oxygen on ZnO was monitored by measuring the capacit ance of two contacting crystals which have depletion layers originated from the interaction between oxygen and ZnO at 298 K-473 K. An admiss ion of oxygen to the sample induced an irreversible increase in the de pth and the amount of adsorbed oxygen was less than 0.001 monolayer in the experimental condition. The relation between pressure of oxygen a nd variation of the depth was tested from the view point of Langmuir o r Freundlich isotherm: Using Hall effect measurement and kinetic exper iment, a model equation on the adsorption process was proposed. From t he results, it was suggested that oxygen adsorption depended on the ra te of electron transfer from ZnO to oxygen while the amount of adsorbe d oxygen was kinetically restricted by the height of surface potential barrier.