Is crystalline ZnO(000 (1) over bar) O-face surface believed to be enriched by Zn atoms? This study may get the answer. We proposed a simplified model to simulate surface concentration ratio on (000 (1) over bar)-O or (0001)-Zn surface based on the hard-sphere model. The simulation ratio was performed by integrating electron signals from the assumed Auger emission, in which the electron mean free path and relative atomic layer arrangements inside the different polarity ZnO crystal surface were considered as relevant parameters. After counting more than 100 experimental observations of Zn/O ratios, the high frequency peak ratio was found at around 0.428, which was near the value predicted by the proposed model using the IMFP database. The ratio larger than the peak value corresponds to that observed in the annealed samples. A downward trend of the ratio evaluated on the post-sputtering sample indicates the possibility of a Zn-enriched phase appearing on the annealed O-face surface. This phenomenon can further elucidate the O-deficiency debate on most ZnO materials. (C) 2012 Elsevier B. V. All rights reserved.