Island growth kinetics during vapor deposition of Cu onto the Zn-terminated ZnO(0001) surface

Abstract

During the vapor deposition of Cu onto the Zn-terminated ZnO(0001) surface, it has previously been observed that at room temperature and below, the Cu grows first as two-dimensional islands up to a certain critical coverage ( θ 1,cr) near 0.3 monolayers. As the Cu coverage increases above θ 1,cr, these islands thicken into three-dimensional particles but the clean ZnO spaces between the Cu particles fill only very slowly. This occurs due to a kinetic limitation, since the islands thermodynamically prefer to be thicker and larger. Here, the dependencies of the critical coverage upon the substrate temperature and Cu vapor flux are measured. No significant change in critical coverage is seen when the flux is varied by ∼30-fold, but it decreases weakly with temperature. These trends are discussed within a kinetic model which incorporates the various Cu adatom migration and island nucleation steps.