Abstract
Unbiased Monte Carlo procedures are applied to investigate the structure of Cu clusters of various sizes deposited over reconstructed polar ZnO surfaces.
Highlights
This argument is entirely consistent with the observed patterns of Cu cluster growth on the Znterminated surface obtained from the global optimisation studies performed in the present work; for both the O-adatom and Zn-vacancy reconstructions, planar Cu growth does occur for smaller numbers of Cu atoms, and as can be seen for the larger Cu8, Cu2 and Cu50 systems, 3D Cu cluster growth does take place instead of continued planar cluster growth once the Cu cluster meets the boundaries imposed by the undercoordinated surface O atoms
The interatomic potentials used in the present work have already been demonstrated to be highly successful in obtaining low-energy structures for Cu clusters adsorbed on the non-polar ZnO surface, and are an effective means of screening potential structures in a computationally expedient manner
The reconstructed polar ZnO surface explored in the present work shows surface features that consist of undercoordinated Zn and O atoms that deviate considerably from typical surface and bulk Zn and O coordination environments present in the non-polar ZnO surface that was used as a model for tting the Cu–ZnO potentials
Summary
Cu/ZnO-based catalysts have long been used for a variety of industrially and environmentally important processes, including methanol synthesis,[1,2,3,4,5,6,7,8,9,10] methanol steam reforming,[11,12] and the water-gas shi reaction;[13,14] yet despite the extensive use of these catalysts, much remains to be fully understood in terms of the role of ZnO in facilitating catalytic activity and the effect of ZnO surface structure in determining Cu cluster growth. The dominant facets of wurzite ZnO are the non-polar (1010) and (1120) surfaces, and the polar (0001) and (0001) facets; clearly, the different surface structures presented. STM studies reported that different Cu cluster growth behaviours were observed for the Zn- and O-terminated surfaces.[19,20] Three-dimensional Cu cluster growth and surface pits with O-terminated edges, which have been suggested to act as Cu nucleation sites, were observed on the Zn-terminated surface.[20] In contrast, for the O-terminated surface, 2-D Cu clusters were observed, a more detailed analysis was limited by the limitations of the STM on O-teminated surfaces..
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