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摘要
The growth of platinum film on MgO(001) was analyzed in a combined experimental and theoretical study. Experiments were performed by grazing-incidence x-ray diffraction at small [grazing-incidence small-angle x-ray scattering (GISAXS)] and wide [grazing-incidence x-ray scattering (GIXS)] angles, and the theory coupled ab initio calculations on model Pt/MgO(001) systems and large-scale simulations of supported Pt clusters using a coordination-dependent interaction potential. GISAXS data showed that the cluster aspect ratio is constant at all studied temperatures with a tendency to faceting at 1000 K. The cluster spacing at the early stage of the growth is characteristic of a growth on defects, while the particle size obeys a d similar to t(0.5) power law assigned to dynamic coalescence. All Pt films deposited at 1000 K show the [100](001)(Pt)parallel to[100](001)(MgO) epitaxy. As the cluster size increases, the in-plane Pt-Pt distance increases above the bulk value (0.393 nm), passes through a maximum (0.398 nm) at a thickness of t=0.6 nm, and then relaxes back to the bulk value through interfacial dislocations, a behavior predicted by calculation and which appears typical of (001) epitaxy. Finally, the formation of dislocations arising from the Pt/MgO(001) mismatch of -6.83% is evidenced. Below 1000 K, due to a minimization of the surface energy of the film, the (111)(Pt)parallel to(001)(MgO) epitaxy dominates. Beside the expected [1(1) over bar 0](111)(Pt)parallel to[110](001)(MgO) orientation, another epitaxy is revealed, i.e., [1(1) over bar 0](111)(Pt)parallel to[100](001)(MgO). Moreover, families of orientations slightly rotated relative to the former epitaxy are evidenced. Calculations reveal that intermediate minima in energy appear at angles that depend on the size of the particles. Comparison between Ni/, Pd/, Pt/, and Ag/MgO(001) shows that the progressive weakening of the metal-MgO bonding in this order explains the decrease in adhesion energy as well as in metal-MgO distance, which are experimentally and/or theoretically observed through that series.
- 出版日期2007-8
- 单位中国地震局
