Size- and temperature-dependent epitaxy for a strong film-substrate mismatch: The case of Pt/MgO(001)
- Institut des NanoSciences de Paris, CNRS UMR 7588-Universites Pierre et Marie Curie (Paris 6) et Denis Diderot (Paris 7), Campus Boucicaut, 140 Rue de Lourmel, 75015 Paris (France)
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{approx}t{sup 0.5} power law assigned to dynamic coalescence. All Pt films deposited at 1000 K show the [100](001){sub Pt} parallel [100](001){sub 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){sub Pt} parallel (001){sub MgO} epitaxy dominates. Beside the expected [110](111){sub Pt} parallel [110](001){sub MgO} orientation, another epitaxy is revealed, i.e., [110](111){sub Pt} parallel [100](001){sub 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.
- OSTI ID:
- 21055131
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 76, Issue 7; Other Information: DOI: 10.1103/PhysRevB.76.075409; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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