Morphological effects induced by the formation of a Pt-adatom lattice gas on Pt(111) (original) (raw)
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Thermal stability of ultrathin Pt layers deposited onto TiO 2 (1 1 0)-(1 Â n) surface was studied by scanning tunneling microscopy in the temperature range of 300-1200 K. Besides the formation of 3D particles and the gradual sintering of the initial clusters, a unique morphological feature-one monolayer (ML) deep vacancy-islands (pits)-developed as a result of annealing above 1000 K. This appeared on the atomic terraces of the substrate covered by Pt of a few percent monolayer. The edge of these pits were typically decorated by Pt nanoparticles grown during the annealing procedure, showing that the bonding between the admetal and the substrate is the strongest at these sites. The formation of the vacancy-islands can be explained by the decoration process activated by the thermal treatment above 500 K. Depending on the Pt coverage, two types of morphological states can be distinguished: (1) at very low coverages (<0.05 ML) one pit contains one Pt nanoparticle; (2) in the case of higher coverages (>0.15 ML) few Pt nanoparticles are localized in a particular vacancy-island of round shape, typically at the perimeter of the pit.
Low-Temperature Homoepitaxial Growth of PT(111) in Simulated Vapor-Deposition
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By different annealing procedures the (1 x2) and the (1 x4) structures on Pt(ll0) are produced on the clean surface. Both structures are verified by STM and LEED. AES shows very low impurity levels of C, O, S, Si and Ca in both cases. In case of the (1 x4) structure, Si and/or SiOx signals are not significantly higher than in case of the (1 x2) structure. The (1 x 2) structure is combined with a perfect "fish-scale" pattern of the step structure. The (1 x 4) structure is connected with large fiat terraces bound by steep ledges of a height of 30-40 A,. The (1 x 4) structure is identified as a paired-row (1 x 2) structure.
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At temperatures around 373 K, Ru growth on Pt(1 1 1) proceeds via nucleation and growth of bilayer islands [H.E. Hoster et al., Phys. Chem. Chem. Phys. 3 (2001) 337]. The influence of the deposition temperature on the Ru growth behavior on Pt(1 1 1) was studied by scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES) in the temperature range between 303 and 773 K. The data reveal a distinct change in the growth characteristics, most important the change from the growth of bilayer Ru islands to monolayer islands, at temperatures between 523 and 573 K. Based on AES data and on atomic resolution STM images, these changes are associated with the onset and increasing contribution of surface alloy formation via Pt-Ru exchange and, at T > 673 K, alloy formation in near surface regions. Consequences of these data for the mechanism of bilayer growth and the underlying physical origin are discussed.
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Simulations of Homoepitaxial Growth of PT(111): Island Shapes and the Growth Mode
APS, 1997
Experimental observations of homoepitaxial growth of Pt(111) have shown a surprising richness of transitions in the island shape and the growth mode as functions of temperature. We present a set of kinetic Monte Carlo simulations capable of reproducing the various observed dendritic and compact island shapes, and the unexpected transition to reentrant layer by layer growth. The simulations are based on the available experimental information, and Effective Medium Theory energy barrier calculations. The variations in island shape are explained in terms of the mobility and stability of adatoms and rows of atoms attached to the island edges, and the transition to reentrant layer-by-layer growth is found to be caused by a transition in the island shape.
On the origin of Ru bilayer island growth on Pt(111)
Vacuum, 2009
Depending on the growth temperature, Ru growth on Pt(111) proceeds preferentially via nucleation and growth of bilayer islands [Hoster HE, Iwasita T, Baumgä rtner H, Vielstich W. Phys Chem Chem Phys 2001;3:337]. The physical origin for this growth behaviour was investigated by scanning tunnelling microscopy. The role of the lattice mismatch is elucidated by comparing Ru growth on Pt(111) with that on a pseudomorphic Pt monolayer film on an Ru(0001) substrate, where lattice misfit is absent. The results are interpreted using existing concepts on the adsorption properties of bimetallic surfaces, the consequences of our results and our mechanistic interpretation on the understanding of bilayer island growth in metal-on-metal epitaxy in general are discussed.
Growth of FeOx on Pt(111) studied by scanning tunneling microscopy
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1994
We have studied the growth of iron oxide films on Pt(11l) using scanning tunneling microscopy. The system has been found to depend sensitively on the temperature and oxygen pressure used to form the oxide. As the coverage is varied from below a monolayer to multi layers of approximately four or five lavers thick, three different ordered structures are observed as well as regimes in which the iron oxide" appears disordered. For coverages ~ I ML, the iron oxide is FeO and a large lattice mismatch between the iron oxide and platinum governs the growth process. The first ordered structure occurs at a monolayer coverage and has a large unit cell where ~'8 lattice spacings of the FeO fit ~-9 of the Pt(11l) surface. At higher coverages, ~3 X ,;3R30° and 2X2 [w. Weiss, A. Barbieri, M. A. Van Hove, and G. A. Somorjai, Phys. Rev. Lett. 71, 1884 (1993)] ordered structures are observed. These can be ascribed to a-Fe203 and Fe304 phases respectively which are the equilibrium phases for thc oxygen pressures and temperatures used in growing the iron oxide. A disordered multilayer growth is also observed.