Showing papers by "Harald Brune published in 1997"

Chapter 5 Heteroepitaxial metal growth: the effects of strain

Abstract: Keywords: Nucleation ; Aggregation ; Self-Assembly ; Epitaxial Growth Reference LNS-CHAPTER-1997-001 Record created on 2009-04-14, modified on 2017-05-12

Nucleation and Growth of Cu/Ni(100):. a Variable Temperature STM Study

Abstract: A detailed study of the nucleation and growth of Cu on Ni(100) as a function of substrate temperature and deposition rate by variable temperature STM is reported. By the quantitative analysis of the saturation island density as a function of temperature and flux for submonolayer coverages, we have deduced the migration barrier (0.35 eV), the dimer bond energy (0.46 eV) as well the sizes of the the critical nuclei. Because the dimer bond energy is large with respect to the migration barrier, a well-defined transition from a critical nucleus of 1 to 3 has been observed, as expected from the adsorption site geometry on square lattices. The large dimer bond energy of Cu on Ni(100) is one of the physical reasons for the recently uncovered strain relief mechanism via internal {111} faceting. The substantially increased island density on mono- and bilayer copper films on Ni(100) with respect to multilayer films might also be attributed to the enhanced lateral bonding.

Surface diffusion in metal epitaxy - Strain effects

Abstract: A method is presented to measure both the barriers for intra- and interlayer diffusion for an epitaxial system with great accuracy. It is based upon the application of mean-field nucleation theory to variable temperature STM data. The validity and limits of applying nucleation theory to extract barriers for terrace diffusion are discussed in comparison to alternative methods like Kinetic Monte-Carlo (KMC) simulations. With this approach, a pronounced influence of strain on intra- and interlayer diffusion was established for Ag self diffusion on strained and unstrained Ag(111) surfaces. The strained surface was the pseudomorphic Ag monolayer on Pt(111) which is under 4.3% compressive strain. The barrier for terrace diffusion is observed to be substantially lower on the strained, compared to the unstrained Ag/Ag(111) case, 60±10 meV and 97±10 meV, respectively. A general method for the quantitative determination of the additional barrier for descending at steps is presented. It is based on the measurement of the nucleation rate on top of previously prepared adlayer islands as a function of island size and temperature. Application of this method reveals a considerable effect of strain also on interlayer diffusion. The additional barrier for interlayer diffusion decreases from 120±15 meV for Ag(111) homoepitaxy to only 30±5 meV for diffusion from the strained Ag layer down to the Pt(111) substrate. These examples illustrate the strong influence of strain on the intra- and interlayer mass transport which leads to a new concept of layer-dependent nucleation kinetics for heteroepitaxial systems. Finally, we discuss the relation between corner diffusion and island shapes. Low temperature aggregation on hexagonally close-packed metal surfaces generally is dominated by the microscopic difference between two edge orientations giving rise to anisotropic corner (and edge) diffusion. It is demonstrated how this anisotropy gives rise to dendritic island shapes with trigonal symmetry.

Submonolayer Nucleation and Growth of Copper on Ni(100)

Abstract: Island densities and island sizes can be varied or even tailored by choice of external parameters in molecular beam epitaxy, i. e., by the choice of substrate temperature, deposition rate, and coverage. We present a comprehensive study of the nucleation kinetics of Cu on Ni(100) using variable temperature scanning tunneling microscopy. The analysis of the saturation island density as a function of substrate temperature and deposition rate reveals that the smallest stable island abruptly changes from a dimer to a tetramer. The sizes of the critical nuclei are determined from the rate dependence of the saturation island density using mean-field nucleation theory consistent with results from the island size distribution using scaling theory. From the Arrhenius-plot, the microscopic quantities (migration barrier and dimer bond energy) have been deduced.