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FZJ-2019-00617

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Untersuchungen zum heteroepitaktischen Wachstum im Submonolagenbereich mittels Streuung thermischer Heliumatome

Krzyzowski, M. A. (Corresponding author)FZJ*

1995
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/21352

Report No.: Juel-3077

Abstract: Heteroepitaxial growth of thin metal films on metal surfaces has been analyzed in the submonolayer regime by thermal helium atom scattering (TEAS). Experiments have been performed on two different substrates: the non-reconstructed Pt(111) surface and the Au(111) surface which exhibits a long-range (~ 22 x $\sqrt{3}$)-reconstruction. Ag was deposited on the Pt substrate and Co on the Au substrate. Based on the analysis of the growth of Ag on Pt(111) it is found that below T = 45K the monomer is the stable nucleus. At these low temperatures small islands are formed with mean size and separation depending on the deposition rate and temperature. It is shown that these structures are not thermally stable and that their arrangement is governed by kinetic processes. Upon increasing the deposition temperature the size of the critical nucleus increases and the growth mode changes from a three dimensional growth to a layer-by-layer growth based on a "step flow" mechanism. At all temperatures the growth of the first Ag layer is pseudomorphic (i. e. with the same lattice parameter and orientation as the Pt(111) substrate). Surprisingly, at a deposition temperature of about T = 600 K, however, submonolayer deposition of Ag again leads to the formation of small islands with an initial diameter of about 10 $\mathring{A}$. Furthermore, these islands are arranged in a rather regular pattern. The size as well as the separation of the islands depends neither on the deposition rate nor on the deposition temperature. To generate this structure the Pt(111) surface covered with submonolayer amounts of Ag only has to be heated once above a critical temperature of about T = 600 K. It is demonstrated that these quasi-regularly arranged islands represent the thermal equilibrium configuration. For this phase two distinct structural phase transitions are observed: (i) Upon increasing the Ag coverage the structure of the Ag islands changes from a two-dimensional array of compact islands (disk phase) with an average separation of about 30 $\mathring{A}$ at $\Theta$ = 0.2 ML to a one-dimensional "striped" pattern at coverages around $\Theta$ = 0.5 ML with approximately the same average distance of $\approx$ 30 $\mathring{A}$ but no preferential orientation of the stripes. (ii) An order-/ disorder-transition with a critical temperature of about T$_{c}$ = 620 K. At low coverage (disk phase) the regular arrangement of the islands is destroyed whereas at higher coverage (stripe phase) the one-dimensional structure startsto meander and to disintegrate into smaller clusters. The existence of disk and stripe phases as well as the observed transitions can be understood within a simple model based on elastic interactions (originating from the lattice mismatch of the Ag adlayer and the Pt(111) substrate). A main result of this model is that the ratio between the initial size of an island and the minimum separation between islands (i. e. the minimum periodicity of the pattern) is 1/3 and that this ratio does not depend on the symmetry of the pattern (stripes vs. disks). This result is corroborated by the present experiments. A comparison of the structure with a regular arrangement of Ag islands obtained after [...]

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1. Publikationen vor 2000 (PRE-2000)

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1. 899 - ohne Topic (POF3-899) (POF3-899)

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