Initial Stages of Deposition-Concurrent Surface Segregation in Fe/Au Epitaxial Multilayers on GaAs(001)
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INITIAL STAGES OF DEPOSITION-CONCURRENT SURFACE SEGREGATION IN Fe/Au EPITAXIAL MULTILAYERS ON GaAs(001) KEN-ICHI SANO* AND TStUGIO MIYAGAWA* Research Institute for Metal Surfaces of High Performance Inc. (RIMES), c/o Technical Research Division, Kawasaki Steel Corporation, Chiba 260, Japan * On leave from Technical Research Division, Kawasaki Steel Corporation. ABSTRACT RHEED and AES studies showed deposition-concurrent surface segregation (DCSS) consists of two stages: an initial and a continuous segregation stage. The dominant terms of the enthalpies of DCSS were shown to be the difference between the surface energies of the film and the substrate material. INTRODUCTION Deposition-concurrent surface segregation (DCSS) is a term we use here for a phenomenon where a substrate material with a surface energy less than that of a film material segregates during deposition [1-3]. Recently, this phenomenon has been attracting the interest of researchers searching for a technique to control film growth mode by mediating the surface energy using a surfactant [4-10]. With the proper use of DCSS, the effective surface energy of a film can be reduced to change the growth mode from the island to the layer-by-layer type. It is natural that such usage requires a more thorough understanding of the phenomenon and its mechanism. In Ref. 1, we have discussed the fundamental characteristics of this phenomenon observed during the epitaxial growth of Fe/Au multilayers on GaAs(001) substrates, and have proposed a two stage mechanism for DCSS: an initial segregation stage and a continuous segregation stage. During the initial segregation stage, deposited atoms react with a substrate material to form an initial segregation layer. During the continuous segregation stage, the segregated atoms continuously keep their position atop the film surface without being buried under depositing atoms. In this paper, we have experimentally investigated the microscopic processes involved in the early phase of DCSS in Fe/Au multilayers grown on GaAs(001) substrates, using in situ observation techniques. The two stages of DCSS were individually examined from a thermodynamic view point based on the "macroscopic atom model" of Miedema et al. [11].
EXPERIMENTAL We used an ultrahigh vacuum (UHV)
deposition system equipped with re-
flection high energy electron diffraction (RHEED) and pWger electron spectroscopy (AES). The base pressure of the systenm9was 2x107 Torr, while the pressure during deposition was kept below 5x10 Torr. Both Fe and Au were evaporated using electron beam guns, the deposition rate monitored by crystal thickness meters being 0.02nm/s. The acceleration voltage of the RHEED beam was 20kV, with a typical angle of incidence of 0.750. The specular reflection intensity of RHEED was measured by a video system consisting of a charge coupled device (CCD) camera and a personal computer. Sputter etching with Ar ions was conducted at an acceleration voltage of 3kV. GaAs(001) substrates of 12.5x12.5x0.6mm were chemically etched in a 3H 2 0+H2 0 2
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