Surface structure and metal epitaxy: Ag/Cu(111)
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Surface structure and metal epitaxy: Ag/Cu(111) Kenji Umezawa1, Shigemitsu Nakanishi1, and Walter M. Gibson2 Department of Materials Sciences, Osaka Prefecture University, 1-1 Gakuen-Cho, Sakai, Osaka 599-8531, Japan 2 Department of Physics, The University at Albany, SUNY, 1400 Washington Avenue, Albany, NY 12222, U.S.A. 1
ABSTRACT We have investigated the growth of 3 ML (mono-layer) of Ag on Cu(111) for substrate temperatures from 170 through 640 K by using time of flight-impact collision ion scattering spectroscopy (TOF-ICISS). Two different types of epitaxial growth exist: Ag [112] //Cu [112] (type-n) and Ag [112] //Cu [112] (type-r). The growth modes of the Ag thin films on Cu(111) surfaces depend strongly on the temperature during deposition with the Ag(111) planes having a preferred orientation of either type-n growth mode or type-r growth mode as a function of the Cu substrate temperature. The experimental results concerning Ag/Cu(111) show many similarities to those in the previous study of Au/Ni(111). This would suggest that an observed oscillation in the growth mode, dependent on the substrate temperature during deposition may a general phenomenon on solid surfaces, in cases of large misfit since it has now been seen for both Au/Ni(111) and Ag/Cu(111) systems.
INTRODUCTION Understanding and controlling growth morphologies requires detailed knowledge of microscopic processes for both fundamental and technological reasons. Recent advances in epitaxial growth techniques have greatly expanded our capabilities to grow artificially structured materials, which cannot be found in nature [1]. Epitaxial growth can produce films with significant strain, or, in some cases, a crystal lattice structure different from the bulk material. Especially, heteroepitaxy often involves lattice mismatch between the deposited film and the substrate that will produce strain at the interface between the deposited film and the substrate. It is also well known that different growth modes can result from changes in the substrate temperature as well as the deposition rate [2]. The Ag/Cu(111) system can be considered as representative of the case: a large deposition atom and small substrate atom for two species which are almost completely immiscible in the bulk [3, 4]. The Ag/Cu(111) combination has a large lattice mismatch (13%); the nearest neighbor distances of bulk Ag(111) and Cu(111) are 2.89 Å and 2.56 Å, respectively [5]. The Ag/Cu(111) system is very similar to the Au/Ni(111) system. The lattice mismatch between Au and Ni is 16 %; the nearest neighbor distances of bulk Au(111) and Ni(111) are 2.88 Å and 2.49Å, respectively. Elemental Au-Ni is also immiscible in the bulk [6]. In both cases, Low Energy Electron Diffraction (LEED) patterns display (9×9) structures at a coverage of 1 ML [7, 8]. In a previous study, we investigated the surface structure and metal epitaxy for the Au/Ni(111) system by using impact collision ion scattering spectroscopy (ICISS) [9, 10]. We showed that two simple, symmetric growth modes dominate the order
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