Surfactant Mediated Epitaxial Growth of Co on Au(111) Surface
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Surfactant Mediated Epitaxial Growth of Co on Au(111) Surface Masao Kamiko, Sang-Mun Oh, Hiroaki Chihaya, Hiroyuki Mizuno, Junhua Xu1, Lihua Yu1, Isao Kojima1, and Ryoichi Yamamoto Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, JAPAN. 1 National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 5, Higashi 1-1, Tsukuba, Ibaraki 305-8565, JAPAN ABSTRACT We have chosen Bi as the surfactant atom in the heteroepitaxial growth of Co on Au(111). It was found that Bi induces layer-by-layer (LBL) growth at room temperature. With pre-deposition of 0.2 ~ 0.8Å Bi on Au(111) prior to the evaporation of Co, more long-lasting RHEED intensity oscillations were observed and this implies that it induces the LBL growth of Co film. The result of the dependence of the growth behavior as a function of Bi layer thickness suggests that there is a suitable amount of Bi surfactant layer that induces the smoother LBL growth. A surface segregation of Bi was found at the top of surface and acts as a surfactant by promoting the interlayer transport. INTRODUCTION Surfactant epitaxy has been known as a useful method for changing the thin film growth mode from 3D-island formation to LBL growth [1][2]. The drastic surfactant effects in the growth of metal on metal have been reported by van der Vegt et al. [3]. Furthermore, it is reported that surfactant is also effective for suppression of twin formation in Co/Cu bilayers [4]. We have chosen Bi as the surfactant atoms in the heteroepitaxial growth of Co on Au(111). In order to be used as a surfactant, some conditions must be satisfied. The surfactant atoms must float up to the surface. In other words, it should be more stable on the surface than into the film. Mae et al. investigated how the surfactant atoms segregate on the surface by computer simulations using the modified embedded atom method (MEAM) [5]. The calculations have indicated that the most important characteristic of the surfactant should have a larger atomic radius than that of film and substrate atoms, and it is favorable for the surfactant to have smaller cohesive energy or surface energy than that of the film and the substrate elements and to be immiscible with them. Bi has a much smaller surface energy and a much larger atomic radius compared to Co and Au. We have also confirmed from phase diagram that Bi does not alloy with Co and Au less than 100˚C. From these reasons, Bi is a good candidate as surfactant atoms in the heteroepitaxial growth of Co on Au(111). In this paper, we report the influence of the Bi surfactant on the heteroepitaxial growth of Co on Au(111), combining RHEED and Atomic Force Microscopy (AFM) measurements, as well as Auger depth profiling analysis. EXPERIMANTAL DETAILS The experiments have been carried out in a growth chamber of molecular beam epitaxy
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(MBE) equipped with RHEED. The base pressure was 10-10 Torr range and the pressure during deposition did not exceed 5×10-9 Torr. Co, A
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