Epitaxial growth of (001) and (111) Ni films on MgO substrates
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Epitaxial growth of (001) and (111) Ni films on MgO substrates Rosa Alejandra Lukaszew1, Vladimir Stoica, Ctirad Uher and Roy Clarke Physics Department, University of Michigan, Ann Arbor 1 Presently at the Department of Physics and Astronomy, University of Toledo, Ohio. ABSTRACT Metal-ceramic interfaces are important in applications as diverse as magnetic storage media and supported catalysts. It is very important to understand how the crystallography and microstructure of metallic films deposited onto ceramic substrates depend on growth and/or annealing conditions so that their physical properties (e.g. magnetic, electronic, etc.) can be tailored for specific applications. To this end, we have studied the epitaxial growth and annealing of (001) and (111) Ni films MBE grown on MgO substrates, where we have observed the evolution of the surface using correlated insitu RHEED (reflection high-energy-electron diffraction) and STM (scanning tunneling microscopy) measurements. INTRODUCTION We have previously shown that epitaxial single-crystal magnetic thin films may be used in spin-dependent tunneling applications [1]. In general, the magnetic properties, particularly the anisotropy [2], of epitaxial thin films are dominated by the crystallographic structure of the metal/substrate interface as well as the surface quality. In addition, for spin-dependent tunneling devices, the roughness at the surface must be very small in order to ensure the integrity of the subsequent deposition of ultra-thin, pinhole-free insulating layers. Thus, we have considered the growth of magnetic films on MgO substrates, which can be prepared with very smooth surfaces [3]. Theoretical studies have indicated that for Ni films grown on MgO substrates, Ni is expected to strongly interact with MgO [4]. Various researchers have studied the orientation of Ni films on MgO substrates under various growth conditions [5], and some reports indicate that Ni may form an epitaxial relationship with Ni[001]//MgO[001] and Ni(010)//MgO(010) for films deposited using dc sputtering on MgO substrates held at 100oC [6]. There are also reports on epitaxial growth of fcc metals on surfaces with hexagonal surface symmetry such as MgO (111) [7]. Sandström et al. [8] have shown that at growth temperatures between 300oC and 400oC it is possible to grow smooth oriented single domain epitaxial films on MgO substrates, utilizing dc magnetron sputtering in an ultra high vacuum (UHV) chamber. In the following, we present our studies on the molecular beam epitaxy (MBE) growth/annealing and in-situ surface structural characterization of single domain Ni films grown on (001) and (111) oriented MgO substrates. EXPERIMENTAL The Ni films were grown in an MBE VG 80 M system with a background pressure < 5 x 10–11 torr. Ni was evaporated from a 99.999% pure source. The deposition P3.29.1
rate was 0.5Å /sec. The substrates used in the experiment were 0.5 mm thick, 1 x 1 cm2 pre-polished MgO (001) and (111) oriented single crystals, which were heat-treated in UHV at 800oC for 1 hr. Th
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