Micron thick epitaxial (100) Ag film growth on MgO
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Micron thick epitaxial (100) Ag film growth on MgO A. C. Carter, W. Chang, S. B. Qadri, J. S. Horwitz, Robert Leuchtner, and D. B. Chrisey Naval Research Laboratory, Washington, DC 20375 (Received 18 July 1997; accepted 12 February 1998)
Epitaxial films of (100) Ag were deposited onto (100) MgO substrates to a thickness of 4 mm with no evidence of (111) nucleation. Deposited films were smooth and had large areas, 50 3 50 microns square, free of morphological defects. Films were deposited using ˚ Ag (100) a two-step process. First, pulsed laser deposition was used to grow a 1000 A seed layer on the MgO substrate. Second, e-beam evaporation was used to grow the film to the desired thickness. The high quality of the resulting films will allow them to be used as templates for further epitaxial deposition of other applied materials.
The growth of metals onto ionic substrates has been the subject of extensive investigation since the 1960’s.1–8 Applications that require metal-ionic substrate technology include composites, protective coatings, catalysis, electronic packaging, and thin film technology.8 Of particular interest was epitaxial deposition of Ag onto (100) and (111) oriented MgO.4–8 Originally it was thought that epitaxial island growth of Ag on MgO began with nucleation at impurities or lattice defects on the surface. However, careful studies showed this not to be true and it was determined that even though the lattice misfit of Ag on MgO (2.8%) is relatively small, atomic bonding of the Ag to the surface is the dominating influence on the epitaxy of Ag on MgO.1,7 It was maintained that epitaxial growth of Ag onto MgO by evaporation techniques was very sensitive to minor differences in surface quality and deposition temperature, deposition rate, and background pressure.5 For these reasons studies of Ag epitaxy on MgO were performed with strict control of deposition conditions on very clean surfaces or surfaces cleaved in vacuum. In this communication we describe the growth of up to 4 mm thick epitaxial Ag films on (100) MgO using a combination of pulsed laser deposition (PLD) and e-beam deposition techniques. The production of these films is unique because it is relatively easy, occurs over a wide variety of deposition conditions, only takes a few hours, and is much less sensitive to substrate cleanliness than most previous studies. The quality of the Ag films allowed them to serve as a template for (100) Ba0.5 Sr0.5 TiO3 growth, and they were thick enough to be used as low loss substrates for ferroelectric thin film high frequency (GHz) tunable microwave applications.9 Commercially purchased (100) and (110) MgO substrates were used as is or with minimal cleaning using a cotton swab and methanol. For the growth of the Ag seed layer by PLD, the substrate was bonded to a stainless steel heater using silver paint for good thermal contact. Before deposition the substrate was heated to 1418
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 6, Jun 1998
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