Crystal orientation and surface morphology of face-centered-cubic metal thin films deposited upon single-crystal ceramic
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Cu, Pt, Ag, and Au were deposited on (100)-oriented ceramic substrates (SrTiO3, LaAlO3, and MgO). Over a wide range of temperatures (room temperature to 600 °C), Cu films were (100)-oriented and exhibited cube-on-cube epitaxy. Epitaxial Pt(100) films were obtained only at high temperature; oriented Pt(111) films were obtained at lower temperatures. Ag and Au were never obtained as purely (100)-oriented samples, although the amount of (100)-film increased with increasing temperature. Three-dimensional islands formed for all metals at higher temperatures, while flatter film surfaces developed at lower temperatures. At any given temperature, the surface roughness of films on SrTiO3(100) increased in the order Pt < Cu < Au < Ag. The variations in film structural characteristics are described well by considering the metals’ (i) surface/interfacial energies, (ii) surface energy anisotropies, and (iii) surface diffusion coefficients. Flat, epitaxial growth is promoted by low-energy interfaces, low surface energy anisotropies, and slow surface diffusion.
I. INTRODUCTION
The growth of thin metal films is of considerable scientific and technological interest because supported metals are currently in wide use as electrodes, interconnects, magnetic layers, and catalysts.1–6 For metal films to be of practical engineering use, such as interconnects in circuits, it is important to control their crystalline properties (orientation, grain size)7–11 as well as their morphological features (three-dimensional particles or flat layers).12–15 The high degree of structural perfection required for some technological applications can sometimes be attained only through the growth of epitaxial films, in which a definite relationship exists between the crystal axes of the film and substrate. In many instances, epitaxial metal films must be deposited on ceramic or semiconducting substrate layers,1,16,17 and the attainment of high-quality films will depend strongly on the nature of the metal/substrate interface. Unfortunately, the general characteristics of metal/ceramic interfaces are still not well understood. Thus, it is of interest to study what factors affect the structural properties of metal/ceramic multilayers. The crystalline orientation of face-centered-cubic (fcc)
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0014 J. Mater. Res., Vol. 22, No. 1, Jan 2007
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metal films grown on ceramic substrates depends strongly on both the thermodynamic and kinetic factors of the particular deposition method used, especially deposition temperature.18–35 For the case of fcc metals, the close-packed {111} planes have the lowest relative surface energy36,37; thus, some amount of interfacial stabilization from the substrate will always be necessary to promote the growth of (100)-oriented fcc metals. The nature/amount of the interfacial stabilization for any given metal/ceramic pair is difficult to quantify and may depend on various factors, whic
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