Orientation Selection and Microstructural Evolution of Epitaxial Pt Films on (001) MgO
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PAUL C. MCINTYRE, CARL J. MAGGIORE, and MICHAEL NASTASI
Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos, NM 87545
ABSTRACT
Thin platinum films were deposited at several different deposition rates and with varying thickness on (001)-cut MgO single crystal substrates by electron beam evaporation. A mixture of two epitaxial Pt orientations were detected in the films by X-ray diffiraction and planar ion channeling experiments: (001) [100] Pt/I (001) [100] MgO (the "cube-on-cube" orientation) and (111) [110] Pt //(001) [110] MgO. The effect of deposition rate on film orientation indicated the (111) Pt orientation was preferred under conditions of high driving force for nucleation. The volume fraction of the films occupied by the (111) orientation increased with nominal film thickness, at a constant substrate temperature and deposition rate. This result indicates crystallites having the (111) Pt orientation grew more quickly following nucleation than the (001). The mosaic spread of the Pt orientations decreased markedly as the nominal film thickness increased from - 1.5 nm (isolated islands) to 20 nm (continuous film). INTRODUCTION
Epitaxial metal films evaporated on to ionic substrates have been studied for many years."' 2 Initially, epitaxial deposition was seen as a simple means of preparing thin, high quality metal crystals for fundamental structural studies. More recently, possible technological applications in information storage and processing have caused renewed interest in thin metal films and multilayers.3, 4 Epitaxial platinum films deposited on to (001) MgO substrates have been investigated as initial epilayers in Pt/Fe multilayers intended for magneto-optic media. 5' 6 Lu et al. 7 have also used platinum thin films on (001) MgO as an epitaxial electrode material for growth of highly-oriented BaTiO 3 films. The present work is intended to develop a more detailed understanding of the nature and mechanisms of orientation selection inPt films deposited on to the (001) MgO surface. 4 Noble metal films deposited on to (001) MgO through a variety of deposition techniques ' 5 9 , ' frequently have a mixed orientation with both (001) and (111) planes parallel to the substrate surface. The (111) orientation tends to dominate in polycrystalline Pt films deposited on to nonlattice-matched substrates because the (111) plane has the lowest surface energy and fastest inplane growth rate infcc metals. Lairson et al. 5 prepared Pt films on (001) MgO by magnetron sputtering with substrate heating that were essentially completely (111)-oriented at 400°C and almost completely (001)-oriented at 680 0C. The (001)-oriented Pt films prepared at high substrate temperatures had a "cube-on-cube" epitaxial relationship with the substrate. They also found that deposition of an initial thin "seed" layer of iron on to (001) MgO, prior to Pt deposition, resulted in nucleation and growth of platinum films that contained only the "cube-oncube" orientation; the (111) Pt orientation was completely supp
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