Growth mode and atomic structure of ultrathin Fe films on Rh{001} determined by quantitative low-energy electron diffraction.

Abstract

The epitaxial growth of Fe on Rh{001} at room temperature is studied by means of quantitative low-energy electron diffraction and Auger electron spectroscopy. The Fe films are pseudomorphic to the substrate and grow in the layer-by-layer mode for at least three layers---no attempts were made to determine the growth mode above this thickness. The spacing between Fe and Rh at the substrate-film interface remains approximately the same (about 1.75 \AA{}), within experimental error, when the Fe films grow from one to two and three layers. The Fe-Fe interlayer spacing in the bilayer films is also about the same (1.73 \AA{}), but in the three-layer film the first two interlayer spacings collapse to about 1.65 \AA{}. Thicker (eight- to ten-layer) Fe films have bulk spacings of 1.56 \AA{} and a 5.8%-expanded surface interlayer spacing (1.65 \AA{}). These films have a compressive strain in the film plane (the misfit to Rh{001} is -6.3%) and have a body-centered-tetragonal structure. Elastic strain analysis shows that the equilibrium (i.e., the unstrained) phase is bcc Fe; the bulk interlayer spacing in the films is expanded by 8.7% over the equilibrium value of bcc Fe (1.43 \AA{}) as a consequence of the epitaxial strain in the plane of the layers, and the atomic volume is reduced by 4.5%.