LOW-ENERGY-ELECTRON DIFFRACTION STUDY OF THE GROWTH OF ULTRATHIN FILMS OF FACE-CENTERED-CUBIC CO ON RH(001)

The epitaxial growth of Co on Rh{001} at room temperature is studied by means of quantitative low-energy electron diffraction and Auger electron spectroscopy. The Co films are found to grow pseudomorphic to the substrate in the layer-by-layer mode for at least two layers. The interlayer spacing between the monolayer and the substrate is 1.77 +/- 0.03 angstrom. The first and second interlayer spacings for a bilayer film are 1.60 +/- 0.04 and 1.75 +/- 0.04 angstrom, respectively. Strained pseudomorphic films of up to 10 layers could be grown with a bulk lattice spacing of 1.60 +/- 0.03 k and a 3.1%-expanded first interlayer spacing (1.65 +/- 0.03 angstrom). An elastic strain analysis shows that the equilibrium (unstrained) phase of these Co films is face-centred cubic: the bulk interlayer spacing is contracted by 9.7% with respect to the equilibrium value (1.772 angstrom) as a consequence of the large positive planar epitaxial strain produced by the 7.3% lattice mismatch between FCC Co and Rh.