In-plane lattice spacing oscillatory behaviour during the two-dimensional hetero- and homoepitaxy of metals

The present paper is devoted to the analysis of in-plane lattice spacing oscillations (IPLSOs) during two-dimensional hetero- and homoepitaxial growth on (001) surfaces of cubic metals using reflection high-energy electron diffraction (RHEED). Our aim was to check systematically the agreement between experimental results and theoretical predictions. We have selected the most significant heteroepitaxial systems B/A with a misfit positive (V/Fe, Mn/Fe), negative (Ni/Fe, Ni/V, Co/Cu) or close to zero (Fe/Cu, Co/Ni). The phase relationships between the different oscillating physical parameters [RHEED intensity, full-width at half maximum (FWHM) of diffraction streaks and in-plane lattice spacing] are examined, as well as the azimuthal dependence of the elastic relaxation process. A general good agreement between experimental data and theory was observed. However, for some systems (Ni/Fe, V/Fe), we prove a strong anisotropy of the phenomenon along the [10] and [11] azimuths of the square surface lattice. We also focus on the case of homoepitaxial growth and search for a convincing demonstration of IPLSOs in this specific case. The influence of substrate temperature and azimuthal dependance are also investigated. Surprisingly, very large relaxation effects are observed and seem to be correlated to the occurrence of surface reconstruction and/or surface contamination. Finally, an anisotropic character was again observed on V and Nb (001) surfaces. The morphology of the two-dimensional islands during growth or/and anisotropic surface reconstructions could explain such anisotropy.