Epitaxial Growth of Co and Ru on Pt(111)

Abstract

The epitaxial growth of Co/Ru on a well-defined Pt(111) electrode surface has been studied as a function of deposition potentials by the reflection high-energy electron diffraction (RHEED). For ∼1 to 2 ML coverage, Co growth on Pt(111) proceeds initially via nucleation and formation of patchy islands with various levels, and the grain boundaries likely enhance the CoO and Co3O4 cluster formation after emersion. At ∼3 to 4 ML coverage, 2D islands covered by CoO surface layer, in incoherent epitaxy on Pt(111), are observed, and the twinned Co clusters are for the first time detected at ∼5 ML thick islands, showing a Stranski–Krastanov growth mode. Greater than 5 to 6 ML coverage leads to 3D cluster formation growth in the (111) orientation aligned along the Co [110] to the Pt [110] direction. For Ru on Pt(111), at ∼0.2 ML coverage Ru islands are mainly monolayer high with a pseudomorphic growth; beyond this coverage (∼0.6 ML), concurrent growth of higher layers leads to predominantly bilayer island formation, showing an incommensurate growth. Greater than 1 ML coverage develops multilayer islands growing in the (0001) orientation and aligned the [11–20] direction to the [110] Pt direction. The acquired reciprocal lattice net of Co(110)*fcc differs considerably from that of an Ru(110)hcp*, which allows a reliable phase determination of Co/Ru deposits on Pt(111).