Structure and growth of holmium on W(110)

The interaction of holmium (Ho) with the W(110) surface has been studied using time resolved in situ scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). For a coverage up to 0.5 ML, Ho forms chains along [11̄0] which are compressed in [001] direction with increasing coverage. Above 0.5 ML a transition from the chain structure to a nearly relaxed monolayer of Ho takes place which is the starting point for statistical growth at 300 K. The hcp bulk structure of Ho visible as an A–B–A–B stacking appears during growth of triangular islands already starting in the second layer. At 550 K Ho grows in the Stranski–Krastanov growth mode with large islands being mobile on a time scale of minutes. On stepped regions of the substrate, a stress-driven directed motion of complete islands ‘downwards’ perpendicular to the step edges is found.