Initial stages of Pt nanowire formation on Ge(001)

Recently, the formation of defect- and kink-free Pt nanowires with a cross section of only one atom and lengths up to 500 nm on Ge(001) surfaces was reported. Here we present scanning tunneling microscopy data that reveal the initial stages of the Pt nanowire formation process. Upon room temperature deposition the Pt atoms first dive into the Ge(001) substrate. However, annealing at temperatures of 1000 K or higher causes the Pt atoms to pop up again. The Pt atoms form dimers and are positioned within the troughs between the substrate dimer rows. The Pt-Pt dimer bond is aligned along the substrate dimer bonds. Most of the Pt dimers are found in isolation or units of two dimers. Amazingly the Pt dimers in the trough seem to push both neighboring substrate dimer rows apart, leading to a zipper like structure. In case the concentration of Pt dimers within a trough is sufficiently high, they rotate by 90 degrees and line-up in virtually perfect Pt chains.