Atomic configuration and phase transition of Pt-induced nanowires on a Ge(001) surface studied using scanning tunneling microscopy, reflection high-energy positron diffraction, and angle-resolved photoemission spectroscopy

The atomic configuration and electronic band structure of Pt-induced nanowires on a Ge(001) surface are investigated using scanning tunneling microscopy, reflection high-energy positron diffraction, and angle-resolved photoemission spectroscopy. A previously proposed theoretical model, composed of Ge dimers on the top layer and buried Pt arrays in the second and fourth layers [Vanpoucke et al., Phys. Rev. B 77, 241308(R) (2008)], is found to be the fundamental structure of the observed nanowires. At low temperatures ($T<80$ K), each Ge dimer is alternately tilted in the surface normal direction (asymmetric), causing a p(4×4) periodicity. At high temperatures ($T>110$ K), each Ge dimer is flat with respect to the horizontal axis (symmetric), giving rise to p(4×2) periodicity. Upon the above phase transition, the electronic band dispersion related to the Ge dimers in the deeper energy region shifts to the Fermi level.