Structural phase transition of Pt/Ge(001) surface studied by reflection high-energy positron diffraction

Mochizuki, Izumi; Fukaya, Yuki   ; Kawasuso, Atsuo

Defect-free quasi-one chain with the single atomic width is reconstructed on the Ge(001) surface by a Pt adsorption of sub-atomic layer. Recently, it has been reported that the atomic chain undergoes the Peierls transition about 80 K. But, the electronic property, the atomic arrangements and displacements in the phase transition are not yet elucidated. Using reflection high-energy positron diffraction (RHEPD), we have reported that the rocking curve in a one-beam condition matches the dynamical calculation assuming the Nano-Wire (NW) model suggested by Vanpoucke et al. However, they have also proposed several NW models with different Pt coverages and have argued that the phase transition derives from the change of the Pt coverage. In this study, we have tried to determine the atomic arrangement, the Pt coverage and the displacements in the phase transition by using RHEPD with a many-beam condition. The rocking curve shows a good agreement with the calculated curve assuming the NW model with the Pt coverage of 0.75 ML, while the curve does not agree with the curves from the Pt coverage of 0.8125 or 0.875 ML. In addition, the change of rocking curves in the phase transition shows that the structural phase transition is caused by the height difference of the topmost Ge dimer atoms making the p(44) structure.