Pt-chain induced formation of Ge nanowires on the Ge(001) surface

A new reconstructed Pt/Ge(001)-4 × 2 surface structure of 0.25 ML Pt deposition is suggested based on density functional theory. The Ge dimers form nanowire arrays on a Pt-chain modified Ge(001) surface in which the chain is located between the two quasi-dimer rows and below the Ge nanowire. The simulated scanning tunneling microscope (STM) images of the surface are in excellent agreement with the previously observed STM features and sample bias dependence. It is the nanowire Ge dimers and not the Pt atoms that contribute to the STM images for occupied states at high sample biases, contrary to what has always been assumed in experiments. The surface bands of the Pt chain and quasi-dimer rows exhibit quasi-one-dimensional metallic behavior in the direction of the nanowire. When changing from the 4 × 2 to the 4 × 4 structure, there are likely pseudogaps opened at the new surface Brillouin zone boundary, which simultaneously reduce the metallicity. This may be related to the Peierls instability. The interaction between the Pt chain and the quasi-dimer row, as well as the inter-quasi-dimer row interaction, is of essential importance for stabilization.