Scanning tunneling microscopy study of self-organized Au atomic chain growth on Ge(001)

Abstract

Gold deposition onto Ge(001) at $675\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ led to self-organized atomic chains in $(4\ifmmode\times\else\texttimes\fi{}2)$ and $\mathrm{c}(8\ifmmode\times\else\texttimes\fi{}2)$ surface reconstructions. The chains were separated by $1.6\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and ran up to several hundred nanometers long. The Au-induced domains showed alternating white and gray chains in STM images that could be explained by $\mathrm{Au}\text{\ensuremath{-}}\mathrm{Au}$ and mixed $\mathrm{Au}\text{\ensuremath{-}}\mathrm{Ge}$ dimer rows, respectively. The chains showed a zigzag pattern attributed to dimer buckling. Bias-dependent STM imaging suggested that the Au chains were metallic nanowires. The chains, however, were not defect-free and contained missing dimer vacancies. The Ge terraces adjacent to the Au nanowire domains contained a high density of $(1+2+1)$ dimer vacancy defects that tended to run along [100] and [310] directions. The above results show strong similarities with those obtained for Pt on Ge(001) but are very different from those for Ag, which only weakly interacted with Ge(001), and thus support models suggesting stronger bonding of low-coordinated atoms of the $5d$ metals compared to the corresponding $4d$ metals.