New Model System for a One-Dimensional Electron Liquid: Self-Organized Atomic Gold Chains on Ge(001)

Unique electronic properties of self-organized Au atom chains on Ge(001) in novel $c(8\times 2)$ long-range order are revealed by scanning tunneling microscopy. Along the nanowires an exceptionally narrow conduction path exists which is virtually decoupled from the substrate. It is laterally confined to the ultimate limit of single atom dimension, and is strictly separated from its neighbors, as not previously reported. The resulting tunneling conductivity shows a dramatic inhomogeneity of 2 orders of magnitude. The atom chains thus represent an outstandingly close approach to a one-dimensional electron liquid.

Figure 1

STM images of $\mathrm{Au}/\mathrm{Ge}(001)$. (a) Overview of nanowires ($720\AA \times 350\AA$, $+1.8\mathrm{V}$). (b) Close-up ($100\AA \times 120\AA$, $+1.6\mathrm{V}$). The nanowire spacing is 16 Å, with even intensity in 1D direction. (c) LEED image at 29 eV, showing a $c(8\times 2)$ structure, with dual domains.

Figure 2

(a) STM image at 1.5 V, 0.5 nA with weak modulation corresponding to $c(8\times 2)$ unit cell. Length profiles confirm 8 Å periodicity. (b) Lateral height profile of nanowires at $-2.1\mathrm{V}$. (c) Lateral profile comparison. ($A$) Nanowire data [center profile (b)], $\sim 7.2\AA$ FWHM. ($B$) Single Au atom on alumina [19]. ($C$) Calculation for Na atom on metal surface [17], offset for clarity. ($D$) Au dimer on alumina [19]. The nanowire profile matches best with the single atom data.

Figure 3

(a) STM image at $-0.6\mathrm{V}$, $70\AA \times 100\AA$ of defect region with nanowire interdigitation, providing evidence for a strict spatial separation. (b) Bias series of STM images ($100\AA \times 100\AA$), with positive bias, (c) negative bias. It shows persistence of identical structure independent of bias with sharp ridge and 1D charge delocalization.

Figure 4

(a) Differential conductivity on nanowire top and in between at 300 K. The ratio amounts to $\sim 2$ orders of magnitude, reflecting a pronounced inhomogeneity. (b) ARPES along 1D direction with $h\nu =21.2\mathrm{eV}$ ($T\sim 80\mathrm{K}$). A metallic Au-induced electron band is identified.