Localized Molecular Constraint on Electron Delocalization in a Metallic Chain

An artificial quantum structure consisting of a single CO molecule adsorbed on a Au chain was assembled by manipulating single Au atoms on NiAl(110) at 12 K with a scanning tunneling microscope (STM). The CO disrupts the delocalization of electron density waves in the chain, as it suppresses the coupling between neighboring chain atoms. The possibility to specify the CO position on the chain allows controlled modification of the electronic properties in a quantum system. Inelastic electron tunneling spectroscopy with the STM provides vibrational characterization of the adsorbed CO.

Figure 1

STM topographic images of (a),(c) a bare ${\mathrm{A}\mathrm{u}}_{11}$ chain on NiAl(110) and (b),(d) a ${\mathrm{A}\mathrm{u}}_{11}$ chain with a single CO molecule adsorbed at the 6th atom (image sizes $50\AA \times 50\AA$). Images were taken at 0.1 nA and 0.1 V (a),(b) and 2.0 V (c),(d).

Figure 2

$dI/dV$ spectra of (a) a bare ${\mathrm{A}\mathrm{u}}_7$ chain and (b) a ${\mathrm{A}\mathrm{u}}_7$ chain with a single CO molecule adsorbed on the 5th atom, taken at positions indicated in the insets. The broken lines in (b) show spectra of bare ${\mathrm{A}\mathrm{u}}_2$ and ${\mathrm{A}\mathrm{u}}_4$ chains for comparison. The tunneling gap was set at $V_{\mathrm{s}\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}\mathrm{e}}=2.5\mathrm{V}$, $I=0.1\mathrm{n}\mathrm{A}$.

Figure 3

$dI/dV$ microscopy images of (a) a bare ${\mathrm{A}\mathrm{u}}_{11}$ chain and (b) a ${\mathrm{A}\mathrm{u}}_{11}$ chain with a CO molecule adsorbed on the 6th atom, taken at indicated sample bias (image sizes $50\AA \times 50\AA$, $I=0.1\mathrm{n}\mathrm{A}$).

Figure 4

(a) Vibrational spectra of a ${\mathrm{A}\mathrm{u}}_7$ chain with a CO molecule adsorbed at the 5th atom, taken at the positions indicated in (b). The tunneling gap was set at $V_{\mathrm{s}\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}\mathrm{e}}=0,1\mathrm{V}$, $I=0.1\mathrm{n}\mathrm{A}$. Topographic and vibrational images of a ${\mathrm{A}\mathrm{u}}_7$ chain with a CO molecule adsorbed on (b) the 5th atom and (c) the 7th atom (image sizes $45\AA \times 45\AA$, $V_{\mathrm{s}\mathrm{a}\mathrm{m}\mathrm{p}\mathrm{l}\mathrm{e}}=37\mathrm{m}\mathrm{V}$, $I=1.0\mathrm{n}\mathrm{A}$).