Conductance of atomic-scale Pb contacts in an electrochemical environment

Atomic-sized lead (Pb) contacts are deposited and dissolved in an electrochemical environment, and their transport properties are measured. Due to the electrochemical fabrication process, deformation-induced mechanical strain is largely avoided, and we obtain conductance histograms with sharply resolved, individual peaks. Charge transport calculations based on density-functional theory for various ideal Pb contact geometries are in good agreement with the experimental results. Depending on the atomic configuration, single-atom-wide contacts of one and the same metal yield very different conductance values.

Figure 1

(Color online) Schematic of the experimental setup. Pb is deposited and dissolved electrochemically in the narrow gap between two gold WEs on a glass substrate and the conductance of the contact is measured simultaneously. The potentials of the WEs with respect to the lead RE and the lead CE are set by a potentiostat.

Figure 2

(Color online) Conductance histogram of electrochemically fabricated atomic-sized Pb contacts. The inset shows two typical conductance-time traces for deposition and dissolution processes.

Figure 3

(Color online) Geometries of single-atom contacts, their transmission as a function of the energy, and the LDOS of that atom in the narrowest part of the junction, which is indicated by an arrow in the geometries. The transmission $\tau ={\sum }_i{\tau }_i$ is resolved into the contributions ${\tau }_i$ from individual transmission channels and the LDOS into its orbital components (Ref. 26). The crystallographic orientation of the semi-infinite electrodes is [(a)–(c)] $⟨100⟩$, [(d)–(f)] $⟨110⟩$, and [(g)–(i)] $⟨111⟩$, respectively. Vertical dashed lines indicate the Fermi energy at $E_F=-3.76\text{eV}$.

Figure 4

(Color online) Dependence of the conductance $G$ and the total energy $E_{tot}$ on the distance $d$ between the tip atoms for the different dimer configurations with [(a) and (b)] $⟨100⟩$, [(c) and (d)] $⟨110⟩$, and [(e) and (f)] $⟨111⟩$ crystallographic orientation. In addition to $G={\sum }_i{G}_i$ the contributions from the individual transmission channels $G_i=G_0{\tau }_i$ are shown. In each plot the $y$ axis on the left refers to $G$ and $G_i$ (solid lines) and that on the right to $E_{tot}$ (dashed lines). Dotted vertical lines indicate the distances $d$ with minimal $E_{tot}$.