Effect of alkali-metal adsorption on the conductance of a molecular device

We show by first-principles density functional calculations that the adsorption of potassium on the platinum electrodes of a benzene dithiolate molecular wire junction will modify the energy-level alignments of the device. But near the Fermi energy, the energy levels, which correspond to sulfur orbitals, are quite inert to the work function change of the electrode due to a strong terminal atom/metal bonding. Our results demonstrate unambiguously that while the coadsorption of potassium on the electrodes may influence the conductance of a molecular device, it cannot change the conductance in a drastic way as the transmission peak near the Fermi level shifts only slightly with the introduction of potassium atoms.

Figure 1

(Color online) Calculation model for (a) a benzene thiolate molecule $(-\mathrm{S}-{\mathrm{C}}_6{\mathrm{H}}_5)$ adsorbed on Pt(111) surface and (b) a benzene dithiolate molecule $(-\mathrm{S}-{\mathrm{C}}_6{\mathrm{H}}_4-\mathrm{S}-)$ sandwiched between Pt(111) surfaces, with the coadsorption of K.

Figure 2

(Color online) Local density of states projected onto the terminal S atom (thin lines) and the whole benzene thiolate molecule (thick lines) when adsorbed on Pt(111) surface, with (black lines) and without (red lines) coadsorption of K. The Fermi energy is set as zero. On the top are the energy levels of an isolated benzene thiolate molecule.

Figure 3

(Color online) Local density of states projected onto the S atom (thin lines) and the whole benzene dithiolate molecule (thick lines) when sandwiched between Pt(111) surfaces, with (black) and without (red) coadsorption of K on one electrode. The Fermi energy is set as zero. On the top are the energy levels of an isolated benzene thiolate molecule.

Figure 4

(Color online) The transmission $T\left(\epsilon \right)$ through a benzene dithiolate molecule sandwiched between Pt electrodes, with (black line) and without (red line) of coadsorption of K. The Fermi energy is set as zero.