Electron Transport Suppression from Tip−π State Interaction on Si(100)-2 × 1 Surfaces

Abstract

We investigate the electron transport between a scanning tunneling microscope tip and Si(100)-2 × 1 surfaces with four distinct configurations by performing calculations using density functional theory and the nonequilibrium Green's function method. Interestingly, we find that the conducting mechanism is altered when the tip-surface distance varies from large to small. At a distance larger than the critical value of 4.06 Å, the conductance is increased with a reduction in distance owing to the π state arising from the silicon dimers immediately under the tip; this in turn plays a key role in facilitating a large transmission probability. In contrast, when the tip is closer to the substrate, the conductance is substantially decreased because the π state is suppressed by the interaction with the tip, and its contribution in the tunneling channels is considerably reduced.

Conductance of a Single Magnesium Porphine Molecule on an Insulating Surface

“…A slab was adopted to model the substrate, shown in Figure a, that consists of a NaCl bilayer (25 atoms per layer) and a Au(111) bilayer. Two semi-infinite Au(111) nanowires were used as the top and bottom electrodes to reduce computational cost. , The cone-shaped tip was obtained by sharpening the terminal of the top electrode. The orientation of the MgP molecule with respect to the NaCl lattice was defined by the angle θ between the Mg–N and Na–Cl bonds, as shown in Figure b.…”