Electron transport enhanced by electrode surface reconstruction: a case study of C-60-based molecular junctions

The effects of surface reconstruction on electron transport of two monolayers of C-60 sandwiched between two Cu(111) bulk electrodes have been investigated by density functional theory (DFT) calculations combined with a nonequilibrium Green's function technique. Two markedly different electrode surface structures have been considered, which have been obtained in previous experimental works: one with an unreconstructed perfect surface and the other with a surface reconstruction with a 7-atom-missing hole per (4 x 4) Cu(111) cell. The results indicate that surface reconstruction induces an increase of more than 50% in the current at low bias. Molecular-orbital projected density of states (MO-PDOS) analysis reveals that the change in transport properties originates from the enhanced orbital-dependent electrode-molecule coupling and the increased charge transfer from electrodes to molecules. Our current work suggests that surface reconstruction could play a very important role in the electron transport properties; and hence surface reconstruction (or more generally realistic atomic contact details) should be taken into full consideration in the simulation and design of molecular devices, especially when it is expected to reproduce computationally the experimental observations.