Negative Differential Resistance in Single-Molecule Junctions Based on Heteroepitaxial Spherical Au/Pt Nanogap Electrodes

Single-molecule junctions exploit the internal structure of molecular orbitals to construct a new class of functional quantum devices. The demonstration of negative differential resistance (NDR) in single-molecule junctions is direct evidence of quantum mechanical tunneling through a molecular orbital. Here, a pronounced NDR effect is reported with a peak-to-valley ratio of 30.1 on a single-molecule junction of π-conjugated quinoidal-fused oligosilole derivatives, Si2 × 2, embedded between the unique electroless gold-plated heteroepitaxial spherical Au/Pt nanogap electrodes. This NDR feature persists in a consecutive endurance test of 180 current traces. the thermally stable NDR effects in the Si2 × 2 single-molecule junctions between 9 and 300 K are demonstrated. The density functional theory calculations under electric fields indicate that the NDR effect can be ascribed to the bias-dependent resonant tunneling transport via the polarized HOMO, which has asymmetrically changed electrode coupling with increased bias voltages. The results confirm a promising electrical platform for constructing functional quantum devices at the single-molecule level.