Tip-contact related low-bias negative differential resistance and rectifying effects in benzene-porphyrin-benzene molecular junctions

The electronic transport properties of benzene-porphyrin-benzene (BPB) molecules coupled to gold (Au) electrodes were investigated. By successively removing the front-end Au atoms, several BPB junctions with different molecule-electrode contact symmetries were constructed. The calculated current-voltage (I-V) curves depended strongly on the contact configurations between the BPB molecules and the Au electrodes. In particular, a significant low-voltage negative differential resistance effect appeared at -0.3 V in the junctions with pyramidal electrodes on both sides. Along with the breaking of this tip-contact symmetry, the low-bias negative differential resistance effect gradually disappeared. This tip-contact may be ideal for use in the design of future molecular devices because of its similarity with experimental processes.