Stability of rectification of iron porphyrin molecular junctions

• Studied rectification of Fe-Porphyrin molecule with two deposition techniques: drop-dry method and 60 s deposition method.
• Observed stable rectification from drop-dry deposition of Fe-Porphyrin on Au substrate.
• Discussed possible mechanisms of the stability of rectification.

We report rectification from porphyrin molecules ligated to an iron atom. Current-voltage (IV) curves were measured from the molecules using a conductive atomic force microscope (AFM). Molecules were deposited on a substrate from template-stripped gold from 1 μM iron porphyrin solution by either a drop-dry or 60 s deposition method. The measured IV curves from the drop-dry samples were stable. Statistical analysis of the IV curves showed that the distribution of the threshold voltages (0.543 V - 0.588 V) and rectification ratios (34–42) from the drop-dry samples are confined to a smaller range than the threshold voltages (0.2 V - 0.7 V) and rectification ratios (2.5–162) from the 60 s samples. The fluctuations in the IV curve from the 60 s deposition samples can be explained by local joule heating. The roughness of the topography was analyzed to understand the difference in IV measurements between the two types of samples. The stability of the rectification from the drop-dry samples is attributed to good thermal contact between the AFM tip and the molecules on the substrate.