Temperature dependent electron transport and inelastic electron tunneling spectroscopy of porphyrin molecular junctions

We report electron transport measurements through a metal-molecule-metal junction of free base or zinc porphyrin molecules. Junctions are formed by zig-zag electromigration of a gold nanowire. Inelastic electron tunneling spectroscopy measurements were performed at 4.3 K to confirm the presence of molecules in the junction and to measure the vibrational modes of the molecular junction. Temperature dependent current/voltage measurements are performed in order to determine that the electron conduction mechanism through these molecular junctions is direct tunneling. The electron attenuation coefficient (β0) was also calculated; the average β0 for free base and zinc porphyrin was 0.231 ± 0.133 Å−1 and 0.188 ± 0.049 Å−1, respectively. The barrier height was experimentally found to be 1.6 eV and 1.1 eV for FBP and Zn-P SAMs on Au, respectively.