| AVS 54th International Symposium | |
| Electronic Materials and Processing | Tuesday Sessions |
| Session EM-TuM |
| Session: | Molecular Electronics |
| Presenter: | A.K. Mahapatro, Purdue University |
| Authors: | A.K. Mahapatro, Purdue University J. Ying, Purdue University B. Muralidharan, Purdue University S. Datta, Purdue University T. Ren, Purdue University D.B. Janes, Purdue University |
| Correspondent: | Click to Email |
Electronic properties of various organic molecules have been studied for potential nanoelectronics and sensor applications. Studies of redox active molecules can allow investigation of the energy-band alignments of the molecular levels with respect to the contact Fermi levels and studies of molecules in specific charge states. A recently developed technique to efficiently fabricate stable nanogap molecular junctions (NMJs)1 are used in this study for room-temperature electrical measurements through single/few molecule systems. Electronic properties of redox active molecules Oligo(phynilene ethylene), OPE and trans-Ru2(ap)4(C=CC6H4S-)2, where (ap)4 is 2-anilinopyridinate, are studied by localizing the molecules in the NMJs. The current-voltage characteristics of the OPE devices exhibit switching behavior at a threshold voltage between 1.6 V and 3.0 V. The di-ruthenium devices exhibit a negative differential resistance region, corresponding to an irreversible current peak at a bias voltage of ~ 0.3-0.4 V, followed by a conductance peak at higher bias. A theoretical model using sequential tunneling Coulomb blockade model2 explains the current peak in terms of a blocking transport level that cannot be emptied easily, causing the conducting level to float out of the bias window as a result of Coulomb repulsion. Assuming equal capacitive coupling at both the metal-molecule contacts,3 the observed conductance peak positions at ±0.25 ±0.05 V and ±1.05 ±0.15 V correspond to molecular level energies of EHOMO = 5.23 eV and ELUMO = 4.6 eV for the di-ruthenium molecule. These values are in close agreement with the molecular level energies estimated from the measured oxidation and reduction peaks in cyclic voltammetry.4 The current study demonstrates that devices employing redox active molecules, in which the molecular levels are close to the metal Fermi level, allow resonant tunneling and could provide suitable structures for memory or chemical sensing applications.
1 A. K. Mahapatro, S. Ghosh, and D. B. Janes, IEEE Trans. Nanotech., 5, 232 (2006).
2 B. Muralidharan and S. Datta, Preprint, arXiv:cond-mat/0702161 (2007).
3 S. Datta, W. Tian, S. Hong, R. Reifenberger, J. I. Henderson, and C. P. Kubiak, Phys. Rev. Lett. 79, 2530 (1997).
4 T. Ren et. al., J. Organ. Chem., 690, 4734 (2005).