Measurement of thermopower and current-voltage characteristics of molecular junctions to identify orbital alignment

Tan, Aaron; Sadat, Seid; Reddy, Pramod
January 2010
Applied Physics Letters;1/4/2010, Vol. 96 Issue 1, p013110
Academic Journal
We report an experimental technique that concurrently measures the Seebeck coefficient and the current-voltage (I-V) characteristics of a molecular junction to determine the identity and the effective energetic separation of the molecular orbital closest to the electrodes’ Fermi level. Junctions created by contacting a gold-coated atomic force microscope tip with a monolayer of molecules assembled on a gold substrate were found to have a Seebeck coefficient of (+16.9±1.4) μV/K. This positive value unambiguously shows that the highest occupied molecular orbital (HOMO) dominates charge transport. Further, by analyzing the (I-V) characteristics, the HOMO level is estimated to be ∼0.69 eV with respect to the Fermi level.


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