# Mechanism of Rectification in Tunneling Junctions Based on Molecules with Asymmetric Potential Drops

 Title: Mechanism of Rectification in Tunneling Junctions Based on Molecules with Asymmetric Potential Drops Author: Nijhuis, Christian A.; Reus, William F.; Whitesides, George M. Note: Order does not necessarily reflect citation order of authors. Citation: Nijhuis, Christian A., William F. Reus and George M. Whitesides. Mechanism of rectification in tunneling junctions based on molecules with asymmetric potential drops. Journal of the American Chemical Society 132(51): 18386-18401. Full Text & Related Files: Nijhuis_MechanismRectification.pdf (3.774Mb; PDF)  Nijhuis_MechanismRectification.doc (3.281Mb; Microsoft Word) Abstract: This paper proposes a mechanism for the rectification of current by self-assembled monolayers (SAMs) of alkanethiolates with Fc head groups (SC$$_{11}$$Fc) in SAM-based tunneling junctions with ultra-flat Ag bottom electrodes and liquid metal (Ga$$_2$$O$$_3$$/EGaIn) top electrodes. A systematic physical-organic study based on statistically large numbers of data (N = 300−1000) reached the conclusion that only one energetically accessible molecular orbital (the HOMO of the Fc) is necessary to obtain large rectification ratios $$R \approx 1.0 \times 10^{2} (R = |J(−V)|/|J(V)|$$ at $$±1$$ V$$)$$. Values of R are log-normally distributed, with a log-standard deviation of 3.0. The HOMO level has to be positioned spatially asymmetrically inside the junctions (in these experiments, in contact with the Ga$$_2$$O$$_3$$/EGaIn top electrode, and separated from the Ag electrode by the SC$$_{11}$$ moiety) and energetically below the Fermi levels of both electrodes to achieve rectification. The HOMO follows the potential of the Fermi level of the Ga$$_2$$O$$_3$$/EGaIn electrode; it overlaps energetically with both Fermi levels of the electrodes only in one direction of bias. Published Version: doi:10.1021/ja108311j Other Sources: http://gmwgroup.harvard.edu/pubs/pdf/1105.pdf http://gmwgroup.unix.fas.harvard.edu/pubs/pdf/1105.pdf Terms of Use: This article is made available under the terms and conditions applicable to Open Access Policy Articles, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#OAP Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:9821907

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