Nijhuis, Christian A.Reus, William F.Whitesides, George2012-10-312010Nijhuis, 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): 18386-18401.0002-78631520-5126http://nrs.harvard.edu/urn-3:HUL.InstRepos:9821907This 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.en-USself-assembled monolayersnegative differential resistanceunimolecular electronic devicesgallium-indium EGaINelectrical rectificationhexadecylquinolinium tricyanoquinodimethanidealkanethiol monolayersorganic materialscharge-transportmetal junctionJournal Article2012-10-3110.1021/ja108311j