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Issue 3, 2012
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Structure Matters: Correlating temperature dependent electrical transport through alkyl monolayers with vibrational and photoelectron spectroscopies

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Abstract

Freezing out of molecular motion and increased molecular tilt enhance the efficiency of electron transport through alkyl chain monolayers that are directly chemically bound to oxide-free Si. As a result, the current across such monolayers increases as the temperature decreases from room temperature to ∼80 K, i.e., opposite to thermally activated transport such as hopping or semiconductor transport. The 30-fold change for transport through an 18-carbon long alkyl monolayer is several times the resistance change for actual metals over this range. FTIR vibrational spectroscopic measurements indicate that cooling increases the packing density and reduces the motional freedom of the alkyl chains by first stretching the chains and then gradually tilting the adsorbed molecules away from the surface normal. Ultraviolet photoelectron spectroscopy shows drastic sharpening of the valence band structure as the temperature decreases, which we ascribe to decreased electron–phonon coupling. Although conformational changes are typical in soft molecular systems, in molecular electronics they are rarely observed experimentally or considered theoretically. Our findings, though, indicate that the molecular conformational changes are a prominent feature, which imply behavior that differs qualitatively from that described by models of electronic transport through inorganic mesoscopic solids.

Graphical abstract: Structure Matters: Correlating temperature dependent electrical transport through alkyl monolayers with vibrational and photoelectron spectroscopies

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Publication details

The article was received on 05 Sep 2011, accepted on 08 Nov 2011 and first published on 25 Nov 2011


Article type: Edge Article
DOI: 10.1039/C1SC00639H
Chem. Sci., 2012,3, 851-862

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    Structure Matters: Correlating temperature dependent electrical transport through alkyl monolayers with vibrational and photoelectron spectroscopies

    H. Shpaisman, O. Seitz, O. Yaffe, K. Roodenko, L. Scheres, H. Zuilhof, Y. J. Chabal, T. Sueyoshi, S. Kera, N. Ueno, A. Vilan and D. Cahen, Chem. Sci., 2012, 3, 851
    DOI: 10.1039/C1SC00639H

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