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Ultramicroscopy. 2008 Sep;108(10):1101-5. doi: 10.1016/j.ultramic.2008.04.022. Epub 2008 May 7.

A study on conformational changes by electron charges in viologen single molecules by using STM.

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  • 1Department of Electrical Engineering and Nano Engineering, Dong-A University, Busan 604-714, Korea.


The topography of self-assembled viologen derivatives (VC(8)SH, VC(10)SH, HSC(8)VC(8)SH, and HSC(10)VC(10)SH) molecules on an octanethiol (C(8)) self-assembled monolayer (SAM) modified gold surface was measured using ultrahigh-vacuum scanning tunneling microscopy (UHV-STM). We demonstrate here a novel matrix SAM appropriate for isolation of the viologen molecules. The C(8) was used for a matrix SAM, in which the VC(8)SH, VC(10)SH, HSC(8)VC(8)SH, and HSC(10)VC(10)SH were inserted at molecular lattice defects. The isolated single molecules of viologen derivatives inserted in the matrix SAM were observed as protrusions in STM topography using a constant current mode. We measured the topographic heights (VC(8)SH: 1.53 nm, VC(10)SH: 2.01 nm, HSC(8)VC(8)SH: 2.71 nm, and HSC(10)VC(10)SH: 3.3 nm) of the molecular protrusions using STM. Also, changes in the central axis of viologen molecules were observed as VC(8)SH (0.5-0.73 nm), VC(10)SH (0.4-0.74 nm), HSC(8)VC(8)SH (0.67-0.84 nm), and HSC(10)VC(10)SH (0.67-0.99 nm), respectively.

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