AVS 53rd International Symposium
    Electronic Materials and Processing Friday Sessions
       Session EM-FrM

Paper EM-FrM1
Scanning Tunneling Microscopy Study of Azobenzene and Azobenzene-Derivatives

Friday, November 17, 2006, 8:00 am, Room 2001

Session: Molecular Electronics
Presenter: Y.S. Cho, Seoul National University, Korea
Authors: Y.S. Cho, Seoul National University, Korea
B.Y. Choi, Seoul National University, Korea
H.J. Yang, Seoul National University, Korea
Y. Kuk, Seoul National University, Korea
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Conjugated molecular chains exhibit good conductivity with @pi@ bonding for the carrier transport. If two disconnected parts of a conducting molecular chain are connected by a bond with two coupled potential energy surfaces with 2 degrees of freedom, the resulting chain will reveal non-linear characteristics. It has been shown experimentally in a scanning tunneling microscopy (STM) that these kinds of molecules switch between two potential energy minima and function as nano-molecular switches.@footnote 1@ Chemical isomers are the most appropriate target molecules, because they have the same molecular formula and connectivity but different geometric structures and conductivities. We studied geometric and electonic structures of isolated azobenzene and azobenzene derivative molecules adsorbed on Au (111) surface with scanning tunneling microscopy and spectroscopy(STM) at 5K. These molecules have two stereoisomers which can be transformed to each other by UV irradiation or thermal energy. We could induce this transformation by tunneling electrons using STM tip. In the case of azobenzne, the trans-to-cis transition is induced at ~-1.5V and the cis-azobenzene returned back ~+2.5 V. We studied three different kinds of azobenzene-derivatives; EtO-Az-C10, EtO-Az-C6, CF@sub 3@-Az-C10. Each derivative has a long alkyl-chain which enable us to control the length of switching molecules. We will show the coverage dependance of the HOMO-LUMO state and the conformational change by STM tip in azobenzene-derivatives. This results could be an possible implication to mechanism of organic-based conformational switch. @FootnoteText@ @footnote 1@ Byoung-Young Choi et al., PRL 96, 156106 (2006).