AVS 52nd International Symposium
    Electronic Materials and Processing Thursday Sessions
       Session EM1-ThM

Paper EM1-ThM11
Observation of trans-to-cis in Azobenzene by Spatially Resolved Scanning Tunneling Spectroscopy

Thursday, November 3, 2005, 11:40 am, Room 309

Session: Molecular Electronics
Presenter: B.-Y. Choi, Seoul National University, Korea
Authors: B.-Y. Choi, Seoul National University, Korea
S.-J. Kahng, Korea University, Korea
Y. Kuk, Seoul National University, Korea
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There have been serious efforts to apply various organic molecules to an organic based memory. These molecules change their configuration by a charge transfer between surrounding bonds or to reach an energy minimization state when a bias voltage is reached at a certain voltage. Similar but slightly different organic molecules, photo sensitive molecules, may be used for this application. Scanning tunneling microscopy/spectroscopy experiment was performed on azobenzene single molecule adsorbed on a Au(111) surface in UHV at 5K. Azobenzene has two stereoisomers; trans- and cis-azobenzene which can be transformed to each other by UV irradiation or thermal energy. We could induce the trans-to-cis transition of a single trans-azobenzene by injecting electric pulses by using STM tip and the electronic structure of them were observed in sub-atomic resolution. The tip bias for the trans-to-cis transition is ~1.5V and cis-azobenzene returned back under negative tip bias or in time at the adsorption site. The LUMO state of trans-azobenzene was confined mainly within the benzene segments which were lying parallel to gold substrate. The HOMO state was localized within the nitrogen. Cis-azobenzene shows several spectroscopy results depending on the molecule-surface configuration. We also observed an LDOS of azobenzene on NaCl layers deposited on Cu(111). Adsorbed on NaCl, the azobenzene shows an electronic states which are not coupled to that of the metal surface.