AVS 52nd International Symposium
    Applied Surface Science Monday Sessions
       Session AS-MoP

Paper AS-MoP14
Potential Difference Mapping of Molecules and Particles on Insulating Substrate

Monday, October 31, 2005, 5:00 pm, Room Exhibit Hall C&D

Session: Aspects of Applied Surface Science Poster Session
Presenter: F. Yamada, Osaka University, Japan
Authors: F. Yamada, Osaka University, Japan
T. Matsumoto, Osaka University, Japan
H. Tanaka, Osaka University, Japan
T. Kawai, Osaka University, Japan
Correspondent: Click to Email
A lot of research groups are challenging to fabricate molecular devices by using self-assembly of molecules. For this purpose, the knowledge of local surface potential is essential to understand and control the driving force of the self-assembly. However, it is very difficult to measure the electric properties of nano structures of the molecular devices because such devices are created on an insulating substrate. We report here surface potential measurement of DNA and nanoparticle on an insulating substrate. We used the frequency mode non-contact AFM (FM-ncAFM). NC-AFM is able to measure local electrostatic force with high sensitivity and NC-AFM prevents the charge injection induced by tip-sample contact. The measurement reveals that the potential of DNA is higher than mica and sapphire surface. In this experiment, we demonstrated that the NC-AFM enables us to obtain surface potential images of molecules on insulating substrates. We also measured the d(@DELTA@f)/dV images of DNA and Au nanoparticles on mica. We found that the plots of the d(@DELTA@f)/dV as a function of bias voltage give characteristic slopes indicating the dielectric constants of different absorbates. This result means that this measurement can be used to discriminate surface species on an insulating substrate. To discuss about the contrast mechanism of the surface potential imaging on insulating substrate, this result is beyond the understanding based on Kelvin force microscopy because the surface potential of insulating substrate is indefinable. Then, we calculate electric filed just below the tip apex using finite element method. The calculation results reveals that the electric field just below the tip apex is enough strong to detect the local charge on surface adsorbate even if the substrate is insulator.