AVS 50th International Symposium
    Surface Science Wednesday Sessions
       Session SS+OF-WeA

Paper SS+OF-WeA6
AFM Study of Carboxylic-Acid Functionalized Pentathiophenes on Mica Surfaces

Wednesday, November 5, 2003, 3:40 pm, Room 327

Session: Growth and Characterization of Organic Films
Presenter: J. Chen, Lawrence Berkeley National Laboratory
Authors: J. Chen, Lawrence Berkeley National Laboratory
A.R. Murphy, University of California
D.F. Ogletree, Lawrence Berkeley National Laboratory
M. Salmeron, Lawrence Berkeley National Laboratory
J.M.J. Frechet, Lawrence Berkeley National Laboratory and University of California
Correspondent: Click to Email
We studied SAM films of the oligothiophene derivative (D5TBA @footnote 1@) with AFM to determine its growth and structure and its response to mechanical excitations. We found that self-assembled films formed on mica substrates from hydrophilic (THF) and hydrophobic (chloroform) solutions were totally different in their structure and mechanical properties. In one case methyl groups were exposed while in the other carboxylic groups (COOH) were exposed, resulting in very different friction properties. Friction anisotropy was observed between domains of different orientations. Scanning polarization force microscopy (SPFM) was used to obtain contact potential maps (Kelvin Probe mode) to confirm film structures deduced from contact mode imaging. Generally, deposition from THF solutions produced stable monolayer aggregates with exposed methyl groups. Multilayer regions were sometimes observed, with alternate methyl and carbonxyl group terminations. During contact AFM imaging the third and higher layers could be progressively peeled off by increasing the load applied to the tip, however the second layer was found to incorporate into the first layer in a densification process. Deposition from chloroform solutions usually produced unstable multilayer films with methyl groups contacting the mica surface. @FootnoteText@ @footnote 1@ D5TBA, or 4-(5''''-Decyl-[2,2';5', 2''; 5'', 2'''; 5''', 2''''] pentathiophen-5-yl)-butyric acid, was prepared by Stille cross-coupling methods using functionalized thiophene monomers.