AVS 51st International Symposium
    Organic Films and Devices Wednesday Sessions
       Session OF+EM-WeM

Paper OF+EM-WeM3
AFM Study of @beta@-7T Oligothiophene Films on Mica: Humidity-Dependent Mechanical Properties and Structure

Wednesday, November 17, 2004, 9:00 am, Room 304C

Session: Molecular and Organic Films and Devices - Electronics
Presenter: J.Y. Chen, Lawrence Berkeley National Laboratory
Authors: J.Y. Chen, Lawrence Berkeley National Laboratory
I. Ratera, Lawrence Berkeley National Laboratory
D.F. Ogletree, Lawrence Berkeley National Laboratory
M. Salmeron, Lawrence Berkeley National Laboratory
AR Murphy, University of California, Berkeley
JMJ Frèchet, University of California, Berkeley
Correspondent: Click to Email
Langmuir-Blodgett films of @beta@-7T@footnote1@ oligothiophene, a molecule with potential molecular electronic applications, were transferred to mica and studied with contact AFM. Mono and multilayer films exhibited structural and mechanical properties that depend on humidity, temperature and applied force as well as the LB transfer pressure. We found that monolayers were adsorbed through the carboxylic acid group, exposing the alkyl chains to the air interface. Two structural phases of the molecular film were observed. In the "A" phase the molecules were fully stretched and the film had a height of 2 nm. This phase was stable at high humidity and under low loads. The "B" phase had a height of 1.2 nm and was stable under dry conditions and high loads. Domains of both A and B phases were observed in the same larger islands. Changing humidity reversibly modified the A:B ratio and the sizes of the domains. Heating the samples resulted in an irreversible decomposition of the continuous film islands into small aggregates. @FootnoteText@ @footnote1@ @beta@-7T: a 7 thiophene oligomer with two alkyl side chains and an acetic acid group, 3'',4''''-didecyl-5,2';5',2'';5'',2''';5''',2''''; 5'''',2''''';5''''',2''''''-heptathiophene-4'''-acetic acid.