AVS 45th International Symposium
    Organic Electronic Materials Topical Conference Tuesday Sessions
       Session OE+BI+EM-TuA

Invited Paper OE+BI+EM-TuA1
Structural Characterization of Organic Overlayers Physisorbed on the Surface of Self-Assembled Monolayers (SAMs) of Alkanethiols on Au(111)

Tuesday, November 3, 1998, 2:00 pm, Room 327

Session: Organic Thin Film Growth
Presenter: G. Scoles, Princeton University
Authors: P. Schwartz, Princeton University
D.J. Lavrich, Princeton University
M.C. Gerstenberg, Princeton University
G. Scoles, Princeton University
Correspondent: Click to Email
We have been able to grow well-ordered crystalline monolayers of alkylthiols, and multilayers of dodecane on the surface of alkanethiol SAMs by exposing the surface of the c(4x2) phase of the SAM to the appropriate amount of flux at carefully controlled temperatures. Low energy atomic diffraction shows that all but one of the overlayers proved to be considerably more ordered than the underlying c(4x2) surface as judged by the specular and diffraction peak intensities. While the surfaces of the dodecane overlayers have the same structure whether grown on a C@sub 11@SH or C@sub 10@SH c(4x2), monolayers of C@sub 10@SH on a C@sub 10@SH c(4x2) surface were distinctly different from and of higher quality than monolayers of C@sub 11@SH on a C@sub 11@SH c(4x2) surface. Debye Waller measurements reveal that, besides improving the overall order of the surface, an overlayer has a stiffer surface than the underlying c(4x2) that supports it. Temperature Programmed Desorption experiments have shown that, although the adsorption energy of organic molecules on a gold surface is much greater than that of the bulk heat of vaporization, the adsorption energy of an overlayer on an organic substrate is similar to the bulk value of the overlayer substance as soon as the metal-overlayer distance is greater than 5 Å. To the best of our knowledge, this is the first time that, making use of the great surface specificity of low energy atomic scattering, organic monolayers are structurally characterized after adsorption on an organic substrate of different structure.