AVS 49th International Symposium
    Surface Science Friday Sessions
       Session SS-FrM

Paper SS-FrM7
Temperature-Programmed Desorption and Scanning Tunneling Microscopy Studies of n-Alkane Derivatives on Graphite: Desorption Energetics and the Influence of Functional Groups on Adsorbate Self-Assembly

Friday, November 8, 2002, 10:20 am, Room C-110

Session: Self-Assembly at Surfaces
Presenter: T. Müller, Columbia University
Authors: T. Müller, Columbia University
K.T. Rim, Columbia University
G.W. Flynn, Columbia University
A.V. Teplyakov, University of Delaware
Correspondent: Click to Email
While carbon materials have found many practical applications ranging from sorption and catalyst support to the protection of magnetic storage media, numerous further uses may follow from the more recently discovered allotropes, fullerenes and carbon nanotubes. Alkane derivatives on the inert support provided by graphite can serve as model systems to study organic thin films and two-dimensional self-assembly. In the present study, Temperature Programmed Desorption (TPD) and Scanning Tunneling Microscopy (STM) are utilized to examine the influence of functionalization on the adsorption energetics and self-assembly of n-alkanes on Highly-Oriented Pyrolytic Graphite (HOPG). For adsorption of 1-bromoalkanes, alkanoic acids, and 2-bromoalkanoic acids, full activation of the substrate surface required annealing temperatures of approximately 700 K. Molecular desorption from physisorbed mono- and multilayers was found to exhibit first and zeroth-order kinetics, respectively. A Redhead analysis of monolayer desorption signals uncovered a profound influence of alkane functional groups. As compared with unfunctionalized n-alkanes, the desorption energies of all derivative species studied here exhibit a reduced chain length dependence in conjunction with an increased adsorption energy in the limit of zero chain length. Both effects reach their maximum for 2-bromoalkanoic acids, where (up to 2-bromooctanoic acid) the adsorption energy is nearly independent of the number of methylene units. The presence of functional groups is seen to introduce additional interactions, causing added configurational constraints and a competition with alkyl chain interactions in determining self-assembly patterns. These trends will be discussed in the context of molecular self-assembly information provided by ambient (liquid/solid) and UHV STM studies.