Structural models and thermal desorption energetics for multilayer assemblies of the n-alkanes on Pt(111)

The structural and thermodynamic properties of linear hydrocarbon multilaye r assemblies supported on a Pt(111) single-crystalline substrate are invest igated with temperature-programmed desorption and infrared reflection absor ption spectroscopies. The multilayer assemblies are comprised of all-trans chains preferentially aligned with their ccc places parallel to that of the surface. Coverage-dependent vibrational spectra reveal that the deposition process, up to the first monolayer total coverage, proceeds first via an i sland growth mechanism. This result demonstrates that an important contribu tion is made by (chain-length-dependent) attractive lateral interactions to the binding energies of the monolayer films. The subsequent layers deposit ed in a multilayer appear to contain a modest concentration of conformation al/orientational defects (and perhaps layer misplacements as well). The ene rgetics of the desorption processes for these hydrocarbon assemblies are ra tionalized on the basis of a conserved value of a prototypical segmental he at of adsorption. The kinetic model embodying this description invokes a la yer-by-layer desorption and invokes a central role for lateral interactions and diffusion in maintaining the kinetic competence of a general mechanism of monolayer evaporation from two-dimensional island domains.