| In this thesis, we investigate the surface vibrational dynamics of complex organic films to explore self-assembly and confinement effects, which have implications in diverse fields from medicine to molecular electronics. Three systems are examined: alkanethiol self-assembled monolayers, sulfur hexafluoride mono- and bilayers, and polymer thin films. Helium atom scattering is used as the primarily technique to investigate the structure and dynamics of these systems in a highly surface-sensitive and non-destructive manner.; We have studied the strength of the interaction between alkanethiol self-assembled monolayers and reconstructed Au(111) as a function of monolayer structure. The results show that hexanethiol (C6), like octanethiol (C8), has an incommensurate structure with the reconstructed Au(111) substrate in contrast with decanethiol (C10). The dispersionless single-phonon modes of C6, C8, and C10 are assigned as frustrated translations normal to the surface. The energies of the single-phonon modes are the same for C6 and C8, but 0.7 meV higher for C10. We propose that the difference in energy for C10 is due to its commensurate structure with the reconstructed Au(111) lattice.; The transition from monolayer to bulk behavior is explored using sulfur hexafluoride on reconstructed Au(111). Disordered mono- and bilayers exhibit dispersionless fundamental and overtone phonon modes. We discuss the differences between SF6 and rare gas bilayers.; The bulk of this dissertation explores the effect of nanoconfinement on the surface vibrational dynamics of polymer thin films supported on SiO x/Si(100). For poly(methyl methacrylate), we observe a thickness dependence in the elastic and inelastic scattering regimes. Films several times the bulk radius of gyration (Rg) thick have larger mean-square displacements than films a fraction of Rg thick. In the multiphonon regime, the probability of collisional de-excitation of vibrational modes is reduced for higher molecular weight films at thicknesses of approximately 1/3 Rg and for lower molecular weight films of all thicknesses. We hypothesize that substrate interactions in the thinner films inhibit mobility at the polymer-vacuum interface. In addition, we examine interfacial structure through analysis of poly(methyl methacrylate), polystyrene, and 1,4-trans-polybutadiene spectra and fits to a semiclassical scattering model. |
