ORIENTATION OF SINGLE-CRYSTALLINE PARAFFIN THIN-FILMS FROM TIME-OF-FLIGHT DIRECT RECOIL SPECTROMETRY

The direct recoil (DR) method of the technique of time-of-flight scattering and recoiling spectrometry (TOF-SARS) has been applied to obtain the molecular orientation at the surface of organic polymers. A model system consisting of monocrystalline thin layers of paraffin (hexatricontane) with the lamellae-oriented parallel to the substrate surface (polymer chains perpendicular to the surface) and with the lamellae oriented perpendicular to the substrate surface (polymer chains parallel to the surface) has been studied. The fluxes of H and C atoms recoiling from 4-keV Ar+ collisions with the surface have been measured as a function of the beam incident angle to the surface and the crystal azimuthal angle. The anisotropy observed in the azimuthal angle scans and the relative intensities of the H and O atom recoils in the incident angle scans provide information on the surface structure. The sensitivity of DR to the direction of the molecular backbone and the orientation of the methyl groups at the chain ends are well established.