Self-assembled films of alkyl halides on alkali halides

Monolayer films of four different alkyl halides were prepared by exposing freshly cleaved alkali halide (001) surfaces via immersion for at least 48 h to dilute benzene solutions of these compounds. The thickness and orientation of each film were inferred from the variation with take-off angle of the characteristic atomic peak heights in x-ray photoelectron spectroscopy spectra. For each of these compounds on each alkali halide surface, the spectra indicate that the halogen end of the molecule lies at the substrate interface and the other end points away from the interface. Films of BrCH2(CH2)(4)CH3 were formed by deposition in vacuum on a cleaved KBr(001) target at similar to 140 K. The growth and evolution with thermal cycling of the film up to its desorption temperature at similar to 180 K were followed by monitoring the specular reflection of a helium atomic beam from the surface. Films heated above similar to 170 K appear to anneal to a more ordered structure; helium diffractive scattering from the deposited film taken at similar to 50 K without annealing yielded broad diffraction peaks at the KBr positions, while similar measurements taken after annealing produced sharp diffraction peaks at these angles and at half-order angles as well. Consistent with helium diffraction measurements over a range of azimuths, the structure of this annealed film could be interpreted as one of mixed (1x2) and (2x1) domains. Specular intensity measurements as a function of surface temperature yielded a Debye temperature of the annealed film similar to 95 K. (C) 1996 American Vacuum Society.