Dresden 2009 – wissenschaftliches Programm
DS 16.24: Poster
Dienstag, 24. März 2009, 09:30–12:30, P5
Study of Alkane Structure and Phase Transitions with X-Ray Reflectivity — Valeria del Campo1, Edgardo A. Cisternas1, Ignacio Vergara1, Tomás Corrales1, •Ulrich G. Volkmann1, Haskell Taub2, Haiding Mo3, and Steven Ehrlich3 — 1Surface Lab, Facultad de Física, Pontificia Universidad Católica de Chile, Chile — 2Department of Physics and Astronomy, University of Missouri-Columbia, USA — 3NSLS, Brookhaven National Laboratory, USA.
We study the structure and phase transitions of vapor-deposited films in the range of monolayers of n-dotriacontane with synchrotron X-Ray Reflectivity. The films as deposited present a complete bilayer adjacent to the substrate where the alkanes lay parallel to the surface, and one layer in which the molecules are oriented perpendicular to the surface with an occupancy of ∼70%. After an initial temperature cycle up to 350 K the film forms two perpendicular layers. On heating to 338 K, thickness of the perpendicular layers decrease from 42.5 to 40.7 Å. At 344 K we only detect the signal from the parallel bilayer, which has increased its thickness from 9.2 to 10.4 Å. These transitions are consistent with those found by Bai et al.  with temperature dependent AFM measurements performed on samples grown by dip-coating from solution instead of physical vapor deposition in high vacuum.
 M. Bai et al., Europhys. Lett. 79, 26003 (2007).
This work is supported by Grant Nos. U.S. NSF DMR-0705974, DMR-0454672 in the USA, and FONDECYT 1060628 and 7070248 in Chile.