Gp. Hastie et al., EXAMINATION OF THE STRUCTURE AND MELTING BEHAVIOR OF THIN-FILM N-ALKANES USING ULTRA-SOFT POLARIZED NEAR-EDGE X-RAY-ABSORPTION SPECTROSCOPY, Journal of the Chemical Society. Faraday transactions, 92(5), 1996, pp. 783-789
Citations number
38
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
The use of ultra-soft near-edge X-ray absorption tine structure (NEXAF
S) spectroscopy as a tool for determining the molecular orientations,
and changes in the orientations and conformations, of thin organic fil
ms is presented. Polarisation-dependent NEXAFS measurements made at th
e carbon K-edge reveal that vapour-grown n-alkanes, deposited onto Si(
111), exhibit structures with a high degree of long-range order. The m
olecular tilt angles, with respect to the substrate surface, for n-alk
anes CnH2n+2 in the carbon chain-length range n = 22-60 are found to b
e consistent with their bulk crystallographic structures. Temperature
dependent measurements carried out using simultaneous electron yield a
nd fluorescence yield techniques reveal evidence of surface freezing i
n the longer even n-alkanes (n greater than or equal to 46). Such a pr
ocess is not evident in the shorter alkanes. The potential causes of t
his chain-length dependence are discussed.