THERMAL-PROPERTIES OF PERFLUORINATED N-ALKANOIC ACIDS SELF-ASSEMBLED ON NATIVE ALUMINUM-OXIDE SURFACES

We have examined the thermal and chemical properties of a homologous s eries of long-chain perfluorinated n-alkanoic acids [CF3(CF2)(n)COOH, n=8, 10, 12, 14, 16] self-assembled on native aluminum oxide surfaces using thermal desorption mass spectrometry and monochromatic x-ray pho toelectron spectroscopy. These monolayers were prepared by solution se lf-assembly under ambient conditions on pre-cleaned native aluminum ox ide surfaces and then transferred into an ultrahigh vacuum en environm ent for surface analyses. A chemisorption bond strength of similar to 30 kcal/mol between the reactive acid head group and the native alumin um oxide surface has been derived from thermal desorption studies. Upo n increasing surface temperature, the predominant surface process was found to be molecular desorption. In addition, a minor surface chemica l reaction channel also coexists at elevated temperatures, resulting i n thermal dissociation of the long chain acid molecules and subsequent formation of a partially fluorinated aluminum oxide surface. These se lf-assembled molecular monolayers exhibit remarkable long-term ambient stability (similar to 10(3) h) which improves progressively with incr easing fluorocarbon chain length. (C) 1998 American Vacuum Society.