Growth Dynamics and Morphology of Oleic Acid Vapor-Deposited on a Silica Surface^†

The vapor deposition of oleic acid onto silica surfaces at 25% relative humidity and temperatures ranging from 60 to 80 degrees C is found to proceed in three stages: (I) rapid formation of monolayer-high islands of approximately 100 nm diameter on timescales of a few minutes; (II) relatively little growth over timescales of tens to hundreds of minutes; and (III) a linear increase in apparent thickness as a function of time, characterized by the formation of multilayer islands on time scales of thousands of minutes. The rate of growth in region III is faster at higher temperatures. This growth process is analyzed in the context of the transition from two-dimensional to three-dimensional island growth at submonolayer coverage observed for metal vapor deposition on oxide surfaces. At a relative humidity of 94%, with several layers of water molecules present on the silica surface, the oleic acid wets the surface rather than forming discrete islands.