Self-assembled monolayers (SAMs) formed via chemisorption are important for a variety of surface enhancement and biological applications. We demonstrate that combinatorial spectroscopic ellipsometry (SE) and quartz crystal microbalance with dissipation (QCM-D) provides dynamic, in-situ characterization of the chemisorption process. In agreement with other studies, we find there are two steps for 1-decanethiol, an example alkanethiol SAM, chemisorption onto gold, which are a brief, fast phase followed by one that is long but slower. By using both the optical (SE) and mechanical (QCM-D) techniques, we show that the SAM porosity decreases during the second phase as the coupled ethanol solvent in the disorganized layer is replaced by more alkanethiol. (C) 2010 Elsevier B.V. All rights reserved.