Natascha Knowlton, University of Utah
Chemistry
The chemical derivatization of oxide surfaces (silica, alumina, glass) is critical to the development of separation media, sensing surfaces, or biocompatible interfaces. Presently, there are few analytical methods that allow the detection and characterization of functionalized monolayers on these surfaces. Raman scattering spectroscopy can provide useful structural information in the form of vibrational spectra of molecules of interest, and it is compatible with oxide substrates. Raman scattering, however, is a very weak effect so that its application to detecting monolayers is challenging. In this work, two approaches to detecting and characterizing molecular layers on oxide surfaces with Raman spectroscopy are compared. First, gold colloidal nanoparticles are deposited onto the surface of interest, which enhance the Raman scattering near the gold surface by surface-plasmon resonance. This technique is suitable for ex situ analysis of monolayers on planar surfaces. Secondly, monomolecular layers can also be detected by Raman scattering on porous oxide supports such as alumina or silica without any optical enhancement due to the very high surface area of these materials. Detection in porous particles is compatible with in situ monitoring of surface derivatization reactions. These two methods are compared for monitoring of reactions of silane-coupling agents and their subsequent functional group transformations on glass and silica surfaces.