Where Does It Vibrate? Raman Spectromicroscopy on a Single Molecule

摘要

Acquiring information on individual molecules, for example identity, orientation, and conformation on a sub-nanometer length scale is arguably one of the ultimate goals of chemical analysis. In the case of sohd surfaces and adsorbates, which play an important role in catalysis, the chemical composition is typically probed with surface sensitive, laterally integrating spectroscopic techniques such as X-ray photoelectron spectroscopy. Lateral integration ensures sufficient signal intensity, but necessitates model systems with many identical repeat units. This is achieved by using surfaces of single crystals, which, however, are often not representative as model systems for the-structurally much more complex-real catalysts. Complementary topographic information is obtained with scanning probe techniques of limited sensitivity to chemical composition. Such combinations of nonlocal spectroscopic and chemically insensitive microscopic techniques make it difficult to obtain both chemical and topographic information on the atomic or molecular level, for example from a single adsorbed molecule. Apparently, there is a need for local spectromicroscopic techniques which provide parallel chemical and topographic data with sub-nanometer resolution and which can be applied to chemically and structurally complex samples under a wide range of experimental conditions.