Resonance Raman Spectroscopy of Adsorbed Species on Solid Surfaces

Abstract

Every substance has the “bulk” which occupies almost all its content and the “surface” which is very thin layer enveloping the former. When two or more substances are in contact, the boundary layer constitutes the “interface.” Although the mass of the surface o r interface is negligibly small compared with that of the bulk, the ability of the interface in chemical reactions is far more significant than that of the bulk, because a number of chemical reactions initiate from the interfaces and the reaction rates can be controlled by the use of specifics of the surfaces, especially in catalytic and electrode reactions. Therefore, it is very important to investigate fully the structure and property of the surfaces or interfaces, which must be definitely different from those of the bulk, for elucidation of chemical behavior of materials. The clarification on bulk materials are extensively developed by spectroscopic and diffraction methods. However, as regards the features of the interface, much less knowledge is available at present. It is mainly because that in ordinary experiments, the specimen, consisting of a very small part of surface species and a very large part of bulk materials, even when the adsorbents are porous, cannot represent the characteristic nature of the surface. In other words, the specific character of interface or surface can only be observed in the monoatomic layer o r within the depth of several tens of angstroms from the interface. Besides, the surface species, which play an important role in catalytic o r electrode reactions, are often so unstable that they are detected only in situ measurements.