Surface Enhanced Raman Scattering Imaging of Langmuir-Blodgett Monolayers

摘要

More than a century ago. the first commercail dye was synthesized (Perkin 1856). Dyes are extremely versttile materials intensively investigated for electro-optical applications. Dyes have also played a key role in the development of surface-enhanced Raman scattering (SERS), in fact, a dye (Rhodamine) has been used almost exclusively in the SERS owrk pursuing single molecule detection (SMD spectroscopy)~(1,2). Visible dyes are strongly aborbing materials that present resonance Rman scattering when excited with visible saser~(3). As part of our research program on electroactive organic materials~(4), a systematic study on fabrication and spectroscopic properties of Langmuir and Langmuir-Blodgett (LB) films of perylenetetracarboxylic (PTCD) dyes is in progress~(5-7). In the present report, the surface-enhanced resonance Raman scattering (SERRS) and SERRS imaging of several PTCD molecules on silver island films is discussed. Micro-Rman imaging~(8,9) is a chemically selective surface Raman imaging technique, which is used to achieve a visulaization of the SERRS signal from silver islands coated with one LB monomolecular layer. The results of a temperature dependence study of the SERRS signal are also presented. Finally the sensitivity achieved with this series of dayes is consistently below the attomole detection limit, which make these materials an obvious choice for SMD studies.