A tetrahedral tip as a probe for tip‐enhanced Raman scattering and as a near‐field Raman probe

Abstract

AbstractWe use a tetrahedral glass fragment which is coated with a thin film of gold (T‐tip) to form a local tip source by illuminating the tip from within its transparent glass body. We demonstrate the potential of this apertureless tip source for tip‐enhanced Raman scattering (TERS) as an alternative to the standard scheme with an external illumination. We found that T‐tips with different optical properties result from the process of tip fabrication. For some tips, the Raman signal persists for a small number of molecules picked up by the retraction of the tip from a tunnel contact. In these cases, the tip itself gives rise to the TERS signal without a gold substrate close to the tip. Other tips only exhibit a TERS signal when there is a contact to a gold substrate. Tips covered by Raman active nonresonant molecules serve as a new kind of near‐field Raman probe for local properties of a sample. As the Raman spectrum of the coated tip is sensitive to the local light intensity, it may be used to monitor the field‐enhancement properties of metal films and metal nanostructures. A near‐field Raman probe avoids problems due to bleaching of a fluorescent near‐field probe and, furthermore, such a near‐field Raman probe may be highly selective for specific surface properties. Copyright © 2009 John Wiley & Sons, Ltd.