Application of galvanic displacement for the preparation of substrates for surface-enhanced Raman spectroscopy

There are ample methods for the production of substrates for surface-enhanced Raman spectroscopy (SERS). Such substrates must consist of roughened bulk gold or silver or of nanoparticles made of these metals. The preparation of such morphologies is not trivial. The methods of their production are usually time-consuming and often require expensive apparatus. These that are easy to prepare have their limitations like irreproducibility or low enhancement factor. Often the substrates that are reproducible do not provide high enhancement factor and vice versa. A review of these methods is given in Chapter 1 of this dissertation.;The remainder of this dissertation describes the research performed to explore the applicability of galvanic displacement as a method of production of substrates for SERS. The reduction of silver (predominantly) and gold salts on germanium and silicon supports was studied: The morphology of silver nanoparticles prepared by galvanic displacement can be tuned from smooth, very small particles through larger crystalline grains to micrometer-sized dendritic, or fernlike, structures. Their performance was checked using aromatic thiols as probe molecules. The method was also used to assess its applicability to coat atomic force microscopy tips with silver for tip-enhanced Raman spectroscopy.;When silver particles grown on silicon are allowed to undergo Ostwald ripening before application of an analyte, their surface area decreases and they become smoother. Surprisingly the intensity of the Raman signal arising from adsorbates on silver particles modified in this way more than doubles in comparison to the one arising from nanoparticles with sharp edges. The nature of the enhancing particles has been explored. It was discovered that the silver particles areas that provide the highest Raman intensity (the so-called "hotspots") may not be located on the surface of closely spaced but isolated particles, but rather at the places where the particles merge.;Conditions that allow the production of substrates yielding high enhancement factors were optimized. Galvanic displacement was found to be a very convenient method of preparation of SERS-active substrates. The substrates give excellent enhancement and yet are easy to prepare, inexpensive and give very reproducible intensities for SERS spectra of thiol monolayers.