MORPHOLOGICAL-STUDY OF SILVER COLLOIDS EMPLOYED IN SURFACE-ENHANCED RAMAN-SPECTROSCOPY - ACTIVATION WHEN EXCITING IN VISIBLE AND NEAR-INFRARED REGIONS

The activating effect of chloride, perchlorate, and nitrate anions on different silver colloids used in surface-enhanced Raman spectroscopy is studied. This study is done from a morphological point of view by using transmission electron microscopy and UV-VIS absorption spectroscopy and by relating the morphological changes induced by these anions to the results obtained by means of conventional Raman spectroscopy and Fourier transform Raman spectroscopy. An assessment of the effectiveness of each colloid is made at different excitation lines within the visible and near-infrared regions, An explanation of the mechanism through which these anions exert their activation effect is given on the basis of the morphologies of the particles present in the colloid and the absorption spectrum of each colloid, Modifications of the colloids, either during or after the process in which they were obtained, were made in order to improve their effectiveness when excited in the near-infrared region. (C) 1995 Academic Press, Inc.