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 u sing transmission electron microscopy and UV-VIS absorption spectrosco py and by relating the morphological changes induced by these anions t o the results obtained by means of conventional Raman spectroscopy and Fourier transform Raman spectroscopy. An assessment of the effectiven ess of each colloid is made at different excitation lines within the v isible and near-infrared regions, An explanation of the mechanism thro ugh which these anions exert their activation effect is given on the b asis of the morphologies of the particles present in the colloid and t he 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.