MORPHOLOGICAL-STUDY OF METAL COLLOIDS EMPLOYED AS SUBSTRATE IN THE SERS SPECTROSCOPY

Transmission electronic microscopy (TEM) and ultraviolet-visible absor ption spectroscopy were used to characterize several silver and copper sols employed as substrates in surface enhanced Raman spectroscopy(SE RS). In this study we have focused our attention on the changes observ ed when the large scale roughness is modified by the aggregation agent 1,5-dimethylcytosine (DMC). A previous analysis of several unaggregat ed silver and copper colloids and a comparison with the corresponding aggregated colloids were made, so that a relationship between the morp hology of the aggregates and the SERS results was obtained. Informatio n about the aggregation process of the colloids studied is also presen ted, on the basis of the results obtained from TEM, UV-visible spectro scopy, and the study of the variation of the SERS signal with the conc entration of DMC. From these results, the morphology of the resulting aggregates which yields the most intense SERS signal is inferred. A di fferent aggregation mechanism is suggested for each colloidal metal, a ccording to the remarkably different geometry of the final aggregates observed. This is further attributed to the different sizes of the sim ple particles present in the original colloids. (C) 1994 Academic Pres s, Inc.