B. Vlckova et al., SERS EXCITATION PROFILES OF PHTHALAZINE ADSORBED ON SINGLE COLLOIDAL SILVER AGGREGATES AS A FUNCTION OF CLUSTER-SIZE, JOURNAL OF PHYSICAL CHEMISTRY B, 101(9), 1997, pp. 1588-1593
The wavelength-dependent SERS enhancement and photoreactivity of phtha
lazine (pht) adsorbed on single Ag colloid fractal clusters deposited
out of solution onto a glass surface were determined as a function of
cluster size from the excitation profiles of the SERS spectra of three
individual colloid clusters with dimensions 1.9 x 1.9 mu m, 3.7 x 2.8
mu m and 7.5 x 4.7 mu m. The spectra were correlated with a given clu
ster by using imaging Raman microspectroscopy. The SERS excitation pro
files obtained from various bands observed in the SERS spectra could b
e understood in terms of two wavelength-dependent contributions: (i) t
he photochemical activity which grows monotonically toward the blue in
the spectral range (470-650 nm) used and (ii) the SERS enhancement fu
nction which increases toward the red. The variety of shapes observed
for the excitation profiles can be explained in terms of the relative
contribution of the pht reagent and the photoproduct to the sometimes
overlapping SERS bands. The relative contributions (or lack of overlap
) suggested by the SERS excitation profiles are in good agreement with
the independent assignments of those bands to pht or its photoproduct
. The wavelength-dependent SERS enhancement and the photoreactivity we
re found to be approximately independent of cluster size for the three
clusters studied in keeping with predictions made in the literature r
elating to the optical properties of fractal clusters.