EPR OF ALKYLTHIO MODIFIED GOLD COLLOID

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Several Au colloidal systems have been prepared by subsequent adsorption of long-chain alkanethiol monolayers on their surfaces. The resulting monolayer films are highly ordered for chain lengths of 10 carbon units or greater. Unusual Raman spectra have been observed from these films; a series of new Raman bands appears for longer chain films (nc>10), which has been directly correlated to film crystallinity. In addition, these bands are only observed in the Raman spectra when the excitation wavelength is in the range 620-720 nm; outside this range, the normal group vibrational frequencies of the film are the only bands observed. The resonance process associated with these Raman bands appears to originate from the Au/S interfacial region, and current models of interfacial structure support the formation of polysulfur species at the headgroups of the chemisorbed alkanethiols. Polysulfur chains are expected to be diradicals, and the presence of a radical species would explain the optical absorption appearing so far in the red. Our goal therefore is to ascertain whether or not polysulfur (or any radical species in essence) is present within the film by EPR.