Applied Physics

The Core-Shell of the Matter

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Science  31 Jan 2003:
Vol. 299, Issue 5607, pp. 629
DOI: 10.1126/science.299.5607.629a

In vibrational spectroscopy, the Raman effect, which generally is rather weak, can be enhanced by means of surface plasmons when molecules are adsorbed on the surface of rough silver films. Although the enhancement can be by several orders of magnitude, its variability has limited the easy quantification of spectra. Jackson et al. studied the surface-enhanced Raman scattering (SERS) of nanoparticles in which a dielectric silica core is surrounded by a silver shell, a geometry that can enhance the local electromagnetic field. Experimental studies on cores ranging from 65 to 79 nm and shells with a thickness of 5 to 20 nm show an apparent SERS enhancement of 106 for para-mercaptoaniline molecules adsorbed in aqueous solutions. Because of the reabsorption of signal by nearby core-shells, the actual enhancement is 1012, or comparable to that seen for colloidal silver. The changes in calculated Raman response (as |ERaman|4) with changes in core-shell geometry follow those seen experimentally; thus, the enhancement is not due to other factors (localized plasmons and molecular resonances) proposed to contribute to SERS. — PDS

Appl. Phys. Lett. 82, 257 (2003).

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