Surface enhanced Raman scattering (SERS) by molecules adsorbed at spherical particles: errata

Optical properties of monodispersed hematite hydrosols

The experimentally determined extinction spectra of colloidal hematite, consisting of spherical particles of 0.10, 0.12, 0.13, 0.15, 0.16, and 0.51 microm in modal diameter, respectively, are compared with the corresponding theoretically calculated spectra using the Lorenz-Mie theory. These spectra are most sensitive to the particle size in the 0.10-0.20-microm range due to the damping effects which broaden the resonance at the expense of its height. For large particles (0.51 microm) the extinction becomes independent of the wavelength because of the broader size distribution of the hematite dispersion. As the small particles aggregate, a shoulder appears at 550 nm corresponding to the onset in fluctuations in the extinction efficiency of various sized particles. This shoulder may suggest the existence of certain surface electromagnetic modes caused by aggregation. A comparison is made in the size-dependent extinction efficiency at various wavelengths between colloidal hematite and gold sols.

Mie scattering interferometer and its application to the study of Raman scattering from molecules at a mercury interface

Interference fringes are observed produced by Mie scattering of laser light from a single microstructure or from a random array of microstructures supported above a reflecting surface. These fringes are the basis of a simple interferometer which can be used to measure distances from thousands of angstroms to centimeters. The interferometer is used to measure the height of liquid above a mercury surface. Raman scattering (RS) from the liquid is measured, and an upper limit of 10(3) is placed on the enhancement of RS from molecules at the interface. Enhancement of RS in a wedge between mercury and solid is examined theoretically.

Enhanced fields on large metal particles: dynamic depolarization

Influences of particle size on surface-enhancement processes are discussed in terms of a simple physical model. When the size of a silver sphere is increased, the magnitude of the enhancement exhibits a slight increase followed by a strong decrease. Simultaneously the plasmon resonance is shifted and severely broadened. To interpret these effects, a self-consistent calculation of the particle polarization is performed. Initial increase in magnitude and shift of the resonance are due to dynamic depolarization, whereas the decrease in magnitude and broadening are caused by radiation damping. The importance of higher-order multipoles is assessed by analyzing their contributions separately.

Enhanced Raman scattering from silicon microstructures

Electromagnetic-structure-resonance enhancement of scattering from Si phonon modes is reported for a number of submicrometer structures. Enhancements of greater, similar100 over the Raman intensity from bulk Si are observed for ~0.1-microm-diameter Si spheres. An analytic calculation of the Raman intensity for this geometry is in good qualitative agreement with the experiment and demonstrates that the enhancement arises from the coupling of both the incident and the scattered fields with the low-order-structure resonances in this high-index dielectric.

Surface effects on Raman scattering from Sb deposited on Ag-island films

Surface-enhanced Raman scattering from crystal vibrational modes of a Sb film rather than from vibrational modes of individual molecules has been observed for the first time to our knowledge. A ~20x enhancement of the longitudinal-optical mode (150 cm(-1)) in the Raman spectra of crystalline Sb films deposited on silver-island films was obtained. The excitation profiles, as well as the dependence of Raman intensity on the thickness of Ag films, were studied.

Surface-enhanced Raman scattering from silver particles on polymer-replica substrates

Evaporation of silver onto polymer microstructures produces a particle system for which optical characterization (e.g., absorbance) is possible. Measurements of surface-enhanced Raman scattering from these surfaces are compared with the particle-plasmon resonance model, including radiation-damping effects. The results provide evidence for the correlation between the Raman-excitation resonance and the optical properties of the silver system, supporting the electromagnetic model of surface Raman enhancement.