Low wavenumber Raman scattering of the acoustic vibrational modes of nanoparticles was used for the determination of the size distribution of free dielectric and semiconductor nanoparticles and of nanoparticles embedded in matrices. The theoretical background as well as the experimental results for the free noninteracting nanoparticles and for the nanoparticles in strong interaction with a surrounding matrix is described. The approach is based on a 1/ν dependence of the Raman light‐to‐vibration coupling coefficient and on the fact that each nanocrystallite of diameter D vibrates with its eigenfrequency ν ∼ 1/D. The model calculation considers the inhomogeneous broadening due to contribution from the particles of different sizes, and homogeneous broadening due to interaction of particles with the matrix. The comparison of the calculated and experimental low wavenumber Raman spectra are presented for SnO₂, TiO₂ and CdS free nanoparticles and TiO₂, CdS_xSe_1−x and HfO₂ nanoparticles embedded in a glass matrix. The particle‐size distributions determined by Raman scattering were compared to those found by TEM measurements. Raman spectroscopy proved to be a simple, fast and reliable method for size‐distribution measurements. By an inverse procedure, starting from the Raman spectra and known particle‐size distribution, a new method for the determination of the mean sound velocities of longitudinal and transverse phonons of nanoparticles is described. Copyright © 2007 John Wiley & Sons, Ltd.

Microporous and macro-mesoporous silicon templates for surface-enhanced Raman scattering (SERS) substrates were produced by anodization of low doped p-type silicon wafers. By immersion plating in AgNO₃, the templates were covered with silver metallic film consisting of different silver nanostructures. Scanning electron microscopy (SEM) micrographs of these SERS substrates showed diverse morphology with significant difference in an average size and size distribution of silver nanoparticles. Ultraviolet–visible–near-infrared (UV-Vis-NIR) reflection spectroscopy showed plasmonic absorption at 398 and 469 nm, which is in accordance with the SEM findings. The activity of the SERS substrates was tested using rhodamine 6G (R6G) dye molecules and 514.5 nm laser excitation. Contrary to the microporous silicon template, the SERS substrate prepared from macro-mesoporous silicon template showed significantly broader size distribution of irregular silver nanoparticles as well as localized surface plasmon resonance closer to excitation laser wavelength. Such silver morphology has high SERS sensitivity that enables ultralow concentration detection of R6G dye molecules up to 10⁻¹⁵ M. To our knowledge, this is the lowest concentration detected of R6G dye molecules on porous silicon-based SERS substrates, which might even indicate possible single molecule detection.