ABSTRACT
Optical properties of single diatom frustule valves from two different Coscinodiscus species (C. wailesii and C. centralis) are studied by transmission confocal hyperspectral imaging and numerical calculations. Light convergence, concentration, and trapping effects are observed and depend on both the wavelength and the valve orientation. These effects seem to occur independently of the incident light angle. From our results, a wavelength-dependent multifocal lens behavior can be explained by light diffraction related to the radial symmetry of the multiscaled 3D nanostructure.
Subject(s)
Animal Shells , Diatoms , Microscopy, Confocal , Optical Phenomena , Animals , Spectrum AnalysisABSTRACT
Aggregates of Au nanoparticles have been extremely easily obtained on glass substrates by physical sputtering under primary vacuum. With such a protocol, we demonstrate that it is possible to control the surface plasmon band absorption. Surface enhanced Raman spectroscopy (SERS) experiments were performed with methylene blue, zinc octacarboxyphthalocyanine, 4-aminothiophenol and cysteamine. The correlation between the absorption band and the wavelength giving the highest SERS intensity is clearly observed for methylene blue, in accordance with the electromagnetic enhancement theory. For the other molecules, effects of the chemical enhancement are also observed. In addition, we noticed a strong influence of the nature of the adsorbed molecule on the enhancement factor for a given wavelength. The origin of this feature is discussed in terms of resonant effects or multipolar surface plasmon modes.