Optical extinction spectroscopy used tocharacterize metallic nanowires

L. SCAFFARDI; M. LESTER; D. SKIGIN; J. TOCHO

NANOTECHNOLOGY

IOP

Año: 2007 p. 315402 - 315410

0957-4484

We present a method for sizing metallic nanowires through the analysis of the extinction spectra of the scattered light when the wires are illuminated alternatively with p- and s-polarization waves. The method is applied to isolated silver nanowires in air or immersed in index matching oil.The dielectric function of silver is affected by the size of the cylinders, and its influence on the extinction spectra near the plasmon resonance or near the dip position is considered. Due to the size of the nanocylinders, it is necessary to include two different permittivities in the electromagnetic model to analyse the behaviour of the material under different polarization  incidences. This introduces anisotropy in the system, which comprises isotropic cylinders.The behaviour of the extinction spectra for p-waves allows us todetermine the wire radii, taking into account the plasmon peak position for radii larger than 7 nm, or alternatively, by using the contrast between maximum and minimum intensity near the plasmon frequency, for radii lower than 5 nm. For s-waves, although no plasmon peak appears, we can determine the radii by analysing the contrast between the ridge of the spectra near 260–275 nm and the minimum near 320–330 nm for radii larger than 10 nm, or analysing the slope in the spectra over 350 nm, for radii below10 nm. The present study shows that spectral extinction is a very simple and inexpensive technique that can be useful for characterizing the radius of nanocylinders when electron microscopy (TEM or SEM) is not available.