Core and shell sizing of small silver-coated nanospheres by optical extinctionspectroscopy

Abstract

Silver metal nanoparticles (Nps) are extensively used in different areas of research andtechnology due to their interesting optical, thermal and electric properties, especially forbare core and core–shell nanostructures with sizes smaller than 10 nm. Since theseproperties are core–shell size-dependent, size measurement is important in manipulatingtheir potential functionalization and applications. Bare and coated small silver Npsfabricated by physical and chemical methods present specific characteristics in theirextinction spectra that are potentially useful for sizing purposes. This work presents anovel procedure to size mean core radius smaller than 10 nm and mean shell thicknessof silver core–shell Nps based on a comparative study of the characteristics intheir optical extinction spectra in different media as a function of core radii, shellthickness and coating refractive index. From the regularities derived from theserelationships, it can be concluded that plasmon full width at half-maximum (FWHM)is sensitive to core size but not to coating thickness, while plasmon resonancewavelength (PRW) is related to shell thickness and mostly independent of core radius.These facts, which allow sizing simultaneously both mean core radius and shellthickness, can also be used to size bare silver Nps as a special case of core–shell Npswith zero shell thickness. The proposed method was applied to size experimentalsamples and the results show good agreement with conventional TEM microscopy.