Spectroscopic approach to structure, configuration and size determination of Cu nanoparticles generated by femtosecond laser ablation in liquids

J. M. J. SANTILLÁN; F. A. VIDELA; D. C. SCHINCA; L. B. SCAFFARDI

Porto

Conferencia; RIAO/OPTILAS 2013, VIII Iberoamerican Conference on Optics XI Latinamerican meeting on Optics, Lasers and Applications; 2013

FCUP, Porto, Portugal

In recent years, metallic copper Nps and their oxides have been the subject of intense research due to their potential applications in broad areas of sciences and technology such as chemistry, catalysis, nanofluidics, material science and high temperature superconductors. Copper properties such as high conductivity, photosensitivity and low cost makes it a promising material for chemical, electronic and photonic integration in miniaturized devices for use in biological nanosensors, as well as its capability of insertion in host polymer matrices for nonlinear optical applications. We report on the analysis of structure and sizing of two species (Cu and Cu2O) nanoparticles (Nps) arranged in two structures (bare core or core-shell) and in two configuration types (Cu-Cu2O or Cu2O-Cu), produced by femtosecond (fs) laser ablation of solid copper target in liquids. Optical extinction spectroscopy has demonstrated its ability to size core radius and shell thickness of noble metal Nps through the fitting of the full UV-Vis extinction spectra using Mie’s theory, together with a conveniently modified metal bulk complex dielectric function that includes the size correction of free and bound electrons contributions. From the fit of experimental extinction spectra obtained for different decreasing energies, it is possible to establish a threshold energy value below which the Cu2O-Cu Nps is present. This threshold is dependent on the liquid medium. For water, it is about 150 J, while for acetone it is about 70 J. Possible reasons for the changes in the structural conformation of the core-shell Nps are discussed.