Size,composition and optical properties of copper nanoparticles prepared by laser ablation in liquids

Colloidal copper nanoparticles were prepared by pulsed Nd:YAG laser ablation in water and acetone. Size and optical properties of the nanoparticles were characterized by transmission electron microscopy and UV–visible spectrophotometry, respectively. The copper particles were rather spherical and their mean diameter in water was 30 nm, whereas in acetone much smaller particles were produced with an average diameter of 3 nm. Optical extinction immediately after the ablation showed surface plasmon resonance peaks at 626 and 575 nm for the colloidal copper in water and acetone, respectively. Time evaluation showed a blue shift of the optical extinction maximum, which is related to the change of the particle size distribution. Copper nanoparticles in acetone are yellowish and stable even after 10 months. In water, the color of the blue-green solution was changed to brown-black and the nanoparticles precipitated completely after two weeks, which is assigned to oxidation of copper nanoparticles into copper oxide (II) as was confirmed by the electron diffraction pattern and optical absorption measurements. We conclude that the ablation of bulk copper in water and acetone is a physical and flexible method for synthesis of stable colloidal copper and oxidized copper nanoparticles. PACS 42.62.-b; 81.07.-b; 61.46.+w