Extinction spectroscopy and optical properties for size characterization of silver nanoparticles

MARÍA VIRGINIA ROLDÁN; LUCÍA B. SCAFFARDI; NORA PELLEGRI

Campinas-SP, BRAZIL

Congreso; Iberoamerican Conference on Optics (VI RIAO) and Latinamerican meeting on Optics, Lasers and Applications (IX OPTILAS); 2007

UNICAMP, Brazil

Nanotechnology has been the subject of increasing activity during the last years mainly due to the new optical, magnetic, electric and catalytic properties that metallic nanoparticles present in the development of different nanodevices. Nanoparticles fabrication processes are diverse and the final result for most of the known mechanisms (chemical reduction of Ag ions in aqueous solution with or without stabilizing agent, thermal decomposition in organic solvents, optically induced reduction processes, nanolithography, among others) is characterized by their low-concentration yield. Currently, there is much interest in large volume silver nanoparticles production for direct application in nanostructured devices. This work describes a simple production method for large-volume, low?cost silver nanoparticles fabrication, including a simple technique based on extinction spectroscopy for mean radius determination at different stages of the production process and under different temperature conditions. Silver nanoparticles were obtained from chemical reduction of AgNO3 in ethanol, using an aminosilane as catalyst and stabilizer of the colloidal suspension. The aminosilanes are used as surface modifiers to help avoid agglutination.  An optimal behavior for ATS, N-[3-(trimethoxysilyl)propyl]diethylenetriamine, was found with ratio AgNO3: aminosilane of 1:3-5.  Using optical extinction spectroscopy, the temporal evolution of the size of silver nanoparticles coated with ATS, from the beginning of the reaction to the extraction time was characterized. The method was also applied to study the size evolution with the reaction temperature. In both cases, the width of the plasmon resonance in the extinction spectrum proved to be a useful tool to determine mean radius, especially for sizes below 6 nm. The spectra were interpreted within the framework of Mie theory, including a size-dependent modification of the dielectric function to account for the reduced mean free path of the electrons and their collisions with particle walls [2, 3]. The method is a simple and inexpensive alternative to electronic microscopy.                             REFERENCES [1] Effect of amine groups in the síntesis of Ag nanoparticles using aminosilanes. A. Frattini, N. Pellegri, D. Nicastro, O. de Sanctis. Materials Chemistry and Physics 94, 148-152 (2005). [2] Sizing gold nanoparticles by optical extinction spectroscopy Scaffardi L B, Pellegri N, de Sanctis O, Tocho J O  Nanotechnology 16 158-63 (2005) [3] Size dependence of refractive index of gold nanoparticles Scaffardi L B and Tocho J O  Nanotechnology 17 1309-1315  (2006)