Synthesis and optical characterization of Ag 0 nanoparticles M. Torres-Cisneros a,Ã , C. Vela ´ squez-Ordo ´ nez b , J. Sa ´ nchez-Mondrago ´n b , A. Campero c , O.G. Ibarra-Manzano a , D.A. May-Arrioja b , H. Plascencia-Mora a , A. Espinoza-Caldero ´n a , I. Sukhoivanov a a NanoBioPhotonics Group, Design and Manufacture CA, University of Guanajuato; Salamanca, Guanajuato 36730, Mexico b Photonics Laboratory, Optics Department INAOE, Puebla, Pue. 72000, Mexico c Universidad Auto ´noma metropolitana-Iztapalapa Depto Quı ´mica, Mexico D.F., Mexico article info Available online 25 July 2008 Keywords: Photonics crystals Nano-metallic-particles Nonlinear materials abstract The results of chemical synthesis and optical behavior of silver nanoparticles with sizes ranging from 2–10 nm which were obtained by reduction of Ag + are reported. The material morphology was examined by transmission electron microscopy (TEM) and physical properties were studied by photoluminescence in the range of 400–550 nm using two different excitation wavelengths (320 and 380 nm). The signature provided by the silver plasmon is readily noticed in the silver nanoparticles. The nonlinear optical properties were obtained using a Z-scan setup and agree with previous results obtained by other methods and preparation of samples. In particular, a positive nonlinear refractive index of 5.0115  10 10 m 2 /W was obtained for a broad sample of silver nanoparticles between 2 and 10 nm. The agreement between the properties of the thin film sample and the nanoparticles give emphasis to the Z-scan technique for nonlinearity measurements of much more complex metal– dielectric structures. & 2008 Elsevier Ltd. All rights reserved. 1. Introduction The same basic principles of electromagnetic (EM) transmis- sion and reflection, on dielectric and metals, support two different approaches on photonic crystals (PC) and photonics band gaps (PBG). Each one of them exhibit distinctive characteristics, while the dielectric photonic crystals (DPC) are characterized by the typical stopgap [1], the best well-known feature of metal photonic crystals (MPC) is the peaked transmission structure [2], exhaus- tively studied by Yablonovich et al. on an 1D array of thin metallic films with a thickness of tens of nanometers. Both of them require specific scales because of the particular characteristics of their materials, in the case of DPCs the scale is on the order of wavelengths while for an MPC it is on the order of nanometers. On their own these metal–dielectric structures have already found important applications [3]. The search of new materials in order to build novel devices is now focusing on the fact that the properties of each nanomaterial can be modulated not only through the nature of their constitut- ing units, but also through the distance between particles or the whole system architecture. Core-shell colloidal particles have recently attracted a lot of attention because of the ability to fine-tune their properties. Colloids are ideal building blocks for the creation of PC, because of their ability to self-organize in three-dimensional periodic structures with different symmetries. On the other hand, metallic nanoparticles are well-known non- linear materials. Therefore, metallic nanoparticles in a dielectric host are highly attractive to build up nonlinear PC devices. In this work we report the synthesis and characterization of Ag 0 nanoparticles and sub-microspheres of SiO 2 embedded with Ag 0 , as well as their nonlinear optical features in a thin film. 2. Experiment Single dispersed colloidal SiO 2 particles were prepared by the well-known Sto ¨ ber method [4] which consists in the base- catalyzed hydrolysis of tetraetoxilsilano. Aqueous ammonia (11.9ml of NH 3 at 29%) and 88.1ml of ethanol were both mixed in an Erlenmeyer flash. This solution was stirred in a water bath at 20 1C, and followed by the addition of 3.6 ml of tetraetoxilsilano under vigorous stirring. The stirring rate was reduced and was kept at a slow rate for 15h. The solvent was then removed by centrifugation at 3000 rpm for 30 min. This preparation resulted in particles with a diameter between 200 and 400 nm. Silver sols were prepared using 0.1g of AgNO 3 , 100ml of ethanol, two drops of HNO 3 , 0.5 g of hexadecanol, 0.4 ml of glycerol, and 57 ml of hydrazine. This mixture was stirred and refluxed at 60 1C for three days. The absorption band of the colloidal solution was found around 420 nm. This plasmon band is ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/mejo Microelectronics Journal 0026-2692/$ - see front matter & 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.mejo.2008.06.043 Ã Corresponding author. Tel.: +52464 647 9940x2462; fax: +52 464 647 9940x2311. E-mail address: mtorres@salamanca.ugto.mx (M. Torres-Cisneros). Microelectronics Journal 40 (2009) 618– 620