Size saturation in low energy ion beam synthesized Au nanoclusters and their size redistribution with O irradiation B. Joseph, S. Mohapatra, H.P. Lenka, P.K. Kuiri, D.P. Mahapatra * Institute of Physics, Sachivalaya Marg, Bhubaneswar 751 005, India Received 26 July 2004 Received in revised form 9 June 2005; accepted 13 June 2005 Available online 20 July 2005 Abstract Embedded Au nanoparticles have been produced in ordinary silica glass by high dose 32 keV Au  ion implantation. Samples implanted with doses higher than 1 10 16 cm  2 are found to show an absorption band peaked around 535 nm, corresponding to the surface plasmon resonance (SPR) of the Au nanoclusters in silica glass. An increase in the SPR peak intensity with increase in dose has been observed upto a dose ¨4  10 16 cm  2 , after which the absorption intensity shows a saturation. This saturation in the SPR intensity has been explained as coming due to a break up of larger Au nanoparticles formed near the surface by displacement spikes induced by subsequently incident Au ions against their regrowth from the movement of Au atoms towards the surface. Further high dose O implantation at 32 keV has been found to result in a drop in absorption. On the contrary, a 2 MeV O implantation has been found to result in a growth in nanoparticle size resulting in an enhanced absorption. D 2005 Elsevier B.V. All rights reserved. PACS: 41.75.Cn; 61.72.Ww; 78.20.C Keywords: Metal nanoparticles; Negative ion implantation; Optical absorption 1. Introduction Scattering and absorption of light by small particles [1] is a subject of both fundamental and technological interest. Small metal particles are used for many centuries in the art of making stained glass due to their interesting optical properties. For last few decades, there has been a growing interest in the study of optical properties of these systems due to their prospective applications in photonic systems. Optical absorption properties of small particles with size in the range of nanometer depend crucially on the particle size and quantum confinement effects. For metal nanoparticles, the surface plasmon resonance (SPR) is the main feature of the optical response. SPR corresponds to a collective oscillation of the conduction electrons subjected to an electromagnetic excitation. For noble metals the SPR occurs in the visible range, where the absorption band position and its width depend on the intrinsic properties of the clusters and the surrounding medium. Metal nanoclusters (NCs) inside insulating matrices can be synthesized by direct implantation of metal ions into these systems to a concentration above the solubility limit [2–5]. Control over depth profiles with the ability to overcome low solubility restrictions make ion implantation an attractive technique for the synthesis of metal NCs. For high flux implantation, the use of negative ions is more promising than positive ions due to charge-up free implantation [6]. For application purposes, one needs to devise methods to produce NCs with a narrow size distribution. Though high dose implantation is an excellent technique to produce metal NCs, the resulting cluster size distribution is broad. Therefore, there is a need to under- stand their growth processes, which can be helpful regarding a control of their size inside a matrix. In an earlier work [7], we have reported some results regarding low energy O induced size redistribution of Au 0040-6090/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2005.06.024 * Corresponding author. Tel.: +91 674 2301058; fax: +91 674 2300142. E-mail address: dpm@iopb.res.in (D.P. Mahapatra). Thin Solid Films 492 (2005) 35 – 40 www.elsevier.com/locate/tsf