Formation processes of nickel oxide nanoparticles in SiO 2 by metal-ion implantation combined with thermal oxidation H. Amekura * , N. Umeda, Y. Takeda, J. Lu, K. Kono, N. Kishimoto Nanomaterials Laboratory, National Institute for Materials Science, 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan Available online 21 January 2005 Abstract Formation processes of nickel oxide (NiO) nanoparticles (NPs) in silica glass (SiO 2 ) by implantation of 60 keV Ni  ions combined with thermal oxidation are studied using cross-sectional transmission electron microscopy (XTEM) and Rutherford backscattering spectrometry. In as-implanted state, Ni metallic NPs form within the surface layer of 80 nm thick. The mean depth hzi and the standard deviation h(Dz) 2 i 1/2 of Ni atom distribution determined by XTEM were 43 and 15 nm, respectively. After the oxidation at 800 °C for 1 h, hzi and h(Dz) 2 i 1/2 became 47 nm and 20 nm, respectively, i.e. the distribution was almost the same except a small diffusional shift to the deeper region. Mean volume of Ni- and NiO-NPs after heat treatments at 800 °C were 27 and 43 nm 3 , respectively. The larger mean volume of NiO- NPs is explained from the fact that NiO-NPs include both Ni and O atoms, i.e. approximately 2N atoms, while Ni-NPs include Ni atoms only, i.e. N atoms. Both the Ni- and NiO-NPs include 2.4 · 10 3 Ni atoms per NP in average. These results indicate that NiO-NPs are formed by oxidation of Ni-NPs without pronounced redistribution of Ni atoms. Ó 2004 Elsevier B.V. All rights reserved. PACS: 81.16.Pr; 61.46.+w; 68.37.Lp; 82.80.Yc Keywords: Oxide nanoparticle; Ion implantation; NiO; Oxidation; TEM observation 1. Introduction Oxide nanoparticles draw much attention, be- cause of their peculiar optical [1,2], magnetic [3] and catalytic properties, etc. Negative-ion implan- tation is one of the promising methods to fabricate metal nanoparticles (NPs), because of little surface charging, high-purity process and good controlla- bility in fluence, spatial position and depth [4]. Re- cently, oxide NPs have been fabricated in silica glasses (SiO 2 ) by metal-ion implantation and fol- lowing thermal oxidation [5–7]. First, metal NPs are formed by the implantation of the metal atoms of much higher concentration than the solubility limit of the substrate. It is known that a majority 0168-583X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2004.12.039 * Corresponding author. Tel.: +81 29 863 5479; fax: +81 29 863 5599. E-mail address: amekura.hiroshi@nims.go.jp (H. Amekura). Nuclear Instruments and Methods in Physics Research B 230 (2005) 193–197 www.elsevier.com/locate/nimb