Size-controlled synthesis of nickel nanoparticles Y. Hou a,b , H. Kondoh b , T. Ohta b, * , S. Gao a a State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China b Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan Abstract A facile reduction approach with nickel acetylacetonate, Ni(acac) 2 , and sodium borohydride or superhydride leads to monodisperse nickel nanoparticles in the presence of hexadecylamine (HDA) and trioctylphosphine oxide (TOPO). The combination of HDA and TOPO used in the conventional synthesis of semiconductor nanocrystals also provides better control over particle growth in the metal nanoparticle synthesis. The size of Ni nanoparticles can be readily tuned from 3 to 11 nm, depending on the ratio of HDA to TOPO in the reaction system. As-synthesized Ni nanoparticles have a cubic structure as characterized by power X-ray diffraction (XRD), selected-area electron diffraction (SAED). Transmission electron microscopy (TEM) images show that Ni nanoparticles have narrow size distribution. SQUID magnetometry was also used in the characterization of Ni nanoparticles. The synthetic procedure can be extended to the preparation of high quality metal or alloy nanoparticles. # 2004 Elsevier B.V. All rights reserved. PACS: 81.05.Y; 75.50.K; 61.46 Keywords: Synthesis; Nickel; Nanoparticles; Magnetism 1. Introduction With increase interest in fabricating nanodevices with nanosized blocks, much attention has been focused on exploiting a general route to control size and morphology of nanoscale materials [1,2]. In recent years, nanoscale magnetic materials have attracted much interest due to the potential application in magnetic recording technology [3,4]. A flexible synthetic route is indispensable to exploit magnetic storage materials. So far, a number of physical and chemical routes have also been applied to produce nanoscale magnetic materials, including mechanical grinding, sonochemistry, organometallic precursor pyrolysis, metal melt reduction in micelle phase, and electrochemical deposition, etc. [5]. However, the size distribution of the products is not ideal. Recent developments of the organometallic route to produce high quality semiconductor nanocrystals included the www.elsevier.com/locate/apsusc Applied Surface Science 241 (2005) 218–222 * Corresponding author. Tel.: +81 3 5841 4331; fax: +81 3 3812 1896. E-mail address: ohta@chem.s.u-tokyo.ac.jp (T. Ohta), gaoson@pku.edu.en (S. Gao). 0169-4332/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2004.09.045