Colloids and Surfaces A: Physicochemical and Engineering Aspects 197 (2002) 1 – 5 Structural characterization of monolayer and regularly stacked multi-layers composed of silver nanoparticles by using X-ray reflectivity Shuichiro Kuwajima a , Yuji Okada a , Yuji Yoshida a, *, Koji Abe a , Nobutaka Tanigaki a , Tomohiko Yamaguchi a , Hiroshi Nagasawa b , Kenji Sakurai c , Kiyoshi Yase a a National Institute of Materials and Chemical Research, 1 -1 Higashi, Tsukuba 305 -8565, Japan b Osaka City Uniersity, 3 -3 -138, Sugimoto, Sumiyoshi -ku, Osaka 558 -8585, Japan c National Research Institute of Metals, 1 -2 -1 Sengen, Tsukuba 305 -0047, Japan Received 11 September 2000; accepted 24 January 2001 Abstract Layer structures of monolayer and multilayers composed of passivated silver (Ag) nanoparticles are analyzed using X-ray reflectivity (XR) measurements. In the XR profile of the monolayer, the ‘‘Kiessig fringe’’ is observed above the critical angle. A simple layer model is suitable for the nanoparticle layer structure in the low-angle region. A distinct quasi-Bragg reflection (QBR) due to the periodical layer structure appears in the XR profile of multilayers. The estimated periodic distance between the layers is larger than that of a three-dimensional closed packing model, while these particles pack hexagonally in the layer. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Closed pack; Layer structure; Monolayer; Multilayer; Nanoparticle; X-ray reflectivity www.elsevier.com/locate/colsurfa 1. Introduction Recently, ultrafine particles composed of metals and semiconductors are of interest in various research fields, since they bear unique optoelec- tronic and magnetic properties different from bulk ones due to confinement of electron in a small space [1]. Metal nanoparticles also have the potential to construct to single electron transistor (SET) and other new electronic devices. Nagasawa et al. developed a one-step method to produce nanoparticles passivated with alkyl moieties, in which silver salts of fatty acids were decomposed at 250°C under a nitrogen atmo- sphere. The nanoparticles can be spread as a monolayer onto an air/water interface from the toluene dispersion of nanoparticles. A transmis- sion electron micrograph (TEM) showed that these Ag nanoparticles consist of a Ag-core with an average diameter of 5.0 nm surrounded by a * Corresponding author. Tel.: +81-298-616306; fax: +81- 298-616303. E-mail address: kuwajima@nimc.go.jp (Y. Yoshida). 0927-7757/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0927-7757(01)00580-5