Colloids and Surfaces A: Physicochem. Eng. Aspects 338 (2009) 87–92 Contents lists available at ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa Self-assembly of colloidal particles on different surfaces M. Ulmeanu ∗ , M. Zamfirescu, R. Medianu National Institute for Laser, Plasma and Radiation Physics, Laser Department, 409 Atomistilor Str., P.O. Box MG-36, 077125 Magurele, Bucharest, Romania article info Article history: Received 1 September 2008 Received in revised form 14 December 2008 Accepted 31 December 2008 Available online 8 January 2009 Keywords: Colloidal particles Self-assembly Thin films Roughness Contact angle abstract The self-assembly process of colloidal particles on different surfaces: mica, glass, Ag and Au thin films is presented. The quality of the self-assembled monolayers is dependent on the solid concentration of colloidal particles, roughness of the surface, contact angle of the water droplet and chemically produced surface charges on the substrate. The surfaces parameters where analyzed by contact angle measure- ments and atomic force microscopy (AFM). The final deposition was characterized by optical and scanning electron microscopy (SEM). © 2009 Elsevier B.V. All rights reserved. 1. Introduction In the ongoing general trend for miniaturization (one of the driving forces for the field of nanotechnology), optics has shown much more difficulty than electronics to reach the nanometric regime of a dimensionality. The main reason for this delay is the physical limit imposed by diffraction when focusing light. Indeed, the smallest diameter of an optical beam propagating in a dielec- tric medium of refraction index n is of the order of  =  0 /n,  0 being the wavelength in the free space. Confining light from a laser beam down to sub-wavelength sizes imposes a reduction on the dimensionality. Nano-processing using the near-electromagnetic field generated when a small particle is irradiated by a laser pulse has been investigated extensively in recent years [1,2]. Spherical particles are placed on a surface (metal film, silicon or glass sub- strate, etc.) and nanoholes are fabricated at the original position of the particles due to the light enhancement effect [3]. Compar- ing to other existing processing techniques like electron beam and focused ion beam techniques, the laser surface nanopatterning is realizable in a one-step process under simple experimental condi- tions. One of the major parameters responsible for obtaining large areas with ordered nanostructures is related to the ordering of colloidal particles on surfaces to start with the nanopatterning pro- cess. Although, there are in the literature many papers dealing with the self-assembly of colloidal particles, among them the references [4–6], few data presents the self-assembly of colloidal particles on different thin metallic films used as surfaces in the near-field ∗ Corresponding author. E-mail address: magda.ulmeanu@inflpr.ro (M. Ulmeanu). nanostructuring method [7]. In this study, we analyze the deposi- tion of colloidal particles on different surfaces by self-assembly in air. A droplet of colloidal particles is placed on a substrate using a pipette. Following the water evaporation, layers of colloidal parti- cles are self-assembled on the surface. The materials used in this experiment are presented in Section 2. This section gives an insight about the colloidal particles and the surfaces that we have used. For a complete study, we have chosen four surfaces: mica, glass, Ag and Au thin film. In order to create the monolayers we have used purchased silica particles. The mica and glass substrates have been used as they were purchased, while the Ag and Au thin films have been deposited by evaporation techniques. The quality of the self- assembled monolayers is dependent on the solid concentration of colloidal particles, roughness of the surface, contact angle of the droplet on the surfaces, chemically produced surface charges on the substrate and the evaporation time. The surfaces parameters are detailed in the section surface characterization. Contact angle measurements and atomic force microscopy (AFM) measurements have been used to characterize the surfaces. The final deposition was characterized by optical microscopy and scanning electron microscopy (SEM) and the details of these measurements are given in the section self-assembly. 2. Materials and methods 2.1. Colloidal particles Silica colloidal particles (purchased from Polyscience Europe GmbH) with a diameter of 0.75 m and a coefficient of variance of the diameter less than 15% have been used in our experiments. We have chosen this diameter since the femtosecond (fs) laser source to 0927-7757/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2008.12.040