Building Two and Three-dimensional Structures of Colloidal Particles on Surfaces using Optical Tweezers and Critical Poi
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Building Two and Three-dimensional Structures of Colloidal Particles on Surfaces using Optical Tweezers and Critical Point Drying
Dirk L. J. Vossen, Jacob P. Hoogenboom, Karin Overgaag and Alfons van Blaaderen F.O.M. Institute for Atomic and Molecular Physics, Amsterdam, the Netherlands Soft Condensed Matter, Debye Institute, Utrecht University, the Netherlands
ABSTRACT We describe a method for patterning substrates with colloidal particles in any designed twodimensional structure. By using optical tweezers particles are brought from a reservoir to a surface that carries a surface charge opposite to that of the particles. Using this technique large, two-dimensional patterns can be created, where the pattern can be manipulated on a single particle level. We show that these structures can be dried using critical point drying thus preventing distortions due to surface tension forces. After drying patterned surfaces can be used for further processing, which includes repeating the procedure of patterning. We show some first results of three-dimensional structures created using this layer-by-layer method. The method is generally applicable and has been demonstrated for a variety of (core-shell) colloidal particles including particles that are interesting for photonic applications like high-refractive index (ZnS)core – silica shell particles, metallodielectric (gold)-core – silica-shell particles, fluorescently labeled particles and small (several nanometers large) gold particles. Particle sizes used range from a few nanometers to several micrometers.
INTRODUCTION Colloidal particles are the building blocks for materials that find applications in many diverse fields of research. The chemical tunability of particle morphology and typical particle sizes ranging from several nanometer to a few micrometers make colloids suitable for photonic [1-3], electronic [4], magnetic and sensor devices [5, 6]. Two-dimensional arrangements of colloids on substrates are of great interest for most of these applications and have in addition been used to create other nanostructures, e.g., by using them as a mask for lithography [7]. The techniques used for arranging colloids in two-dimensional patterns vary from templatedirected self-assembly [2, 8, 9] and patterning of self-assembled monolayers [10], to direct single-particle patterning [11-13]. Clearly, this last category of methods offers the highest level of control over pattern structure, but it remains a challenge to find a technique that works for a large variety of particle sizes, particle morphologies and substrates and that furthermore can operate at relatively high speed and can be fully automated. To our knowledge, Misawa and co-workers were the first to use optical trapping of micronsized polymeric particles for assembling larger structures [14]. They recently described a technique to position polymeric particles on polymeric [11] substrates using optical tweezers and single-particle photothermal fixation. Local photopolymerization was used by Mio and Marr to fix particles arr
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