Self‐Assembly and Micropatterning of Spherical‐Particle Assemblies

Abstract

Particles show various interesting properties, [1±4] such as photonic bandgaps, [5] electronic-energy transfers in closepacked CdSe [6] or InP, [7] and metal±insulator transitions in silver quantum dots, [8] that are not observed in the bulk forms of the corresponding materials. Various scientific and engineering applications, such as the control of spontaneous emission, zero-threshold lasing, sharp bending of light, and so on, are expected to become possible by using the photonic bandgap and artificially introduced defect states and/or light emitters. Recently, monodisperse particles have been synthesized by various methods. Thus, particles may be treated as if they were atoms, and one-, two-, or three-dimensional arrangements of particles have been studied by many researchers. Materials with micrometer-and submicrometer-scale patterns are expected to be used in desirable devices. We have developed several patterning methods that do not use templates to produce microstructures, such as molds or grooves in static-solution systems [9±11] or in drying processes, [12,13] and have applied these methods to photonic crystals. Microstructures constructed from particles such as micropatterns of particle layers, narrow particle wires, arrays of particle wires, and so on, can be prepared under moderate conditions from self-assembled monolayers (SAMs). Chemical reactions and/or electrostatic interactions between particles, substrates, and solutions can be easily utilized, and experiments can be conducted under well-controlled conditions in a static-solution system because of its static reactions. On the other hand, meniscus and capillary forces can also be easily utilized for assembling particles into close-packed structures during the drying process. However, the interactions between particles, substrate, and solution are difficult to use effectively, and the patterning conditions are hard to control precisely, because this is a dynamic system, and therefore exact nano-or micropatterns are difficult to fabricate. Each patterning system has its own advantages and disadvantages. These self-assembly solution processes do not need preprocessing of micromolds or grooves. However, further progress based on novel concepts is urgently required. Here, we report a novel process to realize micropatterning of spherical-particle assemblies using droplets of colloidal solution and a patterned SAM. This two-solution process was developed to have the advantages of both the static-solution process and the drying process. A combination of interfacing between two solutions and shrinkage of droplets was utilized to obtain a meniscus force to form densely packed particle assemblies; additionally, the static-solution system allows precise control of the conditions. Furthermore, we have developed a novel concept for future photonic crystals. Photonic crystals, in which the refractive index changes periodically, are usually prepared by the assembly of primary particles. However, spherical-particle assemblies can be prepared from primary partic...

Self-assembly Patterning of Nano/Micro-Particles [Translated]^†

“…Nano/micro periodic structures can be prepared with short fabrication time and low energy by selfassembly of mono-dispersed par ticles in which particles and air (wall and air for inverse opal) are arranged periodically 14,15) . Self-assembly and patterning of nano/micro particles have attracted much attention recently 1,2,16,17) . Micropatterns of close-packed particle assemblies with high arrangement accuracy have been realized by using templates such as micromolds 18) , grooves 19) , cylindrical holes 20) or trenches 20) .…”

Self-assembly and Patterning of Nanocrystals

“…Published online 28 We focused on cutting-edge science and technology of Nanocrystals in this book. â€oeNanocrystal†is expected to lead to the creation of new materials with revolutionary properties and functions.…”

“…3.2 Self-assembly patterning of spherical colloidal crystals by two-solution method 28 Micropatterns of spherical particle assemblies were fabricated by two-solution method 28 . Hydrophilic regions of a patterned self-assembled monolayer were covered with methanol solution containing SiO 2 particles and immersed in decalin to control the shape of droplets and gradually dissolve the methanol into decalin.…”

Design of curved photonic crystal using swelling induced instabilities

“…Here, it should be emphasized that the power and versatility of the reported self-assembly method are quite evident with respect to those from published approaches. [11][12][13][14]16,17 The presented approach requires conjoined action of the two self-assembly processes responsible for curvature and crystal formation. It can be viewed as a proof of concept for designing and controlling shape and optical response of colloidal crystals without altering the effective refractive index.…”

“…Recently a few studies pointed out the influence of curvature on the optical properties of 3D photonic crystals (photonic domes) made from low refractive index materials. [15][16][17][18] The presence of curvature causes simultaneous reflection of light from different crystal planes resulting in bright color of microdomes. The bandgap of these curved photonic systems is almost complete (angularly independent) in comparison with the planar match, made from the same low refractive index colloids.…”