We developed a self-assembly process of silica particles to fabricate desired patterns of colloidal crystals having high feature edge acuity and high regularity. A micropattern of colloidal methanol prepared on a self-assembled monolayer in hexane was used as a mold for particle patterning, and slow dissolution of methanol into hexane caused shrinkage of molds to form micropatterns of close-packed SiO2 particle assemblies. This result is a step toward the realization of nano/micro periodic structures for next-generation photonic devices by a self-assembly process.

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...

We developed a novel self-assembly process to fabricate an orderly array of particle wires constructed from a close-packed colloidal crystal without preparation of patterned templates. A substrate was immersed vertically into a SiO2 colloidal solution, and the liquid surface moved downward upon evaporation of solution. Particles formed a mono-/multiparticle layer, which was cut by the periodic drop-off of solution. The orderly array of particle wires was successfully fabricated, showing the suitability of the self-assembly process for the fabrication of nano-/microstructures constructed from nano-/microparticles or blocks. The mechanism of the assembly process and control of thickness, width, and interval of particle wires were further discussed. Moreover, an array of particle wires constructed not from close-packed face-centered cubic (or hexagonal close packed) structure but from two kinds of particles was realized to fabricate an array of particle wires with NaCl structure by this self-assembly process.

No abstract

No abstract