This is a review article oncolloidal self assembly of nanostructures which has so far proven itself quitedifficult. Yet progress is been made andwe will see many derivative applications.
Again, the whole field ofmaterials research and nanosized materials is booming and many approaches arebeen pursued to produce a cornucopia of solutions looking for problems.
It remains to be seen were allthis will take us.
Self-assembled colloidal structures for photonics
MAY 09, 2011
Colloidal crystals for photonics applications.(Left) Colloidal crystals can be formed into any shape to achieve desiredreflectance properties. (Center) Inverse structures can be obtained byinfiltrating the crystal with various materials and then removing the template particles (colloidaltemplating). (Right) Short-range-ordered structures of colloidal particles orcolloidal glasses can be assembled to achieve angle-independent coherentoptical scattering.
Colloidal self-assembly has been investigated as a promising andpractical approach for the fabrication of photonic nanostructures, includingcolloidal crystals, composite and inverse opals, and photonic glasses.Depending on the interactions between the colloidal particles, colloidalstructures can be affected dramatically and modulated by applying an additionalexternal field. Furthermore, in contrast to other approaches, self-assemblednanostructures with large areas or designed shapes can be prepared at low cost.As a result, the use of such colloidal systems has been investigated in manypractical photonic applications. In this review article, we describe thecolloidal self-assembly of periodic and non-periodic photonic nanostructures inbrief and then summarize recent achievements in the field of colloidal photonicnanostructures and their applications, which include displays, optical devices,photochemistry and biological sensors.
Schematic summary of display devices based on colloidal-structured photonics.(a) Passive-mode display with pixelated photonic crystals. (b) Active-modedisplay based on dynamic modulation of lattice constant. (c) Gyricon displaybased on rotation of Janus photonic microspheres. (d) Display device withisotropic colloidal structure of short-range order for angle-independentstructural color.
Over the past few decades, several different approaches have beenemployed to produce colloidal nanostructures in investigations of photonicapplications. This research, conducted by many different research groups, hasexpanded the range of applications to include nonphotonic materials, whichmight result for instance in the convergence of photonics and biomedicalapplications and in energy-harvesting devices. In particular, colloidal crystalsand composite and inverse opals have been investigated and modified forspecific applications. In spite of their limited optical response, or in otherwords their incomplete pseudo-photonic bandgap, they can be successfullyimplemented in relatively simple applications. By adding functional moleculesinto such colloidal nanostructures, photonic crystal-based sensor devices havebeen developed and their technological level has in some cases matured close tothe point of commercialization or the opening of new markets. New types ofphotonic nanostructures, such as photonic glasses, have been introduced forangle-independent light reflection, random lasing and other applications.
In some original applications of photonic crystals, several research groupshave fabricated optical circuits out of colloidal particles and demonstratedtheir great potential. However, it is still difficult to fabricate defect-freecolloidal crystals and then to create prescribed defects because of theinherent defects that arise during self-assembly. As a result, researchactivity in this area has gradually decreased. However, in a new approach, theuse of selective chemical glue on particle surfaces such as DNA or peptides hasbeen proposed. Further developments might enable the fabrication of betterphotonic devices based on colloidal particles. Moreover, recent progress in thesynthesis of nonspherical particles is accelerating research into the colloidalcrystallization of new crystal phases. One promising strategy with strongpotential for producing new photonic properties is the use of directionalinterparticle interaction with chemical patterns on a colloid surface to createand design new types of colloidal lattices.
In some original applications of photonic crystals, several research groupshave fabricated optical circuits out of colloidal particles and demonstratedtheir great potential. However, it is still difficult to fabricate defect-freecolloidal crystals and then to create prescribed defects because of theinherent defects that arise during self-assembly. As a result, researchactivity in this area has gradually decreased. However, in a new approach, theuse of selective chemical glue on particle surfaces such as DNA or peptides hasbeen proposed. Further developments might enable the fabrication of betterphotonic devices based on colloidal particles. Moreover, recent progress in thesynthesis of nonspherical particles is accelerating research into the colloidalcrystallization of new crystal phases. One promising strategy with strongpotential for producing new photonic properties is the use of directionalinterparticle interaction with chemical patterns on a colloid surface to createand design new types of colloidal lattices.
Patterning of photonic crystals. (a) Patterning process for twodifferent colloidal crystals by combining the MIMIC technique and verticaldeposition. (b) The pixelation method for red, green and blue (RGB) colors.Inverse opal with pores filled with SU-8 is exposed twice under UV light via aline-pattern photomask at 0° and 90°. (c) Patterning of one-dimensionalphotonic crystals of colloidal chain-like structures. \
Superparamagnetic particles are aligned into chains under an externalmagnetic field. Selective localized UV exposure then fixes the structure. (d)Optical microscopy image of blue and yellow dot patterns forming the butterflyimage inset.
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