Control of the pore size and connectivity of micro-sphere colloidal crystal lattices has been achieved by a layer-by-layer growth of silica using atmospheric pressure room temperature chemical vapour deposition of silica, a method which largely increases the mechanical stability of the lattice without disrupting its long range order.
The nucleation and growth of mesoporous silica fibers and gyroids was the focus of this kinetic study. The authors obtained images of the smallest objects implicated in the creation of these shapes by tapping-mode atomic force microscopy and transmission electron microscopy. Dynamic light scattering provided temporal information on the size evolution of the growth objects. It is shown that increasing pH correlates with slower nucleation and a shape transition from fibers to gyroids. This knowledge is essential to further advancement of the synthesis of mesoporous materials with controlled morphologies.
The global race for the optically integrated photonic chip is driven by the prospective that miniaturization of optical devices and enhanced chip functionality may revolutionize the manufacture of optical circuits, and the futuristic dream of the all-optical computer may come true. The aim of this article is to take a brief yet critical look at some developments in microsphere self-assembly of colloidal photonic crystals and their technological potential from the perspective of research results that have recently emerged from our materials chemistry group. The focus of the discussion centers on the provocative vision of the "colloidal photonic crystal micropolis", Fig. 1, which depicts the direction in which the colloidal photonic crystal research of our materials chemistry group is heading. It is intended to bring to the forefront the pointed question of whether the most recent versions of colloidal photonic crystals and their integration on chips, developed in our laboratory, can rise to the stringent specifications of structural perfection and optical quality, functionality and complexity that will be demanded for photonic crystal optical devices and optical circuits touted for next generation all-optical chip and telecommunication technologies.
Laser scanning confocal microscopy, advantageous as a non-destructive spatial imaging technique, has been used to probe the internal photonic crystal lattice structure of micron scale core–fluorescein-labeled shell–corona silica microspheres that had been crystallized within anisotropically etched relief patterns in the 100 surface of silicon wafers. Using this method it was possible to determine the three-dimensional positioning of individual microspheres that had been allowed to self-assemble within the confines of square and rectangular shaped pyramidal microwells with sub-micron lateral and vertical spatial resolution. This methodology confirmed that microspheres underwent vectorial crystal growth in the form of a face centered cubic lattice inside the pyramidal microwells in which the 100 face of the photonic crystal was oriented parallel to the 100 surface of the silicon wafer. Furthermore it was feasible to visualize both external and internal defects buried within photonic crystal lattices in the planarized opal-patterned chips.
Herein we report experimental and theoretical analysis of the optical properties of planarized self-assembled colloidal photonic crystals confined within rectangular microchannels. A detailed mapping of the optical features, performed by microspectroscopy, is presented, providing evidence that spherical colloids confined in microchannels crystallize as single-domain colloidal crystal several hundreds of microns long with a very low concentration of intrinsic defects. A study of defective colloidal crystals is also made to illustrate this point. The effect of the different parameters affecting the reflection properties of these structures, such as crystal size, orientation, and nature of the substrate, is also analyzed. We show that the well-defined geometry and dimensions of the channels serve to template colloidal crystals with precise size, shape, and orientation, which imply accurate control of their photonic crystal properties.
Electronically addressable thin films of tin oxide gas sensors with well-defined opaline microstructures and reproducible sensor-to-sensor responses have been fabricated on interdigitated gold microelectrodes through self-assembly growth of a monodisperse polystyrene latex film onto the electrodes followed by infiltration of tin tert-butoxide and calcination of the film.
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The ability to form molded or patterned metal-containing ceramics with tunable properties is desirable for many applications. In this paper we describe the evolution of a ceramic from a metal-containing polymer in which the variation of pyrolysis conditions facilitates control of ceramic structure and composition, influencing magnetic and mechanical properties. We have found that pyrolysis under nitrogen of a well-characterized cross-linked polyferrocenylsilane network derived from the ring-opening polymerization (ROP) of a spirocyclic [1]ferrocenophane precursor gives shaped macroscopic magnetic ceramics consisting of alpha-Fe nanoparticles embedded in a SiC/C/Si(3)N(4) matrix in greater than 90% yield up to 1000 degrees C. Variation of the pyrolysis temperature and time permitted control over the nucleation and growth of alpha-Fe particles, which ranged in size from around 15 to 700 A, and the crystallization of the surrounding matrix. The ceramics contained smaller alpha-Fe particles when prepared at temperatures lower than 900 degrees C and displayed superparamagnetic behavior, whereas the materials prepared at 1000 degrees C contained larger alpha-Fe particles and were ferromagnetic. This flexibility may be useful for particular materials applications. In addition, the composition of the ceramic was altered by changing the pyrolysis atmosphere to argon, which yielded ceramics that contain Fe(3)Si(5). The ceramics have been characterized by a combination of physical techniques, including powder X-ray diffraction, TEM, reflectance UV-vis/near-IR spectroscopy, elemental analysis, XPS, SQUID magnetometry, Mössbauer spectroscopy, nanoindentation, and SEM. Micromolding of the spirocyclic [1]ferrocenophane precursor within soft lithographically patterned channels housed inside silicon wafers followed by thermal ROP and pyrolysis enabled the formation of predetermined micron scale designs of the magnetic ceramic.
A simple, quick, reproducible and inexpensive method is described that combines self-assembly, micro-fluidics and soft lithography, to achieve a novel example of vectorial control of thickness, area, orientation and registry of patterned single crystal silica colloidal crystals in silicon wafers, coined opal chips, for potential applications in photonic chip and lab-on-chip technologies.
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