A simple technique to prepare large-area, regular microstructures in glass containing silver nanoparticles is presented. Here the modification of spatial distribution of the nanoparticles is achieved using a direct current (DC) electric field at moderately elevated temperatures. The technique exploits the recently reported effect of "electric field-assisted dissolution" (EFAD) of silver nanoparticles during which the silver nanoparticles embedded in a glass matrix can be destroyed and dissolved in the glass in form of Ag+ ions by a combination of an intense DC electric field (~1kV) and moderately elevated temperature (~280°C). This process can lead to a total transparency of the nanocomposite glasses, which to our knowledge can not be achieved via any other technique.
In this work, the possibility to produce orderly-oriented array of embedded, 2-D, micron size optical structures in silver-doped nanocomposite glass is demonstrated. This could lead to an easy way for production of many useful optical devices based on the composite materials.
Variations of the refractive index can be utilized in order to shift the stop band in photonic crystals. Here, two- and three-dimensional structures made of macroporous silicon were filled with liquid crystals. Optical investigations in the infrared wavelength range indicate temperature-induced spectral shifts of the edges of stopbands. In addition, the defect modes corresponding to microcavities within the periodic structure can be thermally controlled. Investigations of the director field within the pores by means of 2H-NMR and confocal microscopy indicate that both parallel and escaped radial director fields can appear, depending on the surface treatment of the substrates. In cylindrical pores with a periodic modulation of the pore diameter, the escaped radial director field is modified thereby showing a regular array of disclination rings.
The fabrication of three-dimensional photonic bandgap materials and the controlled incorporation of point, linear and planar defects into these crystals is a major challenge in materials research today. We show in this report that these purposes can be achieved by photoelectrochemical etching of lithographically prestructured silicon. Our advanced etching method allows the fabrication of three-dimensional photonic crystals with simple cubic symmetry. The performed calculations suggest complete bandgaps of 5% for the realized bulk structures. By lithographic prestructuring vertical line and planar defects can be induced, whereas horizontal planar defects can be created during the etching step. By combining both structuring techniques point defects can be fabricated.
The major challenge in todays photonic crystal fabrication is the
experimental realization of perfect, disorder-free structures. Macroporous silicon etching is a versatile technique for the manufacturing of large-scale well-ordered porous materials and
three-dimensional photonic crystals. We investigate the degree of
local disorder by scanning electron microscopy and a subsequent
image processing, as well as the homogeneity of our large area
crystals by an optical two-dimensional mapping. The observed
disorder is related to the applied fabrication parameters. The
deduced dependencies help to avoid disorder and to optimize our