Photonic crystal limitations

These ordered array materials find interest not only in catalysis, but in several other applications, from optical materials, sensors, low-k materials, ionic conductors, photonic crystals, and bio-mimetic materials.Flowever, with respect to these applications, catalysis requires additional specific characteristics, such as the presence of a thermally stable nanostructure, the minimization of grain boundaries where side reactions may occur, and the presence of a porous structure which guarantees a high surface area coupled to low heat and mass transfer limitations. An ordered assembly of ID nanostructures for oxide materials could, in principle, meet these different requirements. 

The Bragg equation for a fee crystal as assumed in the photonic crystal based on polystyrene nanoparticles [154] is expressed in Eq. (82). The spacing between (111) planes in the fee crystal is related to dm. The effective refractive index ( eff) was obtained by considering the long-wavelength limit of the photon-dispersion relation co(k), Eq. (83), where c is the speed of light. 

A major limitation of the sensitivity of this type of sensor is the ability to transfer optical power into the evanescent field. Recent work has incorporated new types of fibers to increase the sensitivity of measurements. Newly developed hollow core fibers, which guide light mainly in the cladding, can be used to couple more power into the sensitive materials [76]. If the hollow core fiber is used as the active sensing area between two silica core fibers, then the transitions between the fibers will force the light to travel from the core into the cladding then back into the core. Another type of fiber is the microstructure fiber or photonic crystal fiber, which incorporates air holes into... 

In spite of its simplicity, the long response time of the hydrogel photonic crystal materials has limited their utility as sensors. This is because of the slow diffusion of analytes in the hydrogel to influence the optical properties. New fabrication procedures of these hydrogel photonic crystal sensors were used to improve the response time. The Lee Group [96] demonstrated a mechanically robust and fast responsive photonic crystal pH sensor, which was fabricated by templated photopolymerization of hydrogel monomers within the interstitial space of a self-assembled colloidal photonic crystal, as shown in Fig. 25. 

The reflectivity and width of the band gaps increase as the refractive index modulation increases. The basic principle for optical limiting by a ID nonlinear photonic crystal material can be understood from Figure 2. Initially, (A), the refractive indices of the different layers are matched, and the sample... 

Figure 2. The concept of a nonlinear photonic crystal optical limiter.

There are several emerging areas of nanophotonics, which include plasmonics, multiple exciton generation, photonic crystals, and upconversion. While these concepts have been applied to the design of solar cells, the exploration of these concepts in the context of water photoelectrolysis devices is limited. It is therefore of interest to consider the ways in which advances in nanophotonics could influence the direction of future work in water photoelectrolysis. This section emphasizes developments in plasmonics that may be useful if successfully applied to water photoelectrolysis. 

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