Slow photons in the fast lane in chemistry
09 Jan 2008-Journal of Materials Chemistry (The Royal Society of Chemistry)-Vol. 18, Iss: 4, pp 369-373
TL;DR: In this paper, the authors look at slow photons mainly through the eye of chemistry and highlight some recent developments in this exciting and emerging field that demonstrate the potential of slow photons in materials chemistry and nanochemistry.
Abstract: A driving force in the rapidly developing field of photonic crystals has been the photonic bandgap, a range of energies where the propagation of light is completely forbidden. The photonic bandgap allows the design of photonic lattices that localize, guide and bend light at sub-micron length scales, providing opportunities for the creation of miniature optical devices and integrated optical circuits to help drive the revolution in photonics. A less well known attribute of photonic crystals is their theoretical ability to slow light to a velocity of zero. This phenomenon can be achieved at the high and low energy edges of photonic stopgaps where the photonic bands are flat and light exists as a standing wave commensurate with the photonic lattice and travels at a group velocity of zero, referred to as “slow photons” herein. It has been shown theoretically that the probability of harvesting slow photons scales inversely with their group velocity. This means that a number of well known photon driven processes and devices in chemistry and physics can be enhanced by capturing this unique property of slow photons. In this paper we will look at slow photons mainly through the eye of chemistry and highlight some recent developments in this exciting and emerging field that demonstrate the potential of slow photons in materials chemistry and nanochemistry.
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TL;DR: A state-of-the-art review of the applications of hierarchically structured porous materials in energy conversion and storage is presented in this paper, where hierarchical porosity and structures have been heavily involved in newly developed energy storage and conversion systems, showing the importance of macrochannels in light related systems such as photocatalysis and photovoltaics.
Abstract: Materials with hierarchical porosity and structures have been heavily involved in newly developed energy storage and conversion systems. Because of meticulous design and ingenious hierarchical structuration of porosities through the mimicking of natural systems, hierarchically structured porous materials can provide large surface areas for reaction, interfacial transport, or dispersion of active sites at different length scales of pores and shorten diffusion paths or reduce diffusion effect. By the incorporation of macroporosity in materials, light harvesting can be enhanced, showing the importance of macrochannels in light related systems such as photocatalysis and photovoltaics. A state-of-the-art review of the applications of hierarchically structured porous materials in energy conversion and storage is presented. Their involvement in energy conversion such as in photosynthesis, photocatalytic H 2 production, photocatalysis, or in dye sensitized solar cells (DSSCs) and fuel cells (FCs) is discussed. Energy storage technologies such as Li-ions batteries, supercapacitors, hydrogen storage, and solar thermal storage developed based on hierarchically porous materials are then discussed. The links between the hierarchically porous structures and their performances in energy conversion and storage presented can promote the design of the novel structures with advanced properties.
784 citations
TL;DR: In this review a panorama is presented of the state of the art in this field with the view to serve a broad community concerned with materials aspects of photonic structures and more so those interested in self-assembly.
Abstract: Photonic crystals have proven their potential and are nowadays a familiar concept. They have been approached from many scientific and technological flanks. Among the many techniques devised to implement this technology self-assembly has always been one of great popularity surely due to its ease of access and the richness of results offered. Self-assembly is also probably the approach entailing more materials aspects owing to the fact that they lend themselves to be fabricated by a great many, very different methods on a vast variety of materials and to multiple purposes. To these well-known material systems a new sibling has been born (photonic glass) expanding the paradigm of optical materials inspired by solid state physics crystal concept. It is expected that they may become an important player in the near future not only because they complement the properties of photonic crystals but because they entice the researchers' curiosity. In this review a panorama is presented of the state of the art in this field with the view to serve a broad community concerned with materials aspects of photonic structures and more so those interested in self-assembly.
606 citations
TL;DR: This tutorial review highlights fundamental aspects of the physics underpinning the science of photonic crystals, insight into building-block assembly routes to the fabrication of different photonic crystal structures and compositions is provided, and a glimpse into future applications is taken.
Abstract: In this tutorial review we highlight fundamental aspects of the physics underpinning the science of photonic crystals, provide insight into building-block assembly routes to the fabrication of different photonic crystal structures and compositions, discuss their properties and describe how these relate to function, and finally take a glimpse into future applications.
590 citations
TL;DR: In this article, the photocatalytic activity of non metal doped titania for a wide variety of pollutants degradation under UV/visible light, with special emphasis on nitrogen doped TiO 2.
Abstract: The multifunctional and advanced semiconductor titania with superior physicochemical and opto-electronic properties is extensively investigated in wastewater purification mainly due to its non-toxicity, favorable band edge positions, water insolubility, multifaceted electronic properties, surface acid–base properties, super hydrophilicity and so on. However, large band gap and massive photogenerated charge carrier recombination hinders its wide application under natural solar light. Thus, altering the surface-bulk structure of titania is a major goal in the area of both materials and environmental chemistry for its better applications. The substitution of p block elements (B, C, N, F, S, P, and I) either at Ti 4+ and O 2− sites is a promising approach to overcome the aforementioned drawbacks. This review focuses on the photocatalytic activity of non metal doped titania for a wide variety of pollutants degradation under UV/visible light, with special emphasis on nitrogen doped TiO 2 . Further improvement in photoactivity of N–TiO 2 is achieved via depositing with noble metals, co-doping with foreign ions, sensitization, surface modifications and heterostructuring with other semiconductors. The mechanism governing the photocatalytic reactions is discussed in the light of charge carrier generation–separation–transfer–recombination dynamics together with pollutant adsorption and their reactions with reactive oxygenated species in liquid or gaseous regime. We are positive that this review article will further stimulate our research interest on this intriguing hot topic.
510 citations
TL;DR: It is shown that colloidal coassembly is available for a range of organometallic sol-gel and polymer matrix precursors, and represents a simple, low-cost, scalable method for generating high-quality, chemically tailorable inverse opal films for a variety of applications.
Abstract: Whereas considerable interest exists in self-assembly of well-ordered, porous "inverse opal" structures for optical, electronic, and (bio)chemical applications, uncontrolled defect formation has limited the scale-up and practicality of such approaches. Here we demonstrate a new method for assembling highly ordered, crack-free inverse opal films over a centimeter scale. Multilayered composite colloidal crystal films have been generated via evaporative deposition of polymeric colloidal spheres suspended within a hydrolyzed silicate sol-gel precursor solution. The coassembly of a sacrificial colloidal template with a matrix material avoids the need for liquid infiltration into the preassembled colloidal crystal and minimizes the associated cracking and inhomogeneities of the resulting inverse opal films. We discuss the underlying mechanisms that may account for the formation of large-area defect-free films, their unique preferential growth along the 110 direction and unusual fracture behavior. We demonstrate that this coassembly approach allows the fabrication of hierarchical structures not achievable by conventional methods, such as multilayered films and deposition onto patterned or curved surfaces. These robust SiO(2) inverse opals can be transformed into various materials that retain the morphology and order of the original films, as exemplified by the reactive conversion into Si or TiO(2) replicas. We show that colloidal coassembly is available for a range of organometallic sol-gel and polymer matrix precursors, and represents a simple, low-cost, scalable method for generating high-quality, chemically tailorable inverse opal films for a variety of applications.
500 citations
Cites background from "Slow photons in the fast lane in ch..."
...Such structures have been shown to be potentially useful in a wide range of fields, including photonics (6–10), tissue engineering (11, 12), sensing (13, 14), and catalysis (10, 15, 16)....
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...Due to the absence of an overlayer, the high porosity of the coassembled films is readily accessible from the top surface, which is especially important for applications in catalysis (10, 15, 16), gas adsorption (55), or tissue engineering (11, 12)....
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References
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TL;DR: The surface-enhanced Raman scattering (SERS) effect was first discovered by Fleischmann, Van Duyne, Creighton, and Creighton as discussed by the authors, who showed that molecules adsorbed on specially prepared silver surfaces produce a Raman spectrum that is at times a millionfold more intense than expected.
Abstract: In 1978 it was discovered, largely through the work of Fleischmann, Van Duyne, Creighton, and their coworkers that molecules adsorbed on specially prepared silver surfaces produce a Raman spectrum that is at times a millionfold more intense than expected. This effect was dubbed surface-enhanced Raman scattering (SERS). Since then the effect has been demonstrated with many molecules and with a number of metals, including Cu, Ag, Au, Li, Na, K, In, Pt, and Rh. In addition, related phenomena such as surface-enhanced second-harmonic generation, four-wave mixing, absorption, and fluorescence have been observed. Although not all fine points of the enhancement mechanism have been clarified, the majority view is that the largest contributor to the intensity amplification results from the electric field enhancement that occurs in the vicinity of small, interacting metal particles that are illuminated with light resonant or near resonant with the localized surface-plasmon frequency of the metal structure. Small in this context is gauged in relation to the wavelength of light. The special preparations required to produce the effect, which include among other techniques electrochemical oxidation-reduction cycling, deposition of metal on very cold substrates, and the generation of metal-island films and colloids, is now understood to be necessary as a means of producing surfaces with appropriate electromagnetic resonances that may couple to electromagnetic fields either by generating rough films (as in the case of the former two examples) or by placing small metal particles in close proximity to one another (as in the case of the latter two). For molecules chemisorbed on SERS-active surface there exists a "chemical enhancement" in addition to the electromagnetic effect. Although difficult to measure accurately, the magnitude of this effect rarely exceeds a factor of 10 and is best thought to arise from the modification of the Raman polarizability tensor of the adsorbate resulting from the formation of a complex between the adsorbate and the metal. Rather than an enhancement mechanism, the chemical effect is more logically to be regarded as a change in the nature and identity of the adsorbate.
5,005 citations
1,168 citations
TL;DR: In this paper, a statistical approach is taken toward the ray optics of optical media with complicated nonspherical and nonplanar surface shapes, where the light in such a medium will tend to be randomized in direction and of 2n2(x) times greater intensity than the externally incident light, where n(x), is the local index of refraction.
Abstract: A statistical approach is taken toward the ray optics of optical media with complicated nonspherical and nonplanar surface shapes. As a general rule, the light in such a medium will tend to be randomized in direction and of 2n2(x) times greater intensity than the externally incident light, where n(x) is the local index of refraction. A specific method for doing optical calculations in statistical ray optics will be outlined. These optical enhancement effects can result in a new type of antireflection coating. In addition, these effects can improve the efficiency as well as reduce the cost of solar cells.
1,138 citations
TL;DR: Cavity ring-down (CRD) spectroscopy as mentioned in this paper is a direct absorption technique, which can be performed with pulsed or continuous light sources and has a significantly higher sensitivity than obtainable in conventional absorption Spectroscopy.
Abstract: Cavity ring-down (CRD) spectroscopy is a direct absorption technique, which can be performed with pulsed or continuous light sources and has a significantly higher sensitivity than obtainable in conventional absorption spectroscopy. The CRD technique is based upon the measurement of the rate of absorption rather than the magnitude of absorption of a light pulse confined in a closed optical cavity with a high Q factor. The advantage over normal absorption spectroscopy results from, firstly, the intrinsic insensitivity to light source intensity fluctuations and, secondly, the extremely long effective path lengths (many kilometres) that can be realized in stable optical cavities. In the last decade, it has been shown that the CRD technique is especially powerful in gas-phase spectroscopy for measurements of either strong absorptions of species present in trace amounts or weak absorptions of abundant species. In this review, we emphasize the various experimental schemes of CRD spectroscopy, and we show how th...
953 citations
TL;DR: By coupling a photonic crystal to a film of TiO(2) nanoparticles, the short circuit photocurrent efficiency across the visible spectrum could be increased by about 26%, relative to an ordinary dye-sensitized nanocrystalline TiO (2) photoelectrode.
Abstract: The light harvesting efficiency of dye-sensitized photoelectrodes was enhanced by coupling a TiO2 photonic crystal layer to a conventional film of TiO2 nanoparticles. In addition to acting as a dielectric mirror, the inverse opal photonic crystal caused a significant change in dye absorbance which depended on the position of the stop band. Absorbance was suppressed at wavelengths shorter than the stop band maximum and was enhanced at longer wavelengths. This effect arises from the slow group velocity of light in the vicinity of the stop band, and the consequent localization of light intensity in the voids (to the blue) or in the dye-sensitized TiO2 (to the red) portions of the photonic crystal. By coupling a photonic crystal to a film of TiO2 nanoparticles, the short circuit photocurrent efficiency across the visible spectrum (400−750 nm) could be increased by about 26%, relative to an ordinary dye-sensitized nanocrystalline TiO2 photoelectrode.
573 citations