Photonic crystals (PhCs) influence the propagation of light by their periodic variation in dielectric contrast or refractive index. This review outlines the attractive optical qualities inherent to most PhCs namely the presence of full or partial photonic band gaps and the possibilities they present towards the inhibition of spontaneous emission and the localization of light. Colloidal self-assembly of polymer or silica spheres is one of the most favoured and low cost methods for the formation of PhCs as artificial opals. The state of the art in growth methods currently used for colloidal self-assembly are discussed and the use of these structures for the formation of inverse opal architectures is then presented. Inverse opal structures with their porous and interconnected architecture span several technological arenas – optics and optoelectronics, energy storage, communications, sensor and biological applications. This review presents several of these applications and an accessible overview of the physics of photonic crystal optics that may be useful for opal and inverse opal researchers in general, with a particular emphasis on the recent use of these three-dimensional porous structures in electrochemical energy storage technology. Progress towards all-optical integrated circuits may lie with the concepts of the photonic crystal, but the unique optical and structural properties of these materials and the convergence of PhC and energy storage disciplines may facilitate further developments and non-destructive optical analysis capabilities for (electro)chemical processes that occur within a wide variety of materials in energy storage research.

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Artificial opal photonic crystals and inverse opal structures – fundamentals and applications from optics to energy storage

Approaches to self-assembly of colloidal monolayers: A guide for nanotechnologists.

On-chip growth of semiconductor metal oxide nanowires for gas sensors: A review

The rational design of heterostructures is highly important for innovative sensor technology to acquire efficient gas detection with optimized gas sensing properties. In the present work, a novel heterostructure of Au/Co3O4/W18O49 hollow spheres is constructed and applied for gas sensor application. The structure-property correlation has been studied by means of X-ray diffraction, X-ray photoelectron spectroscopy, Scanning electron microscope and Transmission electron microscope, as well as comprehensive gas sensing tests. Experiments demonstrate that the Au/Co3O4/W18O49 heterostructure delivers outstanding performances in terms of high sensitivity, fast response-recovery, good selectivity, and very low limit of detection against pristine W18O49 and Co3O4/W18O49. Notably, a very high response (16.7) to 2 ppm triethylamine and a state-of-the-art limit of detection (81 ppb) are obtained. The superior gas sensing properties are attributed to a synergistic combination of the unique porous structure, the p-n heterojunctions between Co3O4/W18O49, and the catalytic spillover effect of Au nanoparticles.

Rational design of Au/Co3O4-functionalized W18O49 hollow heterostructures with high sensitivity and ultralow limit for triethylamine detection

Fast response of sprayed vanadium pentoxide (V 2 O 5 ) nanorods towards nitrogen dioxide (NO 2 ) gas detection

Gas sensors based on aligned arrays of W 18 O 49 nanowires were formed directly via a novel route of in situ thermal oxidation of sputtered W film on the substrate attached patterned Pt electrodes. The well-developed nanowires have diameter of 10–20 nm and show roughly aligned morphology. It is found that the duration of oxygen exposure during thermal annealing plays a crucial role to harvest a pure phase of W 18 O 49 nanowire with desired length. The roughly aligned W 18 O 49 nanowires show favourable microstructure for gas adsorption and rapid gas diffusion. The NO 2 -sensing properties of aligned W 18 O 49 nanowires sensor were evaluated at 50 °C up to 200 °C over NO 2 concentration ranging from 250 ppb to 2.5 ppm. The results indicate that the W 18 O 49 nanowire arrays sensor exhibits good NO 2 -sensing performances at its optimal operating temperature of 150 °C, especially perfect stability and fast response–recovery characteristics. The reliable interface performance and fast gas adsorption–desorption properties of the directly assembled vertically aligned nanowire array attribute to the superior stability and quick response/recovery. The growth mechanism of aligned W 18 O 49 nanowires is proposed based on the direct SEM observations on the intermediate products, and meanwhile the sensing mechanism of the corresponding sensor is analyzed.

Yang Liu

Papers

Thermal-oxidative growth of aligned W18O49 nanowire arrays for high performance gas sensor

Self-assembly of colloidal crystals from polystyrene emulsion at elevated temperature by dip-drawing method

Shell deposition-induced vertically aligned core-shell arrays of W18O49/V2O5 nanorods