Transparent conductors as solar energy materials: A panoramic review

Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection

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Anti-reflective coatings (ARCs) have evolved into highly effective reflectance and glare reducing components for various optical and opto-electrical equipments. Extensive research in optical and biological reflectance minimization as well as the emergence of nanotechnology over the years has contributed to the enhancement of ARCs in a major way. In this study the prime objective is to give a comprehensive idea of the ARCs right from their inception, as they were originally conceptualized by the pioneers and lay down the basic concepts and strategies adopted to minimize reflectance. The different types of ARCs are also described in greater detail and the state-of-the-art fabrication techniques have been fully illustrated. The inspiration that ARCs derive from nature (‘biomimetics’) has been an area of major research and is discussed at length. The various materials that have been reportedly used in fabricating the ARCs have also been brought into sharp focus. An account of application of ARCs on solar cells and modules, contemporary research and associated challenges are presented in the end to facilitate a universal understanding of the ARCs and encourage future research.

Anti-reflective coatings: A critical, in-depth review

▪ Abstract Metal-oxide nanowires can function as sensitive and selective chemical or biological sensors, which could potentially be massively multiplexed in devices of small size. The active nanowire sensor element in such devices can be configured either as resistors whose conductance is altered by charge-transfer processes occurring at their surfaces or as field-effect transistors whose properties can be controlled by applying an appropriate potential onto its gate. Functionalizing the surface of these entities offers yet another avenue for expanding their sensing capability. In turn, because charge exchange between an adsorbate and the nanowire can change the electron density in the nanowire, modifying the nanowire's carrier density by external means, such as applying a potential to the gate, could modify its surface chemical properties and perhaps change the rate and selectivity of catalytic processes occurring at its surface. Although research on the use of metal-oxide nanowires as sensors is still i...

Chemical Sensing and Catalysis by One-Dimensional Metal-Oxide Nanostructures

A 200,000-yr interval of extreme global warming marked the start of the Eocene epoch about 55 million years ago. Negative carbon- and oxygen-isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid (approximately 10,000 yr) input of isotopically depleted carbon. It has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change. Large-scale hydrate melting, however, requires a hitherto unknown triggering mechanism. Here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the Voring and More basins in the Norwegian Sea. We propose that intrusion of voluminous mantle-derived melts in carbon-rich sedimentary strata in the northeast Atlantic may have caused an explosive release of methane--transported to the ocean or atmosphere through the vent complexes--close to the Palaeocene/Eocene boundary. Similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the Siberian Traps (approximately 250 million years ago) and the Karoo Igneous Province (approximately 183 million years ago).

Release of methane from a volcanic basin as a mechanism for initial Eocene global warming

We present a simple, versatile technique for the fabrication of large, three-dimensional gap photonic crystals using glancing angle deposition (GLAD). A tetragonal lattice suitable for a large photonic band gap (PBG) can be synthesized by a regular array of square spiral structures grown from a simple, prepatterned substrate using physical vapor deposition and advanced substrate motion. Tetragonal square spiral crystals with a predicted PBG of up to 15% for a silicon structure can be produced in the visible, NIR, and IR spectrum. These PBG's exhibit good stability for large areas of parameter space that can be readily mapped out by the GLAD process through the variation of deposition parameters.

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Fabrication of Tetragonal Square Spiral Photonic Crystals

We deposited graded-index SiO2 films using glancing angle deposition to produce high-transmission antireflection coatings on glass. Because of the accurate control over the thin-film microstructure provided by this technique, we were able to create graded densities with a Gaussian profile resulting in transmission values greater than 99.9% for a single-layer interface with bandwidths up to 460 nm. The graded-index layer also provides low reflectance at nonnormal angles of incidence with transmission values degrading little for incidence angles up to 30 degrees.

Porous broadband antireflection coating by glancing angle deposition.

We report the fabrication and optical characterization of a tetragonal square spiral photonic crystal with a three-dimensional relative band gap of approximately 10% using the glancing angle deposition (GLAD) technique. This thin film structure is produced in a one-step process that is highly versatile as a wide range of crystal structures can be created simply through the variation of deposition parameters. Measurements indicate upper and lower frequency band edges at vacuum wavelengths of 2.50 and 2.75 μm, in the infrared region of the spectrum.

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Optical properties of a three-dimensional silicon square spiral photonic crystal

Using the glancing angle deposition thin film fabrication technique, it is possible to create tailored, three-dimensional periodic square spiral photonic crystals that exhibit a band of forbidden electromagnetic frequencies related to the dimensions of the nanostructures. Typically, when fabricating square spirals by traditional means, several problems arise due to nonuniform shadowing that results in column broadening and the loss of required periodicity for thicker crystals. Through the use of complex substrate motion that imposes greater restrictions on growth and shadowing, many of these problems have been overcome, in particular through the implementation of two new algorithms: the slow corner and the variable angle post methods. These motion algorithms have been implemented in conjunction with square spiral photonic crystal fabrication to provide more uniform spiral structures along with more stringent periodicity across the crystal that will allow for photonic band gap structures with more ideal ch...

Advanced techniques for the fabrication of square spiral photonic crystals by glancing angle deposition

Using the glancing angle deposition (GLAD) technique, we have fabricated porous, chiral thin films with optically anisotropic helical microstructures that exhibit optical phenomena such as wavelength specific rotation of linearly polarized light. Initial research has shown that the porosity of the films allows for the addition of nematic liquid crystals (NLCs) to the films for promising applications in dynamically switchable devices, while simultaneously enhancing the optical properties of the film. This study describes the fundamental optical behaviour of LC-filled chiral thin films in relation to material, porosity, structure and thickness. It was found that for SiO2 films, the addition of NLCs increased the effective rotatory power by two-fold when compared with results from the film without added LCs. The rotatory power of Al2O3 and MgF2 films, while being similarly increased by the addition of LCs, exhibited a reversal in sign, or direction of rotation, for the visible wavelength spectrum investigate...

Scott R. Kennedy

Papers

Fabrication of Tetragonal Square Spiral Photonic Crystals

Porous broadband antireflection coating by glancing angle deposition.

Optical properties of a three-dimensional silicon square spiral photonic crystal

Advanced techniques for the fabrication of square spiral photonic crystals by glancing angle deposition

Optical activity of chiral thin film and liquid crystal hybrids