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Journal ArticleDOI

Porous broadband antireflection coating by glancing angle deposition.

01 Aug 2003-Applied Optics (Optical Society of America)-Vol. 42, Iss: 22, pp 4573-4579
TL;DR: Grade-index SiO2 films are deposited using glancing angle deposition to produce high-transmission antireflection coatings on glass with accurate control over the thin-film microstructure resulting in graded densities with a Gaussian profile and low reflectance at nonnormal angles of incidence.
Abstract: 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.
Citations
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Journal ArticleDOI
TL;DR: Transparent conductors (TCs) have a multitude of applications for solar energy utilization and for energy savings, especially in buildings as discussed by the authors, which leads naturally to considerations of spectral selectivity, angular selectivity, and temporal variability of TCs, as covered in three subsequent sections.

1,471 citations


Cites background from "Porous broadband antireflection coa..."

  • ...Excellent AR properties have been obtained also with graded-index silica films made by oblique angle deposition [87]; this technique is further discussed in Section 4....

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Journal ArticleDOI
TL;DR: Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection were used in this paper, where the authors proposed a method to eliminate the reflection in optical thin-films.
Abstract: Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection

1,153 citations

Journal ArticleDOI
TL;DR: In this paper, the basic concepts and strategies adopted to minimize reflectance of anti-reflective coatings (ARCs) are described in greater detail and state-of-the-art fabrication techniques have been fully illustrated.
Abstract: 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.

1,047 citations

Journal ArticleDOI
TL;DR: In this paper, the origin of the columnar structure characteristic of GLAD films is discussed in terms of nucleation processes and structure zone models, and the column shape evolves during growth, and power-law scaling behavior is observed as shown in both experimental results and theoretical simulations.
Abstract: Physical vapor deposition under conditions of obliquely incident flux and limited adatom diffusion results in a film with a columnar microstructure. These columns will be oriented toward the vapor source and substrate rotation can be used to sculpt the columns into various morphologies. This is the basis for glancing angle deposition (GLAD), a technique for fabricating porous thin films with engineered structures. The origin of the columnar structure characteristic of GLAD films is discussed in terms of nucleation processes and structure zone models. As deposition continues, the columnar structures are influenced by atomic-scale ballistic shadowing and surface diffusion. Competitive growth is observed where the tallest columns grow at the expense of smaller features. The column shape evolves during growth, and power-law scaling behavior is observed as shown in both experimental results and theoretical simulations. Due to the porous nature of the films and the increased surface area, a variety of chemical applications and sensor device architectures are possible. Because the GLAD process provides precise nanoscale control over the film structure, characteristics such as the mechanical, magnetic, and optical properties of the deposited film may be engineered for various applications. Depositing onto prepatterned substrates forces the columns to adopt a planar ordering, an important requirement for photonic crystal applications.

819 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigate solution-grown ZnO nanostructures as antireflection coating for Si solar cells and compare them to conventional single layer ARCs, finding that nanoscale morphology, controlled through synthetic chemistry, has a great effect on the macroscopic ARC performance.
Abstract: An efficient antireflection coating (ARC) can enhance solar cell performance through increased light coupling. Here, we investigate solution-grown ZnO nanostructures as ARCs for Si solar cells and compare them to conventional single layer ARCs. We find that nanoscale morphology, controlled through synthetic chemistry, has a great effect on the macroscopic ARC performance. Compared with a silicon nitride (SiN) single layer ARC, ZnO nanorod arrays display a broadband reflection suppression from 400 to 1200 nm. For a tapered nanorod array with average tip diameter of 10 nm, we achieve a weighted global reflectance of 6.6%, which is superior to an optimized SiN single layer ARC. Calculations using rigorous coupled wave analysis suggest that the tapered nanorod arrays behave like modified single layer ARCs, where the tapering leads to impedance matching between Si and air through a gradual reduction of the effective refractive index away from the surface, resulting in low reflection particularly at longer wavelengths and eliminating interference fringes through roughening of the air-ZnO interface. According to the calculations, we may further improve ARC performance by tailoring the thickness of the bottom fused ZnO layer and through better control of tip tapering.

615 citations

References
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Journal ArticleDOI
TL;DR: In this paper, it was shown that the presence of many of these minute spheres to a wave-length of light in the glass will account for all the optical properties of "regular" gold ruby glass, and that the irregularities in colour and in polarisation effects sometimes exhibited by gold glass are due to excessive distance between consecutive gold particles or to excessive size of such particles.
Abstract: The present paper contains a discussion of some optical properties of a medium containing minute metal spheres. The discussion is divided into two Parts: the first Part dealing with colours in metal glasses, in which the proportion of volume occupied by metal is small; the second Part dealing with metal films, in which this proportion may have any value from zero to unity. In Part I. the observations of Siedentopf and Zsigmondy beyond the limit of microscopic vision (‘Ann. der Phys.,’ January, 1903) are discussed. It is shown that the particles seen in a gold ruby glass are particles of gold which, when their diameters are less than 0.1μ, are accurately spherical. I have endeavoured to show that the presence of many of these minute spheres to a wave-length of light in the glass will account for all the optical properties of “regular” gold ruby glass, and that the irregularities in colour and in polarisation effects sometimes exhibited by gold glass are due to excessive distance between consecutive gold particles or to excessive size of such particles, the latter, however, involving the former. It is also shown that the radiation from radium is capable of producing in gold glass the ruby colour which is generally produced by re-heating. The method adopted enables us to predict from a knowledge of the metal present in metallic form in a glass what colour that glass will be in its “regular” state.

3,519 citations

Journal ArticleDOI
TL;DR: In this paper, it has been shown that the first stage in the formation of a crystal of those metals is the small sphere; and from observations on the growth of sulphur crystals in CS2, Vogelsang arrived at the conclusion that the small spheres is always the first phase in forming a crystal. But it is by no means necessary that each of these small spheres, formed as crystallisation commences, should give rise to a separate crystal.
Abstract: This paper is an extension of a previous memoir on the “Colours in Metal Glasses and in Metallic Films”; it is concerned with the application of mathematical analysis, akin to that already there developed, to the explanation and coordination of the colours which certain metals are, under a great variety of circumstances, capable of causing. From observations on gold and copper ruby glasses, it has been shown that the first stage in the formation of a crystal of those metals is the small sphere; and from observations on the growth of sulphur crystals in CS2, Vogelsang arrived at the conclusion that the small sphere is always the first stage in the formation of a crystal. He remarked, however, that it is by no means necessary that each of the small spheres, formed as crystallisation commences, should give rise to a separate crystal: the small spheres tend to coagulate, forming first rows and then groups of other and more complicated shapes, until the crystal is ultimately formed. To the intermediate bodies he gives the name of crystallites .

1,022 citations

Journal ArticleDOI
TL;DR: In this article, the authors used computer control of substrate motion to accurately position the substrate and to achieve the desired film structures, including zigzag shaped to helical to four-sided “square” helical.
Abstract: Sculptured thin films with three dimensional microstructure controlled on the 10 nm scale were fabricated with an evaporation technique. Glancing angle deposition (GLAD) and substrate motion were employed to “sculpt” columnar thin film microstructure into desired forms ranging from zigzag shaped to helical to four-sided “square” helical. Computer control of substrate motion was used to accurately position the substrate and to achieve the desired film structures. The growth mechanics of this novel thin film deposition technique are investigated with density measurements, scanning electron microscopy analysis, and measurements of effective refractive index. Adatom diffusion and atomic shadowing are the dominant growth mechanisms with glancing angle deposition conditions creating extreme shadowing. With controlled rotation of the substrate about two axes during deposition, a dense capping layer can be produced on top of the porous sculptured films. The success of the capping process was found to be strongly ...

984 citations

Journal ArticleDOI
TL;DR: In this article, the reflection and transmission properties of moth eye antireflection surfaces are described, and are shown to be equal to those of the best multilayer antire-flection coatings.
Abstract: A ‘moth eye’ antireflection surface is a very fine array of protuberances which behaves as a gradation of refractive index, and which substantially reduces the reflectance. The reflection and transmission properties of such surfaces are described, and are shown to be equal to those of the best multilayer antireflection coatings.

676 citations