Antireflection dielectric

Layer Stacks and Protective Layers. The layer stack of an MO disk consists mainly of an MO layer, a dielectric antirefiection layer, and a metallic reflection layer (Fig. 14). The thickness of the antireflection layer as well as that of the MO layer have to be properly chosen to obtain a maximum magnetooptical figure-of-mefit (FOM). The FOM can be further increased by using a quadfilayer configuration with dielectric layers on both sides of the MO layer. Practical disks use the generalized configuration 50—120-nm dielectric layer, 25—90-nm MO layer, 17—70-nm dielectric layer (for quadfilayer configuration only), and 15—150-nm reflective layer. 

Antireflection coatings are used over the silicon surface which, without the coating, reflects ca 35% of incident sunlight. A typical coating consists of a single layer of a transparent dielectric material with a refractive index of ca 2, which is between the index of siUcon and ait or cover material. Materials such as titanium dioxide, tantalum pentoxide, Ta20, or siUcon nitride, Si N, ca 0.08-p.m thick are common. The coating and a physically textured... 

Both xerogels and aerogels are characteristically high surface area materials (surface areas normally exceed 500 m2/g). Unlike wet gels, many uses exist for dried gels due to their high surface areas and small pore sizes (typically, < 20 nm diameters). Examples include catalyst supports (12.). ultrafiltration media (18), antireflective coatings (19-20), and ultra-low dielectric constant films. (Lenahan, P. M. and Brinker, C. J., unpublished results.)... 

Silicon Nitride. Silicon nitride produced by high-temperature (>700 °C) CVD is a dense, stable, adherent dielectric that is useful as a passivation or protective coating, interlevel metal dielectric layer, and antireflection coating in solar cells and photodetectors. However, these applications often demand low deposition temperatures (<400 °C) so that low-melting-point substrates or films (e.g., Al or polymers) can be coated. Therefore, considerable effort has been expended to form high-quality silicon nitride films by PECVD. 

The main application of amorphous perfluoropolymers is as cladding of optical fibers, antireflective coatings, low dielectric coatings, and in the electronic industry (e.g., photoresists)1012 and as a low-dielectric-constant insulator for high-performance interconnects.13... 

From a theoretical point-of view, significantly higher current densities are feasible, but require further improved front TCO films and perfect mirrors as back reflectors. This is illustrated by the dotted curve in Fig. 8.28, which shows simulations of quantum efficiency for a 1 pm thick pc-Si H solar cell. These simulations reveal a current potential of 29.2 mA cm-2 by improved optical components like reduced parasitic absorption in the front TCO, ideal Lambertian light scattering, dielectric back reflectors, and antireflection coatings on the front side [147]. However, this still has to be achieved experimentally. 

Using an aU-dielectric antireflection (AR) coatings is the proper way to remove the reflection from the front glass surface when the light is emitted through a glass substrate (bottom-emission). 

Optical consideration, metal-dielectric antireflection coating... 

Veiling glare caused by reflection of an automobile instrument panel in the windshield can be reduced by coating the windshield with an antireflective multilayer dielectric coating for oblique incidence [156]. 

There are basically two ways to achieve high visual transmittance simultaneously with high infrared reflectance. One is the use of the interference effect in all-dielectric multilayers, the other is the use of intrinsic optical properties of electrically conducting films such as Au, Ag, and others which have high infrared reflection with relatively low visual absorption. Their suitability as transparent heat mirror can be improved by antireflection coating for the visible. Figure 25 shows an example for such types of heat mirrors, according to Fan et al. [102]. 

The main commercial use of solid SiO is as a vapor-deposition material for the production of SiOx thin films for optical or electronic applications (antireflective coatings, interference filters, beam-splitters, decorative coatings, dielectric layers, isolation layers, electrodes, thin-film capacitors, thin-film transistors, etc.), for diffusion barrier layers on polymer foils or for surface protection layers.Other uses for SiO have been proposed, such as the substitution of elemental silicon in the Muller-Rochow process for the production of organosilicon halides, because solid SiO can be produced at lower temperatures than elemental silicon. 

Fig. n.8 The structure of an OLED with three organic layers and a dielectric cover layer. HTL refers to the hole transport layer, EML to the emission layer, ETL to the electron transport layer. N, and k, are the optical constants of the layers (for their definitions, see Sect. 11.2.3). The dielectric is an antireflection layer. After [6, 10]. 

The general approach used to make a dielectric mirror is to lay down a stack of thin films that have alternately higher and lower refractive indices. Manipulation of the thickness and the refractive index of each layer in the stack allows the optical properties to be modified at will to produce virtually perfect mirrors and virtually perfect antireflection coatings - both of which can be mned to respond to very specific wavelengths - as well as a variety of optical filters. The fabrication of such devices falls... 

The structures that have evolved for ablative-mode optical discs make use of interference effects to minimize the reflectance (R) of the disc in the absence of a hole. A typical ablative-mode optical disc has the structure shown in Figure 5.51. The substrate is an optically transparent material such as polycarbonate, poly(methyl methacrylate), poly(ethylene terephthalate), or poly(vinyl chloride), topped by a subbing layer to provide an optically smooth (to within a fi-action of a nanometer) surface for the recording layer. A metal reflector (typically aluminum) is then incorporated next to a transparent dielectric medium such as spin-coated poly(a-methyl styrene) or plasma-polymerized fluoropolymers. This dielectric spacing layer serves both to satisfy the quarter-wave (2/4) antireflection conditions and to insulate thermally the A1 reflector from the top absorbing layer where the information pits are created. 

MAJOR APPLICATIONS Interlayer dielectrics, high-temperature resins, and organic antireflective coatings. 

CaFa, CeFa, MgFa, ThFa, Dielectric films for multilayer optical coatings (antireflection coatings. 

For air (ni 1) and optical glass (/I2 1.5) R is 4%, whereas lead-crystal glass ( 2 2.1) gives an R of -13%. Equation 32.6 will be very important when we use dielectrics as antireflection coatings (ARCs) we then have to consider two interfaces. The thickness of the films and the nature of the reflecting surface will also be important. Ceramic applications of reflection are numerous but are often linked to refraction. 

Carbon film, which is chemically inert, can be applied as protective coating and antireflection layers for optical components for the infrared range and laser devices, wear protection, dielectric materials, coatings on fusion reactor walls, etc. Superlattices of a-C H and a-Si H have been obtained, and compound layers of a mixture of carbon and silicon have been grown. 

Thin metal and dielectric coatings are used to construct mirrors, antireflection coatings, light valves, laser optics, and lens coatings. 

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