Antireflection

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. 

CH2—CI2—) —(—CF2— CFH—) (39). Ceramic crystals have a higher piezoelectric efficiency. Their high acoustic impedance compared to body tissues necessitates impedance matching layers between the piezoelectric and the tissue. These layers are similar in function to the antireflective coatings on a lens. Polymer piezoelectric materials possess a more favorable impedance relative to body tissues but have poorer performance characteristics. Newer transducer materials are piezoelectric composites containing ceramic crystals embedded in a polymer matrix (see Composite materials, polymer-MATRIX Piezoelectrics). 

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... 

Antireflective (AR) coatings are required on optics to reduce the reflective surface losses. Vitreous siHca coatings in the form of porous or multilayer films are used extensively in this appHcation. Antireflective coatings have been developed which employ coUoidal fused siHca sol—gel particles made from organometaUic materials (253). 

Optical Coatings. Thin surface coatings are appHed to optical components to improve performance. Wideband antireflection coatings for the visible and ir regions need materials with a refractive iadex of for the best efficieacy. Cerium fluoride, a stable material resistant to humidity damage, has a suitable iadex, 1.63 ia the visible, 1.59 ia the iafrared, and is transparent over the range 0.5 p.m to 5 p.m. It is one of the compounds used to build up the multilayers deposited on lenses, sensors, and the like. 

Fig. 13. Schematic cross section of Time-Zero SX-70 integral film. In this film the polymeric acid layer and the timing layer are located beneath the negative layers, rather than in the positive sheet. Time-Zero and all later Polaroid integral films have an antireflection layer coated on the outer surface of the clear...

Optical/antireflective Quantitative depth profiling of multilayered stacks coatings (Si02, Hf02, Ti02, Sn02, InSn Oj, etc.)... 

Fig. 4.50. IBSCA spectra of an antireflective coating on soda-lime glass (Si02-Ti02-Si02/Ti02-substrate) conditions 5 keVAr" bombardment.

Optical coatings Laser protection Fiber optics Scanners Lenses Antireflection UV to IR windows X-ray windows Radomes... 

Horn, M. W., Antireflection Layers and Planarization for Microlithography, Solid State Technology, pp. 57-62 (Nov. 1991)... 

CVD titanium nitride (TiN) is the most important interstitial-nitride coating from an application standpoint. It is used extensively to provide wear resistance and as a diffusion barrier and antireflection coating in semiconductor devices. 1 °]... 

Antireflection coatings, optical waveguides and photoelectrochemical cells. 

A typical semiconductor device (found in the back-end of the line or the interconnects) consists of a layer of glass followed by a sputtered layer of titanium, which is thermally treated to form a titanium silicide. Next, a layer of titanium nitride is deposited on top of the silicide and on the sidewall of the contacts by sputtering or by MOCVD (see Fig. 13.3 in Ch. 13).P ]P ] This layer of TiN acts as a diffusion barrier and an adhesion promoter. It is followed by the main interconnect, which is an aluminum-copper alloy, in turn followed by another layer of TiN, which acts as adhesion and antireflecting layer. 

Zr02, Hf02, Th02) and low refractive index (Si02) for antireflection coalings. 

Nitrides by plasma CVD as antireflection coatings for photovoltaic cells. 

The function of an antireflection (AR) coating is to reduce the surface reflection of optical elements and increase the amount of light transmitted. The glare and ghost images from secondary reflections are minimized. Multiple coatings are now produced that can... 

Figure 15. Antireflection glass mirror coated with a 10 nm layer of Gr, with a 100 nm layer of MgF2 plus a 3 nm layer of Al.

The transparent top contact is deposited last of all, which imposes restrictions on the process temperature. Thermally evaporated ITO and ZnO deposited by metal-organic CVD (MOCVD) are most suitable. At a typical thickness of 70 nm the ITO serves as a good antireflection coating as well. Due to the somewhat high sheet resistance, a metal (Ag) grid is necessary to reduce the series resistance [11]. 

Despite such limitations, plasma-deposited a-C(N) H films were found to be used in a number of applications. The stress reduction induced by nitrogen incorporation [12] and consequent adhesion improvement, allowed the development of a-C(N) H antireflective coatings for Ge-based infrared detectors [13]. It was also found that N can electronically dope a-C H films, and can strongly decrease the defect density, which gives prospects on its use as a semiconductor material [14]. Nitrogen incorporation was also found to decrease the threshold electric field in electron-field emission process [15], making possible the use of a-C(N) H films as an overcoat on emission tips in flat-panel display devices [16]. 

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.)... 

There are also several proposals to use anodic aluminum oxides in producing optoelectronic devices. Porous oxides may find use as antireflecting coatings for optical pathways. Anodic alumina films doped by Eu and Tb are promising for application in electroluminescent cells for TEELs.28... 

Development of multifunctional sol—gel coatings antireflection coatings with enhanced self-cleaning capacity. Solar Energy Materials and Solar Cells, 94, 1081-1088. 

Burunkaya, E., Kesmez, O., Kiraz, N., Camurlu, H.E., Asiltuerk, M. and Arpac, E. (2010) Sn4+ or Ce3+ doped Ti02 photocatalytic nanometric films on antireflective nano-Si02 coated glass. Materials Chemistry and Physics, 120, 272-276. 

Floch H.G., Belleville P.F., Scratch-resistant single-layer antireflective coating by a low-temperature sol-gel route, SPIE Proc. 1758, 135-150, (1992). 

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