INDEX deposition techniques

Rees and co-workers23 first studied the effect of the deposition of thin HRI overlays onto LPGs by analyzing the wavelength shift of the attenuation bands. The Langmuir-Blodgett deposition technique was exploited to deposit an incrementally thicker overlay (up to few hundreds of nanometers) of an organic material whose refractive index was 1.58. 

A better way of achieving a complete 3D photonic band gap is considered to be by constructing a lattice of air balls surrounded by an interconnecting matrix of material with a higher refractive index. The successful construction of such crystals by growth techniques is unlikely and likewise the build up by deposition techniques is no simple procedure. 

Many films deposited on heated substrates (250-350°C) possess packing densities larger than 0.9, so that the changes in refractive index on exposure to the atmosphere are very small and can often be neglected. The effect is even improved with films produced by ion-assisted deposition techniques, such as sputtering and ion plating. 

Next, the sensitivity of this technique to extremely small refractive index changes will also be demonstrated in light of ultrathin photochromic layers self-assembled on glass substrates, but first we discuss the self-assembly and Langmuir deposition techniques. 

In addition to the internal reflection spectroscopic technique, there Is a host of supporting methods. They range from techniques that estimate precise film thickness and refractive Index to techniques that measure surface electrical property and wettability changes that are associated with protein film deposition (13). 

More recently, ZnS-coated PS nanocomposite colloids were synthesized by the chemical bath deposition technique of thioacetamide in the presence of PS seed particles and metal salt [197], It allowed deposition of high refractive index ZnS shells of controlled thickness onto sulfate-modified and plain PS cores of size of about 200-500 nm. In order to prevent aggregations of PS particles, PVP was added during the reaction. The effective refractive index of the ZnS shell-PS core (PS/ZnS) composite particles varied between 1.73 and 1.98 at wavelengths above the optical absorption edge of ZnS. The porosity of the shells was between 12 and 19%, and the core-shell colloids served as building blocks for self-assembly at the submicron length scale [197]. 

One of the most useful applications of ellipsometry has been the routine measurement of silicon dioxide (Si02) film thicknesses grown on silicon. Since the refractive index of Si02 is well known, and does not depend significantly on film deposition technique, nulling ellipsometry measurements are usually sufficient to determine film thickness. 

This technology also allows the control of refractive index profiles by doping. AH vapor-phase techniques use a vapor stream of volatile haUdes such as SiCl, GeCl, BCl, or POCl, and gases such as CI2 or O2. The reactants are oxidized and deposited onto a substrate to produce a soHd glass preform which is then drawn into a fiber. The variations of the technique differ in the way the reactants are oxidized (16). 

Carbon deposition from CO on a cobalt catalyst at low pressures is known to be a structure-sensitive process. CO is adsorbed molecularly on the low index surfaces (Co (0001)), but its dissociation occurs on the Co (1012), Co (1120), and polycrystalline surfaces.5762 Deposition of carbon on Co (1012) and the probable formation of Co3C have been established by Auger emission spectroscopy (AES) and low-energy electron diffraction (LEED) techniques.66... 

Porous Si02 nanoparticles deposited by a common wet-coating sol-gel technique, for instance, form a single-layer, low-refractive-index and cost-efficient antireflective coating on glass as an alternative to common multilayer compositions (Figure 4.3).4 The coating thereby obtained exhibits porosity of up to 50% and a refractive index between 1.25 and 1.3, which corresponds to a transmission maximum up to 99% and an... 

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