Silicon dioxide refractive index

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... 

Silicon dioxide properties depend on the techniques used for oxide growth. The index of refraction for dry oxides decreases when higher processing temperatures are used whereas the oxide density increases. 

The ellipsometric technique described earlier has the unique feature that the index of refraction can be determined independently of the film thickness. Then, knowledge of this index can be used to infer the chemical composition of a film. For example, thin silicon dioxide films have an index of 1.46, while silicon nitride films have a value of 2.0 typically. Now, when either of these films are deposited by PECVD techniques, their stoichiometry can vary depending on deposition conditions. It turns out that this variation in stoichiometry can be related to the measured refractive index. Accordingly, measurements of the refractive index can be used as an approximate guide to film stoichiometry. 

Several grades of colloidal silicon dioxide are commercially available, which are produced by modifying the manufacturing process. The modifications do not affect the silica content, specific gravity, refractive index, color, or amorphous form. However, particle size, surface areas, and densities are affected. The physical properties of three commercially available colloidal silicon dioxides, Aerosil (Degussa), Cab-O-Sil (Cabot Corporation), and Wacker HDK (Wacker-Chemie GmbH) are shown in Tables III, IV and V, respectively. 

The refractive index of a pigment at each wavelength is determined by its crystal structure. Titanium dioxide pigments (rutile and anatase) differ from each other and from other white pigments or crystalline substances, like silicon dioxide, in the proportion of radiant energy that is transmitted, absorbed, or re-... 

Gebbert A et al 1992 Direct observation of antibody binding. Comparison of capacitance and refractive index measurement DECHEMA Biotechnol. Conf. 1992 vol 5, part A Microbial Principles in Bioprocesses Cell Culture Technology, Downstream Processing and Recovery pp 459-62 Stenberg M et al 1979 Silicon-silicon dioxide as an electrode for electrical and ellipsometrical measurements of adsorbed organic molecules J. Colloid Interface Sci. 72 255-63... 

Let us first address internal attenuation. Note that the base material of typical, high-quality optical fibres is ultra-pure silicon dioxide (Si02). To this, impurities are purposely added during fibre manufacture to obtain the desired indices of refraction needed for the core and cladding. Germanium or phosphorus are added to increase the index of refraction of fused silica, whereas boron or fluorine are added to decrease it also, a few other impurities may find their way into the material during fabrication. By and large, the main impurity is... 

Porous silicon materials are described as a mixture of air, silicon, and, in some cases, silicon dioxide. The optical properties of a porous silicon layer are determined by the thickness, porosity, refractive index, and the shape and size of pores and are obtained from both experimental- and model-based approaches. Porous silicon is a very attractive material for refractive index fabrication because of the ease in changing its refractive index. Many studies have been made on one- and two-dimensional refractive index lattice structures. The refractive index is a complex function of wavelength, i.e., n(X) = n(X) — ik(k), where k is the extinction coefficient and determines how light waves propagate inside a material (Jackson 1975). The square of the refractive index is the dielectric function e(co) = n(co), which contributes to Maxwell s equations. 

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. 

---