Silicon dioxide optical properties

Table 3 Selected optical properties of zinc oxide, titanium dioxide, and silicon ...

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. 

Commercially provided 25.4 mm diameter steel balls of two different roughness values were employed in this study. The balls have no preferential surface roughness pattern. The glass disc has 150 mm in diameter and its surface is optically smooth. The silicon dioxide spacer layer about 195 nm thick covers almost entire underside of the glass disc with the exception of a narrow radial strip where only chromium layer is deposited. Scanning probe microscopy examinations of silicon dioxide films shows that they are extremely smooth [14]. Material properties of the contact bodies are summarised in Table 1. The surface roughness parameters of steel balls measured by stylus technique are given in Table 2. 

Several other nanoparticles have been studied because physical properties of the nanostructures differ from the bulk materials [5,6]. Metal nanoparticles such as ZnO and titanium dioxide (Ti02), for example, provide nanocomposites the attractive nonlinear properties that make them ideal candidates for nonlinear optical (NLO) based devices [5]. Porous system-based nanocomposites, including porous materials such as silicon, gallium phosphide, aluminum oxide, and structures based on them, were considered by Golovan et al. [6]. The main focus is on the effect of birefringence, which is caused by the anisotropy of pores in the materials. 

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