Mixed films of TiO_2–SiO_2 deposited by double electron-beam coevaporation

Abstract

<p>We used double electron-beam coevaporation to fabricate TiO(2)-SiO(2) mixed films. The deposition process included oxygen partial pressure, substrate temperature, and deposition rate, all of which were real-time computer controlled. The optical properties of the mixed films varied from pure SiO(2) to pure TiO(2) as the composition of the films varied accordingly. X-ray diffraction showed that the mixed films all have amorphous structure with a SiO(2) content of as low as 11%. Atomic force microscopy showed that the mixed film has a smoother surface than pure TiO(2) film because of its amorphous structure.</p><p>Linear and Bruggeman's effective medium approximation models fit the experimental data better than other models.</p>

Refractive index profile modelling of dielectric inhomogeneous coatings using effective medium theories

“…Finally, depending on the level at which materials are mixed, one effective medium theory will be more appropriate than the other and will give more accurate prediction of the optical properties of the mixture. For example, in the case of SiO 2 -TiO 2 amorphous mixture it has been shown experimentally [13,14] that LL model is more appropriate than BG, although not all the studies are in accordance [15]. (1)…”

Effective medium theories for composite optical materials in spectral ranges of weak absorption: the case of Nb2O5–SiO2mixtures

“…However, failing to fulfil this assumption required in EMTs seems to be more critical for the absorption coefficient than for the refractive index. Other authors also reported a good agreement of EMTs for the refractive index of mixtures that showed no phase separation [11,12]. The reason should be found in the fact that the strong dispersion of the absorption coefficient in weak absorption regions is tightly connected to the sample microstructure (E 0 is the energy separation between bands and  is associated to the presence of tail states due to disorder).…”

“…In addition to expressions (9)-(10), it is possible to make a series expansion in powers of t R in the integrals in (11). Using the sum rules (5), the first two terms of these series expansion are independent of the spectral density function and approximate expressions for the effective dielectric function can be formulated as (for |t R |>>1):…”

“…The most common approach to account for this dependence is the use of the so-called effective medium theories (EMTs), which calculate the optical constants of a mixture in terms of the optical constants of the mixing materials and their volume fractions [9,10]. These theories have been widely used to compute the compositional dependence of the refractive index for different composites [11,12]. On the other hand, the applicability of these theories to compute the absorption coefficient is often overlooked.…”

Ellipsometry and Its Applications in Stoichiometry

“…So the performance of the optical devices can be improved with the higher refractive index (n H -n L ) and thinner thickness of the two materials [119]. It has been reported that MgO can tune the band gap of ZnO from 3.4 to 7.8 eV depending on Mg content in MgO-ZnO composite films [120]. An accurate knowledge about the properties of the dielectric composite will broaden their better application.…”