Anisotropy in thin films: modeling and measurement of guided and nonguided optical properties: application to TiO(2) films

Inverse relationships for reflection diagnostics of uniaxially anisotropic nanoscale films on isotropic materials

The possibilities of determining the parameters of uniaxially anisotropic ultrathin nonabsorbing dielectric films on absorbing or transparent isotropic substrates by surface differential reflectance measurements are analyzed. The analysis is based on analytical reflection formulas obtained in the framework of a long-wavelength approximation. It is shown that, in the case of transparent substrates, it is always possible to determine the thickness of a uniaxially ultrathin film and its four parameters of anisotropy (optical constants n(o) and n(e) and angles θ and φ) simultaneously. However, for such films on absorbing substrates, it is possible to decouple the thickness and optical constants by differential reflectance measurements only if θ≠0. The accuracy of the obtained analytic formulas for determining the parameters of ultrathin films is estimated by computer simulations where the reflection problem was solved numerically on the basis of the rigorous electromagnetic theory for anisotropic layered systems.

Optical diagnostics of anisotropic nanoscale films on transparent isotropic materials by integrating reflectivity and ellipsometry

The reflection of s- and p-polarized electromagnetic plane waves from an anisotropic ultrathin dielectric film on transparent isotropic substrate is investigated in the long-wavelength limit. The analytical approximate formulas are obtained for the reflection coefficients and ellipsometric angles that agree with the exact computer solution of the reflection problem for anisotropic systems. The possibilities of using the obtained expressions for resolving the inverse problem for ultrathin anisotropic dielectric films upon isotropic dielectric substrates are discussed. It is shown that a promising technique for determining the optical constants of anisotropic dielectric films on transparent substrates is the integration of ellipsometry and differential reflectivity.

Optical properties and microstructure of Ta2O5 biaxial film

This study investigates the optical properties and microstructure of Ta(2)O(5) film deposited with the glancing angle deposition technique. The tilted nanocolumn microstructure, examined with scanning electron microscopy, induces the optical anisotropy of thin film. The optical properties of thin film are characterized with an inverse synthesis method. Based on the Cauchy model, the dispersion equations of optical constants of film are determined from the transmittance spectra measured at normal and oblique incidence over 400-800 nm. The starting values derived with an envelope method quicken the optimization process greatly. The dispersion of the principal indices N(1), N(2), and N(3) and the thickness d of thin film are presented statistically. A good agreement between the measured optical properties and theoretical calculation is obtained, which validates the model established for thin film produced by glancing angle deposition.

Analysis of nanostructured porous films by measurement of adsorption isotherms with optical fiber and ellipsometry

An optical method to determine the nanostructure and the morphology of porous thin films is presented. This procedure is based on the response of a side-polished optical fiber with the film under study, when an adsorption-desorption cycle is carried out. Spectroscopic ellipsometry provides additional information about the optical properties and adsorption behavior of the film. Pore size distribution, anisotropy, and inhomogeneity of films can be determined by use of these two complementary techniques. To check the performances and suitability of the optical method, we have characterized a typical porous material: a TiO2 film deposited by evaporation. Water vapor has been used for the adsorption cycles. The well-known columnar structure of the evaporated TiO2 has been evidenced, and the relation between the nanostructure and the optical properties of the film is showed.

Guided-wave technique for the measurement of dielectric thin-film materials' thermal properties

A pump-and-probe setup that uses a totally reflecting prism coupler is presented. Its electromagnetic and thermal models are described. To our knowledge, the first results are given concerning the measurement of thermal properties of thin films.

Artificial anisotropy and polarizing filters

The calculated spectral transmittance of a multilayer laser mirror is used to determine the effective index of the single layer equivalent to the multilayer stack. We measure the artificial anisotropy of photoresist thin films whose structure is a one-dimensional, subwavelength grating obtained from interference fringes. The limitation of the theory of the first-order effective index homogenization is discussed. We designed normal-incidence, polarizing coating and a polarization rotator by embedding anisotropic films in simple multilayer structures.

Angle-resolved ellipsometry of light scattering: discrimination of surface and bulk effects in substrates and optical coatings

Angle-resolved ellipsometry of light scattering is an original technique developed at the Fresnel Institute to identify scattering processes in substrates and multilayers. We extend the investigation because numerous experimental results proved that the technique can be of major interest for analysis of microcomponents and their scattering origins. Surface and bulk effects can be separated in most situations, as well as the oblique growth of materials and the presence of first-order contaminants.

Determination of the refractive indices of layers in a multilayer stack by a guided-wave technique

The m-lines technique is used to measure the refractive indices and thicknesses of layers embedded in a multilayer stack. The multilayer considered is deposited by ion plating. Its formula is silica-H-L-H-L-H-air, where H and L denote Ta(2)O(5) and SiO(2)lambda/4 layers, respectively, with lambda = 514.5 nm. Measurements indicate that the refractive index of Ta(2)O(5) is 5 x 10(-3) greater when the layer is close to air than when the layer is inside the coating and that the Ta(2)O(5) is slightly more birefringent.

Serial bideposition of anisotropic thin films with enhanced linear birefringence

We describe a serial bideposition technique in which a tilted substrate is rotated stepwise by half a turn about a normal axis during the evaporation of a metal oxide from a single electron-beam source. Coatings formed by the new method develop a columnar nanostructure that is perpendicular to the substrate and has greatest width or bunching perpendicular to the common deposition plane. With appropriate choice of deposition parameters, the method produces biaxial films with large birefringence, principal axes aligned parallel and perpendicular to the substrate, and improved uniformity. Measured phase retardances for light incident normally on the films are double the corresponding values for tilted-columnar films.

Empirical equations for the principal refractive indices and column angle of obliquely deposited films of tantalum oxide, titanium oxide, and zirconium oxide

Values of the transmittance T(s) and the phaseretardation D were recorded in situ at two angles duringthe growth of thin films of tantalum oxide, titanium oxide, andzirconium oxide for deposition angles theta(nu) in the range40 degrees -70 degrees . Column angles for the same films were determinedex situ from scanning electron microscopy photographs ofdeposition-plane fractures. We show that the experimental columnangles are smaller than the corresponding values predicted by thetangent-rule equation psi = tan(-1)(0.5 tan theta(nu)) and that the experimental values fit a modifiedform of the equation psi = tan(-1)(E(1) tan theta(nu)) where E(1) is less than 0.5. We also show that theprincipal refractive indices are represented well by quadraticfunctions of the deposition angle, for example, n(1)(theta(nu)) = A(0) + A(2) theta(nu)(2).

Perpendicular-incidence photometric ellipsometry of biaxial anisotropic thin films

A new measurement technique for the characterization of uniaxial as well as biaxial anisotropic surfaces and thin films is introduced. This technique is based on perpendicular-incidence photometric ellipsometry, in which a spectral-photometric dynamic ellipsometer with a rotating polarizer is used. This method is sensitive, contactless, nondestructive, and efficient for the estimation of anisotropic behavior. Furthermore, the spectroscopic measurement directly provides the anisotropy dispersion down to the UV wavelength range. Results on structurally anisotropic HfO(2) coatings are presented.

Modal contours for biaxial thin-film waveguides

The modal characteristics of a general tilted columnar biaxial thin-film waveguide are displayed by the plots of both Snell's law quantity β = n sin θ and the polarization of the evanescent field at the cover interface on a polar diagram. The association of characteristic features in the modal diagram with the basis fields is demonstrated, and the mechanism that allows p and s modes propagating in the deposition plane to overlap, without the modal contours crossing, is explored.

A birefringent prism coupler in guided wave experiments

A rutile prism was used to excite guided waves in a CdS film. The wave vector matching condition was studied under the influence of prism's birefringence. Refractive indices and thickness of the film were determined.