ABSTRACT
We measure polarization resolved reflections from ordered vertical silicon nanowire arrays of two different diameters and compare the results to rigorous coupled wave analysis simulations. Ellipsometric analysis based on anisotropic effective-medium approximation is used to fit the experimental data and estimate the diameter and length of the nanowires. In addition, depolarization of light is observed for wavelengths below 400 nm.
ABSTRACT
This paper reports on a systematic investigation of the optical properties of Ta(1-x)Zr(x)N single-phase and ZrN-Ag multi-phase films fabricated by unbalanced magnetron sputtering using vacuum ultraviolet spectroscopic ellipsometry (VUV-SE). VUV-SE is a newly developed technique that was used to evaluate the strength and energy of the interband electronic excitations/transitions in these films. The energy of the interband transition was found to be altered by any changes in the elemental composition for single-phase materials. For example, it was found to increase with the increase in the covalent character of the bond as more Zr atoms are substituted for by Ta atoms in the ZrN rock-salt structure. In contrast, the peak positions did not vary in the multi-phase structures because the constituent phases were immiscible and retained their electronic structure. However, the strength and width of the interband transition were found to change to reflect changes in phase composition and microstructure. The optical and electronic properties of these materials were simulated using density functional theory (DFT) within the generalized gradient approximation. The calculated refractive indices and density of states were in good agreement with the VUV-SE data.
ABSTRACT
The structural, electronic, optical, and mechanical properties of stoichiometric TaC(x)N(y = 1-x) were simulated using an ab initio calculation based on density functional theory (DFT) within the generalized gradient approximation. The calculations revealed the theoretical lattice parameter, density of states, refractive index, and elastic constants as a function of carbon and nitrogen content. TaC(x)N(y) films were subsequently produced on Si wafers using unbalanced magnetron sputtering. The structural, optical, and mechanical properties were measured using x-ray diffraction/transmission electron microscopy, vacuum ultraviolet spectroscopic ellipsometry, and nanoindentation, respectively. The computational and experimental properties were compared. The lattice parameter, the energy of the 2p bands in the density of states, and the energy of the interband transitions were found to decrease with increasing C content. No significant changes in the elastic constants were observed as a result of substituting N atoms with C atoms. The hardness and the elastic modulus were in the 40 and 380 GPa range, respectively. The experimental Young's modulus was much smaller than the computational one and this discrepancy was attributed to the nanocrystalline nature of the films. Also, the elastic constants were found to decrease dramatically for over-stoichiometric films.
ABSTRACT
A method for the design of cutoff filters is proposed that is based on the use of light at nonnormal angles of incidence and on the use of coating materials with a large dispersion of the optical constants. The optical constants are presented of several films made from indium tin oxide--a material that satisfies this requirement. The filtering is due to absorption, critical angle effects, or both. The theory of this type of filter is described, and the calculated performance of two long-wavelength cutoff filters based on the use of indium tin oxide films is given. The angular performance and the producibility of one of these filters are examined. Some applications for these filters are considered, and the feasibility of producing similar filters for other spectral regions is discussed.
