Iryna Valyukh

Electronic and optical properties of nanocrystalline WO3 thin films studied by optical spectroscopy and density functional calculations

The optical and electronic properties of nanocrystalline WO3 thin films prepared by reactive dc magnetron sputtering at different total pressures (Ptot) were studied by optical spectroscopy and density functional theory (DFT) calculations. Monoclinic films prepared at low Ptot show absorption in the near infrared due to polarons, which is attributed to a strained film structure. Analysis of the optical data yields band-gap energies Eg ≈ 3.1 eV, which increase with increasing Ptot by 0.1 eV, and correlate with the structural modifications of the films. The electronic structures of triclinic δ-WO3, and monoclinic γ- and ε-WO3 were calculated using the Green function with screened Coulomb interaction (GW approach), and the local density approximation. The δ-WO3 and γ-WO3 phases are found to have very similar electronic properties, with weak dispersion of the valence and conduction bands, consistent with a direct band-gap. Analysis of the joint density of states shows that the optical absorption around the band edge is composed of contributions from forbidden transitions (>3 eV) and allowed transitions (>3.8 eV). The calculations show that Eg in ε-WO3 is higher than in the δ-WO3 and γ-WO3 phases, which provides an explanation for the Ptot dependence of the optical data.

Liquid crystal light deflecting devices based on nonuniform anchoring

Tunable liquid crystal light deflecting devices based on nonuniform anchoring energy are proposed. These devices have uniform thicknesses of the layers they are composed of, and beam deviation is controlled with a uniform electrical field. Potential applicability of such an approach in beam deflectors and active lenses is investigated. It is shown that the approach is a competitive alternative to liquid crystal light deflecting devices, in which the needed spatial distribution of liquid crystal molecules is achieved either due to nonuniform thickness or due to generation of nonuniform electrical field.

Spectrophotometric determination of reflective liquid crystal cell parameters

We introduce a method for determination of the optical retardation, its wavelength dispersion, the cell twist angle, and the orientation of the input director in a reflective liquid crystal (LC) ce ...

Characterization of flexible reflective liquid-crystal cells

We consider peculiarities in testing flexible reflective liquid-crystal (LC) cells. Several new methods for measuring optical retardation of filled reflective LC cells on plastic substrates are pro ...

Ellipsometrically determined optical properties of nickel-containing tungsten oxide thin films: Nanostructure inferred from effective medium theory

Films of NixW1−x oxide with 0.05 ≤ x ≤ 0.53 were produced by reactive dc magnetron co-sputtering onto Si. Such films have documented electrochromism. Spectroscopic ellipsometry was used to extract ...

Study on Birefringent Color Generation for a Reflective Ferroelectric Liquid Crystal Display

We study the possibility of a layer of a surface stabilized ferroelectric liquid crystal coupled with several retardation plates for birefringent color generation. Double and single polarizer refle ...

P-70: Characterization of Liquid Crystal Material and Cell by means of Generalized Spectroscopic Ellipsometry

Characterization of Liquid-Crystal Material and Cell by Means of Generalized Spectroscopic Ellipsometry

Using the Jones matrix to model light propagation in anisotropic media

Using a twisted nematic liquid crystal as an example, this paper discusses the use of the Jones matrix to find the parameters of a light wave propagating in an inhomogeneous anisotropic medium, which is represented for the numerical calculations by a sequence of thin homogeneous layers. The accuracy of the result is analyzed as a function of the parameters of the medium and the number of layers into which it is broken up. A criterion is proposed for finding the optimum number of layers.