Serial Bideposition Technique Research Articles

Reflection and transmission of obliquely incident light by chiral sculptured thin films fabricated using asymmetric serial-bideposition technique

Chiral sculptured thin films (STFs) were grown using the asymmetric serial-bideposition (ASBD) technique, whereby (i) two subdeposits of unequal heights are separated by a substrate rotation of 180 deg about the central normal axis, and (ii) consecutive subdeposit pairs are separated by a small substrate rotation δ on the order of a few degrees. Eight samples were prepared with subdeposit heights in ratios of 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 5:1, 7:1, and 9:1. A finely ambichiral STF was also grown. All nine samples were grown with the same vapor flux direction and to have 10 periods with the same thickness. The spectrums of all eight circular remittances of every sample were measured over a wide range of incidence angle θ inc . Redshifting and narrowing of the circular Bragg regime was observed with increasing subdeposit-height ratio for all values of θ inc , arriving at a limit with the 9:1 sample. The finely ambichiral sample has a circular Bragg regime similar to that of the 9:1 sample, but the latter exhibits much better discrimination between incident left circularly polarized light and right circularly polarized light than the former for θ inc larger than about 20 deg.

Dual‐band circular‐polarization filter for obliquely incident light

ABSTRACTChiral sculptured thin films of zinc selenide with different helical periods were deposited on both sides of a glass slide using the serial bideposition technique in order to fabricate a dual‐band circular‐polarization filter polarizer that exhibits two distinct circular Bragg regimes for a wide range (about 45°) of the angle of incidence. This device can be angle tuned within a ±8% spectral range. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2381–2384, 2016

Low-stress phase plates produced by serial bideposition of TiO2thin films

The stresses in thin films are one of the main problems in the development of small dimensions or thin optical components. In order to produce low-tension anisotropic coatings, the characterization of serial bideposition is essential. Structural and optical performance have been tested for anisotropic TiO2 thin films deposited by serial bideposition technique. Three-dimensional surface interferometric measurements were performed for samples deposited at various angles. Also experimental observations of anisotropic tensions in annealed two-dimensional sculptured thin films of TiO2 material are presented. The deposition angle of 80 deg is considered to be the most applicable for developing optical components due to the befitting optical performance and the lowest tensions before and after the annealing.

Optical properties and microstructures of inorganic wave plates prepared by serial bideposition

We investigated the optical characteristics and microstructures of wave plates com- posed of Ta2O5ð100 − x Þþ TiO2ðxÞ and prepared by the so-called serial bideposition technique. While a single-layer film prepared by conventional oblique deposition technique has a tilted columnar structure (i.e., tilted optical axis), a serial bideposition film has a narrow, long col- umnar structure; this ensures that the optical axis of the film is along the quasinormal to the substrate, thus reducing haze. The influence of using additives with Ta2O5 was investigated as well. It was found that additive TiO2 improves optical transmittance at shorter wavelengths. For verifying the advantage of this type of wave plates, quarter wave plates with optimized TiO2 content were fabricated and their optical performance and reliability were evaluated against those of organic-type wave plates. The results show that the inorganic wave plate prepared by serial bideposition is advantageous for applications where high-transmittance and high-temperature durability are essential. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.JNP.8.083991)

Birefringence enhancement in annealed TiO2 thin films

Postdeposition thermal annealing is used to enhance the form birefringence of nanostructured TiO2 thin films grown by electron-beam evaporation using the serial bideposition technique. Thin films were grown on fused silica substrates using oblique deposition angles between 60° and 75° and repetitive 180° substrate rotations to produce birefringent thin films that are structurally anisotropic. Postdeposition annealing in air, between 200 and 900°C, was used to increase the form birefringence of the films by changing the TiO2 phase from the as-deposited amorphous state to a polycrystalline state that exhibits a greater inherent density and larger bulk refractive index. The optical properties, microstructure, and crystallinity were characterized by Mueller matrix ellipsometry, scanning electron microscopy, atomic force microscopy, and x-ray diffraction. It was found that the in-plane birefringence increased significantly upon thermal annealing, in some cases yielding birefringence values that doubled in magnitude, from 0.11 to 0.22 at a wavelength of 550nm for films annealed at 400°C.

Blue-shifting of circular Bragg phenomenon by annealing of chiral sculptured thin films

The wavelength regime of the circular Bragg phenomenon, exhibited by chiral sculptured thin films fabricated using the serial bideposition technique, blue shifts as a result of post-deposition annealing. This blue shift can be attributed to the net effect of three material changes that occur during annealing: a small reduction in helical pitch, an increase in the relative permittivity of the column material changing from amorphous to crystalline, and a density reduction due to columnar thinning from the same amorphous-to-crystalline transition.

On calibration of a nominal structure–property relationship model for chiral sculptured thin films by axial transmittance measurements

A chiral sculptured thin film is fabricated from patinal titanium oxide using the serial bideposition technique. Axial transmittance spectrums are measured over a spectral region encompassing the Bragg regime for axial excitation. The same spectrums are calculated using a nominal structure–property relationship model and the parameter space of the model is explored for best fits of the calculated and measured transmittances. Ambiguity arising on calibrating the model against axial transmittance measurements is shown to be resolvable using non-axial transmittance measurements.

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.