Silver-magnesium fluoride cermet films. 1: Preparation and microstructure

Transmissive Polarizer Metasurfaces: From Microwave to Optical Regimes

Metasurfaces, a special class of metamaterials, have recently become a rapidly growing field, particularly for thin polarization converters. They can be fabricated using a simple fabrication process due to their smaller planar profile, both in the microwave and optical regimes. In this paper, the recent progress in MSs for linear polarization (LP) to circular polarization (CP) conversion in transmission mode is reviewed. Starting from history, modeling and the theory of MSs, uncontrollable single and multiple bands and LP-to-CP conversions, are discussed and analyzed. Moreover, detailed reconfigurable MS-based LP-to-CP converters are presented. Further, key findings on the state-of-the-arts are discussed and tabulated to give readers a quick overview. Finally, a conclusion is drawn by providing opinions on future developments in this growing research field.

Advanced multi-component nanostructures designed by dynamic shadowing growth

Dynamic shadowing growth is a simple and powerful nanofabrication technique that combines oblique angle deposition with substrate manipulation in a thin film deposition system, which mainly utilizes self-shadowing effect to form well-aligned nanorod arrays. Many unique nanostructures have been fabricated or designed by properly programming the substrate motions, deposition sources, deposition rates, and shadowing effects in multi-step shadowing growth processes. The formed nanostructures have found many promising applications such as chemical and biological sensors, energy storages, nanomotors, etc., due to their unique characteristics of well-controlled morphologies, structures, and compositions. This review is focused on the design and fabrication of both compositionally and morphologically complex nanostructure arrays by multilayer and co-deposition shadowing growth techniques, and the emphasis will be put on the design and fabrication of multi-component nanostructures with different morphologies.

Inverse Transport Problems for Composite Media

For two-component ceramic metal composites we address the inverse problem of estimating the volume fraction occupied by each component from measurements of the transmission and absorption coefficients at various frequencies of the applied radiation. We devise the algorithms, each based on representation formulas and bounds for the complex dielectric constant that were developed by Bergman and Milton. One inversion algorithm works remarkably well when the measurements are exact but fails completely when small errors are present. The second random throw algorithm works well when the measurement errors are large but is computationally intensive and is limited to small data sets. The third method based on single and two-point inversion, while not so accurate, is simple and efficient. The last two algorithms are implemented with experimental data and good agreement is obtained with the experimentally measured true volume fraction.

Electrical impedance spectroscopy as a potential tool for recovering bone porosity

This paper deals with the recovery of porosity of bone from measurements of its effective electrical properties. The microstructural information is contained in the spectral measure in the Stieltjes representation of the bone effective complex permittivity or complex conductivity and can be recovered from the measurements over a range of frequencies. The problem of reconstruction of the spectral measure is very ill-posed and requires the use of regularization techniques. We apply the method to the effective electrical properties of cancellous bone numerically calculated using micro-CT images of human vertebrae. The presented method is based on an analytical approach and does not rely on correlation analysis nor on any a priori model of the bone micro-architecture. However the method requires a priori knowledge of the properties of the bone constituents (trabecular tissue and bone marrow). These properties vary from patient to patient. To address this issue, a sensitivity analysis of the technique was performed. Normally distributed random noise was added to the data to simulate uncertainty in the properties of the constituents and possible experimental errors in measurements of the effective properties. The values of porosity calculated from effective complex conductivity are in good agreement with the true values of bone porosity even assuming high level errors in the estimation of the bone components. These results prove the future potential of electrical impedance spectroscopy for in vivo monitoring of level and treatment of osteoporosis.

Optical Properties of Ag-TiO(2) Nanocermet Films Prepared by Cosputtering and Multilayer Deposition Techniques

Ag-TiO(2) nanocermet thin films, deposited for optical filtering applications by two sputtering techniques, codeposition and multilayer deposition, exhibit surface plasmon absorption in the spectral range 450-500 nm. The cosputtering technique induces a columnar growth, whereas multilayer deposition produces a more-random distribution of silver inclusions. Both films have large, flat silver grains at the air-cermet interface. An optical double-heterogeneous layer model based on the experimental morphological parameters of the films accounts well for their experimental transmittance, notably for extra absorption near 700 nm, which is attributed to a surface plasmon in the flat silver grains of the surface.

Silver-magnesium fluoride cermet films. 2: Optical and electrical properties

We discuss the optical properties of Ag-MgF(2) and voided silver cermets. We show that the former system is intrinsically three phase, because of the presence of voids, and that it cannot be regarded as made up of two synthesized phases. We show that the optical behavior of our voided silver cermets is not in keeping with the Maxwell-Garnett and effective media models, but that it can be used in a model-independent way to yield structural information about the cermets. We discuss the interesting optical properties of one cermet in the transition or optical crossover region. We also present data on the electrical resistivity of both types of cermet.