When ellipsometry works best: a case study with transparent conductive oxides

As the library of potential materials with plasmonic behavior in the infrared (IR) grows, we must carefully assess their suitability for nanophotonic applications. This assessment relies on knowledge of the materials’ optical constants, best determined via spectroscopic ellipsometry (SE). Transparent conductive oxides are great candidates for IR plasmonics due to their low carrier concentration (compared to noble metals) and the ability to tailor their carrier concentration by manipulating the defect composition. When the carrier concentration becomes low enough, phonon and defect states become the dominant mechanisms of absorption in the IR spectral range, leading to near-IR (NIR) tailing effects. These NIR tailing effects can be misinterpreted for free carrier absorption, rendering NIR-visible-ultraviolet-SE (NIR-VIS-UV-SE) incapable of reliably extracting the carrier transport properties. In this work, we report the limitations of NIR-VIS-UV and IR-SE (in terms of carrier concentration) by investigating the transport mechanisms of indium tin oxide, aluminum-doped zinc oxide and gallium-doped zinc oxide. We find regions of carrier concentration where NIR-VIS-UV-SE cannot reliably determine the transport properties and we designate material-dependent and application-specific confidence factors for this case. For IR-SE, the story is more complex, and so we investigate the multifaceted influences on the limitations, such as phonon behavior, grain size, presence of a substrate, film thickness, and measurement noise. Finally, we demonstrate the importance of identifying the IR optical constants directly via IR-SE (rather than by extrapolation from NIR-VIS-UV-SE) by means of comparing specific figures of merits (Faraday and Joule numbers), deemed useful indicators for plasmonic performance

Positioning variation modeling for aircraft panels assembly based on elastic deformation theory

Dimensional variation in aircraft panel assembly is one of the most critical issues that affects the aerodynamic performance of aircraft, due to elastic deformation of parts during the positioning and clamping process. This paper proposes an assembly deformation prediction model and a variation propagation model to predict the assembly variation of aircraft panels, and derives consecutive 3-D deformation expressions which explicitly describe the nonlinear behavior of physical interaction occurring in compliant components assembly. An assembly deformation prediction model is derived from equations of statics of elastic beam to calculate the elastic deformation of panel component resulted from positioning error and clamping force. A variation propagation model is used to describe the relationship between local variations and overall assembly variations. Assembly variations of aircraft panels due to positioning error are obtained by solving differential equations of statics and operating spatial transformations of the coordinate. The calculated results show a good prediction of variation in the experiment. The proposed method provides a better understanding of the panel assembly process and creates an analytical foundation for further work on variation control and tolerance optimization

Gravitational waves from single neutron stars: an advanced detector era survey

With the doors beginning to swing open on the new gravitational wave astronomy, this review provides an up-to-date survey of the most important physical mechanisms that could lead to emission of potentially detectable gravitational radiation from isolated and accreting neutron stars. In particular we discuss the gravitational wave-driven instability and asteroseismology formalism of the f- and r-modes, the different ways that a neutron star could form and sustain a non-axisymmetric quadrupolar "mountain" deformation, the excitation of oscillations during magnetar flares and the possible gravitational wave signature of pulsar glitches. We focus on progress made in the recent years in each topic, make a fresh assessment of the gravitational wave detectability of each mechanism and, finally, highlight key problems and desiderata for future work.Comment: 39 pages, 12 figures, 2 tables. Chapter of the book "Physics and Astrophysics of Neutron Stars", NewCompStar COST Action 1304. Minor corrections to match published versio