Electrical conduction and optical properties of doped silicon-on-insulator photonic crystals

We investigate the electrical properties of silicon-on-insulator (SOI) photonic crystals as a function of both doping level and air filling factor. The resistance trends can be clearly explained by the presence of a depletion region around the sidewalls of the holes that is caused by band pinning at the surface. To understand the trade-off between the carrier transport and the optical losses due to free electrons in the doped SOI, we also measured the resonant modes of L3 photonic crystal nanocavities and found that surprisingly high doping levels, up to 1018 / cm3, are acceptable for practical devices with Q factors as high as 4× 104. © 2011 American Institute of Physics.

A graphene-based large area surface-conduction electron emission display

The fabrication and functionality of a 21 cm graphene-based transverse electron emission display panel is presented. A screen-printed triode edge electron emission geometry has been developed based on chemical vapor deposited (CVD) graphene supported on vertically aligned carbon nanotubes (CNT) necessary to minimize electrostatic shielding induced by the proximal bulk substrate. Integrated ZnO tetrapod electron scatterers have been shown to increase the emission efficiency by more than 90%. Simulated electron trajectories validate the observed emission characteristics with driving voltages less than 60 V. Fabricated display panels have shown real-time video capabilities that are hysteresis free (<0.2%), have extremely stable lifetimes (<3% variation over 10 h continuous operation) in addition to rapid temporal responses (<1 ms). © 2013 Elsevier Ltd. All rights reserved.

The inverse problem in magnetic force microscopy--inferring sample magnetization from MFM images.

Nanomagnetic structures have the potential to surpass silicon's scaling limitations both as elements in hybrid CMOS logic and as novel computational elements. Magnetic force microscopy (MFM) offers a convenient characterization technique for use in the design of such nanomagnetic structures. MFM measures the magnetic field and not the sample's magnetization. As such the question of the uniqueness of the relationship between an external magnetic field and a magnetization distribution is a relevant one. To study this problem we present a simple algorithm which searches for magnetization distributions consistent with an external magnetic field and solutions to the micromagnetic equations' qualitative features. The algorithm is not computationally intensive and is found to be effective for our test cases. On the basis of our results we propose a systematic approach for interpreting MFM measurements.

Application of the multi-objective Alliance algorithm to a benchmark aerodynamic optimization problem

This paper introduces a new version of the multiobjective Alliance Algorithm (MOAA) applied to the optimization of the NACA 0012 airfoil section, for minimization of drag and maximization of lift coefficients, based on eight section shape parameters. Two software packages are used: XFoil which evaluates each new candidate airfoil section in terms of its aerodynamic efficiency, and a Free-Form Deformation tool to manage the section geometry modifications. Two versions of the problem are formulated with different design variable bounds. The performance of this approach is compared, using two indicators and a statistical test, with that obtained using NSGA-II and multi-objective Tabu Search (MOTS) to guide the optimization. The results show that the MOAA outperforms MOTS and obtains comparable results with NSGA-II on the first problem, while in the other case NSGA-II is not able to find feasible solutions and the MOAA is able to outperform MOTS. © 2013 IEEE.

A framework for the analysis of thermal losses in reciprocating compressors and expanders

This article presents a framework that describes formally the underlying unsteady and conjugate heat transfer processes that are undergone in thermodynamic systems, along with results from its application to the characterization of thermodynamic losses due to irreversible heat transfer during reciprocating compression and expansion processes in a gas spring. Specifically, a heat transfer model is proposed that solves the one-dimensional unsteady heat conduction equation in the solid simultaneously with the first law in the gas phase, with an imposed heat transfer coefficient taken from suitable experiments in gas springs. Even at low volumetric compression ratios (of 2.5), notable effects of unsteady heat transfer to the solid walls are revealed, with thermally induced thermodynamic cycle (work) losses of up to 14% (relative to the work input/output in equivalent adiabatic and reversible compression/expansion processes) at intermediate Péclet numbers (i.e., normalized frequencies) when unfavorable solid and gas materials are selected, and closer to 10-12% for more common material choices. The contribution of the solid toward these values, through the conjugate variations attributed to the thickness of the cylinder wall, is about 8% and 2% points, respectively, showing a maximum at intermediate thicknesses. At higher compression ratios (of 6) a 19% worst-case loss is reported for common materials. These results suggest strongly that in designing high-efficiency reciprocating machines the full conjugate and unsteady problem must be considered and that the role of the solid in determining performance cannot, in general, be neglected. © 2014 Richard Mathie, Christos N. Markides, and Alexander J. White. Published with License by Taylor & Francis.

Modeling current-voltage behaviour in oxide TFTs combining trap-limited conduction with percolation

Current-voltage behaviour of oxide TFTs is modeled based on trap-limited conduction and percolation theories. The mobility has a power-law dependence, in which percolation controls the exponent while trap states determine constant term in the power law. The proposed model, which is fully physically-based, provides a good agreement with measured transistor characteristics as well as transient operations of fabricated pixel test circuits for oxide-based OLED displays. © 2013 Society for Information Display.