Oxygen vacancy defects in Ta2O5 showing long-range atomic re-arrangements

The structure, formation energy, and energy levels of the various oxygen vacancies in Ta2O5 have been calculated using the λ phase model. The intra-layer vacancies give rise to unusual, long-range bonding rearrangements, which are different for each defect charge state. The 2-fold coordinated intra-layer vacancy is the lowest cost vacancy and forms a deep level 1.5 eV below the conduction band edge. The 3-fold intra-layer vacancy and the 2-fold inter-layer vacancy are higher cost defects, and form shallower levels. The unusual bonding rearrangements lead to low oxygen migration barriers, which are useful for resistive random access memory applications. © 2014 AIP Publishing LLC.

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.

Role of f electrons in the Fermi surface of the heavy fermion superconductor beta-YbAlB4.

We present a detailed quantum oscillation study of the Fermi surface of the recently discovered Yb-based heavy fermion superconductor beta-YbAlB4. We compare the data, obtained at fields from 10 to 45 T, to band structure calculations performed using the local density approximation. Analysis of the data suggests that f holes participate in the Fermi surface up to the highest magnetic fields studied. We comment on the significance of these findings for the unconventional superconducting properties of this material.

Band alignment between Ta2O5 and metals for resistive random access memory electrodes engineering

Band alignment of resistive random access memory (RRAM) switching material Ta2O5 and different metal electrode materials was examined using high-resolution X-ray photoelectron spectroscopy. Schottky and hole barrier heights at the interface between electrode and Ta2O 5 were obtained, where the electrodes consist of materials with low to high work function (Φ m, v a c from 4.06 to 5.93 eV). Effective metal work functions were extracted to study the Fermi level pinning effect and to discuss the dominant conduction mechanism. An accurate band alignment between electrodes and Ta2O5 is obtained and can be used for RRAM electrode engineering and conduction mechanism study. © 2013 American Institute of Physics.

Nature of the electronic band gap in lanthanide oxides

Accurate electronic structures of the technologically important lanthanide/rare-earth sesquioxides (Ln2O3, with Ln=La, ⋯,Lu) and CeO2 have been calculated using hybrid density functionals HSE03, HSE06, and screened exchange (sX-LDA). We find that these density functional methods describe the strongly correlated Ln f electrons as well as the recent G0W0@LDA+U results, generally yielding the correct band gaps and trends across the Ln period. For HSE, the band gap between O 2p states and lanthanide 5d states is nearly independent of the lanthanide, while the minimum gap varies as filled or empty Ln 4f states come into this gap. sX-LDA predicts the unoccupied 4f levels at higher energies, which leads to a better agreement with experiments for Sm2O 3, Eu2O3, and Yb2O3. © 2013 American Physical Society.

Properties of electrons and holes during femtosecond cooperative emission

Spectral and energetic characteristics of the cooperative recombination of high density electrons and holes in bulk GaAs are experimentally studied at room temperature. It is shown that the properties and parameters of femtosecond superradiant pulses are conditioned by the collective properties of electrons and holes. Electron-hole pairing and the formation of a short-living coherent e-h BCS state distinguish strongly the regime of cooperative emission from all radiative e-h recombination regimes, which have been observed earlier. The dependences of the energy gap (the order parameter), the Fermi energy, and the band gap of the coherent e-h BCS state on the concentration of electron-hole pairs are obtained.

Cell shape changes indicate a role for extrinsic tensile forces in Drosophila germ-band extension.

Drosophila germ-band extension (GBE) is an example of the convergence and extension movements that elongate and narrow embryonic tissues. To understand the collective cell behaviours underlying tissue morphogenesis, we have continuously quantified cell intercalation and cell shape change during GBE. We show that the fast, early phase of GBE depends on cell shape change in addition to cell intercalation. In antero-posterior patterning mutants such as those for the gap gene Krüppel, defective polarized cell intercalation is compensated for by an increase in antero-posterior cell elongation, such that the initial rate of extension remains the same. Spatio-temporal patterns of cell behaviours indicate that an antero-posterior tensile force deforms the germ band, causing the cells to change shape passively. The rate of antero-posterior cell elongation is reduced in twist mutant embryos, which lack mesoderm. We propose that cell shape change contributing to germ-band extension is a passive response to mechanical forces caused by the invaginating mesoderm.

A Bayesian wavelet-based multidimensional deconvolution with sub-band emphasis

This paper proposes a new algorithm for waveletbased multidimensional image deconvolution which employs subband-dependent minimization and the dual-tree complex wavelet transform in an iterative Bayesian framework. In addition, this algorithm employs a new prior instead of the popular ℓ1 norm, and is thus able to embed a learning scheme during the iteration which helps it to achieve better deconvolution results and faster convergence. © 2008 IEEE.

Directly-modulated DS-DBR tunable laser for uncooled C-band WDM system

A tunable DS-DBR laser is demonstrated for uncooled WDM C-band channel generation with tight spacing (SOGHz) and low thermal drift (±2.5GHz) up to 70°C. 2.5Gb/s direct modulation with transmission over a 75km link is achieved. © 2000 Optical Society of America.

The ensemble statistics of the band-averaged energy of a random system

This paper is concerned with the response statistics of a dynamic system that has random properties. The frequency-band-averaged energy of the system is considered, and a closed form expression is derived for the relative variance of this quantity. The expression depends upon three parameters: the modal overlap factor m, a bandwidth parameter B, and a parameter α that defines the nature of the loading (for example single point forcing or rain-on-the-roof loading). The result is applicable to any single structural component or acoustic volume, and a comparison is made here with simulation results for a mass loaded plate. Good agreement is found between the simulations and the theory. © 2003 Published by Elsevier Ltd.

Low loss HF band SOI wine glass bulk mode capacitive square-plate resonator

This paper reports on the design and electrical characterization of a single crystal silicon micromechanical square-plate resonator. The microresonator has been excited in the anti-symmetrical wine glass mode at a resonant frequency of 5.166 MHz and exhibits an impressive quality factor (Q) of 3.7 × 106 at a pressure of 33 mtorr. The device has been fabricated in a commercial foundry process. An associated motional resistance of approximately 50 kΩ using a dc bias voltage of 60 V is measured for a transduction gap of 2 νm due to the ultra-high Q of the resonator. This result corresponds to a frequency-Q product of 1.9 × 1013, the highest reported for a fundamental mode single-crystal silicon resonator and on par with some of the best quartz crystal resonators. The results are indicative of the superior performance of silicon as a mechanical material, and show that the wine glass resonant mode is beneficial for achieving high quality factors allowed by the material limit. © 2009 IOP Publishing Ltd.

Athermal colourless C-band optical transmitter for passive optical networks

A new control algorithm with reduced mode-hopping is demonstrated for uncooled WDM C-band channel generation from a DS-DBR laser with 100GHz spacing and low thermal drift up to 70°C. 10Gb/s external modulation with transmission over a 25km link is achieved. ©2010 IEEE.