Accurate first principles detailed balance determination of Auger recombination and impact ionization rates in semiconductors

The technologically important problem of predicting Auger recombination lifetimes in semiconductors is addressed by means of a fully first--principles formalism. The calculations employ highly precise energy bands and wave functions provided by the full--potential linearized augmented plane wave (FLAPW) code based on the screened exchange local density approximation. The minority carrier Auger lifetime is determined by two closely related approaches: \emph{i}) a direct evaluation of the Auger rates within Fermi's Golden Rule, and \emph{ii}) an indirect evaluation, based on a detailed balance formulation combining Auger recombination and its inverse process, impact ionization, in a unified framework. Calculated carrier lifetimes determined with the direct and indirect methods show excellent consistency \emph{i}) between them for $n$-doped GaAs and \emph{ii}%) with measured values for GaAs and InGaAs. This demonstrates the validity and accuracy of the computational formalism for the Auger lifetime and indicates a new sensitive tool for possible use in materials performance optimization.Comment: Phys. Rev. Lett. accepte

Impact ionization in GaAs: a screened exchange density functional approach

Results are presented of a fully ab-initio calculation of impact ionization rates in GaAs within the density functional theory framework, using a screened-exchange formalism and the highly precise all-electron full-potential linearized augmented plane wave (FLAPW) method. The calculated impact ionization rates show a marked orientation dependence in {\bf k} space, indicating the strong restrictions imposed by the conservation of energy and momentum. This anisotropy diminishes as the impacting electron energy increases. A Keldysh type fit performed on the energy-dependent rate shows a rather soft edge and a threshold energy greater than the direct band gap. The consistency with available Monte Carlo and empirical pseudopotential calculations shows the reliability of our approach and paves the way to ab-initio calculations of pair production rates in new and more complex materials.Comment: 11 pages, 4 figures, Submitted to Phys. Rev.

Anaesthesia for a morbidly obese patient with schizophrenia and intellectual disability

We report the case of a morbidly obese woman with schizophrenia and intellectual disability who underwent dental treatment using general anaesthesia. The 38-year-old patient was 156 cm tall and weighed 140 kg, with a body mass index of 57.5 kg.m-2. Her developmental age was less than five or six years. She had been taking several antipsychotic agents, including haloperidol. Tracheal intubation was performed smoothly and anaesthesia was maintained uneventfully using propofol and remifentanil.This case demonstrates that the method of general anaesthesia presented here can be used safely in managing patients with these kinds of disabilities

Nitrogen doping of TiO2 photocatalyst forms a second eg state in the Oxygen (1s) NEXAFS pre-edge

Close inspection of the pre-edge in oxygen near-edge x-ray absorption fine structure spectra of single step, gas phase synthesized titanium oxynitride photocatalysts with 20 nm particle size reveals an additional eg resonance in the VB that went unnoticed in previous TiO2 anion doping studies. The relative spectral weight of this Ti(3d)-O(2p) hybridized state with respect to and located between the readily established t2g and eg resonances scales qualitatively with the photocatalytic decomposition power, suggesting that this extra resonance bears co-responsibility for the photocatalytic performance of titanium oxynitrides at visible light wavelengths

Ground-state electric quadrupole moment of 31Al

Ground-state electric quadrupole moment of 31Al (I =5/2+, T_1/2 = 644(25) ms) has been measured by means of the beta-NMR spectroscopy using a spin-polarized 31Al beam produced in the projectile fragmentation reaction. The obtained Q moment, |Q_exp(31Al)| = 112(32)emb, are in agreement with conventional shell model calculations within the sd valence space. Previous result on the magnetic moment also supports the validity of the sd model in this isotope, and thus it is concluded that 31Al is located outside of the island of inversion.Comment: 5 page

Strong atomic ordering in Gd-doped GaN

Gd-doped GaN (Ga 1-xGd xN) thin films were grown on a GaN(001) template by radio frequency plasma-assisted molecular beam epitaxy and characterized by means of x-ray diffraction (XRD) and transmission electron microscopy (TEM). Three samples with a different Gd composition were prepared in this study: x = 0.02, 0.05, and 0.08. XRD and TEM results revealed that the low Gd concentration GaN possesses the wurtzite structure. On the other hand, it was found that an ordered phase with a quadruple-periodicity along the [001] direction in the wurtzite structure is formed throughout the film with x = 0.08. We proposed the atomistic model for the superlattice structure observed here. © 2012 American Institute of Physics.Manabu Ishimaru, Kotaro Higashi, Shigehiko Hasegawa, Hajime Asahi, Kazuhisa Sato, and Toyohiko J. Konno, "Strong atomic ordering in Gd-doped GaN", Appl. Phys. Lett. 101, 101912 (2012) https://doi.org/10.1063/1.4751245

General anaesthesia with and without intubation for patients with Cornelia de Lange syndrome

We present the use of different methods of general anaesthesia in two patients with Cornelia de Lange syndrome and its contribution to the patients’ oral health.Case 1: The patient was a 22-year-old woman with Cornelia de Lange syndrome who underwent dental treatment under general anaesthesia. She exhibited the physical characteristics of Cornelia de Lange syndrome, including a small mouth, thin lips, short limbs, stiffness of joints and intellectual disability. General anaesthesia without intubation was performed safely eight times. No other complications except hypersensitivity to hypnotic agents were observed.Case 2: The patient was a 10-year-old boy with Cornelia de Lange syndrome who underwent dental treatment under general anaesthesia. He had a history and symptoms of obstructive airway disorders in addition to showing physical characteristics of the syndrome similar to those seen in Case 1. General anaesthesia with nasal intubation was performed safely twice. Computed tomography (CT) of his head and neck produced unremarkable results. These cases demonstrate that both general anaesthesia with and without nasal intubation can be safely used in managing individuals with Cornelia de Lange syndrome during dental treatment.Keywords: general anaesthesia; Cornelia de Lange syndrome; dental treatmen

Measurement of parity-nonconserving rotation of neutron spin in the 0.734-eV p-wave resonance of 139La^{139}La

The parity nonconserving spin rotation of neutrons in the 0.734-eV p-wave resonance of $^{139}La$ was measured with the neutron transmission method. Two optically polarized $^3He$ cells were used before and behind a a 5-cm long $^{139}La$ target as a polarizer and an analyzer of neutron spin. The rotation angle was carefully measured by flipping the direction of $^3He$ polarization in the polarizer in sequence. The peak-to-peak value of the spin rotation was found to be $(7.4 \pm 1.1) \times 10^{-3}$ rad/cm which was consistent with the previous experiments. But the result was statisticallly improved. The s-p mixing model gives the weak matrix element as $xW = (1.71 \pm 0.25)$ meV. The value agrees well with the one deduced from the parity-nonconserving longitudinal asymmetry in the same resonance

Optical band edge shift of anatase cobalt-doped titanium dioxide

We report on the optical properties of magnetic cobalt-doped anatase phase titanium dioxide Ti_{1-x}Co_{x}O_{2-d} films for low doping concentrations, 0 <= x <= 0.02, in the spectral range 0.2 to 5 eV. For well oxygenated films (d << 1) the optical conductivity is characterized by an absence of optical absorption below an onset of interband transitions at 3.6 eV and a blue shift of the optical band edge with increasing Co concentration. The absence of below band gap absorption is inconsistent with theoretical models which contain midgap magnetic impurity bands and suggests that strong on-site Coulomb interactions shift the O-band to Co-level optical transitions to energies above the gap.Comment: 5 pages, 4 figures, 1 table; Version 2 - major content revisio

X-ray diffraction measurements of the c-axis Debye-Waller factors of YBa2Cu3O7 and HgBa2CaCu2O6

We report the first application of x-rays to the measurement of the temperature dependent Bragg peak intensities to obtain Debye-Waller factors on high-temperature superconductors. Intensities of (0,0,l) peaks of YBa2Cu3O7 and HgBa2CaCu2O6 thin films are measured to obtain the c-axis Debye-Waller factors. While lattice constant and some Debye-Waller factor measurements on high Tc superconductors show anomalies at the transition temperature, our measurements by x-ray diffraction show a smooth transition of the c-axis Debye-Waller factors through T$_c$. This suggests that the dynamic displacements of the heavy elements along the c-axis direction in these compounds do not have anomalies at Tc. This method in combination with measurements by other techniques will give more details concerning dynamics of the lattice.Comment: 4 pages, 2 figures. To be published in Physical Review B (Brief Report