Hydrogen and muonium in diamond: A path-integral molecular dynamics simulation

Isolated hydrogen, deuterium, and muonium in diamond have been studied by path-integral molecular dynamics simulations in the canonical ensemble. Finite-temperature properties of these point defects were analyzed in the range from 100 to 800 K. Interatomic interactions were modeled by a tight-binding potential fitted to density-functional calculations. The most stable position for these hydrogenic impurities is found at the C-C bond center. Vibrational frequencies have been obtained from a linear-response approach, based on correlations of atom displacements at finite temperatures. The results show a large anharmonic effect in impurity vibrations at the bond center site, which hardens the vibrational modes with respect to a harmonic approximation. Zero-point motion causes an appreciable shift of the defect level in the electronic gap, as a consequence of electron-phonon interaction. This defect level goes down by 70 meV when replacing hydrogen by muonium.Comment: 11 pages, 8 figure

Nonlinear properties of AlGaAs waveguides in continuous wave operation regime

Aluminum Gallium Arsenide (AlGaAs) is an attractive platform for the development of integrated optical circuits for all-optical signal processing thanks to its large nonlinear coefficients in the 1.55-μm telecommunication spectral region. In this paper we discuss the results of the nonlinear continuous-wave optical characterization of AlGaAs waveguides at a wavelength of 1.55 μm. We also report the highest value ever reported in the literature for the real part of the nonlinear coefficient in this material (Re(γ) ≈521 W<sup>−1</sup>m<sup>−1</sup>)

Using data smartly ? moving towards a smart city

The eThekwini Transport Authority (ETA) is currently developing and pursuing smart city strategies and interventions to make eThekwini more caring and liveable. A key component of smart cities is to use data smartly. This includes measuring, monitoring and evaluating the effectiveness of current projects and programmes. To this end a GIS based tool comprising databases from various sectors has been developed to allow the ETA to research and evaluate the effectiveness of past and current management, maintenance and sector specific strategies.Paper presented at the 35th Annual Southern African Transport Conference 4-7 July 2016 "Transport ? a catalyst for socio-economic growth and development opportunities to improve quality of life", CSIR International Convention Centre, Pretoria, South Africa.The Minister of Transport, South AfricaTransportation Research Board of the US

Diffusion of hydrogen in crystalline silicon

The coefficient of diffusion of hydrogen in crystalline silicon is calculated using tight-binding molecular dynamics. Our results are in good quantitative agreement with an earlier study by Panzarini and Colombo [Phys. Rev. Lett. 73, 1636 (1994)]. However, while our calculations indicate that long jumps dominate over single hops at high temperatures, no abrupt change in the diffusion coefficient can be observed with decreasing temperature. The (classical) Arrhenius diffusion parameters, as a consequence, should extrapolate to low temperatures.Comment: 4 pages, including 5 postscript figures; submitted to Phys. Rev. B Brief Repor

MgZnO/AlGaN heterostructure light-emitting diodes

We report on p-n junction light-emitting diodes fabricated from MgZnO/ZnO/AlGaN/GaN triple heterostructures. Energy band diagrams of the light-emitting diode structure incorporating piezoelectric and spontaneous polarization fields were simulated, revealing a strong hole confinement near the n-ZnO/p-AlGaN interface with a hole sheet density as large as 1.82x10(13) cm(-2) for strained structures. The measured current-voltage (IV) characteristics of the triple heterostructure p-n junctions have rectifying characteristics with a turn-on voltage of similar to3.2 V. Electron-beam-induced current measurements confirmed the presence of a p-n junction located at the n-ZnO/p-AlGaN interface. Strong optical emission was observed at similar to390 nm as expected for excitonic optical transitions in these structures. Experimental spectral dependence of the photocurrent confirmed the excitonic origin of the optical transition at 390 nm. Light emission was measured up to 650 K, providing additional confirmation of the excitonic nature of the optical transitions in the devices

Ferromagnetic transition metal implanted ZnO: a diluted magnetic semiconductor?

Recently theoretical works predict that some semiconductors (e.g. ZnO) doped with magnetic ions are diluted magnetic semiconductors (DMS). In DMS magnetic ions substitute cation sites of the host semiconductor and are coupled by free carriers resulting in ferromagnetism. One of the main obstacles in creating DMS materials is the formation of secondary phases because of the solid-solubility limit of magnetic ions in semiconductor host. In our study transition metal ions were implanted into ZnO single crystals with the peak concentrations of 0.5-10 at.%. We established a correlation between structural and magnetic properties. By synchrotron radiation X-ray diffraction (XRD) secondary phases (Fe, Ni, Co and ferrite nanocrystals) were observed and have been identified as the source for ferromagnetism. Due to their different crystallographic orientation with respect to the host crystal these nanocrystals in some cases are very difficult to be detected by a simple Bragg-Brentano scan. This results in the pitfall of using XRD to exclude secondary phase formation in DMS materials. For comparison, the solubility of Co diluted in ZnO films ranges between 10 and 40 at.% using different growth conditions pulsed laser deposition. Such diluted, Co-doped ZnO films show paramagnetic behaviour. However, only the magnetoresistance of Co-doped ZnO films reveals possible s-d exchange interaction as compared to Co-implanted ZnO single crystals.Comment: 27 pages, 8 figure

Surface and electronic structure of MOCVD-grown Ga(0.92)In(0.08)N investigated by UV and X-ray photoelectron spectroscopies

The surface and electronic structure of MOCVD-grown layers of Ga(0.92)In(0.08)N have been investigated by means of photoemission. An additional feature at the valence band edge, which can be ascribed to the presence of In in the layer, has been revealed. A clean (0001)-(1x1) surface was prepared by argon ion sputtering and annealing. Stability of chemical composition of the investigated surface subjected to similar ion etching was proven by means of X-ray photoemission spectroscopy.Comment: 13 pages, 6 figure