A. Rivera

Pandemic (H1N1) 2009 in breeding turkeys, Valparaiso, Chile.

Pandemic (H1N1) 2009 virus was detected in breeding turkeys on 2 farms in Valparaiso, Chile. Infection was associated with measurable declines in egg production and shell quality. Although the source of infection is not yet known, the outbreak was controlled, and the virus was eliminated from the birds.

Hydrogen-related hole capture and positive charge build up in buried oxides

Abstract We contribute with this paper to the understanding of positive charge build up upon hole injection in SiO 2 known to be an important degradation process. Our results are in agreement with a recently proposed model of charge generation [4,6] . We have observed the release of HD molecules upon hole injection in MOS capacitors that received a post-metallisation annealing in 100 kPa D 2 at 680 K. We provide evidence that the release of every HD molecule is related to the capture of one hole by one O 3 Si–D centre. This centre is converted into the neutral O 3 Si centre accompanied by the liberation of one deuteron D + , which, when neutralised, recombines with H giving the observed HD and when trapped, is responsible for the positive charge build up. The release of HD is suppressed when the number of generated O 3 Si centres is high enough to trap all the generated HD. This occurred when only 25% of the initial O 3 Si–D groups had dissociated by hole trapping. The positive charge build up was found to be dependent on the sample treatment indicating the strong influence of external sources of hydrogen in the described processes. The O 3 Si groups generated upon hole injection were found to be located close to the surface, distributed over a layer with a thickness dependent on strength of the electric field applied during the hole injection, i.e. 220 nm for 1.0 MV/cm and 400 nm for 2.0 MV/cm.

Oxygen-related defects in the top silicon layer of SIMOX ; the effect of thermal treatments

Commercial wafers of silicon implanted with oxygen (SIMOX), with a 190 nm silicon top layer and 360 nm buried oxide layer, were analysed using positron beam spectroscopy. Depth profiles of defects have been obtained in the depth range from 0 to 2 μm. The S parameter, related to annihilations with low-momentum electrons, has a value 10% lower in the top layer than in the silicon substrate. This low value can uniquely be ascribed to annihilations in oxygen-related traps. Positron beam analysis indicates that these defects are probably negatively charged and present at parts per million levels or lower. These defects escape detection by transmission electron microscopy, which suggests that the size of the defects must be smaller than 1 nm. By exposing the samples to deuterium plasma, these defects are passivated. In addition, the effects of annealing the samples from 600 to 800°C in deuterium ambients with pressures between 75 and 1000 kPa were studied. After these treatments, the annihilation parameters for defects in the top layer are very close to those of bulk silicon, indicating passivation of the oxygen-related defects. Further annealing in vacuum leads to a reversible process independent of the previous treatments applied to the samples. Thus, positron analysis has provided information about the existence and evolution of oxygen-related defects in the top layer of SIMOX.

In situ mechanical, temperature and gas exposure treatments of materials combined with variable energy positron beam techniques

An overview is given of the extension of the Delft variable energy positron (VEP) beam facility with equipment for in situ heating, cooling, 4-point bending, hydrogen permeation and gas ad- and absorption of bulk materials, surfaces and interfaces.

The behaviour of deuterium incorporated into the buried oxide of SIMOX

Abstract The buried oxide (BOX) layer of SIMOX samples was implanted with 20–30 keV D+ ion implantation at doses from 1014 to 10 16 cm −2 . Other samples were exposed to pure deuterium gas (0–1 MPa) at temperatures in the range 800–1100 K. Thermal desorption spectrometry (TDS) revealed two main trapping sites for deuterium in the buried oxide. The first releases deuterium at ∼900 K (activation energy ∼2.5 eV) and the second at ∼1250 K (activation energy ∼3.4 eV). They are attributed to dissociation of Si–D and Si–OD groups, respectively. The first peak is dominant in the implanted samples while the second is the dominant one for samples exposed to deuterium gas. The formation of the Si–OD groups is a temperature-activated process. The trapping of deuterium in the implanted samples is related to implantation-induced vacancy-like defects that are detected by means of positron beam analysis (PBA). Annealing at 900 K leads to a complete defect recovery. Deuterium profiling by SIMS confirms the trapping in the defects.

Interaction of deuterium with SIMOX buried oxide

Abstract We have studied SIMOX buried oxide samples implanted with D + (10 14 –10 15 cm −2 ) or annealed in D 2 (300–500 kPa at 1073 K). Thermal desorption spectrometry (TDS) performed on these samples after removal of the top Si layer shows two main peaks related to release of deuterium from Si–D and Si–OD defects. The first peak is dominant in implanted samples and the second in deuterium-annealed samples. In TDS experiments on samples with top layer the deuterium release is limited by diffusion in SiO 2 , D 2 -cracking at the Si/SiO 2 interface and permeation through the top Si layer. In these samples the D 2 signal is related to release through lateral surfaces, whereas the HD signal is produced by release through the top Si layer.