Characterisation and optimisation of PECVD SiNx as an antireflection coating and passivation layer for silicon solar cells

In this work, we investigate how the film properties of silicon nitride (SiNx) depend on its deposition conditions when formed by plasma enhanced chemical vapour deposition (PECVD). The examination is conducted with a Roth & Rau AK400 PECVD reactor, where the varied parameters are deposition temperature, pressure, gas flow ratio, total gas flow, microwave plasma power and radio-frequency bias voltage. The films are evaluated by Fourier transform infrared spectroscopy to determine structural properties, by spectrophotometry to determine optical properties, and by capacitance–voltage and photoconductance measurements to determine electronic properties. After reporting on the dependence of SiNx properties on deposition parameters, we determine the optimized deposition conditions that attain low absorption and low recombination. On the basis of SiNx growth models proposed in the literature and of our experimental results, we discuss how each process parameter affects the deposition rate and chemical bond density. We then focus on the effective surface recombination velocity S eff, which is of primary importance to solar cells. We find that for the SiNx prepared in this work, 1) S eff does not correlate universally with the bulk structural and optical properties such as chemical bond densities and refractive index, and 2) S eff depends primarily on the defect density at the SiNx-Si interface rather than the insulator charge. Finally, employing the optimized deposition condition, we achieve a relatively constant and low S eff,UL on low-resistivity (≤1.1 Ωcm) p- and n-type c-Si substrates over a broad range of n = 1.85–4.07. The results of this study demonstrate that the trade-off between optical transmission and surface passivation can be circumvented. Although we focus on photovoltaic applications, this study may be useful for any device for which it is desirable to maximize light transmission and surface passivation.This work was supported by an Australian Research Council Linkage between The Australian National University and Braggone Oy under Grant LP0989593

Doctrine of the Protection of Nationals Abroad: Rise of the Non-Combatant Evacuation Operation

The purpose of this Article is to show that the doctrine of the protection of nationals abroad exists within the right of self-defense; with contours of the doctrine shaped in recent years by the practice of states in their conduct of NEO. This right is limited to the removal of the intervening state‘s citizens abroad through the use of force subject to necessity and proportionality in order to move the foreign nationals to a safe location, Part II discusses the origin of the doctrine of protection of nationals abroad and the legal bases that have been used to justify that protection. It also considers the impact of the misuse of the doctrine throughout its evolution. This explanation includes the claim that the protection of nationals abroad does not impugn Article 2(4) of the U.N. Charter which prohibits a state‘s use of force against another state and the justification that the protection of nationals is an exercise of the right of self-defense which complies with a state‘s right of self-defense enshrined in Article 51 of the UN Charter. It assesses the doctrine‘s place in self-defense at customary international law. Furthermore, this Article reviews state practice and the debate that has ensued among states and academics when states have asserted the doctrine to justify their use of force abroad. This Article also assesses the difficulties in determining the legality of the doctrine based upon the divided opinion of states. Part III surveys the military operational doctrine pertaining to NEO. Part IV assesses the recent invocation of the doctrine by the Russian Federation in its conflict in South Ossetia. Part V provides an analysis of the how NEOs as state practice have acted to limit the extent of protection to nationals abroad. Finally, in Part VI this Article concludes with an assessment of the state of the doctrine in contemporary international law

Degradation of oxide-passivated boron-diffused silicon

Recombination in oxide-passivated boron-diffused silicon is found to increase severely at room temperature. The degradation reaction leads to a 45 fold increase in emitter recombination that saturates in ∼120 days, irrespective of whether the samples received a forming-gas anneal. The degradation was also examined for diffusions stored at 50, 75, and 100 °C. The results indicate that the degradation follows a second-order reaction where the time constant of one component of the reaction is 10–40 times shorter than the other, and where the activation energy of the fast reaction is 0.19±0.05 eV. Subsequent to degradation, annealing in air reduces the recombination with increasing anneal temperature saturating at ∼300 °C to a value that is about four times higher than the predegradation value. A likely cause of this degradation is a reaction of atomic hydrogen at the silicon-oxide-silicon interface

Recombination and thin film properties of silicon nitride and amorphous silicon passivated c-Si following ammonia plasma exposure

Recombination at silicon nitride (SiNx) and amorphous silicon (a-Si) passivated crystalline silicon (c-Si) surfaces is shown to increase significantly following an ammonia (NH₃) plasma exposure at room temperature. The effect of plasma exposure on chemical structure, refractive index, permittivity, and electronic properties of the thin films is also investigated. It is found that the NH₃ plasma exposure causes (i) an increase in the density of Si≡N₃ groups in both SiNx and a-Si films, (ii) a reduction in refractive index and permittivity, (iii) an increase in the density of defects at the SiNx/c-Si interface, and (iv) a reduction in the density of positive charge in SiNx. The changes in recombination and thin film properties are likely due to an insertion of N–H radicals into the bulk of SiNx or a-Si. It is therefore important for device performance to minimize NH₃ plasma exposure of SiNx or a-Si passivating films during subsequent fabrication steps

Vibrations of a Columnar Vortex in a Trapped Bose-Einstein Condensate

We derive a governing equation for a Kelvin wave supported on a vortex line in a Bose-Einstein condensate, in a rotating cylindrically symmetric parabolic trap. From this solution the Kelvin wave dispersion relation is determined. In the limit of an oblate trap and in the absence of longitudinal trapping our results are consistent with previous work. We show that the derived Kelvin wave dispersion in the general case is in quantitative agreement with numerical calculations of the Bogoliubov spectrum and offer a significant improvement upon previous analytical work.Comment: 5 pages with 1 figur

Evolutionary diversification of an ancient gene family (rhs) through C-terminal displacement

<p>Abstract</p> <p>Background</p> <p><it>Rhs </it>genes are prominent features of bacterial genomes that have previously been implicated in genomic rearrangements in <it>E. coli</it>. By comparing <it>rhs </it>repertoires across the Enterobacteriaceae, this study provides a robust explanation of <it>rhs </it>diversification and evolution, and a mechanistic model of how <it>rhs </it>diversity is gained and lost.</p> <p>Results</p> <p><it>Rhs </it>genes are ubiquitous and comprise six structurally distinct lineages within the Enterobacteriaceae. There is considerable intergenomic variation in <it>rhs </it>repertoire; for instance, in <it>Salmonella enterica</it>, <it>rhs </it>are restricted to mobile elements, while in <it>Escherichia coli </it>one <it>rhs </it>lineage has diversified through transposition as older lineages have been deleted. Overall, comparative genomics reveals frequent, independent gene gains and losses, as well as occasional lateral gene transfer, in different genera. Furthermore, we demonstrate that Rhs 'core' domains and variable C-termini are evolutionarily decoupled, and propose that <it>rhs </it>diversity is driven by homologous recombination with circular intermediates. Existing C-termini are displaced by laterally acquired alternatives, creating long arrays of dissociated 'tips' that characterize the appearance of <it>rhs </it>loci.</p> <p>Conclusion</p> <p><it>Rhs </it>repertoires are highly dynamic among Enterobacterial genomes, due to repeated gene gains and losses. In contrast, the primary structures of <it>Rhs </it>genes are evolutionarily conserved, indicating that <it>rhs </it>sequence diversity is driven, not by rapid mutation, but by the relatively slow evolution of novel core/tip combinations. Hence, we predict that a large pool of dissociated <it>rhs </it>C-terminal tips exists episomally and these are potentially transmitted across taxonomic boundaries.</p

Some old movies become classics - a case study determining the scientific value of ROV inspection footage on a platform on Australia\u27s North West Shelf

The global oil and gas industry holds a vast archive of Remotely Operated Vehicle (ROV) inspection footage potentially containing useful long-term data on marine biological communities. With the upcoming era of decommissioning of oil and gas structures, it is timely to assess the usefulness of this footage for researching these communities. We used ROV inspection footage to characterize the sessile invertebrates and fishes associated with the Goodwyn Alpha Production Platform (GWA) on the North West Shelf of Australia between depths of 10 and 125 m during 2006 and 2008. Depth was a major driver of invertebrate assemblages, most likely due to specific requirements such as light, and differences between years were most likely from the physical detachment of species by cyclones and internal waves. Phototrophic species were mostly limited to the upper 50 m of the platform, including the hard coral Pocillopora sp. and the soft corals Nephthea sp. and Scleronephthya sp. In contrast, heterotrophic species including sponges, anemones, bryozoans, hydroids, bivalves such as Lopha folium and the hard coral Tubastrea spp., were distributed across all depths. We observed 1791 fish from at least 10 families and 19 species, including commercial species such as crimson seaperch (Lutjanus erythropterus), red emperor (L. sebae), saddle-tailed seaperch (L. malabaricus), mangrove jack (L. argentimaculatus) and trevally (Caranx spp.). Fish density increased significantly with depth during 2008, from a mean of 23 fish/50 m2 between 10 and 25 m to 3373 fish/50 m2 at 125 m, where small unidentified baitfish were abundant. The highest densities of commercial species occurred between 25 and 75 m depth, suggesting that mid-depth platform sections had high habitat value, a consideration when selecting decommissioning options. The greatest difficulties using the video were the poor lighting and resolution that inhibited our ability to identify sessile species with high taxonomic precision. However, the footage was useful for evaluating high-level biodiversity of the platform, understanding how fish and invertebrate communities changed with depth and comprehending the dynamic nature of the invertebrate community over time. Understanding the habitat value of structures will be necessary for making environmentally sound decommissioning decisions in the future