Impact of firing on surface passivation of p-Si by SiO2/Al and SiO2/SiNx/Al stacks

Firing impacts on surface passivation provided by a SiO2 and SiO2/SiNx stack with evaporated Al films are studied by capacitance-based techniques on MIS capacitors. For devices with insulator layers consisting solely of as-deposited SiO2, the densities of either interface states (Dit) or fixed charges (Qfc) are hardly influenced by firing. Capping the SiO2 layer with a SiNx layer results in a shift of the peak activation energy of Dit toward the valence band (Ev) of Si. Firing this SiO2/SiNx stack leads to an increase of Qfc, a reduction of Dit, and a moderate shift of peak activation energy of Dit toward Ev. Co-firing with the Al film on top significantly reduces the Qfc, Dit, and Dit peak activation energy, which is resulting from the atomic hydrogen passivation. These results are of particular interest for the development of solar cells with rear surface passivation and local contacts

Passivation of a Metal Contact with a Tunneling Layer

AbstractThe potential of contact passivation for increasing cell performance is indicated by several results reported in the literature. However, scant characterization of the tunneling layers used for that purpose has been reported. In this paper, contact passivation is investigated by insertion of an ultra-thin AlOx layer between an n-type emitter and a Ti/Pd/Ag contact. By using a 1.5nm thick layer, an increase of the minority carrier lifetime by a factor of 2.7 is achieved. Since current-voltage measurements indicate that an ohmic behavior is conserved for AlOx layers as thick as 1.5nm, a 1.5nm AlOx layer is found to be a candidate of choice for contact passivation

In Vitro Effect of Porphyromonas gingivalis Methionine Gamma Lyase on Biofilm Composition and Oral Inflammatory Response

Methanethiol (methyl mercaptan) is an important contributor to oral malodour and periodontal tissue destruction. Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum are key oral microbial species that produce methanethiol via methionine gamma lyase (mgl) activity. The aim of this study was to compare an mgl knockout strain of P. gingivalis with its wild type using a 10-species biofilm co-culture model with oral keratinocytes and its effect on biofilm composition and inflammatory cytokine production. A P. gingivalis mgl knockout strain was constructed using insertion mutagenesis from wild type W50 with gas chromatographic head space analysis confirming lack of methanethiol production. 10-species biofilms consisting of Streptococcus mitis, Streptococcus oralis, Streptococcus intermedius, Fusobacterium nucleatum ssp polymorphum, Fusobacterium nucleatum ssp vincentii, Veillonella dispar, Actinomyces naeslundii, Prevotella intermedia and Aggregatibacter actinomycetemcomitans with either the wild type or mutant P. gingivalis were grown on Thermanox cover slips and used to stimulate oral keratinocytes (OKF6-TERT2), under anaerobic conditions for 4 and 24 hours. Biofilms were analysed by quantitative PCR with SYBR Green for changes in microbial ecology. Keratinocyte culture supernatants were analysed using a multiplex bead immunoassay for cytokines. Significant population differences were observed between mutant and wild type biofilms; V. dispar proportions increased (p<0.001), whilst A. naeslundii (p<0.01) and Streptococcus spp. (p<0.05) decreased in mutant biofilms. Keratinocytes produced less IL-8, IL-6 and IL-1α when stimulated with the mutant biofilms compared to wild type. Lack of mgl in P. gingivalis has been shown to affect microbial ecology in vitro, giving rise to a markedly different biofilm composition, with a more pro-inflammatory cytokine response from the keratinocytes observed. A possible role for methanethiol in biofilm formation and cytokine response with subsequent effects on oral malodor and periodontitis is suggested

Predictive modelling of L and H confinement modes and edge pedestal characteristics

The results of predictive self-consistent modelling of plasma parameters in low (L) and high (H) confinement modes by the one-dimensional transport code RITM, with particular emphasis on the properties of the edge transport barrier, are presented and discussed. The same transport model is used under both L- and H-mode conditions and includes contributions from ion temperature gradient (ITG), trapped electron, drift Alfven (DA) and drift resistive ballooning instabilities described in the fluid approximation. The computations predict the formation of the edge transport barrier at a high enough heating power due to stabilization of ITG and DA modes, dominating the edge transport in the L-mode, through the effects of the density gradient and the pressure gradient at low collisionality, respectively. The calculated radial profiles and scalings for pedestal and confinement characteristics are compared with measurements on JET, DIII-D and JT-60U tokamaks

On the difference of H-mode power threshold in divertor and limiter tokamaks

The difference in the H-mode power threshold in divertor and limiter configurations is numerically investigated by analysing the effect of boundary conditions imposed on the last closed magnetic surface (LCMS) and given by prescribed density and temperature e-folding lengths, delta(n) and delta(T), respectively. It is demonstrated that the variation of delta(n) and delta(T) significantly affects the H-mode power threshold. This is explained by the change in the balance between conductive and convective heat losses at the edge. For the ratio delta(n)/delta(T) large enough, when the convective loss does not exceed 45% of the total power, the threshold agrees well with the experimental multi-machine scaling for divertor tokamaks. With reduction in delta(n)/delta(T) and increase in convective loss above this critical level, the power threshold significantly exceeds the scaling, in agreement with observations on different limiter tokamaks. By considering the power and particle balances in the scrape-off layer it is shown that the ratio delta(n)/delta(T) is controlled by the distance which recycling neutrals pass before entering the confined plasma and which is normally much larger in divertor machines than in the limiter ones. The calculations for the limiter tokamak TEXTOR have predicted the experimentally found conditions for the L-H transition in advance