Experimental and theoretical study of heterogeneous iron precipitation in silicon

Heterogeneous iron precipitation in silicon was studied experimentally by measuring the gettering efficiency of oxide precipitate density of 1×10exp10cm−3. The wafers were contaminated with varying iron concentrations, and the gettering efficiency was studied using isothermal annealing in the temperature range from 300 to 780°C. It was found that iron precipitation obeys the so called s-curve behavior: if iron precipitation occurs, nearly all iron is gettered. For example, after 30 min annealing at 700°C, the highest initial iron concentration of 8×10exp13cm−3 drops to 3×10exp12cm−3, where as two lower initial iron concentrations of 5×10exp12 and 2×10exp13cm−3 remain nearly constant. This means that the level of supersaturation plays a significant role in the final gettering efficiency, and a rather high level of supersaturation is required before iron precipitation occurs at all. In addition, a model is presented for the growth and dissolution of iron precipitates at oxygen-related defects in silicon during thermal processing. The heterogeneous nucleation of iron is taken into account by special growth and dissolution rates, which are inserted into the Fokker-Planck equation. Comparison of simulated results to experimental ones proves that this model can be used to estimate internal gettering efficiency of iron under a variety of processing conditions.Peer reviewe

Modeling phosphorus diffusion gettering of iron in single crystal silicon

We propose a quantitative model for phosphorus diffusion gettering (PDG) of iron in silicon, which is based on a special fitting procedure to experimental data. We discuss the possibilities of the underlying physics of the segregation coefficient. Finally, we show that the proposed PDG model allows quantitative analysis of gettering efficiency of iron at various processing conditions.Peer reviewe

Modeling boron diffusion gettering of iron in silicon solar cells

In this paper, a model is presented for boron diffusion gettering of iron in silicon during thermal processing. In the model, both the segregation of iron due to high boron doping concentration and heterogeneous precipitation of iron to the surface of the wafer are taken into account. It is shown, by comparing simulated results with experimental ones, that this model can be used to estimate boron diffusion gettering efficiency of iron under a variety of processing conditions. Finally, the application of the model to phosphorus diffusion gettering is discussed.Peer reviewe

Oxidovanadium(v) complexes with L-proline-based amino acid phenolates

L-proline was used to prepare chiral, tridentate amino acid phenol proligands H2L1-4. These proligands react with vanadium precursors VO(acac)(2,) VOSO4 center dot 5H(2)O and VO(OPr)(3) in methanol to form the corresponding oxidoalkoxidovanadium(v) complexes 1-4. The complexes crystallize from methanol, and are octahedrally co-ordinated with a general formula [VO(L1-4)(OMe)(MeOH)]. In solution, however, they adopt several different conformations or isomeric structures depending on the solvent

Quantitative copper measurement in oxidized p-type silicon wafers using microwave photoconductivity decay

We propose a method to measure trace copper contamination in p-type silicon using the microwave photoconductivity decay (μ-PCD) technique. The method is based on the precipitation of interstitial copper, activated by high-intensity light, which results in enhanced minority carrier recombination activity. We show that there is a quantitative correlation between the enhanced recombination rate and the Cu concentration by comparing μ-PCD measurements with transient ion drift and total reflection x-ray fluorescence measurements. The results indicate that the method is capable of measuring Cu concentrations down to 10exp10cm−3. There are no limitations to wafer storage time if corona charge is used on the oxidized wafer surfaces as the charge prevents copper outdiffusion. We briefly discuss the role of oxide precipitates both in the copperprecipitation and in the charge carrier recombination processes.Peer reviewe

Beyond a war of words? Assessing tensions on the Korean peninsula

An exchange of bellicose rhetoric between North Korea and the US has caused serious global concerns about a possible military conflict. The methodical advances of the North Korean leadership, the limitations of the US’s actual policy options, and China’s meagre leverage are key determinants in shaping further developments.</p

Patient satisfaction in the long-term effects of Eustachian tube balloon dilation is encouraging

Object: To investigate the long-term effects of balloon Eustachian tuboplasty (BET) from patient’s perspective and to discover which symptoms of Eustachian tube dysfunction (ETD) benefit the most from BET.Method: We designed a retrospective postal questionnaire based on the seven-item ETD questionnaire (ETDQ-7). Our questionnaire covered the severity of present ETD symptoms in comparison with the preoperative situation, the severity of current overall ear symptoms, and possible surgical interventions after BET. Forty-six patients treated in our institution between 2011 and 2013 fulfilled the inclusion criteria and 74% (34 patients; total 52 ears treated with BET) returned the questionnaire with a mean follow-up time of 3.1 years (range 1.8-4.6 years).Results: Pain in the ears, feeling of pressure in the ears, and feeling that ears are clogged had reduced in 75% of the ears that suffered from these symptoms preoperatively. Seventy-seven percent of all the responders felt that their overall ear symptoms were reduced. Altogether, 82% of all the patients stated that they would undergo BET again if their ear symptoms returned to the preoperative level.Conclusion: Patient satisfaction in the long-term effects of BET is encouraging. These results may help clinicians in preoperative patient selection and counselling.</p

Stereospecific modulation of GABA(A) receptor function by urocanic acid isomers

A deamination product of histidine, urocanic acid, accumulates in the skin of mammals as trans-urocanic acid. Ultraviolet (UV) irradition converts it to the cis-isomer that is an important mediator in UV-induced immunosuppression. We have recently shown that urocanic acid interferes with the agonist binding to GABAA receptors. We now report that the effects of urocanic acid on binding of a convulsant ligand (t-butylbicyclo[35S]phosphorothionate) to GABAA receptors in brain membrane homogenates are dependent on pH of the incubation medium, the agonistic actions being enhanced at the normal pH of the skin (5.5). Using Xenopus laevis oocytes expressing recombinant rat alpha1beta1gamma2S GABAA receptors, the low pH potentiated the direct agonistic action of trans-urocanic acid under two-electrode voltage-clamp, whereas cis-urocanic acid retained its low efficacy both at pH 5.5 and 7.4. The results thus indicate clear differences between urocanic acid isomers in functional activity at one putative receptor site of immunosuppression, the GABAA receptor, the presence of which in the skin remains to be demonstrated.</p

Recyclizations of 2-aminobenzylimines and thioaroylhydrazones of N-substituted N-hydroxy-3-oxobutanamides

A universal scheme is proposed for the molecular design of heterocyclic recyclizations by replacing the exocyclic hydroxyl groups in exo-trig- ring-chain tautomeric molecules with substituted amines or hydrazines. The practical applicability of this approach is demonstrated by the condensations of 5-hydroxy-5-methyl-3-isoxazolidinones with thioaroyl-hydrazines and 2-aminomethylaniline. The condensation products were studied by modern 1H, 13C and 15N NMR spectroscopic methods using three solvents: CDCl3, DMSO[D6] and CD3CN. The solvent was found to have a strong effect to the relative amounts of the tautomers