| 1. |
- Hoffmann, L., et al.
(författare)
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Weakly bound carbon-hydrogen complex in silicon
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:24, s. 16659-16666
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Tidskriftsartikel (refereegranskat)abstract
- Local vibrational modes of a weakly bound carbon-hydrogen complex in silicon have been identified with infrared-absorption spectroscopy. After implantation of protons at ∼20 K and subsequent annealing at 180 K, two carbon modes at 596 and 661 cm-1, and one hydrogen mode at 1885 cm-1 are observed. The three modes originate from the same complex, which is identified as bond-centered hydrogen in the vicinity of a nearby substitutional carbon atom. Ab initio theory has been applied to calculate the structure and local modes of carbon-hydrogen complexes with hydrogen located at the first, second, and third nearest bond-center site to substitutional carbon. The results support our assignment.
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| 2. |
- Lavrov, E.V., et al.
(författare)
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Combined infrared absorption and modeling study of a dicarbon-dihydrogen defect in silicon
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 62:19, s. 12859-12867
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Tidskriftsartikel (refereegranskat)abstract
- Crystalline silicon samples doped with carbon were irradiated with electrons and subsequently implanted with protons. Infrared-absorption measurements revealed local modes of hydrogen and carbon at 2967.4, 911.7, and 654.7 cm-1, which originate from the same defect. Measurements on samples codoped with different carbon and hydrogen isotopes showed that the defect contains two equivalent carbon and two equivalent hydrogen atoms. From uniaxial stress measurements, the defect is found to display trigonal symmetry. Ab initio local-density-functional theory was applied to calculate the structure and local vibrational modes of defects with pairs of equivalent carbon and hydrogen atoms. Based on these results, the observed local modes are ascribed to a defect with two adjacent substitutional carbon atoms, each of which binds a hydrogen atom located between the carbon atoms.
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| 3. |
- Lavrov, E. V., et al.
(författare)
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Local vibrational modes of two neighboring substitutional carbon atoms in silicon
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 62:1, s. 158-165
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Tidskriftsartikel (refereegranskat)abstract
- Infrared absorption measurements on n-type silicon doped with carbon and irradiated with electrons at room temperature have revealed new absorption lines at 527.4 and 748.7 cm-1, which originate from the same defect. The 748.7-cm-1 line is observed only when the sample is cooled in the dark and the spectrum is measured through a low-pass filter with cutoff frequency below 6000 cm-1. Light with frequency above 6000 cm-1 removes this line and generates the 527.4-cm-1 line. Comparison with spectra recorded on irradiated silicon doped with 13C shows that the two lines represent local vibrational modes of carbon. The annealing behavior of the 748.7-cm-1 line is identical to that of the EPR signal originating from the negative charge state of two adjacent substitutional carbon atoms (Cs-Cs)-. The 527.4- and 748.7-cm-1 lines are ascribed to the E modes of Cs-Cs in the neutral and negative charge states, respectively. The structure and local vibrational modes of (Cs-Cs)0 and (Cs-Cs)- have been calculated by ab initio local density functional theory. The calculated structures agree qualitatively with those obtained previously by Hartree-Fock methods, but the calculated Si-C and C-C bond lengths differ somewhat. The calculated local mode frequencies are in good agreement with those observed. The formation of Cs-Cs has also been investigated. It is suggested that the center is formed when a vacancy is trapped by the metastable substitutional carbon-interstitial carbon center, Cs-Ci.
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| 4. |
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| 5. |
- Prokunina, Ludmila, et al.
(författare)
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A regulatory polymorphism in PDCD1 is associated with susceptibility to systemic lupus erythematosus in humans
- 2002
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Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 32:4, s. 666-669
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Recension (övrigt vetenskapligt/konstnärligt)abstract
- Systemic lupus erythematosus (SLE, OMIM 152700) is a complex autoimmune disease that affects 0.05% of the Western population, predominantly women. A number of susceptibility loci for SLE have been suggested in different populations, but the nature of the susceptibility genes and mutations is yet to be identified. We previously reported a susceptibility locus (SLEB2) for Nordic multi-case families. Within this locus, the programmed cell death 1 gene (PDCD1, also called PD-1) was considered the strongest candidate for association with the disease. Here, we analyzed 2,510 individuals, including members of five independent sets of families as well as unrelated individuals affected with SLE, for single-nucleotide polymorphisms (SNPs) that we identified in PDCD1. We show that one intronic SNP in PDCD1 is associated with development of SLE in Europeans (found in 12% of affected individuals versus 5% of controls; P = 0.00001, r.r. (relative risk) = 2.6) and Mexicans (found in 7% of affected individuals versus 2% of controls; P = 0.0009, r.r. = 3.5). The associated allele of this SNP alters a binding site for the runt-related transcription factor 1 (RUNX1, also called AML1) located in an intronic enhancer, suggesting a mechanism through which it can contribute to the development of SLE in humans.
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| 6. |
- Andersen, O., et al.
(författare)
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Electrical activity of carbon-hydrogen centers in Si
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:23, s. 235205-1
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Tidskriftsartikel (refereegranskat)abstract
- The electrical activity of Cs-H defects in Si has been investigated in a combined modeling and experimental study. High-resolution Laplace capacitance spectroscopy with the uniaxial stress technique has been used to measure the stress-energy tensor and the results are compared with theoretical modeling. At low temperatures, implanted H is trapped as a negative-U center with a donor level in the upper half of the gap. However, at higher temperatures, H migrates closer to the carbon impurity and the donor level falls, crossing the gap. At the same time, an acceptor level is introduced into the upper gap making the defect a positive-U center.
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| 7. |
- Andersen, O., et al.
(författare)
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Piezospectroscopic analysis of the hydrogen-carbon complexes in silicon
- 2001
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308, s. 139-142
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Tidskriftsartikel (refereegranskat)abstract
- We have observed the donor (Ec-0.22 eV) and acceptor (Ec-0.16 eV) levels related to hydrogen-carbon complexes in silicon. The donor level is only detected at low temperatures after proton implantation. This hydrogen-carbon complex irreversibly reconfigures at temperatures above 225 K to a configuration characterized by the acceptor level, which is stable up to room temperature. The same acceptor level is also observed after atomic hydrogen diffusion. We have used Laplace transform deep level transient spectroscopy (DLTS) to show the influence of uniaxial stress on the electron emission process and the effect of the stress-induced alignment for the acceptor state. The pattern of the Laplace DLTS peak splittings indicate a trigonal symmetry of the defect. First principles calculations were carried out on the hydrogen-carbon defects with a view of determining their electrical levels and stress response for comparison with the experimental results.
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| 8. |
- Andersson, B Erik, et al.
(författare)
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Incomplete degradation of polycyclic aromatic hydrocarbons in soil inoculated with wood-rotting fungi and their effect on the indigenous soil bacteria
- 2003
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Ingår i: Environmental Toxicology and Chemistry. ; 22:6, s. 1238-43
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Tidskriftsartikel (refereegranskat)abstract
- Soil artificially contaminated with fluorene, phenanthrene, pyrene, and benz[a]anthracene was inoculated with the wood-rotting fungi Pleurotus ostreatus and Antrodia vaillantii. During 12 weeks of incubation, polycyclic aromatic hydrocarbon (PAH) degradation and the formation of persistent degradation products were monitored by chemical analysis. In addition, the effect on the indigenous soil bacteria was studied by plate count techniques and by measuring the concentration of bacteria-specific phospholipid fatty acids (PLFAs). In both soils inoculated with fungi, the PAH degradation was enhanced compared to the control soil without fungi. The white-rot fungus P. ostreatus accelerated the degradation rate radically the first weeks, while the effect of the brown-rot fungus was more pronounced at later stages during the 12-week study. In a soil with no amendments, the final degradation result was similar to that in the soil with added fungi, although the degradation pattern for the individual PAHs was different. Furthermore, the degradation by P. ostreatus was accompanied by an accumulation of PAH metabolites, that is, 9-fluorenone, benz[a]anthracene-7,12-dione, and two compounds identified as 4-hydroxy-9-fluorenone and 4-oxapyrene-5-one, that was not seen in the other soils. The inoculation with the white-rot fungus also had a large negative effect on the indigenous soil bacteria. This could be an important drawback of using the white-rot fungus P. ostreatus in soil bioremediation since a sequential fungal–bacterial degradation probably is needed for a complete degradation of PAHs in soil. In the soil inoculated with A. vaillantii, on the other hand, no metabolites accumulated, and no negative effects were observed on the indigenous microorganisms.
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| 9. |
- Blumenau, AT, et al.
(författare)
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Dislocation structures in diamond : density-functional based modelling and high-resolution electron microscopy
- 2004
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Ingår i: Defect and Diffusion Forum. - Zürich : Trans Tech Publications. - 1012-0386 .- 1662-9507. ; 226-228, s. 11-30
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Tidskriftsartikel (refereegranskat)abstract
- The core structures of perfect 60 and edge dislocations in diamond are investigated atomistically in a density-functional based tight-binding approach, and their dissociation is discussed both in terms of structure and energy. Furthermore, high resolution electron microscopy is performed on dislocation cores in high-temperature, high-pressure annealed natural brown diamond, and HRTEM image simulation allows a comparison of theoretically predicted and experimentally observed structures.
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| 10. |
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