| 1. |
- Coutinho, J., et al.
(författare)
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Interstitial carbon-oxygen center and hydrogen related shallow thermal donors in Si
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 65:1, s. 014109-11
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Tidskriftsartikel (refereegranskat)abstract
- The interstitial carbon-oxygen defect is a prominent defect formed in e-irradiated Cz-Si containing carbon. Previous stress alignment investigations have shown that the oxygen atom weakly perturb the carbon interstitial but the lack of a high-frequency oxygen mode has been taken to imply that the oxygen atom is severely affected and becomes overcoordinated. Local vibrational mode spectroscopy and ab initio modeling are used to investigate the defect. We find new modes whose oxygen isotopic shifts give further evidence for oxygen overcoordination. Moreover, we find that the calculated stress-energy tensor and energy levels are in good agreement with experimental values. The complexes formed by adding both single (CiOiH) and a pair of H atoms (CiOiH2), as well as the addition of a second oxygen atom, are considered theoretically. It is shown that the first is bistable with a shallow donor and deep acceptor level, while the second is passive. The properties of CiOiH and CiO2iH are strikingly similar to the first two members of a family of shallow thermal donors that contain hydrogen.
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| 2. |
- Coutinho, J., et al.
(författare)
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Over-coordinated oxygen in the interstitial carbon-oxygen complex
- 2001
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308, s. 305-308
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Tidskriftsartikel (refereegranskat)abstract
- The interstitial carbon-oxygen complex is one of the most prominent defects formed in e-irradiated Cz-Si containing carbon. Stress alignment investigations have shown that the oxygen atom only perturbs the carbon interstitial but the lack of a high frequency oxygen mode has been taken to imply that the oxygen atom is over-coordinated. Local vibrational mode spectroscopy and ab initio modeling are used to investigate the defect. We find new modes whose oxygen isotopic shifts, along with the piezoscopic stress-energy tensor support the trivalent model, thus providing evidence for oxygen over-coordination.
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| 3. |
- Coutinho, J., et al.
(författare)
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Thermal double donors and quantum dots
- 2001
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 87:23, s. 235501-
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Tidskriftsartikel (refereegranskat)abstract
- Combined local mode spectroscopy and ab initio modeling are used to demonstrate for the first time that oxygen atoms in thermal double donors (TDD) in Si are in close proximity. The observed vibrational modes in 16O, 18O, and mixed isotopic samples are consistent with a model involving [110] aligned oxygen chains made up of an insulating core lying between electrically active ends. The model also explains the minute spin density observed on oxygen in TDD+ as well as the piezospectroscopic tensors of the donors. The analogy between the thermal donors and quantum dots is emphasized.
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| 4. |
- Markevich, V. P., et al.
(författare)
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Observation and theory of the V-O-H2 complex in silicon
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:19, s. 12964-12969
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of hydrogen with radiation-induced defects (RD's) in Czochralski-grown silicon crystals has been studied by infrared-absorption spectroscopy and ab initio modeling. Hydrogen and/or deuterium was introduced into the crystals by indiffusion from H2 (D2) gas at 1200-1300 °C. The samples were subsequently irradiated with fast electrons (E=2-4 MeV) and annealed in the temperature range of 100-600 °C. The centers produced by the irradiation were the same in both the untreated and treated cases, namely the A-center, Ci-Oi complex, and divacancy. A heat treatment of the H-treated samples resulted in the enhanced loss of these centers and the formation of centers containing hydrogen. The disappearance of the A centers in the temperature range of 100-150 °C is correlated with the appearance of three local vibrational modes (LVM's) at 943.5, 2126.4, and 2151.5 cm-1. The isotopic shifts of these lines were obtained from measurements on the samples doped with hydrogen and deuterium. The lines are identified as related to stretching vibrational modes of a complex that consists of one oxygen and two hydrogen atoms sharing a vacancy site (V-O-H2 complex). Ab initio calculations are used to explore the structures and properties of this defect. The origin of other LVM bands, which were observed upon annealing, is discussed.
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| 5. |
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| 6. |
- Murin, L.I., et al.
(författare)
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Isotopic effects on vibrational modes of thermal double donors in Si and Ge
- 2001
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308-310, s. 290-293
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Tidskriftsartikel (refereegranskat)abstract
- The local vibrational modes of thermal double donors in Si and Ge are investigated by FTIR and ab initio modelling. At most, two oxygen modes are detected from each donor, which exhibit regular shifts with increasing donor number. By using mixtures of 16O and 18O, it is found that in Si the upper band does not yield any new modes suggesting that any oxygen atom is decoupled from any other. However, the lower frequency bands exhibit unique mixed modes proving for the first time that oxygen atoms are coupled together and in close spatial proximity. Ab initio calculations demonstrate that the modes and their isotopic shifts are consistent with a model involving two parallel chains of oxygen atoms linking second neighbour Si atoms, terminated by O-atoms close to the normal position for interstitial O. © 2001 Elsevier Science B.V. All rights reserved.
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| 7. |
- Clanet, M, et al.
(författare)
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A randomized, double-blind, dose-comparison study of weekly interferon beta-1a in relapsing MS
- 2002
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Ingår i: Neurology. - 1526-632X. ; 59:10, s. 1507-1517
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Tidskriftsartikel (refereegranskat)abstract
- Background: Interferon beta-1a (IFNbeta-1a; Avonex) is effective for the treatment of relapsing MS; however, the optimal dose of IFNbeta-1a is not known. Objective: To determine whether IFNbeta-1a 60 mug IM once weekly is more effective than IFNbeta-1a 30 mug IM once weekly in reducing disability progression in relapsing MS. Methods: In a double-blind, parallel-group, dose-comparison study, 802 patients with relapsing MS from 38 centers in Europe were randomized to IFNbeta-1a 30 mug (n = 402) or 60 mug (n = 400) IM once weekly for greater than or equal to36 months. The primary endpoint was disability progression, defined as time to a sustained increase of greater than or equal to1.0 point on the Expanded Disability Status Scale (EDSS) persisting for 6 months. Additional endpoints included relapses, MRI, safety, immunogenicity, and subgroup analyses of disability progression. Results: Both groups showed equal rates of disability progression (hazard ratio, 0.96; 95% CI, 0.77 to 1.20; p = 0.73). In both groups the proportion of subjects with progression of disability by 36 months estimated from Kaplan-Meier curves was 37%. No dose effects were observed on any of the secondary clinical endpoints. Only one MRI measure at one time point, number of new or enlarging T2 lesions at month 36 compared with month 24, showed a difference favoring the 60-mug dose. Both doses were well tolerated; however, slightly higher incidences of flulike symptoms and muscle weakness were observed in the 60-mug group. The incidences of neutralizing antibodies (titers greater than or equal to20) were 2.3% in the 30-mug group and 5.8% in the 60-mug group. Conclusion: There was no difference between IFNbeta-1a 30 mug and 60 mug IM in clinical or MRI measures.
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| 8. |
- Coutinho, J., et al.
(författare)
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Effect of stress on the energy levels of the vacancy-oxygen-hydrogen complex in Si
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:18, s. 184106-1
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Tidskriftsartikel (refereegranskat)abstract
- The piezospectroscopic properties of the VOH defect in Si are found using stress Laplace deep level transient spectroscopy (DLTS) and are compared with local density-functional calculations of (i) the acceptor level and its shift under stress, and (ii) the alignment of the neutral center under stress. The theory is able to account for two acceptor levels observed for 〈100〉, 〈111〉, and 〈110〉 stress even though additional splitting is expected for a defect with static C1h symmetry. This is related to (i) a rapid reorientation of the H atom within the defect at temperatures at which the DLTS experiments are carried out, and (ii) the small effect of stress on two orientations of the defect under 〈110〉 stress. The theory is also able to give a quantitative account of the alignment of the center. The effect of stress on the reorientation barrier of the defect is also investigated. The reorientation barrier of the defect in its positive charge state is found theoretically to be very small, consistent with the lack of any splitting in the donor level under stress.
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| 9. |
- Markevich, V.P., et al.
(författare)
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Electronic properties of vacancy-oxygen complexes in SiGe alloys
- 2003
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Ingår i: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 340, s. 790-4
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Tidskriftsartikel (refereegranskat)abstract
- Capacitance transient techniques, combined with ab initio modeling, were employed to study the electronic properties and structure of vacancy-oxygen (VO) complexes in unstrained Czochralski-grown Si1-xGex crystals (0
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