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| 2. |
- Hosia, W., et al.
(författare)
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Folding into a ß-Hairpin Can Prevent Amyloid Fibril-Formation
- 2004
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 43:16, s. 4655-4661
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Tidskriftsartikel (refereegranskat)abstract
- The tetrapeptide KFFE is one of the shortest amyloid fibril-forming peptides described. Herein, we have investigated how the structural environment of this motif affects polymerization. Using a turn motif (YNGK) or a less rigid sequence (AAAK) to fuse two KFFE tetrapeptides, we show by several biophysical methods that the amyloidogenic properties are strongly dependent on the structural environment. The dodecapeptide KFFEAAAKKFFE forms abundant thick fibril bundles. Freshly dissolved KFFEAAAKKFFE is monomeric and shows mainly disordered secondary structure, as evidenced by circular dichroism, NMR spectroscopy, hydrogen/deuterium exchange measurements, and molecular modeling studies. In sharp contrast, the dodecapeptide KFFEYNGKKFFE does not form fibrils but folds into a stable ß-hairpin. This structure can oligomerize into a stable 12-mer and multiples thereof, as shown by size exclusion chromatography, sedimentation analysis, and electrospray mass spectrometry. These data indicate that the structural context in which a potential fibril forming sequence is present can prevent fibril formation by favoring self-limiting oligomerization over polymerization.
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| 3. |
- Morvan, E, et al.
(författare)
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Damage reduction in channeled ion implanted 6H-SiC
- 2000
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Ingår i: SILICON CARBIDE AND RELATED MATERIALS - 1999 PTS, 1 & 2. ; , s. 893-896
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Konferensbidrag (refereegranskat)abstract
- We compare damage effects of “random” (off-axis) and [0001] aligned implants of 1.5 MeV Al into 6H-SiC. Both channeled and random equivalent SIMS profiles have been used to adjust model parameters of the simulator. Depth resolved Raman measurements show that at ion doses below similar to 5x10(14) cm(-2), the integral damage is reduced by a factor of similar to2.5 for the channeled implant. This confirms the corresponding reduction of defect concentrations predicted by simulations.
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| 4. |
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| 5. |
- Zimmermann, U, et al.
(författare)
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Electrical characterization of high-voltage 4H-SiC diodes on high-temperature CVD-grown epitaxial layers
- 2002
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Ingår i: Materials Science Forum, Vols. 389-393. ; , s. 1285-1288
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Konferensbidrag (refereegranskat)abstract
- High-temperature chemical vapour deposition (HTCVD) in a vertical chimney reactor was used to grow thick low-doped epitaxial layers of 4H silicon carbide. These layers were used as drift layers in a combined process to manufacture both bipolar and unipolar high-voltage diodes. The resulting diodes were characterized electrically in order to gain knowledge about the electric quality of the HTCVD epitaxial layers to assess the high-voltage properties of this material.
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| 6. |
- Bratus, V. Y., et al.
(författare)
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Vacancy-related defects in ion-beam and electron irradiated 6H-SiC
- 2001
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 184:04-jan, s. 229-236
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Tidskriftsartikel (refereegranskat)abstract
- A brief review is given on EPR study of irradiation-induced defects in SiC. The results of low-temperature study of Ky1 and Ky2 centers reveal for both of them the C-S symmetry, spin S = 1/2 and close coincidence of the g-tensor components. For Ky2 defect the principal values of g-tensor have been determined as g(z) = 2.0048, g(x) = 2.0022 and g(y) = 2.0037, where z and x directions reside in the (11 (2) over bar0) plane and the z-axis makes up an angle 65 degrees with the c-axis. The same residence of z- and x-axis and an angle 59 degrees are found for Ky1 center, g(z) = 2.0058, g(x) = 2.0025 and g(y) = 2.0023. A comparison of experimental and calculated hyperfine (HF) parameters is presented which suggests that Ky2 and Ky1 defects can be assigned to the positively charged carbon vacancy in 6H-SiC. The EPR study of defects created along the Al+ ion track in n-type 6H-SiC shows that lineshape, linewidth and integral intensity of the EPR signal reflect the state of damaged layer generated by ion implantation. A variation of defect density with annealing is reported and defect origin is discussed.
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| 7. |
- David, M. L., et al.
(författare)
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Electrically active defects in irradiated 4H-SiC
- 2004
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 95:9, s. 4728-4733
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Tidskriftsartikel (refereegranskat)abstract
- 4H-SiC epilayers were irradiated with either protons or electrons and electrically active defects were studied by means of deep level transient spectroscopy. Motion of defects has been found to occur at temperature as low as 350-400 K. Indeed, the application of an electric field has been found to enhance modifications in defect concentrations that can also occur during long time annealing at elevated temperature. Two levels have been revealed and labeled B and M. Two other levels, referred to as S-1 and S-2 and located at 0.40 and 0.71 eV below the conduction band edge have been studied in detail (capture cross sections, profiling, formation energy, activation energy during annealing). The S-1 and S-2 levels have been found to exhibit a one to one relation and are proposed to be two charge states of the same acceptor center, labeled the S center.
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