| 1. |
- Emmoth, Birger, et al.
(author)
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In-situ measurements of carbon and deuterium deposition using the fast reciprocating probe in TEXTOR
- 2009
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In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 390-91, s. 179-182
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Journal article (peer-reviewed)abstract
- Silicon samples were exposed in the scrape-off layer of the TEXTOR plasma using a fast reciprocating probe, with the aim of studying carbon deposition and deuterium retention during Dynamic Ergodic Divertor (DED) operation. Separate samples were exposed for 300 ms at the flat-top phase of neutral beam heated discharges. The exposure conditions were varied on a shot-to-shot basis by external magnetic perturbations generated by the DED in the m/n = 3/1, DC regime, base configuration. Nuclear Reaction Analysis (NRA) was used to characterise collector sample surfaces after their exposure. Enhanced concentrations of both carbon and deuterium (C 3-10 x 10(16) at./cm(2), D 8-60 x 10(15) at./cm(2)) were found. The D/C ratio was less than unity which indicates that most of the carbon and deuterium were co-deposited. Carbon e-folding lengths of about 2 cm were found on both toroidal sides of the probe independent of DED perturbations.
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| 2. |
- Alfieri, G., et al.
(author)
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Defect energy levels in hydrogen-implanted and electron-irradiated n-type 4H silicon carbide
- 2005
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 98:11
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Journal article (peer-reviewed)abstract
- Using deep level transient spectroscopy (DLTS), we have studied the energy position and thermal stability of deep levels in nitrogen doped 4H-SiC epitaxial layers after 1.2 MeV proton implantation and 15 MeV electron irradiation. Isochronal annealing was performed at temperatures from 100 to 1200 degrees C in steps of 50 degrees C. The DLTS measurements, which were carried out in the temperature range from 120 to 630 K after each annealing step, reveal the presence of ten electron traps located in the energy range of 0.45-1.6 eV below the conduction band edge (E-c). Of these ten levels, three traps at 0.69, 0.73, and 1.03 eV below E-c, respectively, are observed only after proton implantation. Dose dependence and depth profiling studies of these levels have been performed. Comparing the experimental data with computer simulations of the implantation and defects profiles, it is suggested that these three new levels, not previously reported in the literature, are hydrogen related. In particular, the E-c-0.73 eV level displays a very narrow depth distribution, confined within the implantation profile, and it originates most likely from a defect involving only one H atom.
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| 3. |
- Borseth, T. M., et al.
(author)
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Annealing study of Sb+ and Al+ ion-implanted ZnO
- 2005
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In: Superlattices and Microstructures. - : Elsevier BV. - 0749-6036 .- 1096-3677. ; 38:4-6, s. 464-471
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Journal article (peer-reviewed)abstract
- In this work we have studied diffusion and electrical activation in Al+ and Sb+ implanted ZnO samples using secondary ion mass spectrometry (SIMS), scanning spreading resistance microscopy (SSRM) and scanning capacitance microscopy (SCM). The samples were hydrothermally grown and post-implant annealing was performed at 800, 900 and 1000 degrees C in pure oxygen atmosphere, After each annealing step the samples were characterized with SSRM/SCM and SIMS. The thermal treatments did not induce any significant impurity redistribution as measured by SIMS, while electrical compensation is observed by SSRM/SCM for the Sb-implanted sample yielding less n-doping than in the as-grown samples. In the Al-implanted samples, an increase in carrier concentration is observed; we ascribe this to Al-related donors and possibly interstitial lithium, a common residual impurity in the samples that have been shown to be very mobile by SIMS.
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| 4. |
- Covacu, Ruxandra, et al.
(author)
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Nitric oxide exposure diverts neural stem cell fate from neurogenesis towards astrogliogenesis
- 2006
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In: Stem Cells. - : Oxford University Press (OUP). - 1066-5099 .- 1549-4918. ; 178, s. 268-268
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Journal article (other academic/artistic)abstract
- Regeneration of cells in the central nervous system is a process that might be affected during neurological disease and trauma. Because nitric oxide (NO) and its derivatives are powerful mediators in the inflammatory cascade, we have investigated the effects of pathophysiological concentrations of NO on neurogenesis, gliogenesis, and the expression of proneural genes in primary adult neural stem cell cultures. After exposure to NO, neurogenesis was downregulated, and this corresponded to decreased expression of the proneural gene neurogenin-2 and beta-III-tubulin. The decreased ability to generate neurons was also found to be transmitted to the progeny of the cells. NO exposure was instead beneficial for astroglial differentiation, which was confirmed by increased activation of the Janus tyrosine kinase/signal transducer and activator of transcription transduction pathway. Our findings reveal a new role for NO during neuroinflammatory conditions, whereby its proastroglial fate-determining effect on neural stem cells might directly influence the neuroregenerative process.
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| 5. |
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| 6. |
- Slotte, J., et al.
(author)
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Fluence, flux, and implantation temperature dependence of ion-implantation-induced defect production in 4H-SiC
- 2005
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 97:3
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Journal article (peer-reviewed)abstract
- Vacancy-type defect production in Al- and Si-implanted 4H-SiC has been studied as a function of ion fluence, ion flux, and implantation temperature in the projected ion range region by positron annihilation spectroscopy and Rutherford backscattering techniques. Ion channeling measurements show that the concentration of displaced silicon atoms increases rapidly with increasing ion fluence. In the ion fluence interval of 10(13)-10(14) cm(-2) the positron annihilation parameters are roughly constant at a defect level tentatively associated with the divacancy VCVSi. Above the ion fluence of 10(14) cm(-2) larger vacancy clusters are formed. For implantations as a function of ion flux (cm(-2) s(-1)), ion channeling and positron annihilation measurements behave similarly, i.e., indicating increasing damage in the projected range region with increasing ion flux. However, for samples implanted at different temperatures the positron annihilation parameter S shows a clear minimum at approximately 100 degreesC, whereas the normalized backscattering yield decrease continuously with increasing implantation temperature. This is explained by the formation of larger vacancy clusters when the implantation temperature is increased.
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| 7. |
- Svensson, B.G., et al.
(author)
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Ion implantation processing and related effects in SiC
- 2006
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In: Silicon Carbide and Related Materials 2005, Pts 1 and 2. - 9780878494255 ; , s. 781-786
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Conference paper (peer-reviewed)abstract
- A brief survey is given of some recent progress regarding ion implantation processing and related effects in 4H- and 6H-SiC. Four topics are discussed; an empirical ion range distribution simulator, dynamic defect annealing during implantation, formation of highly p(+)-doped layers, and deactivation of N donors by ion-induced defects.
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| 8. |
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| 9. |
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| 10. |
- Vines, L., et al.
(author)
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Scanning probe microscopy of single Au ion implants in Si
- 2006
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In: Materials science & engineering. C, biomimetic materials, sensors and systems. - : Elsevier BV. - 0928-4931 .- 1873-0191. ; 26:07-maj, s. 782-787
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Journal article (peer-reviewed)abstract
- We have studied 5 MeV Au2+ ion implantation with fluences between 7 x 10(7) and 2 x 10(8) cm(-2) in Si by deep level transient spectroscopy (DLTS) and scanning capacitance microscopy (SCM). The DLTS measurements show formation of electrically active defects such as the two negative charge states of the divacancy (V-2(=/-) and V-2(-/0)) and the vacancy-oxygen (VO) center. It is observed that the intensity of the V-2(=/-) peak is lower compared to that of V-2(-/0) by a factor of 5. This has been attributed to a highly localized distribution of the defects along the ion tracks, which results in trapping of the carriers at V-2(-/0) and incomplete occupancy of V-2(=/-). The SCM measurements obtained in a plan view show a random pattern of regions with a reduced SCM signal for the samples implanted with fluence above 2 x 10(8) cm(-2). The reduced SCM signal is attributed to extra charges associated with acceptor states, such as V-2(-/0), formed along the ion tracks in the bulk Si. Indeed, the electron emission rate from the V-2(-/0) state is in the range of 10 kHz at room temperature, which is well below the probing frequency of the SCM measurements, resulting in freezing of electrons at V-2(-/0).
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| 11. |
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| 12. |
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| 13. |
- Vines, L., et al.
(author)
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Visualization of MeV ion impacts in Si using scanning capacitance microscopy
- 2006
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:8
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Journal article (peer-reviewed)abstract
- Scanning capacitance microscopy (SCM) of 3 MeV Au2+ ion implanted Si have been performed for doses between 2x10(8) and 5x10(9) cm(-2). The measurements show a random pattern of reduced SCM signal (charge trapping) correlated with the ion impacts. These features have a lateral dimension of 150-600 nm and reveal a pronounced dose dependence. It is argued that the Fermi level near the impacts and along the ion tracks is modified (pinned) due to deep acceptor states formed by the penetrating ions. Substantial evidence for this argument is provided by SCM images obtained at different temperatures, where a strong correlation is revealed between the probing frequency and the emission rate of the single negative acceptor level of divacancy. To the best of our knowledge, this is a direct observation of signatures for individual ion impacts in Si by an electrical scanning technique.
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| 14. |
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| 15. |
- Wong-Leung, J., et al.
(author)
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Ion implantation in 4H-SiC
- 2008
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In: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 266:8, s. 1367-1372
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Journal article (peer-reviewed)abstract
- Silicon carbide offers unique applications as a wide bandgap semiconductor. This paper reviews various aspects of ion implantation in 4H-SiC studied with a view to optimise ion implantation in silicon carbide. Al, P and Si ions with keV energies were used. Channelling effects were studied in both a-axis and c-axis crystals as a function of tilts along major orthogonal planes and off the major orthogonal planes. Major axes such as [0 0 0 1] and the [ 1 1 (2) over bar 0] and minor axis like the [1 1 (2) over bar 3] showed long channelling tails and optimum tilts for minimising channelling are recommended. TEM analyses of the samples showed the formation of (0 0 0 1) prismatic loops and the (1 1 (2) over bar 0) loops as well,in both a and c-cut crystals. We also note the presence of voids only in P implanted samples implanted with amorphising doses. The competing process between damage accumulation and dynamic annealing was studied by determining the critical temperature for the transition between crystalline and amorphous SiC and an activation energy of 1.3 eV is extracted.
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