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- Aavikko, R., et al.
(författare)
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Clustering of vacancy defects in high-purity semi-insulating SiC
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:8, s. 085208-
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Tidskriftsartikel (refereegranskat)abstract
- Positron lifetime spectroscopy was used to study native vacancy defects in semi-insulating silicon carbide. The material is shown to contain (i) vacancy clusters consisting of four to five missing atoms and (ii) Si-vacancy-related negatively charged defects. The total open volume bound to the clusters anticorrelates with the electrical resistivity in both as-grown and annealed materials. Our results suggest that Si-vacancy-related complexes electrically compensate the as-grown material, but migrate to increase the size of the clusters during annealing, leading to loss of resistivity. © 2007 The American Physical Society.
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| 4. |
- Dekker, Joost, et al.
(författare)
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Definition and Characteristics of Behavioral Medicine, and Main Tasks and Goals of the International Society of Behavioral Medicine : an International Delphi Study
- 2021
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Ingår i: International Journal of Behavioral Medicine. - New York : Springer. - 1070-5503 .- 1532-7558. ; 28:3, s. 268-276
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Tidskriftsartikel (refereegranskat)abstract
- Background: In the past decades, behavioral medicine has attained global recognition. Due to its global reach, a critical need has emerged to consider whether the original definition of behavioral medicine is still valid, comprehensive, and inclusive, and to reconsider the main tasks and goals of the International Society of Behavioral Medicine (ISBM), as the umbrella organization in the field. The purpose of the present study was to (i) update the definition and scope of behavioral medicine and its defining characteristics; and (ii) develop a proposal on ISBM's main tasks and goals.Method: Our study used the Delphi method. A core group prepared a discussion paper. An international Delphi panel rated questions and provided comments. The panel intended to reach an a priori defined level of consensus (i.e., 70%).Results: The international panel reached consensus on an updated definition and scope of behavioral medicine as a field of research and practice that builds on collaboration among multiple disciplines. These disciplines are concerned with development and application of behavioral and biomedical evidence across the disease continuum in clinical and public health domains. Consensus was reached on a proposal for ISBM's main tasks and goals focused on supporting communication and collaboration across disciplines and participating organizations; stimulating research, education, and practice; and supporting individuals and organizations in the field.Conclusion: The consensus on definition and scope of behavioral medicine and ISBM's tasks and goals provides a foundational step toward achieving these goals.
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- Gogova, D., et al.
(författare)
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Investigation of the structural and optical properties of free-standing GaN grown by HVPE
- 2005
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 38:14, s. 2332-2337
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Tidskriftsartikel (refereegranskat)abstract
- The potential of the high-growth rate hydride vapour phase epitaxy technique and laser lift-off for the fabrication of free-standing GaN substrates is explored. Structural and optical properties of 300 νm thick free-standing GaN have been investigated employing different analytical techniques. The x-ray diffraction (XRD) measurements prove good crystalline quality of the material grown. A comparatively low value of (3 ± 1) × 1016 cm-3 of Ga vacancy-related defects is inferred from positron annihilation spectroscopy data. Complete strain relaxation is observed on the Ga-polar face of the free-standing GaN by XRD and Raman spectroscopy measurements. The strain-free homoepitaxy will significantly reduce the defect density, and thus an improvement of the device performance and lifetime can be realized. © 2005 IOP Publishing Ltd.
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| 6. |
- Gogova, Daniela, et al.
(författare)
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Optical and structural characteristics of virtually unstrained bulk-like GaN
- 2004
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Ingår i: Japanese Journal of Applied Physics. - 0021-4922 .- 1347-4065. ; 43:4A, s. 1264-1268
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Tidskriftsartikel (refereegranskat)abstract
- Bulk-like GaN with high structural and optical quality has been attained by hydride vapor-phase exitapy (HVPE). The as-grown 330 mum-thick GaN layer was separated from the sapphire substrate by a laser-induced lift-off process. The full width at half maximum values of the X-ray diffraction (XRD) omega-scans of the free-standing material are 96 and 129 arcsec for the (1 0 -1 4) and (0 0 0 2) reflection, respectively, which rank among the smallest values published so far for free-standing HVPE-GaN. The dislocation density determined by plan-view TEM images is 1-2 x 10(7) cm(-2). Positron annihilation spectroscopy studies show that the concentration of Ga vacancy related defects is about 1.5 x 10(16) cm(-3). The high-resolution XRD, photoluminescence, mu-Raman, and infrared spectroscopic ellipsometry measurements consistently prove that the free-standing material is of high crystalline quality and virtually strain-free. Therefore it is suitable to serve as a substrate for stress-free growth of high-quality III-nitrides based device heterostructures.
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| 7. |
- Gogova, D., et al.
(författare)
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Optical and structural studies of high-quality bulk-like GaN grown by HVPE on a MOVPE AlN buffer layer
- 2006
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 21:5, s. 702-708
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Tidskriftsartikel (refereegranskat)abstract
- High-quality 400 ?m thick GaN has been grown by hydride vapour phase epitaxy (HVPE) on (0 0 0 1) sapphire with a 2 ?m thick AlN buffer layer. The material's crystalline quality and homogeneity was verified by x-ray diffraction (XRD), low-temperature photoluminesence (LT-PL) and LT cathodoluminescence. Plan-view transmission electron microscopy images reveal a low dislocation density of ~1.25 × 107 cm-2. The residual stress of the material was studied by two complementary techniques. LT-PL spectra show the main neutral donor bound exciton line at 3.4720 eV. This line position suggests virtually strain-free material with a high crystalline quality as indicated by the small full width at half maximum value of 0.78 meV. The presence of well resolved A- and B-free excitons in the LT-PL spectra and the absence of a yellow luminescence band prove the high quality of the HVPE-GaN in terms of purity and crystallinity. These findings are consistent with the XRD results, implying the high crystalline quality of the material grown. Hence, the material studied is well suited as a lattice parameter and thermal-expansion- coefficient matched substrate for further homoepitaxy, as needed for high-quality III-nitride device applications. Strain-free homoepitaxy on native substrates is needed to decrease considerably the defect density and in that way an improvement of the device's performance and lifetime can be achieved. © 2006 IOP Publishing Ltd.
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| 8. |
- Gogova, Daniela, 1967-, et al.
(författare)
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Strain-free bulk-like GaN grown by hydride-vapor-phase-epitaxy on two-step epitaxial lateral overgrown GaN template
- 2004
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 96:1, s. 799-806
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Tidskriftsartikel (refereegranskat)abstract
- Crack-free bulk-like GaN with high crystalline quality has been obtained by hydride-vapor-phase-epitaxy (HVPE) growth on a two-step epitaxial lateral overgrown GaN template on sapphire. During the cooling down stage, the as-grown 270-μm-thick GaN layer was self-separated from the sapphire substrate. Plan-view transmission electron microscopy images show the dislocation density of the free-standing HVPE-GaN to be ∼2.5×107 cm−2 on the Ga-polar face. A low Ga vacancy related defect concentration of about 8×1015 cm−3 is extracted from positron annihilation spectroscopy data. The residual stress and the crystalline quality of the material are studied by two complementary techniques. Low-temperature photoluminescence spectra show the main neutral donor bound exciton line to be composed of a doublet structure at 3.4715 (3.4712) eV and 3.4721 (3.4718) eV for the Ga- (N-) polar face with the higher-energy component dominating. These line positions suggest virtually strain-free material on both surfaces with high crystalline quality as indicated by the small full width at half maximum values of the donor bound exciton lines. The E1(TO) phonon mode position measured at 558.52 cm−1 (Ga face) by infrared spectroscopic ellipsometry confirms the small residual stress in the material, which is hence well suited to act as a lattice-constant and thermal-expansion-coefficient matched substrate for further homoepitaxy, as needed for high-quality III-nitride device applications. © 2004 American Institute of Physics.
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- Insulander Björk, Klara L, 1982, et al.
(författare)
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Commercial thorium fuel manufacture and irradiation: Testing (Th,Pu)O-2 and (Th,U)O-2 in the "Seven-Thirty" program
- 2015
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 75, s. 79-86
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Tidskriftsartikel (refereegranskat)abstract
- Thorium based fuels are being tested in the Halden Research Reactor in Norway with the aim of producing the data necessary for licensing of these fuels in today's light water reactors. The fuel types currently under irradiation are thorium oxide fuel with plutonium as the fissile component, and uranium fuel with thorium as an additive for enhancement of thermo-mechanical and neutronic fuel properties. Fuel temperatures, rod pressures and dimensional changes are monitored on-line for quantification of thermo-mechanical behavior and fission gas release. Preliminary irradiation results show benefits in terms of lower fuel temperatures, mainly caused by improved thermal conductivity of the thorium fuels. In parallel with the irradiation, a manufacturing procedure for thorium-plutonium mixed oxide fuel is developed with the aim to manufacture industrially relevant high-quality fuel pellets for the next phase of the irradiation campaign.
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| 10. |
- Insulander Björk, Klara L, 1982, et al.
(författare)
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Irradiation testing of enhanced uranium oxide fuels
- 2019
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 125, s. 99-106
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Tidskriftsartikel (refereegranskat)abstract
- Enhanced uranium oxide fuel types are being tested in the Halden Research Reactor in Norway with the aim is to assess the effect that these enhancements have on fuel performance. Fuel temperatures, rod pressures and dimensional changes are being monitored online and an extensive post-irradiation examination programme is planned. Preliminary data show that fuel centerline temperatures can be lowered by addition of ThO2 to the fuel matrix, or by incorporating Cr or SiO2-TiO2 as a network structure within the fuel. In parallel, two types of cladding coatings are tested in order to investigate their in-core properties. No abnormal behaviour has been noted during the first 100 days of irradiation.
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