| 1. |
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| 2. |
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| 3. |
- 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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| 5. |
- 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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| 9. |
- 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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| 11. |
- Kilpelainen, S., et al.
(författare)
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Stabilization of Ge-rich defect complexes originating from E centers in Si(1-x)Ge(x):P
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:13, s. 132103-
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Tidskriftsartikel (refereegranskat)abstract
- Thermal evolution of vacancy complexes was studied in P-doped ([P] = 10(18) cm(-3)) proton irradiated Si(1-x)Ge(x) with Ge contents of 10%, 20%, and 30% in the range of 250-350 degrees C using positron annihilation spectroscopy. The radiation damage recovers in the course of anneals but the final state differs from that in as-grown samples indicating the presence of small Ge clusters in the samples, contrary to the initially random Ge distribution. The activation energy for the annealing process was estimated to be 1.4+/-0.3 eV and attributed to the dissociation energy of the vacancy-phosphorus-germanium (V-P-Ge) complex.
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| 12. |
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| 13. |
- Koskelo, O., et al.
(författare)
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The effect of a material growth technique on ion-implanted Mn diffusion in GaAs
- 2009
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Ingår i: Semiconductor Science and Technology. - : IOP Publishing. - 0268-1242 .- 1361-6641. ; 24:4
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion of ion-implanted Mn in semi-insulating (SI) and liquid encapsulated Czochralski (LEC)-grown GaAs has been determined employing the modified radiotracer technique. The effect of the growth technique and conditions on Mn diffusion in low temperature molecular beam epitaxy (LT-MBE)-grown GaAs has also been studied. Two distinct diffusion components appear in ion-implanted Mn diffusion in GaAs: slow and fast. As the diffusivity for the SI material is slightly higher than that for the LT-grown material, it is observed that the diffusivity of the fast component retards with increasing initial concentrations of Ga sublattice defects. At the same time the Mn concentration in the tail part of the diffusion profile is higher in the LT-grown material. Ga vacancy-assisted clustering of Mn is proposed as a likely reason for the observed effects.
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| 14. |
- Monemar, Bo, 1942-, et al.
(författare)
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Dominant shallow acceptor related to oxygen and hydrogen in GaN
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 376-377, s. 440-443
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Tidskriftsartikel (refereegranskat)abstract
- We present new photoluminescence (PL) data of deliberately O-doped and Mg-doped GaN layers grown by MOCVD. The combination of these data with positron annihilation spectroscopy (PAS) and SIMS results obtained on the same samples shows a clear correlation of the PL intensity of the acceptor related emissions at 3.466 and 3.27 eV (at 2 K) with O doping. The acceptor is stable upon annealing in N-2 in our highly resistive samples, while it is known be unstable in p-GaN. Our tentative conclusion is that this very commonly occurring acceptor is either a V-Ga-O-H complex or a second configuration of the Mg acceptor containing H.
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| 15. |
- Monemar, Bo, 1942-, et al.
(författare)
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Oxygen related shallow acceptor in GaN
- 2005
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Ingår i: MRS Fall Meeting,2004. - : Materials Research Society. ; , s. E5.10.11-E5.10.11
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 16. |
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| 17. |
- Segercrantz, N., et al.
(författare)
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Defect studies in MBE grown GaSb1-x Bi x layers
- 2014
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Ingår i: AIP Conference Proceedings. - : AIP Publishing LLC. - 1551-7616 .- 0094-243X. ; 1583, s. 174-177
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Konferensbidrag (refereegranskat)abstract
- Positron annihilation spectroscopy in Doppler broadening mode is used to study epitaxial layers of GaSb 1-x Bi x on undoped GaSb. The samples were grown by Molecular Beam Epitaxy at different temperatures and with different Bi/Sb beam equivalent pressure ratios resulting in Bi concentrations of 0-0.7 %. The results show a relationship between the growth parameters and Doppler broadening parameters. Incorporating Bi into GaSb decreases the vacancy concentration in the epitaxial layers compared to the sample with no Bi in the epitaxial layer.
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| 18. |
- Segercrantz, N, et al.
(författare)
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Defect studies in MBE grown GaSbBi layers
- 2013
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Ingår i: 27th International Conference on Defects in Semiconductors 2013, Bologna, Italy, 2013.
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Konferensbidrag (refereegranskat)
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| 19. |
- Segercrantz, N., et al.
(författare)
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Point defect balance in epitaxial GaSb
- 2014
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:8, s. art. no. 082113-
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Tidskriftsartikel (refereegranskat)abstract
- Positron annihilation spectroscopy in both conventional and coincidence Doppler broadening mode is used for studying the effect of growth conditions on the point defect balance in GaSb:Bi epitaxial layers grown by molecular beam epitaxy. Positron annihilation characteristics in GaSb are also calculated using density functional theory and compared to experimental results. We conclude that while the main positron trapping defect in bulk samples is the Ga antisite, the Ga vacancy is the most prominent trap in the samples grown by molecular beam epitaxy. The results suggest that the p–type conductivity is caused by different defects in GaSb grown with different methods.
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| 20. |
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| 21. |
- Tengborn, Elisabeth, 1978, et al.
(författare)
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Effect of the misorientation of the 4H-SiC substrate on the open volume defects in GaN grown by metal-organic chemical vapor deposition
- 2006
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Ingår i: Applied Physics Letters. ; 89:091905, s. 3-
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Tidskriftsartikel (refereegranskat)abstract
- Positron annihilation spectroscopy has been used to study GaN grown by metal-organic chemical vapor deposition on misoriented 4H-SiC substrates. Two kinds of vacancy defects are observed: Ga vacancies and larger vacancy clusters in all the studied layers. In addition to vacancies, positrons annihilate at shallow traps that are likely to be dislocations. The results show that the vacancy concentration increases and the shallow positron trap concentration decreases with the increasing substrate misorientation.
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| 22. |
- Tuomisto, F., et al.
(författare)
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Defect distribution in a-plane GaN on Al2 O3
- 2007
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 90:12
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Tidskriftsartikel (refereegranskat)abstract
- The authors studied the structural and point defect distributions of hydride vapor phase epitaxial GaN film grown in the [11-20] a direction on (1-102) r -plane sapphire with metal-organic vapor phase deposited a-GaN template using transmission electron microscopy, secondary ion mass spectrometry, and positron annihilation spectroscopy. Grown-in extended and point defects show constant behavior as a function of thickness, contrary to the strong nonuniform defect distribution observed in GaN grown along the [0001] direction. The observed differences are explained by orientation-dependent and kinetics related defect incorporation. © 2007 American Institute of Physics.
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| 23. |
- Tuomisto, F, et al.
(författare)
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Dissociation of V-Ga-O-N complexes in HVPE GaN by high pressure and high temperature annealing
- 2006
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 243:7, s. 1436-1440
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Tidskriftsartikel (refereegranskat)abstract
- We have used positron annihilation spectroscopy to study the high-pressure annealing induced thermal recovery of vacancy defects in free-standing GaN grown by hydride vapor phase epitaxy (HYPE). The results show that the in-grown Ga vacancy complexes recover after annealing at 1500-1700 K. Comparison of the experimental positron data with ab-initio calculations indicates that the Doppler broadening measurement of the electron momentum distribution is sensitive enough to distinguish between the N and O atoms surrounding the Ga vacancy. We show that the difference between the isolated V-Ga in electron irradiated GaN and the V-Ga-O-N complexes in highly O-doped GaN is clear, and the Ga vacancy related defect complexes that start dissociating at 1500 K can be identified as V-Ga-O-N pairs.
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| 24. |
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| 25. |
- Tuomisto, F, et al.
(författare)
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Ga sublattice defects in (Ga,Mn)As: Thermodynamical and kinetic trends
- 2004
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Ingår i: Physical Review Letters. - 1079-7114. ; 93:5
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Tidskriftsartikel (refereegranskat)abstract
- We have used positron annihilation spectroscopy and infrared absorption measurements to study the Ga sublattice defects in epitaxial Ga1-xMnxAs with Mn content varying from 0% to 5%. We show that the Ga vacancy concentration decreases and As antisite concentration increases with increasing Mn content. This is in agreement with thermodynamical considerations for the electronic part of the formation energy of the Ga sublattice point defects. However, the absolute defect concentrations imply that they are determined rather by the growth kinetics than by the thermodynamical equilibrium. The As antisite concentrations in the samples are large enough to be important for compensation and magnetic properites. In addition, the Ga vacancies are likely to be involved in the diffusion and clustering of Mn at low annealing temperatures.
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| 26. |
- Tuomisto, F, et al.
(författare)
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Observation of vacancies in Ga1-xMnxAs with positron annihilation spectroscopy
- 2003
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Ingår i: Acta Physica Polonica. Series A: General Physics, Physics of Condensed Matter, Optics and Quantum Electronics, Atomic and Molecular Physics, Applied Physics. - 0587-4246. ; 103:6, s. 601-606
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Tidskriftsartikel (refereegranskat)abstract
- Positron annihilation spectroscopy can be used to determine the role of vacancy defects in semiconductors, by identification and quantification of the vacancies and their chemical surroundings. We have studied 0.5-0.8 mum thick low temperature MBE GaMnAs layers with Mn content 0.5-5% and different As-2 partial pressures at growth. The Doppler broadening results show that the Ga vacancy concentration in the layers decreases with increasing Mn content and decreasing As-2 partial pressure.
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| 27. |
- Tuomisto, F., et al.
(författare)
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Vacancy defect distribution in heteroepitaxial a-plane GaN grown by hydride vapor phase epitaxy
- 2007
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Ingår i: Journal of Crystal Growth. - : Elsevier BV. - 0022-0248 .- 1873-5002. ; 300:1, s. 251-253
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Tidskriftsartikel (refereegranskat)abstract
- We have used positron annihilation spectroscopy to study the native vacancy distribution in a-plane heteroepitaxial GaN. We show that the Ga vacancy concentration is independent of the layer thickness in the range from 5 to 25 µ m. This is strikingly different from the behavior in c-plane GaN, where the Ga vacancy concentration decreases dramatically with the distance from the GaN/sapphire interface. This difference in the native vacancy profiles is tentatively correlated with the differences in the O impurity and dislocation density profiles in the polar and non-polar materials. © 2006 Elsevier B.V. All rights reserved.
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| 28. |
- Warnecke, J., et al.
(författare)
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Investigating Global Convective Dynamos with Mean-field Models : Full Spectrum of Turbulent Effects Required
- 2021
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 919:2
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Tidskriftsartikel (refereegranskat)abstract
- The role of turbulent effects for dynamos in the Sun and stars continues to be debated. Mean-field (MF) theory provides a broadly used framework to connect these effects to fundamental magnetohydrodynamics. While inaccessible observationally, turbulent effects can be directly studied using global convective dynamo (GCD) simulations. We measure the turbulent effects in terms of turbulent transport coefficients, based on the MF framework, from an exemplary GCD simulation using the test-field method. These coefficients are then used as an input into an MF model. We find a good agreement between the MF and GCD solutions, which validates our theoretical approach. This agreement requires all turbulent effects to be included, even those which have been regarded as unimportant so far. Our results suggest that simple dynamo models, as are commonly used in the solar and stellar community, relying on very few, precisely fine-tuned turbulent effects, may not be representative of the full dynamics of dynamos in global convective simulations and astronomical objects.
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