| 1. |
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| 2. |
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| 3. |
- Svensson, C. E., et al.
(författare)
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Smooth Termination of Rotational Bands in 62Zn: Evidence for a Loss of Collectivity
- 1998
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Ingår i: Physical Review Letters. - 1079-7114. ; 80:12, s. 2558-2561
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Tidskriftsartikel (refereegranskat)abstract
- Two sets of strongly coupled rotational bands have been identified in Zn-62. These bands have been observed up to the terminating states of their respective configurations. Lifetime measurements indicate that the transition quadrupole moments in these bands decrease as termination is approached. These results establish the first terminating states of rotational bands in the A similar to 60 mass region and confirm the predicted loss of collectivity associated with smooth band termination.
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| 4. |
- Hosseinzadeh, Griffin, et al.
(författare)
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Weak Mass Loss from the Red Supergiant Progenitor of the Type II SN 2021yja
- 2022
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 935:1
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Tidskriftsartikel (refereegranskat)abstract
- We present high-cadence optical, ultraviolet (UV), and near-infrared data of the nearby (D approximate to 23 Mpc) Type II supernova (SN) 2021yja. Many Type II SNe show signs of interaction with circumstellar material (CSM) during the first few days after explosion, implying that their red supergiant (RSG) progenitors experience episodic or eruptive mass loss. However, because it is difficult to discover SNe early, the diversity of CSM configurations in RSGs has not been fully mapped. SN 2021yja, first detected within approximate to 5.4 hours of explosion, shows some signatures of CSM interaction (high UV luminosity and radio and x-ray emission) but without the narrow emission lines or early light-curve peak that can accompany CSM. Here we analyze the densely sampled early light curve and spectral series of this nearby SN to infer the properties of its progenitor and CSM. We find that the most likely progenitor was an RSG with an extended envelope, encompassed by low-density CSM. We also present archival Hubble Space Telescope imaging of the host galaxy of SN 2021yja, which allows us to place a stringent upper limit of less than or similar to 9 M-circle dot; on the progenitor mass. However, this is in tension with some aspects of the SN evolution, which point to a more massive progenitor. Our analysis highlights the need to consider progenitor structure when making inferences about CSM properties, and that a comprehensive view of CSM tracers should be made to give a fuller view of the last years of RSG evolution.
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| 5. |
- J T Simms, R J T, et al.
(författare)
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Micro-Raman spectroscopy as a voltage probe in AlGaN/GaN heterostructure devices: Determination of buffer resistances
- 2011
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Ingår i: SOLID-STATE ELECTRONICS. - : Elsevier Science B.V., Amsterdam.. - 0038-1101. ; 55:1, s. 5-7
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Tidskriftsartikel (refereegranskat)abstract
- A time-resolved micro-Raman technique was developed to probe the transient voltage in the GaN buffer layer of AlGaN/GaN heterostructure devices. The transient potential distribution under Ohmic contacts of devices behaved like a capacitance-resistance coupled network, with a decrease in amplitude and phase shift of the potential as a function of operating voltage frequency. This phenomenon was used to extract a value of 0.6 M Omega/square for sheet resistance of the AIN nucleation layer at the GaN/SiC interface from the characteristic RC value of the network. This demonstrates the effectiveness of this voltage probe technique as a non-invasive method of characterizing nucleation layers.
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| 6. |
- Reinke, Beth A, et al.
(författare)
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Diverse aging rates in ectothermic tetrapods provide insights for the evolution of aging and longevity
- 2022
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Ingår i: Science. - : American Association for the Advancement of Science. - 0036-8075 .- 1095-9203. ; 376:6600, s. 1459-1466
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Tidskriftsartikel (refereegranskat)abstract
- Comparative studies of mortality in the wild are necessary to understand the evolution of aging; yet, ectothermic tetrapods are underrepresented in this comparative landscape, despite their suitability for testing evolutionary hypotheses. We present a study of aging rates and longevity across wild tetrapod ectotherms, using data from 107 populations (77 species) of nonavian reptiles and amphibians. We test hypotheses of how thermoregulatory mode, environmental temperature, protective phenotypes, and pace of life history contribute to demographic aging. Controlling for phylogeny and body size, ectotherms display a higher diversity of aging rates compared with endotherms and include phylogenetically widespread evidence of negligible aging. Protective phenotypes and life-history strategies further explain macroevolutionary patterns of aging. Analyzing ectothermic tetrapods in a comparative context enhances our understanding of the evolution of aging.
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| 7. |
- Engelbrecht, J A A, et al.
(författare)
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The origin of a peak in the reststrahlen region of SiC
- 2012
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Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 407:10, s. 1525-1528
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Tidskriftsartikel (refereegranskat)abstract
- A peak in the reststrahlen region of SiC is analyzed in order to establish the origin of this peak. The peak can be associated with a thin damaged layer on the SiC wafers, and a relation is found between surface roughness and the height of this peak, by modeling the damaged layer as an additional layer when simulating the reflectivity from the wafers.
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| 8. |
- Mullins, S. M., et al.
(författare)
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Strong population of a superdeformed band in Eu142
- 1995
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Ingår i: Physical Review C. - 0556-2813. ; 52:1, s. 99-103
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Tidskriftsartikel (refereegranskat)abstract
- A superdeformed band has been found in Eu142. It is populated with 1.2(2)% of the total -ray intensity that decayed into Eu142 via the reaction Sn120(27Al,5n)142Eu at 152 MeV. The strength of the band is similar to that previously reported in Eu143, where the superdeformed band is populated with an intensity of 1.1(1)%. This is unexpected, since both total Routhian surface (TRS) and cranked modified oscillator (MO) calculations predict that the superdeformed band in Eu143 becomes yrast at lower spin than that in Eu142. This difference is 4Latin small letter h with stroke in the MO calculations and 8Latin small letter h with stroke in the TRS. Extrapolation of the normal-deformed yrast states in Eu143 shows, however, that a difference of 8Latin small letter h with stroke in spin corresponds to a change in the relative energy of the superdeformed and normal-deformed yrast lines of only 1 MeV.
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| 9. |
- Riedel, Gernot J, et al.
(författare)
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Reducing Thermal Resistance of AlGaN/GaN Electronic Devices Using Novel Nucleation Layers
- 2009
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Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 30:2, s. 103-106
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Tidskriftsartikel (refereegranskat)abstract
- Currently, up to 50% of the channel temperature in AlGaN/GaN electronic devices is due to the thermal-boundary resistance (TBR) associated with the nucleation layer (NL) needed between GaN and SiC substrates for high-quality heteroepitaxy. Using 3-D time-resolved Raman thermography, it is shown that modifying the NL used for GaN on SiC epitaxy from the metal-organic chemical vapor deposition (MOCVD)-grown standard AIN-NL to a hot-wall MOCVD-grown AIN-NL reduces NL TBR by 25%, resulting in similar to 10% reduction of the operating temperature of AlGaN/GaN HEMTs. Considering the exponential relationship between device lifetime and temperature, lower TBR NLs open new opportunities for improving the reliability of AlGaN/GaN devices.
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| 10. |
- van Rooyen, I J, et al.
(författare)
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The effect of grain size and phosphorous-doping of polycrystalline 3C-SiC on infrared reflectance spectra
- 2012
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Ingår i: Journal of Nuclear Materials. - : Elsevier. - 0022-3115 .- 1873-4820. ; 422:1-3, s. 103-108
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Tidskriftsartikel (refereegranskat)abstract
- The effect of P-doping and grain size of polycrystalline 3C-SiC on the infrared reflectance spectra is reported. The relationship between grain size and full width at half maximum (FWHM) suggest that the behavior of the 3C-SiC with the highest phosphorous doping level (of 1.2 x 10(19) at. cm(-3)) is different from those with lower doping levels (andlt;6.6 x 10(18) at. cm(-3)). It is also further demonstrated that the plasma resonance frequency (omega(p)) is not influenced by the grain size.
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| 11. |
- Breyer, F., et al.
(författare)
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TPL-2 kinase induces phagosome acidification to promote macrophage killing of bacteria
- 2021
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Ingår i: Embo Journal. - : EMBO. - 0261-4189 .- 1460-2075. ; 40:10
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Tidskriftsartikel (refereegranskat)abstract
- Tumour progression locus 2 (TPL-2) kinase mediates Toll-like receptor (TLR) activation of ERK1/2 and p38 alpha MAP kinases in myeloid cells to modulate expression of key cytokines in innate immunity. This study identified a novel MAP kinase-independent regulatory function for TPL-2 in phagosome maturation, an essential process for killing of phagocytosed microbes. TPL-2 catalytic activity was demonstrated to induce phagosome acidification and proteolysis in primary mouse and human macrophages following uptake of latex beads. Quantitative proteomics revealed that blocking TPL-2 catalytic activity significantly altered the protein composition of phagosomes, particularly reducing the abundance of V-ATPase proton pump subunits. Furthermore, TPL-2 stimulated the phosphorylation of DMXL1, a regulator of V-ATPases, to induce V-ATPase assembly and phagosome acidification. Consistent with these results, TPL-2 catalytic activity was required for phagosome acidification and the efficient killing of Staphylococcus aureus and Citrobacter rodentium following phagocytic uptake by macrophages. TPL-2 therefore controls innate immune responses of macrophages to bacteria via V-ATPase induction of phagosome maturation.
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| 12. |
- Doyle, J. P., et al.
(författare)
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Characterization of deep level defects in 4H and 6H SiC via DLTS, SIMS and MeV e-beam irradiation
- 1996
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Ingår i: III-nitride, SiC and diamond materials for electronic devices. ; , s. 519-524
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Konferensbidrag (refereegranskat)abstract
- Electrically active defects in both 4H and 6H polytypes of SiC have been observed through the use of deep level transient spectroscopy (DLTS). Schottky contacts were grown by VPE with doping concentrations, the epitaxial layer having a doping concentration in the range of 10 exp 14/cu cm to 10 exp 17/cu cm. Numerous levels have been found in the as-grown n-type 6H-SiC samples, and SIMS and MeV electron irradiation have been employed to correlate the defect levels to impurities or structural defects. In contrast, only a single level is observed in the as-grown 4H-SiC samples.
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| 13. |
- Engelbrecht, J.A. A., et al.
(författare)
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Impact of dielectric parameters on the reflectivity of 3C-SiC wafers with a rough surface morphology in the reststrahlen region
- 2014
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Ingår i: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 439, s. 115-118
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Tidskriftsartikel (refereegranskat)abstract
- A layer-on-substrate model is used to obtain the infrared reflectance for 3C-SiC with a rough surface morphology. The effect of varying dielectric parameters of the "damaged layer" on the observed reflectivity of the 3C-SiC in the reststrahlen region is assessed. Different simulated reflectance spectra are obtained to those if the dielectric parameters of the "substrate" were varied. Most notable changes in the shape of the simulated reststrahlen peak are observed for changes in the high frequency dielectric constant, the phonon damping constant, the phonon frequencies and "thickness" of damaged surface layer.
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| 14. |
- Engelbrecht, J. A. A., et al.
(författare)
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Notes on the plasma resonance peak employed to determine doping in SiC
- 2015
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Ingår i: Infrared physics & technology. - : ELSEVIER SCIENCE BV. - 1350-4495 .- 1879-0275. ; 72, s. 95-100
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Tidskriftsartikel (refereegranskat)abstract
- The doping level of a semiconductor material can be determined using the plasma resonance frequency to obtain the carrier concentration associated with doping. This paper provides an overview of the procedure for the three most common polytypes of SiC. Results for 3C-SiC are presented and discussed. In phosphorus doped samples analysed, it is submitted that the 2nd plasma resonance cannot be detected due to high values of the free carrier damping constant gamma. (C) 2015 Elsevier B.V. All rights reserved.
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| 15. |
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| 16. |
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| 17. |
- Janzen, Viktor, et al.
(författare)
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Hematopoietic stem cell responsiveness to exogenous signals is limited by Caspase-3
- 2008
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Ingår i: Cell Stem Cell. - : Elsevier BV. - 1934-5909. ; 2:6, s. 584-594
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Tidskriftsartikel (refereegranskat)abstract
- Limited responsiveness to inflammatory cytokines is a feature of adult hematopoietic stem cells and contributes to the relative quiescence and durability of the stem cell population in vivo. Here we report that the executioner Caspase, Caspase-3, unexpectedly participates in that process. Mice deficient in Caspase-3 had increased numbers of immunophenotypic long-term repopulating stem cells in association with multiple functional changes, most prominently cell cycling. Though these changes were cell autonomous, they reflected altered activation by exogenous signals. Caspase-3(-/-) cells exhibited cell type-specific changes in phosphorylated members of the Ras-Raf-MEK-ERK pathway in response to specific cytokines, while notably, members of other pathways, such as pSTAT3, pSTAT5, pAKT, pp38 MAPK, pSmad2, and pSmad3, were unaffected. Caspase-3 contributes to stem cell quiescence, dampening specific signaling events and thereby cell responsiveness to microenvironmental stimuli.
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| 18. |
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| 19. |
- Lundqvist, Björn, et al.
(författare)
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Thermal conductivity of isotopically enriched silicon carbide
- 2013
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Ingår i: THERMINIC 2013 - 19th International Workshop on Thermal Investigations of ICs and Systems, Proceedings. - : IEEE. ; , s. 58-61, s. 58-61
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Konferensbidrag (refereegranskat)abstract
- Since the semiconductor silicon carbide presents attractive opportunities for the fabrication of novel electronic devices, there is significant interest in improving its material quality. Shrinking component sizes and high demands for efficiency and reliability make the capability to release excess heat an important factor for further development. Experience from Si and Diamond tells us that isotopic enrichment is a possible way to increase the thermal conductivity. We have produced samples of 4H-SiC that contain 28Si and 12C to a purity of 99.5%. The thermal conductivity in the c-direction of these samples has been measured by a transient thermoreflectance method. An improvement due to enrichment of at least 18% was found. The result is valid for a temperature of 45K above room temperature. A preliminary study of the temperature dependence of the thermal conductivity demonstrates a strong temperature dependence in agreement with earlier reports for 4H. © 2013 IEEE.
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| 20. |
- Naguleswaran, S., et al.
(författare)
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Magnetic and intruder rotational bands in In-113
- 2005
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 72:4, s. 044304-
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Tidskriftsartikel (refereegranskat)abstract
- Excited states in In-113 were populated via the reactions Mo-100(O-18,p4n)In-113 and Pd-110(Li-7,4n)In-113. The two known Delta J=2 intruder bands, based on the pi g(7/2)circle times d(5/2) and pi h(11/2) orbitals, have been extended by 8h to spins (49/2(+))h and (55/2(-))h, respectively. The previous finding of three sequences of Delta J=1 gamma-ray transitions has been confirmed. A self-consistent cranked shell-model calculation gives a good description of the contrasting alignment patterns of the two Delta J=2 intruder bands. The intruder bands, the known sequences of M1 transitions, and spherical levels together represent a coexistence of three different excitation modes in this nucleus.
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| 21. |
- Nguyen, Son Tien, 1953-, et al.
(författare)
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Electron-paramagnetic-resonance studies of defects in electron-irradiated p-type 4H and 6H SiC
- 1999
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Ingår i: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 273-274, s. 655-658
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Tidskriftsartikel (refereegranskat)abstract
- Defects in p-type 4H and 6H SiC irradiated by 2.5 MeV electrons were studied by electron paramagnetic resonance (EPR). Two anisotropic EPR spectra, labeled I and II, were observed in both 4H and 6H SiC. These spectra demonstrating triclinic symmetry of the center can be described by an effective electron spin S=1/2. The angle α between the direction of the principal gz of the g-tensors and the c-axis is determined as 63° and 50° for spectra I and II, respectively. In the 6H polytype, a third also similar EPR spectrum was detected. Based on their similarity in the electronic structure (electron spin, symmetry, g values), annealing behavior and temperature dependence, these spectra are suggested to be related to the same defect occupying different inequivalent lattice sites in 4H and 6H SiC. A pair between a silicon vacancy and an interstitial is a possible model for the defect.
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| 22. |
- Nilsson, Daniel, et al.
(författare)
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Highly Si-doped Al0.72Ga0.28N layers: n-type conductivity bound by the process temperature
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Establishing n- and p- type conductivity via intentional doping in epitaxial layers is fundamental to any semiconductor material system and its relevant device applications. Process parameters such as temperature, precursor gas-flow-rates and pressure may all control intentional doping in metal-organic chemical vapour deposition (MOCVD) of semiconductor materials. The incorporation of impurities such as carbon and oxygen may also be affected by the same process parameters, and the concentration of these impurities has a direct impact on the electrical, optical and thermal properties of epitaxial layers, as has been observed in the MOCVD of technologically-important III-V semiconductor materials such as AlGaAs and GaN.
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| 23. |
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| 24. |
- Storasta, Liutauras, et al.
(författare)
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Deep levels created by low energy electron Irradiation in 4H-SiC
- 2004
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 96:9, s. 4909-4915
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Tidskriftsartikel (refereegranskat)abstract
- With low energy electron irradiation in the 80-250 keV range, we were able to create only those intrinsic defects related to the initial displacements of carbon atoms in the silicon carbide lattice. Radiation induced majority and minority carrier traps were analyzed using capacitance transient techniques. Four electron traps (EH1, Z1/Z2, EH3, and EH7) and one hole trap (HS2) were detected in the measured temperature range. Their concentrations show linear increase with the irradiation dose, indicating that no divacancies or di-interstitials are generated. None of the observed defects was found to be an intrinsic defect-impurity complex. The energy dependence of the defect introduction rates and annealing behavior are presented and possible microscopic models for the defects are discussed. No further defects were detected for electron energies above the previously assigned threshold for the displacement of the silicon atom at 250 keV. © 2004 American Institute of Physics. 10.1063/1.1778819.
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| 25. |
- Telemeco, Rory S., et al.
(författare)
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Physiology at near-critical temperatures, but not critical limits, varies between two lizard species that partition the thermal environment
- 2017
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Ingår i: Journal of Animal Ecology. - : Wiley. - 0021-8790 .- 1365-2656. ; 86:6, s. 1510-1522
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms that mediate the interaction between the thermal environment and species ranges are generally uncertain. Thermal environments may directly restrict species when environments exceed tolerance limits (i.e. the fundamental niche). However, thermal environments might also differentially affect relative performance among species prior to fundamental tolerances being met (i.e. the realized niche). We examined stress physiology (plasma glucose and corticosterone), mitochondrial performance and the muscle metabolome of congeneric lizards that naturally partition the thermal niche, Elgaria multicarinata (southern alligator lizards; SALs) and Elgaria coerulea (northern alligator lizards; NALs), in response to a thermal challenge to quantify variation in physiological performance and tolerance. Both NAL and SAL displayed physiological stress in response to high temperature, but neither showed signs of irreversible damage. NAL displayed a higher baseline mitochondrial respiration rate than SAL. Moreover, NAL substantially adjusted their physiology in response to thermal challenge, whereas SAL did not. For example, the metabolite profile of NAL shifted with changes in key energetic molecules, whereas these were unaffected in SAL. Our results indicate that near-critical high temperatures should incur greater energetic cost in NAL than SAL via an elevated metabolic rate and changes to the metabolome. Thus, SAL displace NAL in warm environments that are within NAL's fundamental thermal niche, but relatively costly. Our results suggest that subcritical thermal events can contribute to biogeographic patterns via physiological differences that alter the relative costs of living in warm or cool environments.
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| 26. |
- Tien Son, Nguyen, et al.
(författare)
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Negative-U System of Carbon Vacancy in 4H-SiC
- 2012
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 109:18, s. 187603-
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Tidskriftsartikel (refereegranskat)abstract
- Using electron paramagnetic resonance (EPR), energy levels of the carbon vacancy (V-C) in 4H-SiC and its negative-U properties have been determined. Combining EPR and deep-level transient spectroscopy we show that the two most common defects in as-grown 4H-SiC-the Z(1/2) lifetime-limiting defect and the EH7 deep defect-are related to the double acceptor (2 - vertical bar 0) and single donor (0 vertical bar +) levels of V-C, respectively.
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| 27. |
- ul-Hassan, Jawad, et al.
(författare)
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Control of epitaxial graphene thickness on 4H-SiC(0001) and bufferlayer removal through hydrogen intercalation
- 2012
-
Ingår i: Materials Science Forum (Volumes 717 - 720). - : Trans Tech Publications Inc.. ; , s. 605-608
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Konferensbidrag (refereegranskat)abstract
- We report graphene thickness, uniformity and surface morphology dependence on thegrowth temperature and local variations in the off-cut of Si-face 4H-SiC on-axis substrates. Thetransformation of the buffer layer through hydrogen intercalation and the subsequent influence onthe charge carrier mobility are also studied. A hot-wall CVD reactor was used for in-situ etching,graphene growth in vacuum and the hydrogen intercalation process. The number of graphene layersis found to be dependent on the growth temperature while the surface morphology also depends onthe local off-cut of the substrate and results in a non-homogeneous surface. Additionally, the influence of dislocations on surface morphology and graphene thickness uniformity is also presented.
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| 28. |
- van Rooyen, I J, et al.
(författare)
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Effects of phosphorous-doping and high temperature annealing on CVD grown 3C-SiC
- 2012
-
Ingår i: Nuclear Engineering and Design. - : Elsevier. - 0029-5493 .- 1872-759X. ; 251:SI, s. 191-202
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Tidskriftsartikel (refereegranskat)abstract
- The integrity and property behavior of the SiC layer of the Tr-isotropic (TRISO) coated particle (CP) for high temperature reactors (HTR) are very important as the SiC layer is the main barrier for gaseous and metallic fission product release. This study describes the work done on un-irradiated SiC samples prepared with varying phosphorus levels to simulate the presence of phosphorus due to transmutation. Si-30 transmutes to phosphorous (P-31) and other transmutation products during irradiation, which may affect the integrity of the SiC layer. The P-doping levels of the SiC samples used in this study cover the range from 1.1 x 10(15) to 1.2 x 10(19) atom/cm(3) and are therefore relevant to the PBMR operating conditions. Annealing from 1000 degrees C to 2100 degrees C was performed to study the possible changes in nanostructures and various properties due to temperature. Characterization results by X-ray diffraction (XRD), secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM). transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM), are reported in this article. As grain boundary diffusion is identified as a possible mechanism by which Ag-110m, one of the fission activation products, might be released through intact SiC layer, grain size measurements is also included in this study. Temperature is evidently one of the factors/parameters amongst others known to influence the grain size of SiC and therefore it is important to investigate the effect of high temperature annealing on the SiC grain size. The ASTM E112 method as well as electron back scatter diffraction (EBSD) was used to determine the grain size of various commercial SiC samples and the SiC layer in experimental PBMR Coated Particles (CPs) after annealing at temperatures ranging from 1600 degrees C to 2100 degrees C. The HRTEM micrograph of the decomposition of SiC at 2100 degrees C are shown and discussed. Nanotubes were not identified during the TEM and HRTEM analysis although graphitic structures were identified. The preliminary conclusion reached is that the P-content at these experimental levels (1.1 x 10(15) to 1.2 x 10(19) atom/cm(3)) does not have a significant influence on the nanostructure of SiC at high temperatures without irradiation.
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| 29. |
- Zimmermann, F., et al.
(författare)
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Origin of orange color in nominally undoped HVPE GaN crystals
- 2017
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Ingår i: Optical materials (Amsterdam). - : ELSEVIER SCIENCE BV. - 0925-3467 .- 1873-1252. ; 70, s. 127-130
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Tidskriftsartikel (refereegranskat)abstract
- In this article we investigated unintentionally doped (UID) GaN grown by hydride vapor phase epitaxy (HVPE) with respect to point defects and impurity concentration. The samples were orange tinted to different extent. Optical analysis was performed by micro-photoluminescence and absorption spectroscopy. Absorption measurements revealed an absorption peak at 1.5 eV related to an internal transition in Mn3+ impurities and a second band with low energy onset at 1.9 eV, both increasing with the extent of orange color. Electron paramagnetic resonance investigations showed the presence of Mn2+ and Fe3+ in the colored crystals. The overall impurity concentration was verified by secondary ion mass spectrometry. Orange tint is associated with an increase of transition metal contamination, especially Mn. Based on these observations we suggest that the orange coloring in the investigated UID HVPE GaN samples is caused by the presence of Mn impurities. (C) 2017 Elsevier B.V. All rights reserved.
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| 30. |
- Aradi, B., et al.
(författare)
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Ab initio density-functional supercell calculations of hydrogen defects in cubic SiC
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:245202
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Tidskriftsartikel (refereegranskat)abstract
- Based on ab initio density-functional calculations in supercells of 3C-SiC, the stable configurations of hydrogen and dihydrogen defects have been established. The calculated formation energies are used to give semiquantitative estimates for the concentration of hydrogen in SiC after chemical vapor deposition, low temperature H-plasma anneal, or heat treatment in high temperature hydrogen gas. Vibration frequencies, spin distributions, and occupation levels were also calculated in order to facilitate spectroscopic identification of these defects. (V+nH) complexes are suggested as the origin of some of the signals assigned earlier to pure vacancies. Qualitative extrapolation of our results to hexagonal polytypes explains observed electrical passivation effects of hydrogen.
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| 31. |
- Aradi, B., et al.
(författare)
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Impurity-controlled dopant activation : Hydrogen-determined site selection of boron in silicon carbide
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 79:17, s. 2746-2748
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Tidskriftsartikel (refereegranskat)abstract
- The geometry and formation energy of substitutional B and Al dopants as well as their complexes with hydrogen have been calculated in 4H-SiC using first-principles methods. Our results show that boron selecting the silicon site and, therefore, getting activated as a shallow acceptor depends on the presence of hydrogen which is promoted into the crystal by boron itself. Without hydrogen, boron would mostly be incorporated at the carbon site. Aluminum does not show this behavior: it always selects the silicon site and is incorporated independently of hydrogen. © 2001 American Institute of Physics.
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| 32. |
- Arneborg, Lars, 1969, et al.
(författare)
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Spatial variability of diapycnal mixing and turbulent dissipation rates in a stagnant fjord basin
- 2004
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Ingår i: Journal of Physical Oceanography. - 0022-3670. ; 34:7, s. 1679-1691
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Tidskriftsartikel (refereegranskat)abstract
- Two microstructure profilers, two ships, and four moorings with acoustic Doppler current profilers and conductivity-temperature loggers were used in an intensive effort to map the spatial and temporal variations of vertical mixing in the stagnant deep basin of Gullmar Fjord, Sweden. During three days in the beginning of August 2001 a continuous time series of turbulent kinetic energy dissipation profiles was obtained with one microstructure profiler at a fixed position near the deepest part of the fjord. During the same period the other microstructure profiler was used to obtain six sections of dissipation through the length of the basin. Two moorings were deployed in the fjord basin for one month from the end of July to the end of August. The mapping of dissipation rates reveals that the dissipation in the deep basin is confined to areas just inside the sill. More than 77% of the dissipation in the fjord basin happens above the sloping bottoms closest to the sill.
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| 33. |
- Berg, Staffan, et al.
(författare)
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In Vitro and In Vivo Evaluation of 3D Printed Capsules with Pressure Triggered Release Mechanism for Oral Peptide Delivery
- 2021
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Ingår i: Journal of Pharmaceutical Sciences. - : Elsevier BV. - 0022-3549 .- 1520-6017. ; 110:1, s. 228-238
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Tidskriftsartikel (refereegranskat)abstract
- In this study a 3D printed capsule designed to break from the physiological pressures in the antropyloric region was evaluated for its ability to deliver the synthetic octapeptide octreotide in beagle dogs when co-formulated with the permeation enhancer sodium caprate. The pressure sensitive capsules were compared to traditional enteric coated hard gelatin capsules and enteric coated tablets. Paracetamol, which is completely absorbed in dogs, was included in the formulations and used as an absorption marker to give information about the in vivo performance of the dosage forms. The pressure sensitive capsules released drug in 50% of the dogs. In the cases where drug was released, there was no difference in octreotide bioavailability or C-max compared to the enteric coated dosage forms. When comparing all dosage forms, a correlation was seen between paracetamol C-max and octreotide bioavailability, suggesting that a high drug release rate may be beneficial for peptide absorption when delivered together with sodium caprate. (C) 2020 Published by Elsevier Inc.
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| 34. |
- Bergsten, Johan, 1988, et al.
(författare)
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Performance Enhancement of Microwave GaN HEMTs Without an AlN-Exclusion Layer Using an Optimized AlGaN/GaN Interface Growth Process
- 2016
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Ingår i: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 1557-9646 .- 0018-9383. ; 63:1, s. 333-338
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Tidskriftsartikel (refereegranskat)abstract
- The impact of the sharpness of the AlGaN/GaN interface in high-electron mobility transistors (HEMTs) is investigated. Two structures, one with an optimized AlGaN/GaN interface and another with an unoptimized, were grown using hot-wall metal-organic chemical vapor deposition. The structure with optimized sharpness of the interface shows electron mobility of 1760 cm(2)/V . s as compared with 1660 cm(2)/V . s for the nonoptimized interface. Gated Hall measurements indicate that the sharper interface maintains higher mobility when the electrons are close to the interface compared with the nonoptimized structure, indicating less scattering due to alloy disorder and interface roughness. HEMTs were processed and evaluated. The higher mobility manifests as lower parasitic resistance yielding a better dc and high-frequency performance. A small-signal equivalent model is extracted. The results indicate a lower electron penetration into the buffer in the optimized sample. Pulsed-IV measurements imply that the sharper interface provides less dispersive effects at large drain biases. We speculate that the mobility enhancement seen AlGaN/AlN/GaN structures compared with the AlGaN/GaN case is not only related to the larger conduction band offset but also due to a more welldefined interface minimizing scattering due to alloy disorder and interface roughness.
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| 35. |
- Beyer, Franziska, et al.
(författare)
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Annealing behavior of the EB-centers and M-center in low-energy electron irradiated n-type 4H-SiC
- 2011
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Ingår i: Journal of Applied Physics. - : American Institute of Physics. - 0021-8979 .- 1089-7550. ; 109:10, s. 103703-
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Tidskriftsartikel (refereegranskat)abstract
- After low-energy electron irradiation of epitaxial n-type 4H-SiC with a dose of 5 x 10(16) cm(-2), the bistable M-center, previously reported in high-energy proton implanted 4H-SiC, is detected in the deep level transient spectroscopy (DLTS) spectrum. The annealing behavior of the M-center is confirmed, and an enhanced recombination process is suggested. The annihilation process is coincidental with the evolvement of the bistable EB-centers in the low temperature range of the DLTS spectrum. The annealing energy of the M-center is similar to the generation energy of the EB-centers, thus partial transformation of the M-center to the EB-centers is suggested. The EB-centers completely disappeared after annealing temperatures higher than 700 degrees C without the formation of new defects in the observed DLTS scanning range. The threshold energy for moving Si atom in SiC is higher than the applied irradiation energy, and the annihilation temperatures are relatively low, therefore the M-center, EH1 and EH3, as well as the EB-centers are attributed to defects related to the C atom in SiC, most probably to carbon interstitials and their complexes.
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| 36. |
- Beyer, Franziska, et al.
(författare)
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Bistable defects in low-energy electron irradiated n-type 4H-SiC
- 2010
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Ingår i: PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS. - : John Wiley and Sons, Ltd. - 1862-6254. ; 4:8-9, s. 227-229
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial n-type 4H-SiC layers were irradiated at room temperature by low-energy electrons. During the annihilation process of the irradiation induced defects EH I and EH3, three new bistable centers, labeled EB centers, were detected in the DLTS spectrum. The reconfigurations of the EB centers (I -andgt; II and II -andgt; I) take place at room temperature with a thermal reconfiguration energy of about 0.95 eV. The threshold energy for moving the Si atom from its site in the SiC crystal structure is higher than the applied irradiation energy; therefore, the EB centers are attributed to carbon related complex defects.
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| 37. |
- Beyer, Franziska, et al.
(författare)
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Capacitance transient study of a bistable deep level in e(-)-irradiated n-type 4H-SiC
- 2012
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Ingår i: Journal of Physics D. - : Institute of Physics. - 0022-3727 .- 1361-6463. ; 45:45
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Tidskriftsartikel (refereegranskat)abstract
- Using capacitance transient techniques, a bistable centre, called FB centre here, was observed in electron irradiated 4H-SiC. In configuration A, the deep level known as EH5 (E-a = E-C - 1.07 eV) is detected in the deep level transient spectroscopy spectrum, whereas for configuration B no obvious deep level is observed in the accessible part of the band gap. Isochronal annealing revealed the transition temperatures to be T-A -andgt; B andgt; 730K and for the opposite process T-B -andgt; A approximate to 710 K. The energy needed to conduct the transformations were determined to be E-A(A -andgt; B) = (2.1 +/- 0.1) eV and E-A(B -andgt; A) = (2.3 +/- 0.1) eV, respectively. The pre-factor indicated an atomic jump process for the opposite transition A -andgt; B and a charge carrier-emission dominated process in the case of B -andgt; A. Minority charge carrier injection enhanced the transformation from configuration B to configuration A by lowering the transition barrier by about 1.4 eV. Since the bistable FB centre is already present after low-energy electron irradiation (200 keV), it is likely related to carbon.
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| 38. |
- Beyer, Franziska, et al.
(författare)
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Defects in low-energy electron-irradiated n-type 4H-SiC
- 2010
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Ingår i: Physica Scripta, vol. T141. - : IOP Publishing. ; , s. 014006-
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Konferensbidrag (refereegranskat)abstract
- The bistable M-center, previously observed in high-energy proton-implanted 4H-SiC, was detected in low-energy electron-irradiated 4H-SiC using deep-level transient spectroscopy (DLTS). Irradiation increased the DLTS signals of the intrinsic defects Z(1/2) and EH6/7 and introduced the frequently observed defects EH1 and EH3. After the M-center is annealed out at about 650K without bias and at about 575K with bias applied to the sample during the annealing process, a new bistable defect in the low temperature range of the DLTS spectrum, the EB-center, evolves. Since low-energy irradiation affects mainly the carbon atoms in SiC, the M-center and the newly discovered EB-center are most probably carbon-related intrinsic defects.
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| 39. |
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| 40. |
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| 41. |
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| 42. |
- Booker, Ian Don, et al.
(författare)
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Carrier Lifetime Controlling Defects Z(1/2) and RB1 in Standard and Chlorinated Chemistry Grown 4H-SiC
- 2014
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 14:8, s. 4104-4110
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Tidskriftsartikel (refereegranskat)abstract
- 4H-SiC epilayers grown by standard and chlorinated chemistry were analyzed for their minority carrier lifetime and deep level recombination centers using time-resolved photoluminescence (TRPL) and standard deep level transient spectroscopy (DLTS). Next to the well-known Z(1/2) deep level a second effective lifetime killer, RB1 (activation energy 1.05 eV, electron capture cross section 2 x 10(-16) cm(2), suggested hole capture cross section (5 +/- 2) x 10(-15) cm(2)), is detected in chloride chemistry grown epilayers. Junction-DLTS and bulk recombination simulations are used to confirm the lifetime killing properties of this level. The measured RB1 concentration appears to be a function of the iron-related Fe1 level concentration, which is unintentionally introduced via the corrosion of reactor steel parts by the chlorinated chemistry. Reactor design and the growth zone temperature profile are thought to enable the formation of RB1 in the presence of iron contamination under conditions otherwise optimal for growth of material with very low Z(1/2) concentrations. The RB1 defect is either an intrinsic defect similar to RD1/2 or EH5 or a complex involving iron. Control of these corrosion issues allows the growth of material at a high growth rate and with high minority carrier lifetime based on Z(1/2) as the only bulk recombination center.
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| 43. |
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| 44. |
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| 45. |
- Carlsson, Patrick, et al.
(författare)
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Deep levels in low-energy electron-irradiated 4H-SiC
- 2009
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Ingår i: PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS. - : Wiley. - 1862-6254. ; 3:4, s. 121-123
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Tidskriftsartikel (refereegranskat)abstract
- Deep levels introduced by low-energy (200 keV) electron irradiation in n-type 4H-SiC epitaxial layers grown by chemical vapour deposition were studied by deep level transient spectroscopy (DLTS) and photoexcitation electron paramagnetic resonance (photo-EPR). After irradiation, several DLTS levels, EH1, EH3, Z(1/2), EH5 and EH6/7, often reported in irradiated 4H-SiC, were observed. In irradiated freestanding films from the same wafer, the EPR signals of the carbon vacancy in the positive and negative charge states, V-C(+) and V-C(-), respectively, can be observed simultaneously under illumination with light of certain photon energies. Comparing the ionization energies obtained from DLTS and photo-EPR, we suggest that the EH6/7 (at similar to E-C - 1.6 eV) and EH5 (at similar to E-C - 1.0 eV) electron traps may be related to the single donor (+ vertical bar 0) and the double acceptor (1- vertical bar 2-) level of V-C, respectively. Judging from the relative intensity of the DLTS signals, the EH6/7 level may also be contributed to by other unidentified defects.
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| 46. |
- Carlsson, Patrick, 1975-, et al.
(författare)
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Electron paramagnetic resonance study on n-type electron-irradiated 3C-SiC
- 2008
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Ingår i: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY. - BRISTOL, ENGLAND : IOP PUBLISHING LTD.
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Konferensbidrag (refereegranskat)abstract
- Electron Paramagnetic Resonance (EPR) was used to study defects in n-type 3C-SiC films irradiated by 3-MeV electrons at room temperature with a dose of 2x10(18) cm(-2). After electron irradiation, two new EPR spectra with an effective spin S = 1, labeled L5 and L6, were observed. The L5 center has C-3v symmetry with g = 2.004 and a fine-structure parameter D = 436.5 x 10(-4) cm(-1). The L5 spectrum was only detected under light illumination and it could not be detected after annealing at similar to 550 C. The principal z-axis of the D tensor is parallel to the < 111 >-directions, indicating the location of spins along the Si-C bonds. Judging from the symmetry and the fact that the signal was detected under illumination in n-type material, the L5 center may be related to the divacancy in the neutral charge state. The L6 center has a C-2v-symmetry with an isotropic g-value of g=2.003 and the fine structure parameters D=547.7 x 10(-4) cm-1 and E=56.2 x 10(-4) cm(-1). The L6 center disappeared after annealing at a rather low temperature (similar to 200 degrees C), which is substantially lower than the known annealing temperatures for vacancy-related defects in 3C-SiC. This highly mobile defect may be related to carbon interstitials.
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| 47. |
- Carlsson, Patrick, 1975-, et al.
(författare)
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EPR and ab initio calculation study on the EI4 center in 4H and 6H-SiC
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 82:23, s. 235203-
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Tidskriftsartikel (refereegranskat)abstract
- We present new results from electron paramagnetic resonance (EPR) studies of the EI4 EPR center in 4H- and 6H-SiC. The EPR signal of the EI4 center was found to be drastically enhanced in electron-irradiated high-purity semi-insulating materials after annealing at 700-750°C. Strong EPR signals of the EI4 center with minimal interferences from other radiation-induced defects in irradiated high-purity semiinsulating materials allowed our more detailed study of the hyperfine (hf) structures. An additional large-splitting 29Si hf structure and 13C hf lines of the EI4 defect were observed. Comparing the data on the defect formation, the hf interactions and the annealing behavior obtained from EPR experiments and from ab initio supercell calculations of different carbon-vacancy related complexes, we suggest a complex between a carbon vacancy-carbon antisite and a carbon vacancy at the third neighbor site of the antisite in the neutral charge state, (VC-CSiVC)0, as a new defect model for the EI4 center.
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| 48. |
- Carlsson, Patrick, 1975-, et al.
(författare)
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Photo-EPR Studies on Low-Energy Electron-irradiated 4H-SiC
- 2009
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Ingår i: Materials Science Forum, Vols. 615-617. - Materials Science Forum Vols. 615-617 : Trans Tech Publications. - 9780878493340 ; , s. 401-404
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Konferensbidrag (refereegranskat)abstract
- Photoexcitation electron paramagnetic resonance (photo-EPR) was used to determine deep levels related to the carbon vacancy (VC) in 4H-SiC. High-purity free-standing n-type 4H-SiC epilayers with concentration of intrinsic defects (except the photo-insensitive SI1 center) below the detection limit of EPR were irradiated with low-energy (200 keV) electrons to create mainly VC and defects related to the C sublattice. The simultaneous observation of and signals, their relative intensity changes and the absence of other defects in the sample provide a more straight and reliable interpretation of the photo-EPR results. The study suggests that the (+|0) level of VC is located at ~EC–1.77 eV in agreement with previously reported results and its single and double acceptor levels may be at ~ EC–0.8 eV and ~ EC–1.0 eV, respectively.
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| 49. |
- Carlsson, Patrick, et al.
(författare)
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Silicon antisite related defects in electron-irradiated p-type 4H- and 6H-SiC
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The electron paramagnetic resonance (EPR) LE5 centers were previously observed in electron-irradiated p-type 4H- and 6H-SiC but have not been identified due to lack of experimental data. In this study, two different Si hyperfine (hf) structures of the LE5 centers have been detected and the corresponding hf tensors have been determined. One structure is due to a very anisotropic hf interaction with one Si atom and the other structure to the hf interaction with two neighboring Si atoms in the basal plane. The obtained g values and Si hf constants are in good agreement with calculated parameters reported for antisite pairs in 4H-SiC. Based on the similarity in the spin-Hamiltonian parameters, the LE5 centers may be the antisite pairs in the positive charge state.
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| 50. |
- Carlsson, Patrick, 1975-, et al.
(författare)
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The EI4 EPR centre in 6H SiC
- 2010
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Ingår i: Physica Scripta, Vol. T141. - : IOP Publishing. ; , s. 014013-
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Konferensbidrag (refereegranskat)abstract
- We present the results of our recent electron paramagnetic resonance (EPR) studies of the EI4 EPR centre in electron-irradiated high-purity semi-insulating 6H SiC. Higher signal intensities and better resolution compared with previous studies have enabled a more detailed study of the hyperfine (hf) structure. Based on the observed hf structure due to the interaction with Si and C neighbours, the effective spin S = 1, the C-1h-symmetry and the annealing behaviour, we suggest a carbon vacancy-carbon antisite complex in the neutral charge state, VCVCCSi0, with the vacancies and the antisite in the basal plane, as a new defect model for the centre.
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