| 1. |
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| 2. |
- ul-Hassan, Jawad, et al.
(author)
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Control of epitaxial graphene thickness on 4H-SiC(0001) and bufferlayer removal through hydrogen intercalation
- 2012
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In: Materials Science Forum (Volumes 717 - 720). - : Trans Tech Publications Inc.. ; , s. 605-608
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Conference paper (peer-reviewed)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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| 3. |
- Engelbrecht, J.A. A., et al.
(author)
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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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In: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 439, s. 115-118
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Journal article (peer-reviewed)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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| 4. |
- Engelbrecht, J. A. A., et al.
(author)
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Notes on the plasma resonance peak employed to determine doping in SiC
- 2015
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In: Infrared physics & technology. - : ELSEVIER SCIENCE BV. - 1350-4495 .- 1879-0275. ; 72, s. 95-100
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Journal article (peer-reviewed)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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| 5. |
- Engelbrecht, J A A, et al.
(author)
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The origin of a peak in the reststrahlen region of SiC
- 2012
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In: Physica. B, Condensed matter. - : Elsevier. - 0921-4526 .- 1873-2135. ; 407:10, s. 1525-1528
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Journal article (peer-reviewed)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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| 6. |
- Fagerlind, Martin, 1980, et al.
(author)
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Influence of Large-Aspect-Ratio Surface Roughness on Electrical Characteristics of AlGaN/AlN/GaN HFETs
- 2012
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In: IEEE Transactions on Device and Materials Reliability. - : Institute of Electrical and Electronics Engineers (IEEE). - 1530-4388 .- 1558-2574. ; 12:3, s. 538-546
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Journal article (peer-reviewed)abstract
- The effect of large-aspect-ratio surface roughness of AlGaN/GaN wafers is investigated. The roughness has a surface morphology consisting of hexagonal peaks with maximum peak-to-valley height of more than 100 nm and lateral peak-to-peak distance between 25 and 100 mu m. Two epitaxial wafers grown at the same time on SiC substrates having different surface orientation and with a resulting difference in AlGaN surface roughness are investigated. Almost no difference is seen in the electrical characteristics of the materials, and the electrical uniformity of the rough material is comparable to that of the smoother material. The reliability of heterostructure field-effect transistors from both materials have been tested by stressing devices for up to 100 h without any significant degradation. No critical effect, from the surface roughness, on device fabrication is experienced, with the exception that the roughness will directly interfere with step-height measurements.
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| 7. |
- Galindo-Uribarri, A., et al.
(author)
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Superdeformation below [Formula Presented]
- 1996
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In: Physical Review C - Nuclear Physics. - 0556-2813. ; 54:2, s. 454-458
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Journal article (peer-reviewed)abstract
- A decoupled rotational band with an average dynamical moment of inertia [Formula Presented] [Formula Presented]/MeV has been observed to high spin in [Formula Presented] [Formula Presented]. The measured quadrupole moment of [Formula Presented] eb is as large as that of the superdeformed band in [Formula Presented]. The large deformation and decoupled character of the band suggests that the odd neutron occupies either the [Formula Presented] orbital or the [Formula Presented] intruder orbital. This is the first example of a superdeformed band extending to high spin below [Formula Presented], a neutron number that has long been considered as the boundary for superdeformation in the [Formula Presented] mass region.
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| 8. |
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| 9. |
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| 10. |
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| 11. |
- Hosseinzadeh, Griffin, et al.
(author)
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The Early Light Curve of SN 2023bee : Constraining Type Ia Supernova Progenitors the Apian Way
- 2023
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In: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 953:1
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Journal article (peer-reviewed)abstract
- We present very early photometric and spectroscopic observations of the Type Ia supernova (SN Ia) 2023bee, starting about 8 hr after the explosion, which reveal a strong excess in the optical and nearest UV (U and UVW1) bands during the first several days of explosion. This data set allows us to probe the nature of the binary companion of the exploding white dwarf and the conditions leading to its ignition. We find a good match to the Kasen model in which a main-sequence companion star stings the ejecta with a shock as they buzz past. Models of double detonations, shells of radioactive nickel near the surface, interaction with circumstellar material, and pulsational delayed detonations do not provide good matches to our light curves. We also observe signatures of unburned material, in the form of carbon absorption, in our earliest spectra. Our radio nondetections place a limit on the mass-loss rate from the putative companion that rules out a red giant but allows a main-sequence star. We discuss our results in the context of other similar SNe Ia in the literature.
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| 12. |
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| 13. |
- Ivanov, I. G., et al.
(author)
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Investigation of intrinsic carbon-related defects in 4H-SiC by selective-excitation photoluminescence spectroscopy
- 2012
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In: Materials Science Forum Vols 717 - 720. - : Trans Tech Publications Inc.. ; , s. 259-262
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Conference paper (peer-reviewed)abstract
- Emission of carbon-related defects is investigated by means of selectively-excited photoluminescence in high purity 4H-SiC electron-irradiated with very low dose. Two new centers with clearly associated phonon replicas are observed, one of which is tentatively assigned to the carbon split interstitial at the hexagonal site. The temperature dependence of the spectrum is also studied and indicates that at least some of the observed luminescence lines arise from recombination of excitons bound to isoelectronic centers.
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| 14. |
- Ivanov, I.G., et al.
(author)
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Phonon energies at the M-point in 4H-SiC
- 1996
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In: 23rd International Conference on the Physics of Semiconductors, vol. 1. - 9810227779 ; , s. 233-236
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Conference paper (other academic/artistic)
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| 15. |
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| 16. |
- Janzen, David L. I., et al.
(author)
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Three novel approaches to structural identifiability analysis in mixed-effects models
- 2019
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In: Computer Methods and Programs in Biomedicine. - : Elsevier BV. - 1872-7565 .- 0169-2607. ; 171, s. 141-152
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Journal article (peer-reviewed)abstract
- Background and objective: Structural identifiability is a concept that considers whether the structure of a model together with a set of input-output relations uniquely determines the model parameters. In the mathematical modelling of biological systems, structural identifiability is an important concept since biological interpretations are typically made from the parameter estimates. For a system defined by ordinary differential equations, several methods have been developed to analyse whether the model is structurally identifiable or otherwise. Another well-used modelling framework, which is particularly useful when the experimental data are sparsely sampled and the population variance is of interest, is mixed-effects modelling. However, established identifiability analysis techniques for ordinary differential equations are not directly applicable to such models. Methods: In this paper, we present and apply three different methods that can be used to study structural identifiability in mixed-effects models. The first method, called the repeated measurement approach, is based on applying a set of previously established statistical theorems. The second method, called the augmented system approach, is based on augmenting the mixed-effects model to an extended state-space form. The third method, called the Laplace transform mixed-effects extension, is based on considering the moment invariants of the systems transfer function as functions of random variables. Results: To illustrate, compare and contrast the application of the three methods, they are applied to a set of mixed-effects models. Conclusions: Three structural identifiability analysis methods applicable to mixed-effects models have been presented in this paper. As method development of structural identifiability techniques for mixed-effects models has been given very little attention, despite mixed-effects models being widely used, the methods presented in this paper provides a way of handling structural identifiability in mixed-effects models previously not possible. (C) 2016 Elsevier Ireland Ltd. All rights reserved.
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| 17. |
- Mullins, S. M., et al.
(author)
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Extruder proton-hole band in the near-drip-line nucleus [Formula Presented] Pr
- 1998
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In: Physical Review C - Nuclear Physics. - 0556-2813. ; 58:5, s. 2626-2630
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Journal article (peer-reviewed)abstract
- The near-drip-line nucleus [Formula Presented] Pr was populated with the reaction [Formula Presented] Mo[Formula Presented] Ca,[Formula Presented] at a beam energy of 175 [Formula Presented] V. Particle-[Formula Presented]-[Formula Presented] coincidences were collected, and the total energy plane gating technique was used to enhance events associated with the [Formula Presented] exit channel. This enabled two new rotational bands to be assigned to [Formula Presented] Pr, including a strongly coupled structure. Its similarity with analogous bands in heavier Pr isotopes suggests this structure is most likely based on a hole in the extruder [Formula Presented]proton orbital. The occupancy of this orbital is associated with enhanced quadrupole deformation in this mass region.
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| 18. |
- Mullins, S. M., et al.
(author)
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Strong population of a superdeformed band in Eu142
- 1995
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In: Physical Review C. - 0556-2813. ; 52:1, s. 99-103
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Journal article (peer-reviewed)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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| 19. |
- Son, N. T., et al.
(author)
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Magnetic resonance identification ofhydrogen at a zinc vacancy in ZnO
- 2013
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25, s. 335804-
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Journal article (peer-reviewed)abstract
- Hydrogen (H) at a zinc vacancy (VZn) in ZnO is identified by electron paramagnetic resonance(EPR) and electron spin echo envelope modulation (ESEEM). In ZnO irradiated by 2 MeVelectrons, a doublet EPR spectrum, labelled S1, is observed. The doublet structure and theaccompanying weak satellites are shown to be the allowed and forbidden lines of the hyperfinestructure due to the dipolar interaction between an electron spin S D 1=2 and a nuclear spinI D 1=2 of 1H located at a VZn. The involvement of a single H atom in the S1 defect is furtherconfirmed by the observation of the nuclear Zeeman frequency of 1H in ESEEM experiments.We show that at a VZn, H prefers to make a short O–H bond with one O neighbour and is offthe substitutional site, forming a low symmetry C1 defect. In this partly H passivated VZn, the unpaired electron localizes on the p orbital of another O neighbour of VZn, and not on the H.
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| 20. |
- Svensson, C. E., et al.
(author)
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Smooth Termination of Rotational Bands in 62Zn: Evidence for a Loss of Collectivity
- 1998
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In: Physical Review Letters. - 1079-7114. ; 80:12, s. 2558-2561
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Journal article (peer-reviewed)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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| 21. |
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| 22. |
- Trinh, X. T., et al.
(author)
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Negative-U behavior of the Si donor in Al0.77Ga0.23N
- 2013
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:4, s. 042101-
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Journal article (peer-reviewed)abstract
- Electron paramagnetic resonance (EPR) spectrum of a shallow donor is observed at low temperatures in darkness in Si-doped Al0.77Ga0.23N epitaxial layers grown on 4H-SiC substrates. It is shown from the temperature dependence of the donor concentration on the neutral donor state measured by EPR that Si is a DX (or negative-U) center but behaves as a shallow donor due to a small separation of only ∼3 meV between the neutral state Ed and the lower-lying negative state EDX. The neutral state is found to follow the effective mass theory with Ed ∼ 52–59 meV.
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| 23. |
- Ul-Hassan, Jawad, et al.
(author)
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Fast growth rate epitaxy on 4((degrees)under-bar) off-cut 4-inch diameter 4H-SiC wafers
- 2014
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In: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2. - : Trans Tech Publications. ; , s. 179-182
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Conference paper (peer-reviewed)abstract
- We report the development of over 100 mu m/h growth rate process on 4-inch diameter wafers using chlorinated growth. The optimized growth process has shown extremely smooth epilayers completely free of surface step-bunching with very low surface defect density, high uniformity in thickness and doping and high run to run reproducibility in growth rate, controlled doping and defect density.
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| 24. |
- Unéus, Lars, et al.
(author)
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The effect of hydrogen diffusion in p- and n-type SiC Schottky diodes at high temperatures
- 2002
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In: Materials Science Forum, Vols. 389-393. ; , s. 1419-1422, s. 1419-1422
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Conference paper (peer-reviewed)abstract
- We present here the effect of a hydrogen anneal at 600degreesC for Schottky sensor devices based on n- and p-type 4H SiC. The devices have gate contacts of Ta/Pt, or TaSix/Pt. The catalytic metal gate dissociates hydrogen and thus promotes diffusion of hydrogen atoms into the SiC, where the atoms will trap or react with different impurities, defects or surface states. This will change parameters such as the carrier concentrations, the defect density of the material or the surface resistivity at the SiC/SiO2 interface. The current-voltage and the capacitance-voltage characteristics were measured before and after annealing in hydrogen and oxygen containing atmosphere, and the results show a reversible effect in the I-V characteristics.
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| 25. |
- van Rooyen, I J, et al.
(author)
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Effects of phosphorous-doping and high temperature annealing on CVD grown 3C-SiC
- 2012
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In: Nuclear Engineering and Design. - : Elsevier. - 0029-5493 .- 1872-759X. ; 251:SI, s. 191-202
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Journal article (peer-reviewed)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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