SwePub - search: WFRF:(Öberg Sven)

Enumeration	Reference	Cover	Find
1.	Wenner, Jörgen, et al. (author) Short-term outcome after laparoscopic and open 360 degrees fundoplication. A prospective randomized trial. 2001 In: Surgical Endoscopy. - : Springer Science and Business Media LLC. - 0930-2794 .- 1432-2218. ; 15:10, s. 1124-8 Journal article (peer-reviewed)abstract BACKGROUND: Despite the lack of randomized trials supporting the laparoscopic approach, laparoscopic antireflux surgery has gained widespread acceptance during the last decade. The aim of this study was to compare the short-term symptomatic and objective outcome after laparoscopic and open 360 degrees fundoplication in a prospective randomized clinical trial. METHODS: Sixty patients with GERD were randomized to undergo either laparoscopic (LF) or open 360 degrees fundoplication (OF). Endoscopy, esophageal manometry, 24-h pH monitoring, clinical symptom evaluation, and symptom scoring according to a validated questionnaire (the Gastrointestinal Symptom Rating Scale [GSRS]) was performed preoperatively and 6 months after surgery. RESULTS: Five patients randomized to the laparoscopic group were converted to open surgery. Esophageal acid exposure was restored to normal in all patients. Lower esophageal sphincter length and resting pressure were significantly increased after both laparoscopic and open fundoplication (p < 0.001); there were no differences between the groups. No significant differences were seen in symptomatic outcome, although there was a trend toward a higher rate of mild dysphagia (p = 0.051) after laparoscopic surgery. GSRS revealed a decrease in reflux score (p < 0.001) and abdominal pain score (p < 0.001) postoperatively. There were no significant differences in GSRS scores between the two groups. CONCLUSION: Laparoscopic 360 degrees fundoplication is as effective in treating reflux disease as open fundoplication. Six months postoperatively, no significant differences were seen in symptomatic or objective outcome. Long-term evaluation is needed.
2.	Adey, J., et al. (author) Degradation of boron-doped Czochralski-grown silicon solar cells 2004 In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 93:5, s. 055504-1 Journal article (peer-reviewed)abstract The formation mechanism and properties of the boron-oxygen center responsible for the degradation of Czochralski-grown Si(B) solar cells during operation is investigated using density functional calculations. We find that boron traps an oxygen dimer to form a bistable defect with a donor level in the upper half of the band gap. The activation energy for its dissociation is found to be 1.2 eV. The formation of the defect from mobile oxygen dimers, which are shown to migrate by a Bourgoin mechanism under minority carrier injection, has a calculated activation energy of 0.3 eV. These energies and the dependence of the generation rate of the recombination center on boron concentration are in good agreement with observations.
3.	Adey, J., et al. (author) Theory of boron-vacancy complexes in silicon 2005 In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:16, s. 165211- Journal article (peer-reviewed)abstract The substitutional boron-vacancy BsV complex in silicon is investigated using the local density functional theory. These theoretical results give an explanation of the experimentally reported, well established metastability of the boron-related defect observed in p-type silicon irradiated at low temperature and of the two hole transitions that are observed to be associated with one of the configurations of the metastable defect. BsV is found to have several stable configurations, depending on charge state. In the positive charge state the second nearest neighbor configuration with C1 symmetry is almost degenerate with the second nearest neighbor configuration that has C1h symmetry since the bond reconstruction is weakened by the removal of electrons from the center. A third nearest neighbor configuration of BsV has the lowest energy in the negative charge state. An assignment of the three energy levels associated with BsV is made. The experimentally observed Ev+0.31 eV and Ev+0.37 eV levels are related to the donor levels of second nearest neighbor BsV with C1 and C1h symmetry respectively. The observed Ev+0.11 eV level is assigned to the vertical donor level of the third nearest neighbor configuration. The boron-divacancy complex BsV2 is also studied and is found to be stable with a binding energy between V2 and Bs of around 0.2 eV. Its energy levels lie close to those of the V2. However, the defect is likely to be an important defect only in heavily doped material.
4.	Adjizian, J.J., et al. (author) DFT study of the chemistry of sulfur in graphite, including interactions with defects, edges and folds 2013 In: Carbon. - : Elsevier BV. - 0008-6223 .- 1873-3891. ; 62, s. 256-262 Journal article (peer-reviewed)abstract Sulfur has several roles, desirable and undesirable, in graphitization. We perform density functional theory calculations within the local density approximation to define the structures and energetics of sulphur in graphite, including its interactions with point defects and edges, in order to understand its role in the later stages of graphitization. We find sulphur does not cross-link layers, except where there are defects. It reacts very strongly with vacancies in neighbouring layers to form a six coordinate split vacancy structure, analogous to that found in diamond. It is also highly stable at basal edge sites, where, as might be expected, the size and valency of sulfur can be easily accommodated. This suggests a role for sulphur in stabilizing graphene edges, and following from this, we show that sulfur dimers can open, i.e. unzip, folds in graphite rapidly and exothermically.
5.	Ahlbäck Öberg, Shirin, 1964-, et al. (author) MOOCs-studenter bildar B-laget 2013 In: Upsala Nya Tidning. - Uppsala : AB Upsala Nya Tidning. - 1104-0173. ; :17/6 Journal article (pop. science, debate, etc.)
6.	Ahlbäck Öberg, Shirin, 1964-, et al. (author) Om universitetet blir aktiebolag 2013 Other publication (pop. science, debate, etc.)
7.	Allali, Naoual, et al. (author) Accurate control of the covalent functionalization of single-walled carbon nanotubes for the electro-enzymatically controlled oxidation of biomolecules 2018 In: Beilstein Journal of Nanotechnology. - : Beilstein-Institut. - 2190-4286. ; 9, s. 2750-2762 Journal article (peer-reviewed)abstract Single-walled carbon nanotubes (SWCNTs) were functionalized by ferrocene through ethyleneglycol chains of different lengths (FcETGn) and the functionalized SWCNTs (f-SWCNTs) were characterized by different complementary analytical techniques. In particular, high-resolution scanning electron transmission microscopy (HRSTEM) and electron energy loss spectroscopy (EELS) analyses support that the outer tubes of the carbon-nanotube bundles were covalently grafted with FcETGn groups. This result confirms that the electrocatalytic effect observed during the oxidation of the reduced form of nicotinamide adenine dinucleotide (NADH) co-factor by the f-SWCNTs is due to the presence of grafted ferrocene derivatives playing the role of a mediator. This work clearly proves that residual impurities present in our SWCNT sample (below 5 wt. %) play no role in the electrocatalytic oxidation of NADH. Moreover, molecular dynamic simulations confirm the essential role of the PEG linker in the efficiency of the bioelectrochemical device in water, due to the favorable interaction between the ETG units and water molecules that prevents π-stacking of the ferrocene unit on the surface of the CNTs. This system can be applied to biosensing, as exemplified for glucose detection. The well-controlled and well-characterized functionalization of essentially clean SWCNTs enabled us to establish the maximum level of impurity content, below which the f-SWCNT intrinsic electrochemical activity is not jeopardized.
8.	Andersen, O., et al. (author) Electrical activity of carbon-hydrogen centers in Si 2002 In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:23, s. 235205-1 Journal article (peer-reviewed)abstract The electrical activity of Cs-H defects in Si has been investigated in a combined modeling and experimental study. High-resolution Laplace capacitance spectroscopy with the uniaxial stress technique has been used to measure the stress-energy tensor and the results are compared with theoretical modeling. At low temperatures, implanted H is trapped as a negative-U center with a donor level in the upper half of the gap. However, at higher temperatures, H migrates closer to the carbon impurity and the donor level falls, crossing the gap. At the same time, an acceptor level is introduced into the upper gap making the defect a positive-U center.
9.	Andersen, O., et al. (author) Piezospectroscopic analysis of the hydrogen-carbon complexes in silicon 2001 In: Physica. B, Condensed matter. - 0921-4526 .- 1873-2135. ; 308, s. 139-142 Journal article (peer-reviewed)abstract We have observed the donor (Ec-0.22 eV) and acceptor (Ec-0.16 eV) levels related to hydrogen-carbon complexes in silicon. The donor level is only detected at low temperatures after proton implantation. This hydrogen-carbon complex irreversibly reconfigures at temperatures above 225 K to a configuration characterized by the acceptor level, which is stable up to room temperature. The same acceptor level is also observed after atomic hydrogen diffusion. We have used Laplace transform deep level transient spectroscopy (DLTS) to show the influence of uniaxial stress on the electron emission process and the effect of the stress-induced alignment for the acceptor state. The pattern of the Laplace DLTS peak splittings indicate a trigonal symmetry of the defect. First principles calculations were carried out on the hydrogen-carbon defects with a view of determining their electrical levels and stress response for comparison with the experimental results.
10.	Andersson, Rune, et al. (author) Skattesystemet ett lappverk – en ny stor reform behövs 2014 In: Dagens nyheter. - 1101-2447. Journal article (pop. science, debate, etc.)
11.	Anrup, Roland, et al. (author) Centrala universitetsvärden hotas av bolagiseringsidén 2013 In: Dagens nyheter. - 1101-2447. Journal article (pop. science, debate, etc.)abstract Högskolestiftelser. Förslaget att driva svenska universitet i stiftelseform öppnar för bolagisering. Men det är ingen riktig utredning, utan en politisk pamflett utan eftertanke. Privatisering av universitet hotar både oberoendet, forskningskvaliteten och samhällsnyttan, skriver 36 forskare vid svenska högskolor och universitet.
12.	Antzutkin, Oleg, et al. (author) Interactions in multi-component mineral systems 2010 Conference paper (other academic/artistic)
13.	Antzutkin, Oleg, et al. (author) Interactions in multi-component mineral systems 2011 Conference paper (other academic/artistic)
14.	Arai, Kazuhiro, et al. (author) The Structure and Determinants of Trust: The Cases of Japan and Sweden 2005 In: Hitotsubashi Journal of Economics. - Tokyo : Sanseido Publishing Company, Ltd.. - 0018-280X. ; 46:2, s. 183-204 Journal article (peer-reviewed)abstract The structure and determinants of trust are analyzed using questionnaire data from a sample of Japanese and Swedish university students. A salient characteristic of this analysis is that it considers various dimensions of trust. There are similarities and differences between the two countries in the relative magnitude of trust belonging to those dimensions. Family trust does not reduce various kinds of trust. It can be inferred from the responses of economics students that education and culture are important determinants of trust. Those who rely heavily on signals for trust decisions are less cooperative and less trustworthy. Some interpretations are given.
15.	Arnrup, Roland, et al. (author) Centrala universitetsvärden hotas av bolagiseringsidén 2013 In: Dagens Nyheter. - Stockholm : AB Dagens Nyheter. - 1101-2447. ; :22 Oktober, 2013 Journal article (pop. science, debate, etc.)
16.	Ashwin, M.J., et al. (author) The bonding of CAs acceptors in InxGa1-xAs grown by chemical beam epitaxy using carbon tetrabromide as the source of carbon 1996 In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 80:12, s. 6754-6760 Journal article (peer-reviewed)abstract InxGa1-xAs layers (0≤x≤0.37) doped with carbon (>1020 cm-3) were grown on semi-insulating GaAs substrates by chemical beam epitaxy using carbon tetrabromide (CBr4) as the dopant source. Hall measurements imply that all of the carbon was present as CAs for values x up to 0.15. The C acceptors were passivated by exposing samples to a radio frequency hydrogen plasma for periods of up to 6 h. The nearest-neighbor bonding configurations of CAs were investigated by studying the nondegenerate antisymmetric hydrogen stretch mode (A-1 symmetry) and the symmetric XH mode (A+1 symmetry) of the H-CAs pairs using IR absorption and Raman scattering, respectively. Observed modes at 2635 and 450 cm-1 had been assigned to passivated Ga4CAs clusters. New modes at 2550 and 430 cm-1 increased in strength with increasing values of x and are assigned to passivated InGa3CAs clusters. These results were compared with ab initio local density functional theory. Modes due to AlInGaCAs clusters were detected in samples containing grown in Al and In. These results demonstrate that for InGaAs, CBr4 is an efficient C doping source since both In-CAs bonds as well as Ga-CAs bonds are formed, whereas there is no evidence for the formation of In-CAs bonds in samples doped with C derived from trimethylgallium or solid sources
17.	Avakyan, Leon, et al. (author) Optoelectronics and defect levels in hydroxyapatite by first-principles 2018 In: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 148:15 Journal article (peer-reviewed)abstract Hydroxyapatite (HAp) is an important component of mammal bones and teeth, being widely used in prosthetic implants. Despite the importance of HAp in medicine, several promising applications involving this material (e.g., in photo-catalysis) depend on how well we understand its fundamental properties. Among the ones that are either unknown or not known accurately, we have the electronic band structure and all that relates to it, including the bandgap width. We employ state-of-the-art methodologies, including density hybrid-functional theory and many-body perturbation theory within the dynamically screened single-particle Green's function approximation, to look at the optoelectronic properties of HAp. These methods are also applied to the calculation of defect levels. We find that the use of a mix of (semi-)local and exact exchange in the exchange-correlation functional brings a drastic improvement to the band structure. Important side effects include improvements in the description of dielectric and optical properties not only involving conduction band (excited) states but also the valence. We find that the highly dispersive conduction band bottom of HAp originates from anti-bonding σ* states along the ⋯OH-OH-⋯ infinite chain, suggesting the formation of a conductive 1D-ice phase. The choice of the exchange-correlation treatment to the calculation of defect levels was also investigated by using the OH-vacancy as a testing model. We find that donor and acceptor transitions obtained within semi-local density functional theory (DFT) differ from those of hybrid-DFT by almost 2 eV. Such a large discrepancy emphasizes the importance of using a high-quality description of the electron-electron interactions in the calculation of electronic and optical transitions of defects in HAp.
18.	Bangert, U., et al. (author) Electron energy loss spectroscopic studies of brown diamonds 2006 In: Philosophical Magazine. - : Informa UK Limited. - 1478-6435 .- 1478-6443. ; 86:29-31, s. 4757-4779 Journal article (peer-reviewed)abstract We investigate both experimentally and theoretically, low-loss electron energy losses in brown type IIa monocrystalline diamonds both before and after high-temperature, high-pressure anneals which remove the brown colouration. We find additional losses within and near the band edge for brown diamond which are significantly reduced after treatment. The additional losses are not associated with dislocations. Graphitic inclusions are detected by EELS as well as TEM studies for some brown diamonds before treatment. These lead to pronounced subgap absorption. However, all brown diamonds exhibit additional losses which are due to point defects lying in the regions between dislocations. First principles theoretical modelling shows that common dislocations are not responsible for the brown colouration but a -bonded vacancy disk lying on {111} planes gives broad bands lying in the diamond band gap, possesses an optical absorption spectrum similar to that of brown diamond, and leads to additional electron energy losses in the band edge region. These and similar defects are suggested to be responsible for the brown colouration. Mechanisms are proposed for their formation and removal.
19.	Bathen, M. E., et al. (author) Anisotropic and plane-selective migration of the carbon vacancy in SiC : Theory and experiment 2019 In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 100:1 Journal article (peer-reviewed)abstract We investigate the migration mechanism of the carbon vacancy (VC) in silicon carbide (SiC) using a combination of theoretical and experimental methodologies. The VC, commonly present even in state-of-the-art epitaxial SiC material, is known to be a carrier lifetime killer and therefore strongly detrimental to device performance. The desire for VC removal has prompted extensive investigations involving its stability and reactivity. Despite suggestions from theory that VC migrates exclusively on the C sublattice via vacancy-atom exchange, experimental support for such a picture is still unavailable. Moreover, the existence of two inequivalent locations for the vacancy in 4H-SiC [hexagonal, VC(h), and pseudocubic, VC(k)] and their consequences for VC migration have not been considered so far. The first part of the paper presents a theoretical study of VC migration in 3C- and 4H-SiC. We employ a combination of nudged elastic band (NEB) and dimer methods to identify the migration mechanisms, transition state geometries, and respective energy barriers for VC migration. In 3C-SiC, VC is found to migrate with an activation energy of EA=4.0 eV. In 4H-SiC, on the other hand, we anticipate that VC migration is both anisotropic and basal-plane selective. The consequence of these effects is a slower diffusivity along the axial direction, with a predicted activation energy of EA=4.2 eV, and a striking preference for basal migration within the h plane with a barrier of EA=3.7 eV, to the detriment of the k-basal plane. Both effects are rationalized in terms of coordination and bond angle changes near the transition state. In the second part, we provide experimental data that corroborates the above theoretical picture. Anisotropic migration of VC in 4H-SiC is demonstrated by deep level transient spectroscopy (DLTS) depth profiling of the Z1/2 electron trap in annealed samples that were subject to ion implantation. Activation energies of EA=(4.4±0.3) eV and EA=(3.6±0.3) eV were found for VC migration along the c and a directions, respectively, in excellent agreement with the analogous theoretical values. The corresponding prefactors of D0=0.54cm2/s and 0.017cm2/s are in line with a simple jump process, as expected for a primary vacancy point defect.
20.	Berezovsky, Vladimir, 1978-, et al. (author) Computational study of the CO adsorption and diffusion in zeolites : validating the Reed–Ehrlich model 2018 In: Adsorption. - : Springer. - 0929-5607 .- 1572-8757. ; 24:4, s. 403-413 Journal article (peer-reviewed)abstract Molecular simulations have been employed to explore at the microscopic scale the adsorption of CO in zeolites (MFI, CHA and DDR). On the basis of classical force fields, grand canonical Monte Carlo simulations are performed to predict the adsorption properties (isotherms) of these types of zeolites up to high pressure. Subsequent careful analysis yields details the microscopic mechanism in play, along the whole adsorption process, together with a considering of the arrangements of CO in MFI at high pressure. This work also summarizes an approach which uses single component diffusion data in prediction of multicomponent diffusion.
21.	Berezovsky, Vladimir, et al. (author) Effect of dipole-dipole interactions between atoms in an active medium 2008 In: Journal of the Optical Society of America. B, Optical physics. - 0740-3224 .- 1520-8540. ; 25:3, s. 458-462 Journal article (peer-reviewed)abstract On the basis of the results of numerical modeling, it is shown that dipole-dipole interactions among atoms in the active medium strongly influences the character of the associated superradiation. The main effect is to make the nuclear subsystem behave chaotically. Its strength increases with the atom density and leads to the suppression of distant collective correlations and superradiation. Near correlations between the atoms are established, causing a confinement effect: a shielding of radiation in the active medium.
22.	Berezovsky, V.V., et al. (author) Effect of the dipole-dipole interaction of particles in an active medium on the character of superradiation 2008 In: Plasma physics reports (Print). - 1063-780X .- 1562-6938. ; 34:7, s. 555-561 Journal article (peer-reviewed)abstract The motion of a system of interacting nonlinear charged oscillators is investigated numerically. Because of nonlinearity, the total collective electric field gives rise to a phasing effect-correlations in the phases of the oscillators. The consequence is superradiation-the enhanced spontaneous short-term emission of the energy stored in the oscillators. It is shown that the oscillations of the oscillators become stochastic because of the dipole-dipole interaction between them and their nearest neighbors. As a result, as the density of the oscillators increases, distant collective correlations are suppressed, superradiation ceases to be generated, and radiation is shielded in the medium. The phenomena considered in the present paper can play an important role in cyclotron emission from a plasma and thus should be taken into account in emission calculations. The process whereby the energy of the transverse electron motion in electron cooling devices decreases is analyzed as an example. This process occurs as a result of the development of cyclotron maser instability and has the nature of superradiation. The onset of correlations between individual electrons moving in their Larmor circles is the initial, linear stage of instability developing in the plasma. Superradiation is the final, nonlinear instability stage.
23.	Blumenau, AT, et al. (author) Dislocation structures in diamond : density-functional based modelling and high-resolution electron microscopy 2004 In: Defect and Diffusion Forum. - Zürich : Trans Tech Publications. - 1012-0386 .- 1662-9507. ; 226-228, s. 11-30 Journal article (peer-reviewed)abstract The core structures of perfect 60 and edge dislocations in diamond are investigated atomistically in a density-functional based tight-binding approach, and their dissociation is discussed both in terms of structure and energy. Furthermore, high resolution electron microscopy is performed on dislocation cores in high-temperature, high-pressure annealed natural brown diamond, and HRTEM image simulation allows a comparison of theoretically predicted and experimentally observed structures.
24.	Blumenau, A.T., et al. (author) Basal plane partial dislocations in silicon carbide 2003 In: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 340, s. 160-164 Journal article (peer-reviewed)abstract Under operating conditions (forward bias) bipolar 4H- and 6H-SiC devices are known to degrade rapidly through stacking fault formation and expansion in the basal plane. It has been suggested that a recombination-enhanced dislocation glide (REDG) mechanism allows the bordering Shockley partial dislocations to overcome their barrier to glide motion and thus results in the observed stacking fault growth. In this work, we investigate the structure and properties of the participating Shockley partials by means of density functional-based atomistic calculations. Their glide motion is modelled in a process involving the formation and subsequent migration of kinks. This in combination with an analysis of the electronic structure of the partials allows an identification of those types which will be affected by the REDG mechanism.
25.	Blumenau, A.T., et al. (author) Density functional based modelling of 30° partial dislocations in SiC 2004 In: Proceedings of the 10th International Conference on Silicon Carbide and Related Materials, ICSCRM 2003. - Stafa-Zuerich : Trans Tech Publications Inc.. - 0878499431 ; , s. 453-456 Conference paper (peer-reviewed)abstract Experiment has shown that 4H- and 6H-SiC pin diodes degrade rapidly during forward biased operation. This degradation is accompanied by the formation and expansion of stacking faults in the basal plane. It is believed that the observed rapid stacking fault growth is due to a recombination-enhanced dislocation glide (REDG) mechanism at the bordering partial dislocations. In our work we investigate the structure and properties of basal plane 30° Shockley partials in SiC by means of density functional based calculations. Barriers to their glide motion, and thus the expansion of the accompanying stacking fault is modelled in a process involving the formation and subsequent migration of kinks in the dislocation. In combination with an analysis of the electronic structure of the partials and stacking faults, this allows an identification of those types of partials which will be affected by the REDG mechanism in this model.
26.	Blumenau, A. T., et al. (author) Dislocation related photoluminescence in silicon 2001 In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 87:18 Journal article (peer-reviewed)abstract Dislocation related photoluminescence in Si and SiGe is attributed to stable interstitial clusters bound to 60° dislocations. Density functional based total energy calculations in Si give binding energies between 1.5 and 3.6 eV for I3 and I4 clusters with 90° and 30° partials. They possess donor levels around Ev+0.4 eV which are consistent with deep level transient spectroscopic studies on p-Si. It is further suggested that the clusters would act as the obstacles to the movement of dislocations which may have been observed in recent transmission electron microscopy studies.
27.	Blumenau, A.T., et al. (author) Dislocations in hexagonal and cubic GaN 2000 In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 12, s. 10223-10233 Journal article (peer-reviewed)abstract The structure and electronic activity of several types of dislocations in both hexagonal and cubic GaN are calculated using first-principles methods. Most of the stoichiometric dislocations investigated in hexagonal GaN do not induce deep acceptor states and thus cannot be responsible for the yellow luminescence. However, it is shown that electrically active point defects, in particular gallium vacancies and oxygen-related defect complexes, can be trapped at the stress field of the dislocations and may be responsible for this luminescence. For cubic GaN, we find the ideal stoichiometric 60° dislocation to be electrically active and the glide set to be more stable than the shuffle. The dissociation of the latter is considered
28.	Blumenau, A.T., et al. (author) Optical bands related to dislocations in Si 2000 In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 12:49, s. 10123-10129 Journal article (peer-reviewed)abstract First-principles calculations are used to investigate the interaction of self-interstitial aggregates with the 90° partial dislocation in Si. We find that I4 is bound to the line with an energy of around 3 eV. The defect causes deep levels to appear in the band gap and optical transitions between these levels may account for the luminescent bands relating to plastically deformed Si.
29.	Blumenau, A.T., et al. (author) Straight and kinked 90° partial dislocations in diamond and 3C-SiC 2002 In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 14:48, s. 12741-12747 Journal article (peer-reviewed)abstract Density-functional based calculations are used to investigate low energy core structures of 90° partial dislocations in diamond and 3C-SiC. In both materials dislocation glide is analysed in terms of kink formation and migration and the fundamental steps to kink migration are investigated. We find the C terminated core structure in SiC to be more mobile than the Si core. However, the Si partial is electrically active and this opens the possibility of recombination-enhanced glide under ionizing conditions or an enhanced mobility in doped material.
30.	Blumenau, A.T., et al. (author) Structure and motion of basal dislocations in silicon carbide 2003 In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 68:17, s. 174108-1 Journal article (peer-reviewed)abstract 30° and 90° Shockley partial dislocations lying in {111} and basal planes of cubic and hexagonal silicon carbide, respectively, are investigated theoretically. Density-functional-based tight-binding total-energy calculations are used to determine the core structure and energetics of the dislocations. In a second step their electronic structure is investigated using a pseudopotential method with a Gaussian basis set. Finally, the thermal activation barriers to glide motion of 30° and 90° Shockley partials are calculated in terms of a process involving the formation and migration of kinks along the dislocation line. The mechanism for enhanced dislocation movement observed under current injection conditions in bipolar silicon carbide devices is discussed.
31.	Blumenau, A.T., et al. (author) The effect of charge on kink migration at 90° partial dislocations in SiC 2005 In: Physica Status Solidi (a) applications and materials science. - : Wiley. - 1862-6300 .- 1862-6319. ; 202:5, s. 877-882 Journal article (peer-reviewed)abstract SiC bipolar devices show a degradation under forward-biased operation which has been linked with a recombination enhanced motion of one of the two glide dislocations having either Si or C core atoms. We have carried out calculations of the core structures and dynamics of partial dislocations in 3C and 2H-SiC using the density functional based codes DFTB and AIMPRO. After in earlier theoretical work we reported on the structure, energetics and electronic activity of both of the Shockley partials, and on the formation and migration barriers of kinks, in this work we present first results on the effect of charge on the disloction kinks. The calculations give insights into the device degradation mechanism.
32.	Breuer, S. J., et al. (author) Interstitial hydrogen and enhanced dissociation of C-H complexes in GaAs 1996 In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 53:24, s. 16289-16296 Journal article (peer-reviewed)abstract Local-density-functional-based ab initio calculations are used to investigate hydrogen and carbon-hydrogen defects in GaAs. The equilibrium structure for both the C-H and C-H- complexes are shown to be similar, with the hydrogen located at a C-Ga bond-centered site. The dissociation of these complexes is investigated and it is found that the energy barrier of 1.84 eV for the process C-H → C- + H+ is substantially lowered to 0.88 eV in the presence of an electron resonantly bound to the defect. This is in good quantitative agreement with recent experiments. Isolated interstitial hydrogen is found to lie at a Ga-As bond-centered site for both H+ and H0 and at an antibonding site relative to a Ga atom for H-. It is also found that the stable form of the hydrogen dimer is a H2 molecule, the dissociation energy of which is 1.64 eV, and that interstitial hydrogen is a negative-U defect. Finally, a mechanism for minority-carrier-induced device degradation is proposed.
33.	Breuer, S.J., et al. (author) Interstitial hydrogen and the dissociation of C-H defects in GaAs 1995 In: Proceedings of the 18th International Conference on Defects in Semiconductors. - : Trans Tech Publications Inc.. ; , s. 951-956 Conference paper (peer-reviewed)abstract Local-density-functional calculations using a real-space cluster approach are used to model interstitial hydrogen in GaAs and the dissociation of the C-H and C-H- complexes. The equilibrium site is found to be on a Ga-As bond axis for H0 and H$+$/ and at a Ga anti-bonding site for H-. It is also shown that a H2 molecule is stable in interstitial space and has a lower energy than the two possible H2* defects and than widely separated single interstitial hydrogen atoms. The study of hydrogen in pure GaAs also yields the result that interstitial hydrogen is a negative-U defect. It is found that the energy barrier to the dissociation of the C-H complex is 1.8 eV, but that this is reduced to 0.9 eV for C-H-. Comparison is made with recent experimental results and implications for current containing devices are discussed.
34.	Budde, M., et al. (author) Identification of the hydrogen-saturated self-interstitials in silicon and germanium 1998 In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 57:18, s. 4397-4412 Journal article (peer-reviewed)abstract Silicon and germanium single crystals are implanted with protons. The infrared-absorption spectra of the samples contain sharp absorption lines due to the excitation of hydrogen-related local vibrational modes. The lines at 743.1, 748.0, 1986.5, and 1989.4 cm-1 in silicon and at 700.3, 705.5, 1881.8, and 1883.5 cm-1 in germanium originate from the same defect in the two materials. Measurements on samples coimplanted with protons and deuterons show that the defect contains two equivalent hydrogen atoms. Uniaxial stress measurements are carried out and a detailed analysis of the results is presented. It is shown that the defect has monoclinic-II symmetry, and the orientations of the Si-H and Ge-H bonds of the defect are determined. Ab initio local-density-functional theory is used to calculate the structure and local vibrational modes of the self-interstitial binding one and two hydrogen atoms in silicon and germanium together with the structure of the self-interstitial itself. The observed properties of the defect are in excellent agreement with those calculated for the self-interstitial binding two hydrogen atoms.
35.	Budde, M., et al. (author) Local modes of the H2* dimer in germanium 1996 In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 54:8, s. 5485-5494 Journal article (peer-reviewed)abstract Local vibrational modes of the H2* defect in crystalline germanium are identified by a combination of infrared-absorption spectroscopy, uniaxial stress measurements, and ab initio theory. Germanium crystals are implanted with protons and/or deuterons at 30 K, and subsequently annealed at room temperature. A number of local vibrational modes of hydrogen are revealed by infrared-absorption spectroscopy. In particular, modes at 765, 1499, 1774, and 1989 cm-1 originate from the same defect which has trigonal symmetry according to the uniaxial stress measurements. The 765-cm-1 mode is two dimensional, while the 1774- and 1989-cm-1 modes are one dimensional. Measurements on samples coimplanted with protons and deuterons show that the defect contains a pair of weakly coupled and inequivalent hydrogen atoms. The 765-, 1499-, 1774-, and 1989-cm-1 modes are ascribed to the H2* defect. The 765-cm-1 mode is a Ge-H bend mode with an overtone at 1499 cm-1 and the modes at 1774 and 1989 cm-1 are Ge-H stretch modes. An excellent fit to the stretch frequencies is obtained with a simple model based on two coupled Morse-potential oscillators. In addition, the model gives intensity ratios in fair agreement with those observed. The structure, the local-mode frequencies, and the isotope shifts of H2* are calculated with ab initio local-density-functional cluster theory. The theoretical frequencies are consistently 5-10 % too high, as expected from the theory which often leads to overbinding. The isotope shifts, however, are in fair agreement with observations. These results provide additional support for our assignments, and show that the 765- and 1774-cm-1 modes primarily involve the hydrogen at the antibonding site, while the 1989-cm-1 mode is related mainly to vibration of the hydrogen near the bond-center site.
36.	Budde, M., et al. (author) The hydrogen-saturated self-interstitial in silicon and germanium 1997 In: Defects in semiconductors. - : Trans Tech Publications Inc.. ; , s. 35-40 Conference paper (peer-reviewed)abstract Infrared absorption spectroscopy is used to study H-related point defects in H+-implanted Si (Si:H) and Ge (Ge:H). The absorption lines at 743.1, 748.0, 1986.5 and 1989.4 cm-1 in Si:H and at 700.3, 705.5, 1881.8 and 1883.5 cm-1 in Ge:H are shown to originate from the same defect containing two equivalent H atoms. Uniaxial stress experiments show that the defects have monoclinic-II symmetry, and the orientations of the two Si-H or Ge-H bonds are determined. The structure and the local vibrational modes of the self-interstitial binding two H atoms (IH2) are calculated with LDF cluster theory. The symmetry, bond-orientations and isotopic frequency-shifts calculated for IH2 are in excellent agreement with those observed for the 743.1-, 748.0-, 1986.5- and 1989.4-cm-1 modes in Si:H and for the 700.3-, 705.5-, 1881.8- and 1883.5-cm-1 modes in Ge:H.
37.	Cai, Hongming, 1956-, et al. (author) A new single fibre laser Doppler flowmeter based on digital signal processing 1996 In: Medical Engineering and Physics. - 1350-4533 .- 1873-4030. ; 18, s. 523-528 Journal article (peer-reviewed)
38.	Cai, Hongming, 1956-, et al. (author) Laser Doppler flowmetry : Charactersistics of a modified single fibre technique 1996 In: Medical Engineering and Physics. - 1350-4533 .- 1873-4030. ; 34 Journal article (peer-reviewed)
39.	Carvahlo, A., et al. (author) Cation-site intrinsic defects in Zn-doped CdTe 2010 In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:7, s. 75215- Journal article (peer-reviewed)abstract The properties of the cation vacancy and the Te antisite, two dominant defects in CdTe and Cd1-xZnxTe alloys grown in Te-rich conditions, are examined using first-principles calculations. First, the structure, electronic levels, and migration paths of V-Cd and Te-Cd in CdTe are studied in detail. Additionally, we analyze the evolution of the stability and electronic properties in Cd1-xZnxTe alloys, taking into account both the role of alloying in the position of the ionization levels and its effects on the equilibrium concentration of those two defects. It is shown that the formation of cation vacancies becomes progressively more favorable as x increases, whereas Te antisites become less stable, backing the trend towards p-type conductivity in dilute Cd1-xZnxTe.
40.	Carvahlo, A., et al. (author) Electronic properties, doping, and defects in chlorinated silicon nanocrystals 2012 In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:4 Journal article (peer-reviewed)abstract Silicon nanocrystals with diameters between 1 and 3 nm and surfaces passivated by chlorine or a mixture of chlorine and hydrogen were modeled using density functional theory, and their properties compared with those of fully hydrogenated nanocrystals. It is found that fully and partially chlorinated nanocrystals are stable, and have higher electron affinity, higher ionization energy, and lower optical absorption energy threshold. As the hydrogenated silicon nanocrystals, chlorinated silicon nanocrystals doped with phosphorus or boron require a high activation energy to transfer an electron or hole, respectively, to undoped silicon nanocrystals. The electronic levels of surface dangling bonds are similar for both types of surface passivation, although in the chlorinated silicon nanocrystals some fall outside the narrower energy gap.
41.	Carvahlo, A., et al. (author) Electronic structure modification of Si nanocrystals with F(4)-TCNQ 2011 In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:12 Journal article (peer-reviewed)abstract We use first-principles models to demonstrate how an organic oxidizing agent F(4)-TCNQ (7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane) modifies the electronic structure of silicon nanocrystals, suggesting it may enhance p-type carrier density and mobility. The proximity of the lowest unoccupied level of F(4)-TCNQ to the highest occupied level of the Si nanocrystals leads to the formation of an empty hybrid state overlapping both the nanocrystal and molecule, reducing the excitation energy to similar to 0.8-1 eV in vacuum. Hence, it is suggested that F(4)-TCNQ can serve both as a surface oxidant and as a mediator for hole hopping between adjacent nanocrystals in p-type doped silicon nanocrystal networks
42.	Carvahlo, A., et al. (author) Studies of the VO centre in Ge using first principles cluster calculations 2006 In: Materials Science in Semiconductor Processing. - : Elsevier BV. - 1369-8001 .- 1873-4081. ; 9:4-5, s. 489-493 Journal article (peer-reviewed)abstract The small or near-zero band gap of germanium found by supercell local density functional treatments causes difficulties in the study of the properties of charged defects in Ge. Here, we use large H-terminated Ge clusters together with a non-linear core corrected (NLCC) Ge pseudopotential to explore the structure, vibrational and electrical properties of the vacancy-oxygen complex (VO). The cluster possesses a gap sufficiently wide to contain defect related energy levels, thus allowing us to model the three charge states of the defect. The local vibrational modes (LVM) calculated for the neutral (VO0), negatively charged (VO-) and double negative (VO=) defect are 602, 684 and 694 cm- 1, and can be favourably compared with experimental values of 621, 669 and 716 cm- 1, respectively [Markevich VP, et al. Physica B 2003; 340-2, 844-8]. Using substitutional gold (Aus) as a marker defect, electric levels of VO are found at E (-/ 0) = Ev + 0.30 eV and E (= /-) = Ec - 0.29 eV, in excellent agreement with the respective experimental enthalpies for hole and electron emission Δ Hh (-/ 0) ≃ 0.32 eV and Δ He (= /-) = 0.26 eV, respectively. Finally, the migration, dissociation and reorientation energies of the defect are also reported.
43.	Carvalho, Alexandra, et al. (author) Boron doped Si nanoparticles : the effect of oxidation 2013 In: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 250:9, s. 1799-1803 Journal article (peer-reviewed)abstract The preferred location of boron in oxidized free-standing Si nanoparticles was investigated using a first-principles density functional approach. The nanoparticles were modeled by a silicon core about 1.5 nm in diameter surrounded by an outer shell of SiO2 with a thickness of about 0.5 nm, and considered negatively charged. The calculated formation energies indicate that B is equally stable in the Si core and in the SiO2 shell, showing preference for interface sites. This indicates that, in contrast with phosphorus, the ratio of the boron concentration in the silicon core to that of the silicon shell will not be improved over one upon thermal annealing.
44.	Carvalho, A., et al. (author) Density-functional theory study of Au, Ag and Cu defects in germanium 2008 In: Materials Science in Semiconductor Processing. - : Elsevier BV. - 1369-8001 .- 1873-4081. ; 11:5, s. 340-343 Journal article (peer-reviewed)abstract Gold, silver and copper defects in germanium are modeled using density functional theory. The structures and electrical properties of the substitutional metals are calculated in excellent agreement with experiment. Interstitial Au, Ag and Cu are found to be shallow donors, in disagreement with a previous assignment of Cui to a hole trap in the lower half of the gap. Substitutional-interstitial metal (Mi - Ms) pairs and metal-vacancy pairs (Ms - V) are also investigated.
45.	Carvalho, A, et al. (author) First-principles study of the diffusion mechanisms of the self-interstitial in germanium 2008 In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:13 Journal article (peer-reviewed)abstract The self-interstitial in germanium can assume multiple configurations depending on the temperature and charge state. Here, we employ a first-principles density functional method to investigate the diffusion mechanisms of this defect. The energy barriers associated with the transformation between different structures are determined by the climbing nudged elastic band method, as a function of the charge state. The relation between the thermodynamic properties of the self-interstitial and the temperature evolution of electron radiation damage in germanium are discussed.
46.	Carvalho, A., et al. (author) Identification of the local vibrational modes of small nitrogen clusters in dilute GaAsN 2007 In: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 401-402, s. 339-342 Journal article (peer-reviewed)abstract Ultra-high-resolution infra-red local vibrational mode (IR LVM) spectroscopy measurements together with density-functional calculations have been used to identify the signatures of close substitutional nitrogen (NAs) pairs in GaAs1 - x Nx alloys with concentrations of x < 0.025. We show that the presence of sub-peaks close to the NAs absorption band can be attributed to nitrogen pairs up to fourth neighbor position. Additionally, we suggest that the nitrogen pairs which give rise to the deepest levels below the conduction band edge are the first to be removed upon annealing
47.	Carvalho, A., et al. (author) Intrinsic defect complexes in CdTe and ZnTe 2011 In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 519:21, s. 7468-7471 Journal article (peer-reviewed)abstract Radiation defects in CdTe and ZnTe are modeled from first principles. The most important intrinsic defects resulting from cation evaporation or displacement are cation vacancies and tellurium anti-sites, electrically active defects characterized by a low formation energy. The reactions between those two defects are investigated. Since cation vacancy clusters of less than four vacancies are not stable, it is argued that cation vacancy aggregation is not a dominant process in near-equilibrium conditions. In-grown or radiation-induced clusters of four cation vacancies may serve as a nucleation center for tellurium precipitation. The formation energy of these small voids is lower in ZnTe than in CdTe. Additionally, cation-anion divacancies are stable in ZnTe and in p-type CdTe.
48.	Carvalho, A., et al. (author) Intrinsic defects in CdTe and CdZnTe alloys 2009 In: Physica. B, Condensed matter. - : Elsevier BV. - 0921-4526 .- 1873-2135. ; 404:23-24, s. 5019-5021 Journal article (peer-reviewed)abstract The Cd vacancy (VCd) and Te anti-site (TeCd) are two dominant defects in CdTe and CdZnTe alloys grown in Terich conditions. We examine the properties of these two intrinsic defects in Cd1-xZnxTe alloys with x < 0:5 using first-principles calculations. It is shown that Cd vacancies become progressively more favourable with increasing Zn content, in contrast with Te anti-sites, which show the opposite behaviour, explaining the trend towards p-type conductivity in Cd1-xZnxTe.
49.	Carvalho, A., et al. (author) Local-density-functional calculations of the vacancy-oxygen center in Ge 2007 In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:11 Journal article (peer-reviewed)abstract We carry out a comprehensive density-functional study of the vacancy-oxygen (VO) center in germanium using large H-terminated Ge clusters. The importance of a nonlinear core correction to account for the involvement of the 3d electrons in Ge-O bonds is discussed. We calculate the electrical levels and the vibrational modes of VO0, VO-, and VO= finding close agreement with experiment. We also explore the reorientation, migration, and dissociation mechanisms of neutral and negatively charged VO and compare the calculated energy barriers with experimental data. We conclude that the defect is likely to anneal through both mechanisms.
50.	Carvalho, A., et al. (author) Oxygen defects in irradiated germanium 2007 In: Journal of materials science. Materials in electronics. - : Springer Science and Business Media LLC. - 0957-4522 .- 1573-482X. ; 18:7, s. 781-786 Journal article (peer-reviewed)abstract The defects present in oxygen-rich irradiated germanium have been extensively characterised from an experimental point of view. Here, we summarise recent theoretical findings obtained using the cluster method and discuss their relation with the experimental data. In order to find a microscopic interpretation of the reactions taking place in this material upon annealing up to 400°C, we performed nudged elastic band (NEB) calculations of the migration and dissociation paths of VO, as well as a modelling of other oxygen-related complexes that are expected to form in this temperature range. Energy barriers of 1.5 (1.1) eV and 1.2 (0.9) eV for the dissociation and migration of the neutral (negatively charged) VO defect are found. We compare these with the activation energies estimated from the analysis of Hall effect, deep level transient spectroscopy (DLTS) and infra-red (IR) spectroscopy annealing data reported in literature.

Skapa referenser, mejla, bekava och länka

Permalink

Träfflista för sökning "WFRF:(Öberg Sven) "

Refine your search

Year