| 1. |
- Gunnbjornsdottir, M. I., et al.
(författare)
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Obesity and nocturnal gastro-oesophageal reflux are related to onset of asthma and respiratory symptoms
- 2004
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Ingår i: Eur Respir J. - : European Respiratory Society (ERS). ; 24:1
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Tidskriftsartikel (refereegranskat)abstract
- Several studies have identified obesity as a risk factor for asthma in both children and adults. An increased prevalence of asthma in subjects with gastro-oesophageal reflux (GOR) and obstructive sleep apnoea syndrome has also been reported. The aim of this investigation was to study obesity, nocturnal GOR and snoring as independent risk factors for onset of asthma and respiratory symptoms in a Nordic population. In a 5-10 yr follow-up study of the European Community Respiratory Health Survey in Iceland, Norway, Denmark, Sweden and Estonia, a postal questionnaire was sent to previous respondents. A total of 16,191 participants responded to the questionnaire. Reported onset of asthma, wheeze and night-time symptoms as well as nocturnal GOR and habitual snoring increased in prevalence along with the increase in body mass index (BMI). After adjusting for nocturnal GOR, habitual snoring and other confounders, obesity (BMI >30) remained significantly related to the onset of asthma, wheeze and night-time symptoms. Nocturnal GOR was independently related to the onset of asthma and in addition, both nocturnal GOR and habitual snoring were independently related to onset of wheeze and night-time symptoms. This study adds evidence to an independent relationship between obesity, nocturnal gastro-oesophageal reflux and habitual snoring and the onset of asthma and respiratory symptoms in adults.
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| 2. |
- Hallén, Anders., et al.
(författare)
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Ion implantation of silicon carbide
- 2002
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - 0168-583X .- 1872-9584. ; 186, s. 186-194
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Tidskriftsartikel (refereegranskat)abstract
- Ion implantation is an important technique for a successful implementation of commercial SiC devices. Much effort has also been devoted to optimising implantation and annealing parameters to improve the electrical device characteristics. However, there is a severe lack of understanding of the fundamental implantation process and the generation and annealing kinetics of point defects and defect complexes. Only very few of the most elementary intrinsic point defects have been unambiguously identified so far. To reach a deeper understanding of the basic mechanisms SiC samples have been implanted with a broad range of ions, energies, doses, etc., and the resulting defects and damage produced in the lattice have been studied with a multitude of characterisation techniques. In this contribution we will review some of the results generated recently and also try to indicate where more research is needed. In particular, deep level transient spectroscopy (DLTS) has been used to investigate point defects at very low doses and transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS) are used for studying the damage build-up at high doses.
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| 3. |
- Janson, M S, et al.
(författare)
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Diffusion of dopants and impurities in device structures of SiC, SiGe and Si
- 2001
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Ingår i: DIFFUSIONS IN MATERIALS. ; , s. 597-609
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Konferensbidrag (refereegranskat)abstract
- Silicon Carbide (SiC) has a high thermal stability and for most elements temperatures in excess of 2000 degreesC are anticipated to reach reasonable diffusivities (greater than or equal to 10(-13) cm(2)/s). We demonstrate, however, that light elements, like hydrogen and lithium, exhibit a considerable mobility already at less than or equal to 400 degreesC, Technologically, the principal interest in these light elements arises because of their ability to electrically passivate shallow acceptors and donors as well as deep level defects in common semiconductors (SiC, Si, GaAs). Indeed, for both hydrogen and lithium the diffusion kinetics is shown to be strongly affected by trapping and de-trapping at boron impurities in the SiC layers. Evidence is also provided that hydrogen migrates as a positively charged ion in p-type SiC. Furthermore, similar to that in crystalline silicon, transient enhanced diffusion of ion-implanted boron is observed in SiC. The initial boron diffusivity during postimplant annealing at 1600 degreesC is enhanced by more than two orders of magnitude compared to equilibrium conditions. For Silicon Germanium (SiGe) diffusion of the n-type dopants Sb and P is studied. Comparing results from strained and relaxed SiGe layers annealed under inert and oxidizing conditions it is unambiguously shown that the diffusion of Sb is almost exclusively mediated by vacancies. On the other hand, P diffusion is predominantly assisted by Si self-interstitials and in this case compositional and strain effects in the SiGe layers are competing.
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| 4. |
- Janson, M S, et al.
(författare)
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Dissociation energy of the passivating hydrogen-aluminum complex in 4H-SiC
- 2001
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Ingår i: Materials Science Forum. ; , s. 427-430
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The thermal stability of the passivating hydrogen-aluminum complex ((HAl)-H-2) in 4H-silicon carbide has been studied by determining the effective diffusion constant for hydrogen in an AI-doped epitaxial layer. Assuming a complex comprised of one H-2 and one AI acceptor ion, the extracted diffusivities provide the dissociation frequency of the complex. The extracted frequencies cover three orders of magnitude and yield a close to perfect fit to an Arrhenius equation with the extracted dissociation energy for the (HAl)-H-2-complex equal to 1.66 (+/-0.05) eV and a pre-exponential attempt frequency nu (0) = 1.7x10(13) s(-1) in good agreement with the expected value for a first order dissociation process.
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| 5. |
- Janson, Martin S., et al.
(författare)
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Electric-field-assisted migration and accumulation of hydrogen in silicon carbide
- 2000
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 61:11, s. 7195-7198
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Tidskriftsartikel (refereegranskat)abstract
- The diffusion of deuterium (H-2) in epitaxial 4H-SiC layers with buried highly Al-acceptor doped regions has been studied by secondary ion mass spectrometry. H-2 was introduced in the near surface region by the use of 20-keV implantation after which the samples were thermally annealed. As a result, an anomalous accumulation of H-2 in the high doped layers was observed. To explain the accumulation kinetics, a model is proposed where positively charged H-2 ions are driven into the high doped layer and become trapped there by the strong electric field at the edges. This effect is important for other semiconductors as well, since hydrogen is a common impurity present at high concentrations in many semiconductors.
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| 6. |
- Linnarsson, Margareta K., et al.
(författare)
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Solubility limit and precipitate formation in Al-doped 4H-SiC epitaxial material
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 79:13, s. 2016-2018
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Tidskriftsartikel (refereegranskat)abstract
- Heavily Al-doped 4H-SiC structures have been prepared by vapor phase epitaxy. Subsequent anneals have been carried out in an Ar atmosphere in a rf-heated furnace between 1500 degreesC and 2000 degreesC for 0.5 to 3 h. Secondary ion mass spectrometry has been utilized to obtain Al concentration versus depth as well as lateral distributions (ion images). Transmission electron microscopy (TEM) has been employed to study the crystallinity and determine phase composition after heat treatment. A solubility limit of similar to 2x10(20) Al/cm(3) (1900 degreesC) is extracted. Three-dimensional ion images show that the Al distribution does not remain homogeneous in layers heat treated at 1700 degreesC or above when the Al concentration exceeds 2x10(20) cm(-3). Al-containing precipitates are identified by energy-filtered TEM.
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| 7. |
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| 8. |
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| 9. |
- Amin, Kawa, et al.
(författare)
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Inflammation and structural changes in the airways of patients with primary Sjogren's syndrome
- 2001
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Ingår i: Respiratory Medicine. - : Elsevier BV. - 0954-6111 .- 1532-3064. ; 95:11, s. 904-910
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Tidskriftsartikel (refereegranskat)abstract
- The present study aimed to compare the cellular pattern and structural changes in the airways of patients with primary Sjögren's syndrome (pSS) with healthy controls. Bronchial biopsy specimens were obtained from seven subjects with pSS and seven healthy controls. All the patients with pSS had increased bronchial responsiveness to methacholine. In the biopsies inflammatory cells, cytokine-producing cells, tenascin and laminin were visual zed by immunostaining. Patients with pSS had a higher number of neutrophils and mast cells than healthy controls, while the number of eosinophils was similar in the two groups. The number of IL-8-positive cells was higher in pSS butthe numbers of IL-4-and IL-5-positive cells were not significantly different between pSS and healthy controls. The numbers of T cells in patients with pSS were higher than in healthy controls, while the numbers of CD25-positive cells were similar to the healthy controls. The degree of epithelial integrity in patients with pSS was significantly lower than in the control group and the tenascin and laminin layers were significantly thicker in the pSS group. There was a correlation between the number of mast cells and the thickness of the tenascin and laminin layers in pSS. In conclusion, we found that the cellular pattern in the bronchial mucosa of patients with pSS displayed large numbers of neutrophils, mast cells and T-lymphocytes. These changes in inflammatory cell numbers seemed to relate to the observed increased epithelial damage and structural changes of the subepithelium. The structural findings, but not the pattern of inflammatory cells, are shared with atopic asthma and may relate to the increased bronchial hyper-responsiveness seen in both diseases.
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| 10. |
- Badel, Xavier, et al.
(författare)
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Formation of pn junctions in deep silicon pores for X-ray imaging detector applications
- 2003
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 509:1-3, s. 96-101
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Tidskriftsartikel (refereegranskat)abstract
- The formation of pn junctions in deep silicon pores has been studied for a new concept of X-ray imaging detectors. The sensitive part of the device is an array of CsI(Tl) columns formed by filling a silicon matrix of pores having pn junctions in their walls. Under X-ray illumination, the CsI(TI) scintillator emits photons that are collected by the pn junctions. Relatively high signal collection efficiency is expected. However, the formation of pn junctions inside pore walls represents a challenging step in the detector fabrication. In this work pore matrices were fabricated in n-type silicon by deep reactive ion etching and by photo-electrochemical etching. The pn junctions were formed either by boron diffusion or deposition of boron doped poly-silicon. Various techniques were used to analyze the transverse depth profiles of boron atoms at different pore depths. The study shows successful results for pn-junctions formed both by diffusion and by poly-silicon deposition.
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