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Search Results: 1 - 10 of 1623 matches for " Ulf Jansson "
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Functionalization and Area-Selective Deposition of Magnetic Carbon-Coated Iron Nanoparticles from Solution
Erika Widenkvist,Oscar Alm,Mats Boman,Ulf Jansson,Helena Grennberg
Journal of Nanotechnology , 2011, DOI: 10.1155/2011/342368
Abstract: A route to area-selective deposition of carbon-coated iron nanoparticles, involving chemical modification of the surface of the particles, is described. Partial oxidative etching of the coating introduces carboxylic groups, which then are esterified. The functionalized particles can be selectively deposited on the Si areas of Si/SiO2 substrates by a simple dipping procedure. Nanoparticles and nanoassemblies have been analyzed using SEM, TEM, and XPS. 1. Introduction Materials composed of nanostructures are of great interest in the search for new functional materials. Magnetic iron nanoparticles are for example potential candidates for a variety of applications ranging from data storage to drug delivery [1–4]. To make use of the size-dependent properties, it is crucial to have means to individualize the nanoparticles in a controlled manner. Many applications also require a simple and reliable process for area-selective deposition of nanoparticles on a surface. In situ growth of nanostructures on the desired surface area often involves relatively high temperatures, which can be a major drawback when it comes to choice of substrate. Significant amounts of impurities in the as-grown material can also be problematic in this approach. Postfabrication assembly of the nanoparticles is a way to overcome these problems, and within this category, solution-based methods are of particular interest due to the scalability. Deposition from solution can be simple, of low-cost and relatively easy to scale up, provided the inherent problem of insolubility and aggregation of the nanostructures in solution is resolved. We have previously developed a solution-based area-selective deposition process for covalently functionalized multiwalled carbon nanotubes (MWCNTs) [5]. The nanotubes form stable solutions, and area-selective deposition on silicon/silicon oxide patterned surfaces was achieved for esterified nanotubes by a dip-rinse-dry protocol. In the present study, we have expanded the scope of our area-selective deposition protocol to also include magnetic carbon-coated Fe nanoparticles produced by laser-assisted chemical vapor deposition (LCVD). The particles consist of a metallic nucleus surrounded by a carbon shell containing both graphitic and amorphous carbon, thus the outer shell would be susceptible for the same type of chemistry as previously developed for carbon nanotubes [6–10]. Removing the amorphous outer layer and exposing the inner graphitic layer should render the functionalization and deposition process equally applicable to the coated iron nanoparticles.
Molecular adsorption in graphene with divacancy defects
Biplab Sanyal,Olle Eriksson,Ulf Jansson,Helena Grennberg
Physics , 2009, DOI: 10.1103/PhysRevB.79.113409
Abstract: We have investigated theoretically the adsorption of molecules onto graphene with divacancy defects. Using ab-initio density functional calculations, we have found that O2, CO, N2, B2 and H2O molecules all interact strongly with a divacancy in a graphene layer. Along with a complex geometry of the molecule-graphene bonding, metallic behavior of the graphene layer in presence of CO and N2 molecules have been found with a large density of states in the vicinity of the Fermi level suggesting an increase in the conductivity. The adsorption of N2 is particularly interesting since the N atoms dissociate in the vicinity of the defects, and take the place where the missing C atoms of the divacancy used to sit. In this way, the defected graphene structure is healed geometrically, and at the same time doped with electron states.
Electronic Structure and Chemical Bonding of Amorphous Chromium Carbide Thin Films
Martin Magnuson,Matilda Andersson,Jun Lu,Lars Hultman,Ulf Jansson
Physics , 2012, DOI: 10.1088/0953-8984/24/22/225004
Abstract: The microstructure, electronic structure, and chemical bonding of chromium carbide thin films with different carbon contents have been investigated with high-resolution transmission electron microscopy, electron energy loss spectroscopy and soft x-ray absorption-emission spectroscopies. Most of the films can be described as amorphous nanocomposites with non-crystalline CrCx in an amorphous carbon matrix. At high carbon contents, graphene-like structures are formed in the amorphous carbon matrix. At 47 at% carbon content, randomly oriented nanocrystallites are formed creating a complex microstructure of three components. The soft x-ray absorption-emission study shows additional peak structures exhibiting non-octahedral coordination and bonding.
Structure and bonding in amorphous iron carbide thin films
Andrej Furlan,Ulf Jansson,Jun Lu,Lars Hultman,Martin Magnuson
Physics , 2015, DOI: 10.1088/0953-8984/27/4/045002
Abstract: We investigate the amorphous structure, chemical bonding, and electrical properties of magnetron sputtered Fe1-xCx (0.21
Crystallization characteristics and chemical bonding properties of nickel carbide thin film nanocomposites
Andrej Furlan,Jun Lu,Lars Hultman,Ulf Jansson,Martin Magnuson
Physics , 2014, DOI: 10.1088/0953-8984/26/41/415501
Abstract: The crystal structure and chemical bonding of magnetron-sputtering deposited nickel carbide Ni$_{1-x}$C$_{x}$ (0.05$\leq$x$\leq$0.62) thin films have been investigated by high-resolution X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and soft X-ray absorption spectroscopy. By using X-ray as well as electron diffraction, we found carbon-containing hcp-Ni (hcp-NiC$_{y}$ phase), instead of the expected rhombohedral-Ni$_{3}$C. At low carbon content (4.9 at\%) the thin film consists of hcp-NiC$_{y}$ nanocrystallites mixed with a smaller amount of fcc-NiC$_{x}$. The average grain size is about 10-20 nm. With the increase of carbon content to 16.3 at\%, the film contains single-phase hcp-NiC$_{y}$ nanocrystallites with expanded lattice parameters. With further increase of carbon content to 38 at\%, and 62 at\%, the films transform to X-ray amorphous materials with hcp-NiC$_{y}$ and fcc-NiC$_{x }$ nanodomain structures in an amorphous carbon-rich matrix. Raman spectra of carbon indicate dominant $sp^{2}$ hybridization, consistent with photoelectron spectra that show a decreasing amount of C-Ni phase with increasing carbon content. The Ni $3d$ - C $2p$ hybridization in the hexagonal structure gives rise to the salient double-peak structure in Ni $2p$ soft X-ray absorption spectra at 16.3 at\% that changes with carbon content. We also show that the resistivity is not only governed by the amount of carbon, but increases by more than a factor of two when the samples transform from crystalline to amorphous.
A first principles study of the stability and mobility of defects in titanium carbide
Mikael R?sander,Biplab Sanyal,Ulf Jansson,Olle Eriksson
Physics , 2013,
Abstract: We have performed density functional calculations of the formation energies of substitutional transition metal (TM) defects, C vacancies, and C interstitial defects in TiC. In addition we have evaluated the migration energy barriers for C atoms in the presence of TM impurities. We find that the solubility of TM impurities taken from the 3d TM series is low and only Sc and V impurities can be dissolved into TiC at equilibrium. In addition, we find that the migration energy barriers of C in TiC are greatly affected by the presence of TM impurities: The migration barriers are generally lower in the presence of impurities compared to pure TiC and show a clear dependence on the atomic size of the TM impurities. We propose that the mobility of C in TiC will be the highest in the presence of TM impurities from the middle of the 3d TM series.
Electronic structure and chemical bonding of nc-TiC/a-C nanocomposites
Martin Magnuson,Erik Lewin,Lars Hultman,Ulf Jansson
Physics , 2011, DOI: 10.1103/PhysRevB.80.235108
Abstract: The electronic structure of nanocrystalline (nc-) TiC/amorphous C nanocomposites has been investigated by soft x-ray absorption and emission spectroscopy. The measured spectra at the Ti 2p and C 1s thresholds of the nanocomposites are compared to those of Ti metal and amorphous C. The corresponding intensities of the electronic states for the valence and conduction bands in the nanocomposites are shown to strongly depend on the TiC carbide grain size. An increased charge-transfer between the Ti 3d-eg states and the C 2p states has been identified as the grain size decreases, causing an increased ionicity of the TiC nanocrystallites. It is suggested that the charge-transfer occurs at the interface between the nanocrystalline TiC and the amorphous C matrix and represents an interface bonding which may be essential for the understanding of the properties of nc-TiC/amorphous C and similar nanocomposites.
Sickness Absence Due to Otoaudiological Diagnoses and Risk of Disability Pension: A Nationwide Swedish Prospective Cohort Study
Emilie Friberg, Catarina Jansson, Ellenor Mittendorfer-Rutz, Ulf Rosenhall, Kristina Alexanderson
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0029966
Abstract: Background Hearing difficulties are a large public health problem. Knowledge is scarce regarding risk of disability pension among people who have been sickness absent due to these difficulties. Methods A cohort including all 4,687,756 individuals living in Sweden in 2005, aged 20–64, and not on disability or old-age pension, was followed through 2009. Incidence rate ratios (RR) of disability pension with 95% confidence intervals (CI) were estimated using Cox proportional hazard models. Results In multivariable models, individuals who had a sick-leave spell due to otoaudiological diagnoses in 2005 had a 1.52-fold (95% CI: 1.43–1.62) increased risk of being granted a disability pension compared to individuals on sick leave due to other diagnoses. Hearing and tinnitus sick-leave diagnoses were associated with risk of disability pension: RR 3.38, 95% CI: 3.04–3.75, and 3.30, 95% CI: 2.95–3.68, respectively. No association was observed between sick leave due to vertigo diagnoses and disability pension whereas otological diagnoses and no sick leave were inversely associated with risk of disability pension compared to non-otoaudiological sick-leave diagnoses. Sick leave due to otoaudiological diagnoses was positively associated with risk of disability pension due to otoaudiological diagnoses and sick leave due to a tinnitus diagnosis was also associated with risk of disability pension due to mental diagnoses. The risk of disability pension among individuals with hearing or tinnitus sick-leave diagnoses was highest in the age group 35–44. Moreover, men had a slightly higher risk. Conclusion This large cohort study suggests an increased risk of disability pension among those with sickness absence due to otoaudiological diagnoses, particularly hearing and tinnitus diagnoses, compared to those with sickness absence due to non-otoaudiological diagnoses.
Gender differences in trends of acute myocardial infarction events: The Northern Sweden MONICA study 1985 – 2004
Dan Lundblad, Lars Holmgren, Jan-H?kan Jansson, Ulf N?slund, Mats Eliasson
BMC Cardiovascular Disorders , 2008, DOI: 10.1186/1471-2261-8-17
Abstract: Diagnosed MI events in subjects aged 25–64 years in the Counties of Norrbotten and V?sterbotten were validated according to the MONICA protocol. The total number of events registered up to January 1, 2005 was 11,763: 9,387 in men and 2,376 in women.The proportion of male/female events has decreased from 5.5:1 to 3:1. For males the reductions were 30% and 70% for first and recurrent MI, respectively, and for women 0% and 40% in the 55–64 year group. For both sexes a 50% reduction in 28-day case fatality was seen in the 25–64 year-group. Mortality was reduced by 69% and 45% in men and women, respectively.First and recurrent events of myocardial infarction was markedly reduced in men over the 20-year observation period, but for women the reduction was seen only for recurrent infarctions. Case fatality, on the other hand, was markedly reduced for both sexes. As a result of the positive effects on incidence and case fatality a substantial reduction was seen in total mortality, most pronounced for men.Coronary heart disease (CHD) is the leading cause of death in Sweden as well as in most Western European countries and in the United States. Incidence and mortality rates in CHD have decreased substantially during the last decades, and this trend seems to continue [1-4].At the start of the MONICA project in 1985 the incidence of, and mortality due to, myocardial infarction (MI) in the two northernmost counties in Sweden were the highest in the country. However, they have gradually approached the national average indicating a faster reduction in Northern Sweden than in the rest of the country [5]. Generally, in the Western world, the decreased mortality in CHD is due to a combination of declining incidence and improved survival. Better primary prevention and improvements in acute coronary care, including secondary prevention, may explain these impressing achievements [1].Gender differences in both events and case-fatality, and thereby also in mortality due to CHD, have been s
Carbon release by selective alloying of transition metal carbides
Mikael R?sander,Erik Lewin,Ola Wilhelmsson,Biplab Sanyal,Mattias Klintenberg,Olle Eriksson,Ulf Jansson
Physics , 2011, DOI: 10.1088/0953-8984/23/35/355401
Abstract: We have performed first principles density functional theory calculations on TiC alloyed on the Ti sublattice with 3d transition metals ranging from Sc to Zn. The theory is accompanied with experimental investigations, both as regards materials synthesis as well as characterization. Our results show that by dissolving a metal with a weak ability to form carbides, the stability of the alloy is lowered and a driving force for the release of carbon from the carbide is created. During thin film growth of a metal carbide this effect will favor the formation of a nanocomposite with carbide grains in a carbon matrix. The choice of alloying elements as well as their concentrations will affect the relative amount of carbon in the carbide and in the carbon matrix. This can be used to design the structure of nanocomposites and their physical and chemical properties. One example of applications is as low-friction coatings. Of the materials studied, we suggest the late 3d transition metals as the most promising elements for this phenomenon, at least when alloying with TiC.
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