Charge state of the O2_{2} molecule during silicon oxidation through hybrid functional calculations

We study the charge state of the diffusing O$_2$ molecule during silicon oxidation through hybrid functional calculations. We calculate charge transition levels of O$_2$ in bulk SiO$_2$ and use theoretical band offsets to align these levels with respect to the Si band edges. To overcome the band-gap problem of semilocal density fuctionals, we employ hybrid functionals with both predefined and empirically adjusted mixing coefficients. We find that the charge transition level $\epsilon^{0/-}$ in bulk SiO$_2$ occurs at $\sim$1.1 eV above the silicon conduction band edge, implying that the O$_2$ molecule diffuses through the oxide in the neutral charge state. While interfacial effects concur to lower the charge transition level, our estimates suggest that the neutral charge state persists until silicon oxidation.Comment: 4 pages, 3 figure

Band Offsets at Semiconductor-Oxide Interfaces from Hybrid Density Functional Calculations

Band offsets at semiconductor-oxide interfaces are determined through a scheme based on hybrid density functionals, which incorporate a fraction $\alpha$ of Hartree-Fock exchange. For each bulk component, the fraction $\alpha$ is tuned to reproduce the experimental band gap, and the conduction and valence band edges are then located with respect to a reference level. The lineup of the bulk reference levels is determined through an interface calculation, and shown to be almost independent of the fraction $\alpha$. Application of this scheme to the Si-SiO$_2$, SiC-SiO$_2$, and Si-HfO$_2$ interfaces yields excellent agreement with experiment.Comment: 4 pages, 4 figure

Defect Energy Levels in Density Functional Calculations: Alignment and Band Gap Problem

For materials of varying band gap, we compare energy levels of atomically localized defects calculated within a semilocal and a hybrid density-functional scheme. Since the latter scheme partially relieves the band gap problem, our study describes how calculated defect levels shift when the band gap approaches the experimental value. When suitably aligned, defect levels obtained from total-energy differences correspond closely, showing average shifts of at most 0.2 eV irrespective of band gap. Systematic deviations from ideal alignment increase with the extent of the defect wave function. A guideline for comparing calculated and experimental defect levels is provided.Comment: 4 pages, 3 figure

First principles investigation of defect energy levels at semiconductor-oxide interfaces: Oxygen vacancies and hydrogen interstitials in the Si-SiO2-HfO2 stack

We introduce a scheme for the calculation of band offsets and defect energy levels at semiconductor-oxide interfaces. Our scheme is based on the use of realistic atomistic models of the interface structure and of hybrid functionals for the evaluation of the electronic structure. This scheme is herein applied to the technologically relevant Si-SiO2-HfO2 stack. Calculated band offsets show a very good agreement with experimental values. In particular, we focus on the energy levels of the oxygen vacancy defect and the interstitial hydrogen impurity. The defect levels are aligned with respect to the interface band structure and determined for varying location in the dielectric stack. The most stable charge states are identified as the Fermi level sweeps through the silicon band gap

Особенности процессов тепло- и массообмена в миниатюрных тепловых трубах

PrioriteringsCentrum har på uppdrag av Socialstyrelsen genomfört en kartläggning av på vilket sätt hälso- och sjukvårdens huvudmän och andra centrala aktörer arbetar med prioriteringar och har utvärderat hur detta arbete överensstämmer med intentionerna i riksdagens beslut om prioriteringar. Vi har även analyserat innehållet i och tillämpningen av riksdagens riktlinjer för prioriteringar i hälso- och sjukvården. Det har skett genom en etisk analys och mot bakgrund av ett stort antal intervjuer i landsting och kommuner samt med representanter för statliga myndigheter och yrkesorganisationer och med ledning av vad som framkommit i tidigare uppföljningar. Vi föreslår i rapporten ett anta förändringar och förtydliganden av riktlinjerna. Vi kan konstatera att sättet att arbeta med prioriteringar i landsting och kommuner inte är helt olikt det som gällde när Prioriteringsdelegationen redovisade en motsvarande uppföljning år 2001. Fortfarande finns knappast några öppna beslut om fördelning och prioritering av resurser om man med öppenhet avser att beslutsfattaren medvetet överväger flera alternativ och att grunderna för besluten är kända för dem som önskar ta del av dem. I situationer då tillgängliga resurser inte befinner sig i paritet med  önskvärda ambitioner får sjukvårdspersonalen ta det största ansvaret för att besluta om och genomföra ransonering av vården. Förutom på chefsnivå tycks dock sjukvårdpersonal fortfarande i liten utsträckning vara medveten om de etiska principer som enligt riksdagsbeslutet ska styra prioriteringar i vården. Få känner till den etiska plattformen med de tre etiska principerna. Lokala mallar eller styrdokument för prioriteringar är ovanliga. Det saknas nödvändiga förutsättningar för att tillämpa riksdagens prioriteringsbeslut och det finns inte heller några tydliga strategier för hur man vill skapa sådana förutsättningar inom landstingen. Den kommunala vård- och omsorgsverksamheten upplever sig fortfarande i ringa utsträckning berörd av den etiska plattformen och prioriteringsprinciperna. Någon gemensam prioritering mellan huvudmännen sker knappast alls. Medborgarna är i mycket liten utsträckning involverade i prioriteringsarbetet. Den ökade öppenheten gentemot brukare innebär oftast att viss information om prioriteringar sker genom traditionella kanaler som patientorganisationer, pensionärsråd och handikappråd och synpunkter inhämtas via allmänna patientenkäter medan klagomål hanteras genom patientnämnder. Vi har också funnit tydliga skillnader när det gäller hur arbetet med prioriteringar bedrivs idag jämfört med för sex år sedan. Genom Socialstyrelsen och Läkemedelsförmånsnämnden har staten tagit  ledningen när det gäller att visa hur prioriteringar kan göras på ett systematiskt och öppet sätt. Detta arbete har resulterat i en tydlig metodutveckling. Idag finns det dessutom flera exempel på konkret utvecklingsarbete och samverkan mellan huvudmän kring det vidare begreppet kunskapsstyrd vård till vilket systematiska prioriteringar är starkt relaterat. Vi kan också notera olika initiativ till vertikala prioriteringar i verksamheten där det framförallt är läkarkåren som engagerat sig; men också enstaka försök med systematiska politiska prioriteringar. Det finns dessutom flera lovande utvecklingsprojekt rörande prioriteringar som initierats av och drivs av sjukvårdspersonal både lokalt och nationellt. Yrkesförbunden är också mer aktiva idag när det gäller att sprida kunskap om prioriteringar...

To accept, or not to accept, that is the question: citizen reactions to rationing. Health Expect. 2011 Oct 28

Abstract Background The publicly financed health service in Sweden has come under increasing pressure, forcing policy makers to consider restrictions. Objective To describe different perceptions of rationing, in particular, what citizens themselves believe influences their acceptance of having to stand aside for others in a public health service. Design Qualitative interviews, analyzed by phenomenography, describing perceptions by different categories. Setting and participants Purposeful sample of 14 Swedish citizens, based on demographic criteria and attitudes toward allocation in health care. Results Participants expressed high awareness of limitations in public resources and the necessity of rationing. Acceptance of rationing could increase or decrease, depending on one's (a) awareness that healthcare resources are limited, (b) endorsement of universal health care, (c) knowledge and acceptance of the principles guiding rationing, and (d) knowledge about alternatives to public health services. Conclusions This study suggests that decision makers should be more explicit in describing the dilemma of resource limitations in a publicly funded healthcare system. Openness enables citizens to gain the insight to make informed decisions, i.e. to use public services or to "opt out" of the public sector solution if they consider rationing decisions unacceptable

On the role of Alkaline Earth Metal Oxides in Environmental Catalysis

In heterogeneous catalysis, metal oxides have various roles: as catalysts, as support material for catalytically active metal particles, as promoters, as stabilizers, or as storage materials. Although their main application is as support material, their role as promoter or storage material becomes increasingly important as emission legislations are becoming more stringent. One such case is the catalytic cleaning of emissions from lean burn gasoline and diesel engines. Running the engine at lean conditions implies that the presently employed catalytic concepts are incapable of continuous NOx reduction. In this thesis, density functional theory (DFT) has been used to study the role of alkaline earth metal oxides, both as a storage material and as a support material for catalytically active metals. The main focus has been NOx storage in barium containing NOx storage and reduction (NSR) catalysts. As the storage material is experimentally ill-defined, different models for the storage material have been investigated (BaO(100), (BaO)9 cluster and BaCO3(110)). An atomistic understanding of species formed upon NO2 exposure to the storage material is presented. The mechanistic understanding comprises a pair-wise adsorption of NO2 with enhanced stability compared with single NO2 adsorption. Moreover, for NO2 storage in BaCO3, the pair-wise mechanism is shown to be crucial for effective surface decarbonation. Ab initio molecular dynamics calculations for NO2 adsorption on BaO(100) have been performed to study the dynamics of adsorbed NO2 molecules. Nitrites and nitrates are found to be mobile on the short time scale of the simulations (~4 ps). The role of oxides as model support material has been studied considering Pt atom, dimer and film adsorption on MgO(100) and BaO(100). For MgO(100), Pd, Ag and Au adsorption have been studied also. Both the metal/metal-oxide bond and support effects on the CO-metal bond upon CO adsorption have been explored. The support is found to prepare Pt for CO adsorption, resulting in both an enhanced Pt-CO bond and support-PtCO bond. However, this effect is only observed for mono-layer metal adsorption. Finally, the CO oxidation reaction is studied over a MgO supported Au nanoparticle. Special focus is given to adsorption and reaction at low-coordinated Au sites at the Au/MgO perimeter and to the effects of dopants. Keywords DFT, adsorption, catalysis, NOx storage, CO oxidation, supported catalysts, metal oxide, BaO, MgO, BaCO3, Au, slab, cluste

On the role of Alkaline Earth Metal Oxides in Environmental Catalysis

In heterogeneous catalysis, metal oxides have various roles: as catalysts, as support material for catalytically active metal particles, as promoters, as stabilizers, or as storage materials. Although their main application is as support material, their role as promoter or storage material becomes increasingly important as emission legislations are becoming more stringent. One such case is the catalytic cleaning of emissions from lean burn gasoline and diesel engines. Running the engine at lean conditions implies that the presently employed catalytic concepts are incapable of continuous NOx reduction. In this thesis, density functional theory (DFT) has been used to study the role of alkaline earth metal oxides, both as a storage material and as a support material for catalytically active metals. The main focus has been NOx storage in barium containing NOx storage and reduction (NSR) catalysts. As the storage material is experimentally ill-defined, different models for the storage material have been investigated (BaO(100), (BaO)9 cluster and BaCO3(110)). An atomistic understanding of species formed upon NO2 exposure to the storage material is presented. The mechanistic understanding comprises a pair-wise adsorption of NO2 with enhanced stability compared with single NO2 adsorption. Moreover, for NO2 storage in BaCO3, the pair-wise mechanism is shown to be crucial for effective surface decarbonation. Ab initio molecular dynamics calculations for NO2 adsorption on BaO(100) have been performed to study the dynamics of adsorbed NO2 molecules. Nitrites and nitrates are found to be mobile on the short time scale of the simulations (~4 ps). The role of oxides as model support material has been studied considering Pt atom, dimer and film adsorption on MgO(100) and BaO(100). For MgO(100), Pd, Ag and Au adsorption have been studied also. Both the metal/metal-oxide bond and support effects on the CO-metal bond upon CO adsorption have been explored. The support is found to prepare Pt for CO adsorption, resulting in both an enhanced Pt-CO bond and support-PtCO bond. However, this effect is only observed for mono-layer metal adsorption. Finally, the CO oxidation reaction is studied over a MgO supported Au nanoparticle. Special focus is given to adsorption and reaction at low-coordinated Au sites at the Au/MgO perimeter and to the effects of dopants. Keywords DFT, adsorption, catalysis, NOx storage, CO oxidation, supported catalysts, metal oxide, BaO, MgO, BaCO3, Au, slab, cluste