This thesis presents a first principle approach to model helium diffusionand retention in molybdenum. Results from electron structure calculations within the framework of density functional theory are used to assess parameters in a rate theory model. The model is used to reproduce experimental desorption spectra, which, to a large degree of accuracy, coincide with experimental data in temperature regions relevant for nuclear fuel applications. The models indicate that produced helium will diffuse out into the fuel pin during operation. However, some helium will be trapped in molybdenum vacancies. The amount of trapped helium will largely depend on the fuel operational temperature. Data presented in the thesis is a first step towards a self consistent dataset of first principle data on helium diffusion in CERMET fuel, one candidate fuel suggested for transmutation of nuclear waste. To realise the use of CERMET fuel, modelling of fuel performance is essential, and to accomplish this, the understanding of helium diffusion and retention in molybdenum is one important aspect.

This Licentiate thesis summarizes the work carried out by the author the years 2004 to 2008 at the University of Iceland and the Royal Institute of Technology (KTH) in Sweden. The aim of the project was to investigate the structure of sapphire (alpha-Al2O3) surfaces, both for pure scientific reasons and also for potential use as substrate for GaN-growth by molecular beam epitaxy. More generally the thesis describes some surface science methods used for investigating the substrates; the general physical back ground, the experi- mental implementation and what information they can give. The described techniques are used for surface analysis on sapphire substrates which have been treated variously in order to optimize them for use as templates for epi- taxial growth of GaN or related III-V compounds. The thesis is based on three published papers. The first paper focuses on the formation a thin AlN layer on sapphire, which may act as a buffer layer for potential epitaxial growth of GaN or any related III-V materials. Two types of sapphire substrates (reconstructed and non- reconstructed) were exposed to ammonia resulting in the formation of AlN on the surface. The efficiency of the AlN formation (nitridation efficiency) for the two surfaces was then compared as a function of substrate temperature through photoelectron spectroscopy and low electron energy diffraction. The reconstructed surface showed a much higher nitridation efficiency than the non-reconstructed surface. In the second paper, the affect of different annealing processes on the sapphire morphology, and thus its capability to act as a template for GaN growth, was studied. Atomic force microscopy, X-ray diffraction analysis together with ellipsometry measurements showed that annealing in H2 ambient and subse- quent annealing at 1300 °C in O2 for 11 hours resulted in high quality and atomically flat sapphire surface suitable for III-V epitaxial growth. The third paper describes the effect of argon sputtering on cleaning GaN surfaces and the possibility of using indium as surfactant for establishing a clean and stoichiometric GaN surface, after such sputtering. Soft sputtering, followed by deposition of 2 ML of indium and subsequent annealing at around 500 °C resulted in a well ordered and clean GaN surface while hard sputtering introduced defects and incorporated both metallic gallium and indium in the surface.

This thesis presents results from numerical simulations of the Nernst effect dueto phase fluctuations in models of two-dimensional granular superconductors. Inaddition other transport properties, such as thermal conductivity and electrical re-sistivity are calculated. The models are based on a phase only description withLangevin or resistively and capacitively shunted Josephson junction (RCSJ) dy-namics, generalized to be valid for any type of two-dimensional lattice structure.All transport coefficients are evaluated from equilibrium correlation functions usingKubo formulas. In Paper I, anomalous sign reversals of the Nernst signal eN , corresponding tovortex motion from colder to hotter regions, are observed. These are attributedto geometric frustration effects close to magnetic fields commensurate with theunderlying lattice structure. The effect is seen also in systems with moderategeometric disorder, and should thus be possible to observe in real two-dimensionalgranular superconductors or Josephson junction arrays. Paper II presents two different derivations of an expression for the heat current inLangevin and RCSJ dynamics. The resulting expression is through our simulationsseen to obey the required Onsager relation, as well as giving consistent resultswhen calculating κ and eN via Kubo formulas and through the responses to anapplied temperature gradient. In zero magnetic field and at low-temperatures, thecontribution to the thermal conductivity κ in RCSJ dynamics is calculated usinga spin-wave approximation, and is shown to be independent of temperature anddiverge logarithmically with system size. At higher temperatures, κ shows a non-monotonic temperature dependence. In zero magnetic field κ has a anomalouslogarithmic size dependence also in this regime. The off-diagonal component ofthe thermoelectric tensor αxy is calculated and displays the very same ∼1/T dependence at low temperatures predicted from calculations based on Gaussiansuperconducting fluctuations.

Graphene is one of the most popular new materials both in the academic and private sectors. Its striking properties allow for radical redesigns of many electronic or storage devices. In this report, first, a brief theoretical description of graphene’s band structure is given using the tight/binding method, along with its unique properties. The principal objective is to explore how such electrical properties lead to spintronics applications. In graphene, due to low spin-orbit coupling, exceptional spin transport is observable. Hence, a practical introduction to some electrical and magnetic measurements on spin-valve devices is followed by some experimental results. In addition, key electrical properties of graphene such as sheet resistance, mobility, and Dirac point are calculated.

No description available.

No description available.

States of matter with quasi-particle excitations that exhibit anyonic statisticsare of great theoretical interest, especially in those cases where the anyons arenon-Abelian. Two of the most promising states that could support non-Abeliananyons are the ν = 5/2 quantum Hall state and the two dimensional p-wavesuperconductor, and they can both be understood as p-wave paired states. Themotivation for the present thesis is to get a better understanding of the theo-retical description of p-wave paired states.In the accompanying paper we construct an effective field theory for the 2Dspin-less p-wave paired superconductor that faithfully describes the topologicalproperties of the bulk state, and also provides a model for the subgap statesat vortex cores and edges. In particular it captures the topologically protectedzero modes and has the correct ground state degeneracy on the torus. Wealso show that our effective field theory becomes a topological field theory in awell defined scaling limit and that the vortices have the expected non-Abelianbraiding statistics.

One effective tool to probe a system revealing topological order is to biparti- tion the system in some way and look at the properties of the reduced density operator corresponding to one part of the system. In this thesis we focus on a bipartition scheme known as the particle cut in which the particles in the system are divided into two groups and we look at the rank of the re- duced density operator. In the context of fractional quantum Hall physics it is conjectured that the rank of the reduced density operator for a model Hamiltonian describing the system is equal to the number of quasi-hole states. Here we consider the Laughlin wave function as the model state for the system and try to put this conjecture on a firmer ground by trying to determine the rank of the reduced density operator and calculating the number of quasi-hole states. This is done by relating this conjecture to the mathematical properties of symmetric polynomials and proving a theorem that enables us to find the lowest total degree of symmetric polynomials that vanish under some specific transformation referred to as clustering transformation.

Denna studie är en bilderboksanalys som utifrån postkolonial teori och den narrativa metoden dekonstruktion syftar till att undersöka hur den Andre framställs i bilderböcker från två olika tidsepoker. Begreppet den Andre innebär de grupper som traditionellt sett är underordnade i samhället och som avviker från normen. Enligt läroplanen för förskolan (lpfö 18) ska pedagoger arbeta med litteratur med barnen, vilket i kombination med värdegrundsuppdraget gör att pedagoger måste vara medvetna om vilka normer som bilderböcker förmedlar. Detta blir ett argument för att studera bilderböcker. I analysen jämförs bilderböcker från en äldre (1918-1965) och en nutida (2006-2018) tidsepok, eftersom det går att säga att litteraturen avspeglar samhället och därför synliggör vilka normer som råder i en specifik tid. Resultatet visar att den Andre framställs som främmande och avvikande samt underordnas vithets- mans- och vuxennormen. Detta gestaltas på olika sätt beroende på vilken funktion den Andre har i berättelsen. När den Andre har rollen som antagonist eller om berättelsen kräver en karaktär som är annorlunda protagonisten så blir hon i högre grad porträtterad som avvikande. I äldre litteratur är den Andre ofta stereotypt framställd, negativt framställd eller exkluderad medan förhållandet i de nutida bilderböckerna framställs som lite mer jämlikt. Framförallt kategorin barn gestaltas som om de har förmåga att definiera sig själva och är inte motsatsen till normen längre. Det framgår av studien att bilderböckerna alltid framställer någon kategori som underordnad normen, oavsett vilken tid de är skrivna i. Den Andre blir stereotypt framställd i både äldre och nutida böcker. Slutsatsen blir således att den Andre som fenomen finns i alla bilderböcker, men att funktionen har ändrats över tid.

<p>Ytterligare forskningsfinansiärer: Knut and Alice WallenbergFoundation for a Fellowship Grant and Project funding (KAW 2015.0043), Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO MatLiUNo. 2009 00971), Swedish Research Council VR-RFI (#2017-00646_9), Swedish Foundation for Strategic Research(contract RIF14-0053)</p>