Recent observational achievements within cosmology and astrophysics have lead to a concordance model in which the energy content in our Universe is dominated by presumably fundamentally new and exotic ingredients – dark energy and dark matter. To reveal the nature of these ingredients is one of the greatest challenges in physics. The detection of a signal in gamma rays from dark matter annihilation would significantly contribute to revealing the nature of dark matter. This thesis presents derived imprints in gamma-ray spectra that could be expected from dark matter annihilation. In particular, dark matter particle candidates emerging in models with extra space dimensions, extending the standard model to be supersymmetric, and introducing an inert Higgs doublet are investigated. In all these scenarios dark matter annihilation induces sizeable and distinct signatures in their gamma-ray spectra. The predicted signals are in the form of monochromatic gamma-ray lines or a pronounced spectrum with a sharp cutoff at the dark matter particle’s mass. These signatures have no counterparts in the expected astrophysical background and are therefore well suited for dark matter searches. Furthermore, numerical simulations of galaxies are studied to learn how baryons, that is, stars and gas, affect the expected dark matter distribution inside disk galaxies such as the Milky Way. From regions of increased dark matter concentrations, annihilation signals are expected to be the strongest. Estimations of dark matter induced gamma-ray fluxes from such regions are presented. The types of dark matter signals presented in this thesis will be searched for with existing and future gamma-ray telescopes. Finally, a claimed detection of dark matter annihilation into gamma rays is discussed and found to be unconvincing.

The intriguing world of microbiology is nowadays accessible for detailed exploration at a single–molecular level. Optical tweezers are a novel instrument that allows for non–invasive manipulation of single cells by the sole use of laser light and operates on the nano– and micrometer scale which corresponds to the same length scale as living cells. Moreover, forces within the field of microbiology are typically in the picoNewton range which is in accordance with the capability of force measuring optical tweezers systems. Both these conformabilities imply that force measuring optical tweezers is suitable for studies of single living cells. This thesis focuses on the mechanisms of bacterial attachments to host cells which constitute the first step in bacterial infection processes. Bacteria bind specifically to host receptors by means of adhesins that are expressed either directly on the bacterial membrane or on micrometer–long adhesion organelles that are called pili. The properties of single adhesin–receptor bonds that mediate adherence of the bacterium Helicobacter pylori are first examined at various acidities. Further on, biomechanical properties of P pili expressed by Escherichia coli are presented to which computer simulations, that capture the complex kinetics of the pili structure and precisely replicate measured data, are applied. Simulations are found to be a powerful tool for investigations of adhesive attributes of binding systems and are utilized in the analyses of the specific binding properties of P pili on a single–pilus level. However, bacterial binding systems generally involve a multitude of adhesin–receptor bonds. To explore bacterial attachments, the knowledge from single–pilus studies is brought into a full multipili attachment scenario which is analyzed by means of theoretical treatments and simulations. The results are remarkable in several aspects. Not only is it found that the intrinsic properties of P pili are composed in an optimal combination to promote strong multipili bindings. The properties of the pili structure itself are also found to be optimized with respect to its in vivo environment. Indeed, the true meaning of the attributes derived at a single–pilus level cannot be unraveled until a multipili–binding system is considered. Whereas detailed studies are presented for the helix–like P pili expressed by Gram–negative Escherichia coli, conceptual studies are presented for the open coil–like T4 pili expressed by Gram–positive Streptococcus pneumoniae. The structural and adhesive properties of these two types of pili differ considerably. These dissimilarities have far–reaching consequences on the adhesion possibilities at both single–pilus and multipili levels which are discussed qualitatively. Moreover, error analyses of conventional data processing methods in dynamic force spectroscopy as well as development of novel analysis methods are presented. These findings provide better understanding of how to perform refined force measurements on single adhesion organelles as well as how to improve the analyses of measurement data to obtain accurate parameter values of biomechanical entities. In conclusion, this thesis comprises a study of bacterial adhesion organelles and the way they cooperate to establish efficient attachment systems that can successfully withstand strong external forces that acts upon bacteria. Such systems can resist, for instance, rinsing effects and thereby allow bacteria to colonize their host. By understanding the complexity, and thereby possible weaknesses, of bacterial attachments, new targets for combating bacterial infections can be identified.

Efforts to improve the optical performance of the indirect bandgap semiconductor silicon (Si) has been a major subject of research in the field of Si photonics due to the promising applications of Si based light emitters and detectors for optical communication. With that motivation three different Si based material systems were investigated; Si:Er/O layered structures, SiGe quantum dots and SiSn nano structures, all grown using the technique of molecular beam epitaxy (MBE). The main focus of this work has been on Si:Er/O layers, which lead to fabrication of Si-based light emitting diodes (LED) emitting at 1.54 mm wavelength. The work on SiGe structures lead to the fabrication of near-infrared light detectors, whereas the SiSn structures have not shown any strong optical character. Studies include epitaxial growth, structural characterization, device processing, electrical and optical characterizations. Material characterization of Si:Er/O structures using analytical electron microscopy (AEM) revealed interesting results with identification of two different type of microstructures in these layers depending on the Er and O concentrations. Several Si:Er/O LEDs were fabricated with different Er and O concentrations and the optical characteristics were investigated in order to find the best doping levels of Er and O for efficient light emission. The electroluminescence measurements revealed a strong 1.54 mm emission from these devices due to the intra 4f shell transition of Er3+ from the excited state (4I13/2) to the ground state (4I15/2). Si:Er/O waveguide LEDs have also been grown on SOI wafers using the optimized structure parameters obtained from mode confinement simulations as well as the microstructure investigations. The Si:Er/O waveguide LEDs are aimed at fabricating a planar Si cavity with Bragg mirrors on both sides to obtain light amplification and realise an electrically pumped Si laser. A focused ion beam (FIB) instrument was used to fabricate the Bragg mirrors but initial attempts did not result in light amplification in our Si:Er/O waveguide cavities. SiGe quantum dots are well-known quantum structures which are formed in a selfassembled fashion from Si/SiGe layer structures with a variety of shapes, sizes and compositions depending mainly on parameters like growth temperature and layer thicknesses. Optical properties of SiGe quantum structures have been studied while there has been little knowledge about their composition. A detailed compositional investigation of different SiGe dots on a nanometer scale was performed using AEM. The results showed a large degree of interdiffusion in large quantum dots, which was consistent with the optical properties of these dots. Using a multiple stack of Ge quantum dots and SiGe quantum wells, MOSFET type photodetectors working at 1.3 – 1.55 mm wavelength have also been fabricated and characterized. Research on the SiSn system was mainly motivated by the possibility to obtain a direct bandgap transition in Si based material as it was predicted theoretically and experimentally observed in the related GeSn material system by other researchers. Structural and optical characterizations of SiSn nano structures were performed. Although the same SiSn nano structures exhibit a weak signature of optical absorption, low temperature photoluminescence measurements did not reveal any emission peaks related to the SiSn dots. / Kisel är den helt dominerande halvledaren för tillverkning av de integrerade kretsar som utgör grunden för vårt nuvarande IT-samhälle. Samtidigt har det inte varit möjligt att använda kisel-komponenter inom det stora optoelektronikområdet, exempelvis i sändare och mottagare för fiberoptisk kommunikation. På grund av de stora fördelar det skulle innebära att kunna integrera optoelektronik med kiselbaserade komponenter på samma halvledarskiva så har det under de senaste åren varit mycket forskning kring möjligheterna att modifiera kisel så att det kan användas inom optoelektronik. I denna avhandling har tre olika materialkombinationer studerats för att undersöka om kiselbaserade material kan användas för emission eller detektion av optiska signaler. Den största delen av arbetet handlar om att tillverka, studera och utnyttja strukturer med låga halter av erbium och syre som kan fungera som lysdioder i det infraröda området med just den våglängd, 1,54 μm, som används i de flesta fall av fiberoptisk kommunikation. Genom att studera hur ljusintensiteten beror på erbium- och syrekoncentrationerna samt den erhållna mikrostrukturen i materialet så har tillverkningen kunnat optimerats för högsta intensitet. Vidare har multilagerstrukturer utvecklats så att ljusemissionen sker ifrån en s.k. vågledare. Målsättningen har varit att skapa möjligheter för att erhålla s.k. stimulerad emission vilket skulle resultera i en kiselbaserad laser. En annan del av avhandlingen berör tillverkning, karakterisering och användning av s.k. germanium kvantprickar som kan erhållas på kiselytor om man belägger ytan med ett antal atomlager av germanium. Dessa öar kan sedan begravas av kisel och får intressanta optiska egenskaper. Studier har gjorts av hur stor interdiffusionen är av kisel och germanium i kvantprickarna vilket påverkar vilka ljusvåglängder som kan absorberas eller emitteras av kvantprickarna. Med hjälp av sådana kvantprickar har detektorer för våglängder 1,3-1,5 μm tillverkats och karakteriserats. Då även tenn/kisel kvantprickar har rapporterats ge användbar absorption av vissa våglängder har en studie genomförts av tillverkning och karakterisering av material som innehåller sådana kvantprickar.

Aluminum nitride (AlN) exhibits a large direct band gap, 6.2 eV, and is thus suitable forsolid state white-light-emitting devices. It is capable in spintronics because of its high Curietemperature if doped with transition metals. AlN can also be used as a buffer layer for growth ofdevice-grade GaN as well as for application in sensors, surface acoustic wave devices, and hightemperatureelectronics. AlN shows excellent field-emission performance in vacuummicroelectronic devices due to its small electron affinity value, which is from negative to 0.6 eV.In this sense, nanostructured AlN, such as AlN nanowires and nanorods, is important forextending our knowledge on the potential of nanodevice applications. For growth of bulk AlN thesublimation- recondensation (a kind of physical vapor transport growth) method is the mostsuccessful and promising crystal growth technique. In thesis the physical vapor transport (PVT) principle has been implemented for synthesisof AlN on 4H-SiC in sublimation epitaxy close space configuration. It has been shown that theAlN crystal morphology is responsive to the growth conditions given by temperature (1650-1900oC) and nitrogen pressure (200-800 mbar) and each morphology kind (platelet-like, needles, columnar structure, continuous layers, and free-standing quasi bulk material) occurs within anarrow window of growth parameters. Controlled operation conditions for PVT growth of wellaligned perfectly oriented arrays of AlN highly symmetric hexagonal microrods have beenelaborated and the mechanism of microrod formation has been elucidated. Special patterned SiCsubstrates have been created which act as templates for the AlN selective area growth. Themicrorods revealed an excellent feature of boundary free coalescence with growth time,eventually forming ~120 μm thick AlN layer which can be easily detached from the SiC substratedue to a remarkable performance of structural evolution. It was discovered that the locally grownAlN microrods emerge from sharp tipped hexagonal pyramids, which consist of the rare 2H-SiCpolytype and a thin AlN layer on the surface. Two unique consequences appear from the finding,the first is that the 2H-SiC polytype facilitates the nucleation of wurtzite AlN, and the second isthat the bond between the low angle apex of the pyramids and the AlN layer is very week, thusallowing an easy separation to yield free standing wafers. AlN nanowires with an aspect ratioas high as 600 have been grown with a high growth rate. Again, they have perfect alignmentalong the c-axis of the wurtzite structure with small tilt given by the orientation of the SiCsubstrate. The nanowires possess a single crystal structure with high perfection, since neitherdislocations nor stacking faults were revealed. The proposed growth concept can be further explored to enlarge the free standing AlNwafers up to a size provided by commercially available SiC four inch wafers. Also, AlN wafersfabricated by the present method may be used as seeds for large boule growth. AlN nanowires, asobtained in this study, can be used for creating a piezoelectric generator and field emitters withhigh efficiency. / Aluminium nitrid (AlN) har ett stort direkt bandgap (6.2 eV) och är lämplig för lysdioder.Det är tillämpligt inom spinnelektronik eftersom det har en hög Marie Curie-temperatur när det ärdopad med övergångsmetaller. AlN kan även användas som ett buffertskikt för tillväxt avkomponentkvalitativt GaN likväl som för sensortillämpningar, ytvågsfilterkomponenter, ochhögtemperaturelektronik. Aluminium nitrid visar excellent fältemission i vakuumkomponenter pågrund av sin låga elektronaffinitet, som är från negativt till 0.6 eV. I det här fallet så ärnanostrukturer av AlN, som nanotrådar och -stavar, viktiga för att utöka vår kunskap ompotentiella nanokomponenter. För tillväxt av AlN är sublimeringsmetoden den mestframgångsrika och lovande framställningstekniken av kristaller. I den här avhandlingen så har principen för den fysiska gastransporttekniken (PVT)implementerats för syntes av AlN på 4H-SiC filmer i en ny konfiguration genomsublimeringsepitaxi. Det demonstreras att morfologin hos AlN visar respons förtillväxtförhållandena som ges av temperatur (1650-1900oC) och kvävetryck (200-800 mbar) ocholika morfologityper (skivlika, trådar, kolumnstrukturer, kontinuerliga skikt, och friståendekvasibulkmaterial)uppstår inom ett snävt fönster av tillväxtparametrar. Kontrollerade operativaförhållanden för PVT-tillväxt av räta perfekt orienterade ansamlingar av symmetriska AlNmikrostavar har utvecklats och deras formationsmekanism diskuterats. Speciellt mönstrade SiCsubstrat har skapats som agerar utgångsmaterial för selektiv AlN tillväxt. Mikrostavarna avslöjarett särdrag av sammanväxning utan gränslinjer med tillväxttid, som formar 120 μm tjocka AlNskikt som lätt kan avskiljas från SiC substratet genom en anmärkningsvärd strukturell evolution.Upptäckten gjordes att lokal tillväxt av AlN mikrostavar uppkommer från skarpa hexagonalapyramider som består av den sällan förekommande 2H-SiC modifikationen och tunna AlN skiktpå ytan. Två unika följder uppkommer genom upptäckten, den första att 2H-SiC modifikationenfrämjar bildning av wurtzite AlN, och den andra att bindningen mellan spetsen av pyramiden ochAlN skiktet är väldigt svag, vilket medger en enkel separering för att erhålla fristående wafers. AlN nanotrådar med ett aspektförhållande så stort som 600 har blivit framställda med högframställningshastighet. Återigen, de har perfekt linjering längs c-axeln av wurtzite-strukturenmed en låg vinkling som ges av orienteringen av SiC substratet. Nanotrådarna har en perfektkristallstruktur eftersom varken dislokationer eller stackningsfel kunde observeras. Det föreslagna framställningskonceptet kan vidare utforskas för att utöka fristående AlNwafers upp till en storlek som ges av kommersiellt tillgängliga SiC fyratumssubstrat. Vidare såkan AlN wafers som framställs genom metoden användas som utgångsmaterial för kristaller förframställning av stora götar. AlN nanotrådar, som utvecklats i denna studie, kan användas för attskapa piezoelektriska generatorer och fältemissionskomponenter med hög effektivitet.

The new LHC particle accelerator now being built at CERN will have a radically increased event rate and higher energy. To accommodate this, instrumentation for LHC experiments has had to be constructed using new ideas and the latest available technology. A part of this effort was the development and test of a digitizer unit for the hadron calorimeter (TileCal) of the ATLAS experiment. To try out ideas and promote system integration, prototypes were tested in a subsystem using a particle beam to simulate the final conditions. During the development of these prototypes an application-specific integrated circuit was constructed to control the digitizer system. Tests made at the test beam facility have verified that all requirements were met. The final digitizer design and its components were radiation tested to verify full functionallity in its radiation environment during the full ATLAS life-span. Test devices were also constructed to test all production units. In addition to the digitizer system, an optical readout link was designed to meet the requirements for the digitizer readout. Preliminary studies indicate that the digitizer could also be used in an upgraded LHC, with presently considered scenarios.

Combustion of biomass and waste has several environmental, economical and political advantages over the use of fossil fuels for the generation of heat and electricity. However, these fuels often have a significantly different composition and the combustion is therefore associated with additional operational problems. A high content of chlorine and alkali metals (potassium and sodium) often causes problems with deposit formation and high temperature corrosion. Some different aspects of these issues are addressed in this thesis. The overall objective of this thesis was to study and highlight different means by which operational problems related to alkali chlorides can be overcome, reduced or prevented. The most important results of this thesis are: (1) A full description of the in-situ alkali chloride monitor, its operational principles, the calibration procedure, and an example of a full-scale application was made public in a scientific publication. (2) Efficient sulfation of gaseous alkali chlorides in a full-scale boiler was achieved by injecting ammonium sulfate in a water solution into the hot flue gas. (3) Reduced deposit growth and corrosion rates were achieved by lowering the alkali chloride concentration in the flue gas by sulfation. (4) Evidence of decreased deposit growth and chlorine content in deposits during peat co-combustion. (5) Results are presented from high temperature corrosion tests with different superheater steels in two different combustion environments. (6) Controlled KCl and NaCl condensation under simulated combustion conditions resulted in deposits which consisted of mostly pure phases, in contrast to the solid solution that would be expected under the prevailing conditions at chemical equilibrium.

This thesis concerns the application of various soft x-ray spectroscopic methods (soft x-ray absorption, SXA, and emission, SXE) to complex, non-vacuum compatible systems, including liquids and multi-phase systems. The design, construction, and application of new instrumentation for in situ spectroscopy is described in detail. This includes sample holders using thin soft x-ray transparent membranes to enable measurements on systems completely isolated from vacuum, enabling flow of e.g. liquid or gas. In particular, a versatile setup for time resolved in situ chemical contrast x-ray transmission microscopy (CCXTM) was constructed and implemented. These instruments are expected to be applicable to a wide range of situations, for example in situ studies of chemical reactions, or biological specimen. The main project concerns atmospheric corrosion of iron in a saline environment, a process that requires the simultaneous presence of the solid (iron, NaCl), liquid (water) and gaseous (air) phases. It is also a highly inhomogeneous process, where lateral and time resolution is important. Using the CCXTM instrumentation, we were able to follow the distribution of all present elements over the sample with time resolution of a few minutes, and also to extract significant chemical information from the absorption edges. We observed e.g. the initial formation of corrosion products and transport of chlorine. Results from SXE measurements on water molecules in micelle structures are presented. A comparison with calculations reveal influence from the counter-ions, but also some spectral changes that may be attributed to water confinement. Also presented are angle dependent soft x-ray emission of liquid water, measuring scattered x-rays from different directions respect to the incident x-ray polarization. Existing preliminary theoretical expectations for the polarization dependence are contradictory. Our experiments show that a small angular anisotropy seems to be retained from the free molecule case.

This Thesis describes the development of the KTH/Stockholm nanofabrication process for diffractive soft x-ray optics. The effort is motivated by the need for and requirement of specially designed diffractive optics and test objects for compact x-ray microscopy as well as optics for other applications such as phase imaging. The optics have been fabricated in-house, in the KTH Nanofabrication Laboratory. The nanofabrication process is based on electron-beam lithography in combination with reactive ion etching (RIE) and nickel electroplating. This process has successfully been used for the fabrication of micro zone plates, condenser zone plates, diffractive optical elements for differential-interference microscopy, and different test structures. Optics with electroplated feature sizes down to 25 nm have been fabricated with high aspect-ratios. Special consideration has been given the reproducibility and optimization of the process parameters. This is essential for improving the yield and quality of the fabricated optics. The work includes, e.g., improved e-beam writing strategies and controlled electroplating. Furthermore, a high diffraction efficiency is necessary for our applications, which are based on compact low-power sources. This requires the fabrication of optics with a high and uniform aspect ratio. For this purpose the electroplating process step has been improved with an in-situ light-transmission-based thickness control method for optimum mold filling, and pulse and pulse-reverse techniques for uniform plating. / QC 20100616

A major task of nuclear structure theory is to develop an effective interaction that is capable to predict properties of nuclei under extreme conditions. In this thesis three different areas of effective interactions have been studied: i) the density dependence, which is of importance for the understanding of neutron stars and neutron rich nuclei; ii) the symmetry energy which governs the evolution of the binding energy with changing N/Z ratio; and iii) the neutron proton pairing energy. The symmetry energy governs the isospin dependent part of the nuclear interaction and determines basic properties of neutron stars. The isospin dependence of short range correlations are in turn important for properties of N ~ Z nuclei as well as symmetric nuclear matter. / QC 20100623

This thesis describes new results obtained from experimental studies of the extremely neutron-deficient isotopes 110Xe, 163Ta, 169Ir, and 172Hg, close to the proton drip-line. The experiments used state-of-the-art equipment for nuclear spectroscopy where a large high resolution Germanium-detector array was coupled to a high-transmission recoil separator.The highly selective recoil-decay tagging technique was applied in order to identify andstudy the most weakly populated reaction channels. The work is based on four experimentsperformed at the Accelerator Laboratory of the University of Jyväskylä, Finland. The experimental techniques used and the experimental set-ups are described. Comparisonbetween experimental results and theoretical predictions are made. The thesis also brieflysummarises the theoretical models employed to interpret the experimental data. The results for 110Xe indicate an emergence of enhanced collectivity near the N=Z linein the region of the nuclear chart above 100Sn. These findings are interpreted as a possible effect of increased neutron-proton isoscalar pair correlations, a residual interaction effect not accounted for in present-day nuclear models. The findings for 163Ta reveal three strongly coupled band structures built on differentquasiparticle configurations. The low-lying yrast band exhibits strong signature splittingindicative of a significant triaxial shape asymmetry. An intriguing possibility exits forenhanced octupole correlation in 163Ta, where the odd-proton is proposed to couple to anoctupole-vibrational phonon. However, further investigations are needed to elucidate thisscenario. Also for 169Ir do the properties of the yrast structure point to a rotational-like behaviourof a moderately deformed nucleus exhibiting a triaxial shape. For neither 163Taor 169Ir do the experimental results fully agree with theoretical predictions for the shapeevolution of the neutron-deficient tantalum and iridium isotopes, approaching the protondrip-line.The nearly constant level spacing in 172Hg between the lowest excited 2+, 4+ and 6+states suggests a transition to a near-spherical harmonic collective vibrational structureas compared with heavier even-even Hg isotopes around the neutron midshell and above.The experimental data have been compared with total Routhian surface calculations and quasiparticle random phase approximation calculations. / QC 20100809