<p>Quasicrystals is a new kind of material that have several interesting aspects to it. The unusual atomic structure entails many anomalous and unique physical properties, for example, high hardness, and extremely low electrical and thermal conductivity. In thin films quasicrystals would enable new functional materials with a combination of attractive properties.In this work, AlCuFe and Nanoflex steel, materials that are known to form quasicrystals in bulk, have been deposited as thin films on Si and Al2O3 substrates using DC magnetron sputtering. These thin films were heat treated, and the formation and growth of different phases, among other approximant and quasicrystalline phases, were studied using mainly in-situ X-ray diffraction.During the project several problems with the formation of quasicrystals were encountered, and it is proposed how to overcome these problems, or even how to make use of them. Finally, the quasicrystalline phase was realized, although it was not completely pure. In the end some suggestions for future work is presented.</p>

A Kitaev quantum spin liquid is a phase of matter predicted to host excitations that can be used to preform fault-tolerant quantum computation. Though the theoretical prediction of such a state is on firm footing, its realisation in real materials has proven to be elusive. Recent developments have suggested honeycomb materials consisting of 3d transition metal ions as possible candidates. The focus of this thesis is the magnetic properties of one such material, K2Ni2–xCoxTeO6. It is part of a family of layered two dimensional materials consisting of honeycomb structured transition metal layers sandwiched between layers of alkali ions. A characterisation of the magnetic properties of K2Ni2–xCoxTeO6 has been carried out with the techniques of muon spin rotation/relaxation/resonance and bulk magnetisation as a function of the chemical composition. Further investigations of the detailed atomic structure and spin order using neutron scattering was also initiated. The results of such characterisations are presented and discussed in this thesis. / En Kitaev kvantspinvätska är en fas av materia som har förespåtts kunna husera exciterade tillstånd som kan användas for att konstruera en kvantdator. Även om de teoretiska rönen är väl underbyggda, har ett förverkligande av en sådan fas i verkliga material varit svår att åstadkomma. Nya rön har pekat ut bikakematerial bestående av 3d övergångsmetaller som potentiella kandidater. Därav fokuserar denna avhandling på ett sådant material, K2Ni2–xCoxTeO6. Det är en del av en familj av liknande material bestående av tvådimensionella lager av bikakeformade övergångsmetaller mellan lager av alkaliska joner. En karaktärisering av de magnetiska egenskaperna av K2Ni2–xCoxTeO6 har utförts genom att analysera data från myon spin rotation/dämpning/resonans samt magnetiserings mätningar som funktion av materialets kemiska samansättning. Ytterligare mätningar av den atomära strukturen och spinordning påbörjades också med hjälp av neutronspridningstekniker. I denna avhandling presenteras och diskuteras resultaten av dessa karaktäriseringar.

This Thesis concerns the development of fullerene-like (FL) carbon nitride (CNx) thin films and the discovery of phosphorus-carbide (CPx) compounds. The work dedicated to CPx include first-principles theoretical simulations of the growth and properties of FL-CPx structures. I have employed DC magnetron sputtering methods to synthesize both CNx and CPx thin films. The deposition conditions for CPx films were chosen on the basis of the theoretical results as well as from the experience from the deposition of FL-CNx thin films. The characterization of the CPx films is divided into three main directions: structural characterization by transmission electron microscopyand scanning electron microscopy, analysis of the amount of elements and chemical bonds presentin the structure by X-ray photoelectron spectroscopy and Auger spectroscopy, and mechanicalproperty analysis by nanoindentation. The CPx films exhibit a short range orderedstructure with FL characteristics for substrate temperature of 300 °C and for a phosphorus content of 10-15 at.%, which isconsistent with the theoretical findings. These films also displayed the best mechanical properties in terms of hardness and resiliency, which are better than those of the corresponding FL-CNx films. For the FL-CNx thin film material, I find that the surface water adsorption is lower compared to commercial computer hard disk top coatings. Following that line the dangling bonds in FL-CNx coatings have been investigated  by electron spin resonance (ESR). The absence of ESR signal for FL-CNx indicates very low density of dangling bonds in the material, which explains the low water adsorption tendency. The potential for using highly elastic FL-CNx coatings in an automotive valve-train environment has also been investigated. CNx coatings of different nitrogen content were investigated using microscopy, wear testing, nanoindentation testing, and in an experimental cam-tappet testing rig. The FL-CNx coating with the higher value of hardness/elastic modulus showed greater durability in cam-tappet wear testing.

Metastable (Ti,Si)N alloy and TiN/SiNx multilayer thin solid films as well as SiNx/TiN surfaces have been explored. Cubic Ti1-xSixN (0≤x≤0.14) films deposited onto cemented carbide (WC-Co) substrates by arc evaporation exhibited a competitive columnar growth mode where the structure transforms to a feather-like nanostructure with increasing Si content as revealed by x-ray diffraction and transmission electron microscopy. X-ray photoelectron spectroscopy revealed the presence of Ti-N and Si-N bonding, but no amorphous Si3N4. Band structure calculations showed that phase separation of NaClstructure Ti1-xSixN solid solution into cubic SiN and TiN phases is energetically favorable. The metastable microstructure, however, was maintained for the Ti0.86Si0.14N film annealed at 900°C, while recrystallization in the cubic state took place at 1100°C annealing during 2h. The Si content influenced the film hardness close to linearly, by combination of solid-solution hardening in the cubic state and defect hardening. For x=0 and x=0.14, nanoindentation gave a hardness of 29.9±3.4 GPa and 44.7±1.9 GPa, respectively. The hardness was retained during annealing at 900°C. Nanostructured materials, e.g., nanocomposites and nanolaminates, are defined by internal interfaces, of which the nature is still under debate. In this work two-phase model systems were explored by depositing SiNx/TiN nanolaminate films, including superlattices containing cubic SiNx, by dual target reactive magnetron sputtering. It is demonstrated that the interfacial phase of SiNx onto TiN(001) and TiN(111) can be crystalline, and even epitaxial with complex surface reconstructions. Using in situ structural analyses combined with ab initio calculations, it is found that SiNx layers grow epitaxially, giving rise to strong interfacial bonding, on both TiN(001) and TiN(111) surfaces. In addition, TiN overlayers grow epitaxially on SiNx/TiN(001) bilayers in nanolaminate structures. These results provide insight into the development of design rules for novel nanostructured materials. / Report code: LiU-TEK-LIC-2006:51.

<p> </p><p>In orthopaedic practice, fractures are usually stabilised with metal screws or rods. This is done in order to keep the fracture parts in place during the rather slow healing process. The healing time can potentially be reduced by local- or systemic treatment with different bone promoting drugs. In later years, lithium, otherwise used to treat bipolar disease, has shown promise to be such a drug.</p><p> </p><p>The aim of this master thesis was to find a way to coat metal bone screws with lithium and to characterise the coating. The coating was to be designed in such a way that it could release lithium to the surrounding bone tissue.</p><p> </p><p>Lithium chloride was incorporated into a titanate sol-gel and attached to silicon wafers and stainless steel screws by dip coating. Wafers were used for initial <em>in vitro</em> studies of how lithium changed coating characteristics. This was studied using ellipsometry, AFM and SEM. Lithium is most probably physisorbed and not incorporated into the network building up the sol-gel. Coating structure is changed as more lithium is incorporated. For large amounts of lithium, the nanoparticles normally formed when curing the sol-gel are inhibited. One effect of this is reduced bioactivity, seen as a reduced ability for calcium phosphate crystals to nucleate on the coating when immersed in simulated body fluid.</p><p>Lithium release was investigated using AAS. Lithium is released from the coating, showing a burst effect. By changing the number of coating layers used, the release profile can be partly altered. The coating was also applied to screws, showing good attachment, and the lithium release profile was similar to the one seen from wafers.</p><p>Finally, a screw model was used in rats to assess the effect of local lithium treatment from screws and systemic lithium treatment on fracture healing. In the model, a screw was inserted in tibia, mimicking a fracture. When the bone around the screw was healed, a pullout test was performed, giving information about the strength of the bone surrounding the screw. No significant difference could be found for either local- or systemic lithium treatment compared to control. However, when evaluating the strength of intact bone in a similar way, a positive effect of systemic lithium treatment could be seen. Therefore, it is still likely that lithium has a positive effect on bone and further studies are needed to fully evaluate its role in fracture healing.</p><p> </p> / <p><p>Vid behandling av benbrott stabiliseras vanligtvis frakturen internt med metallskruvar och</p><p>metallstavar. Detta görs för att hålla brottbitarna på plats under den relativt långsamma läkprocessen. Det är möjligt att minska tiden för frakturläkning genom att lokalt eller systemiskt behandla med olika läkemedel som främjar bentillväxt. På senare år har det presenterats bevis för att litium, som annars används som psykofarmaka, fungerar som ett sådant läkemedel.</p><p> </p><p>Syftet med detta examensarbete var att hitta en metod för att fästa litium på benimplantat. Litium skulle fästas på ett sådant sätt att frisläppning till omgivande vävnad blev möjlig.</p><p> </p><p>Litiumklorid inkorporerades i en titanat-solgel och lager av detta lades på kiselytor och rostfria skruvar genom s.k. ”dip-coating”. Kiselytorna användes för initiala <em>in vitro</em>-studier av hur litium ändrade beläggningens egenskaper. Litium sitter antagligen fast på ytan av det tredimensionella nätverk som utgör solgelen, istället för att sitta inbundet i nätverket. Lagerstrukturen ändras ju mer litium som inkorporeras och vid stora mängder skapas inte de nanopartiklar som vanligtvis finns i en solgel-baserad beläggning. En följd av detta är reducerad bioaktivitet för beläggningen, dvs. en minskad förmåga för kalciumfosfatkristaller att bildas på ytan. Litium frisläpps från beläggningen, dock sker denna frisläppning snabbt. Genom att belägga ytan med flera lager av solgel kan frisläppningskinetiken delvis ändras. Solgelen kunde också med god vidhäftning appliceras på skruvar och frisläppningskinetiken från en skruv är liknande den från en kiselyta.</p>Slutligen användes en skruvmodell i råtta för att undersöka vilken effekt lokal respektive systemisk litiumbehandling har på frakturläkning. I modellen efterliknas ett benbrott genom att en skruv sätts in i skenbenet.  När benvävnaden runt skruven har läkt görs ett utdragstest på skruven vilket ger information om benets styrka. Ingen signifikant skillnad i skruvens utdragskraft kunde ses mellan de båda försöksgrupperna och kontrollgruppen. Däremot hade gruppen som fick systemisk litiumbehandling fått starkare ben totalt, vilket indikerar att litium har effekt på <em>intakt</em> ben. På grund av dessa resultat finns det fortfarande skäl att tro att litium har en positiv påverkan på ben, varför dess effekt på frakturläkning bör undersökas ytterligare. </p>

<p>The high pressure and high temperature (HPHT) behavior of Ti_1-xAl_xN coatings on cutting tool inserts have been of interest for this diploma work. A literature study of HPHT techniques as well as measurement methods has been done. A diamond anvil cell (DAC) would be a good device to achieve high pressure and high temperature conditions on small samples. Another way to obtain these conditions would be a cutting test, which has been performed on a Ti_1-xAl_xN coated cutting tool insert with x = 0.67. Also a cubic press could be used to apply HPHT on a     Ti_1-xAl_xN sample or a large volume press on a whole cutting tool insert. To measure hardness on thin coatings a nanoindentor could be used, which have been done on heat-treated Ti_0.33Al_0.67N and TiN samples. X-ray diffraction (XRD) is a suitable method to measure phase composition of a sample and was performed on the cutting tested insert as well as on an untreated reference insert. Three ways to continue this project have been outlined all starting with more comprehensive cutting tests.</p>

<p>A new NO_x sensor for high-temperature applications has been developed and thouroghly characterised. The sensor layers are a mixed oxide of CoO, MgO and MgO₂ deposited by thermal evaporation with a porous platinum gate on top, deposited by thermal evaporation or sputtering. The sensitivity and selectivity of the sensor is promising and is shown to depend upon the ratio between Co and Mg in the film and a number of competing mechanisms are shown to take place on the sensor surface. Response and recovery of the device is still slow and there are some drift, which are suggested to be due to a restructuring sensor surface during operation that was found by SEM-studies. Finally,the oxide surface has been characterized by XPS and a novel process for deposition of the sensor layers by lift-off technique has been developed.</p>

<p>Metastable (Ti,Si)N alloy and TiN/SiNx multilayer thin solid films as well as SiNx/TiN surfaces have been explored. Cubic Ti1-xSixN (0≤x≤0.14) films deposited onto cemented carbide (WC-Co) substrates by arc evaporation exhibited a competitive columnar growth mode where the structure transforms to a feather-like nanostructure with increasing Si content as revealed by x-ray diffraction and transmission electron microscopy. X-ray photoelectron spectroscopy revealed the presence of Ti-N and Si-N bonding, but no amorphous Si3N4. Band structure calculations showed that phase separation of NaClstructure Ti1-xSixN solid solution into cubic SiN and TiN phases is energetically favorable. The metastable microstructure, however, was maintained for the Ti0.86Si0.14N film annealed at 900°C, while recrystallization in the cubic state took place at 1100°C annealing during 2h. The Si content influenced the film hardness close to linearly, by combination of solid-solution hardening in the cubic state and defect hardening. For x=0 and x=0.14, nanoindentation gave a hardness of 29.9±3.4 GPa and 44.7±1.9 GPa, respectively. The hardness was retained during annealing at 900°C.</p><p>Nanostructured materials, e.g., nanocomposites and nanolaminates, are defined by internal interfaces, of which the nature is still under debate. In this work two-phase model systems were explored by depositing SiNx/TiN nanolaminate films, including superlattices containing cubic SiNx, by dual target reactive magnetron sputtering. It is demonstrated that the interfacial phase of SiNx onto TiN(001) and TiN(111) can be crystalline, and even epitaxial with complex surface reconstructions. Using in situ structural analyses combined with ab initio calculations, it is found that SiNx layers grow epitaxially, giving rise to strong interfacial bonding, on both TiN(001) and TiN(111) surfaces. In addition, TiN overlayers grow epitaxially on SiNx/TiN(001) bilayers in nanolaminate structures. These results provide insight into the development of design rules for novel nanostructured materials.</p> / Report code: LiU-TEK-LIC-2006:51.

<p>During the last decade, AlGaN High Electron Mobility Transistors (HEMTs) have been intensively studied because their fundamental electrical properties make them attractive for highpower microwave device applications. Despite much progress, AlGaN HEMTs are far from fully understood and judged by the number of published papers the understanding of advanced structures is even poorer. This work is an exploration of the electrical and structural properties of advanced HEMT structure containing AlN exclusionlayer and double heterojunctions. These small modifications had great impact on the electrical properties.</p><p>In this work, AlGaN HEMT structures grown on SiC substrates by a hot-wall MOCVD have been characterized for their properties using optical microscopy, scanning electron microscopy, transmission electron microscopy, capacitance/voltage, eddy-current resistivity, and by homebuilt epi-thickness mapping equipment.</p><p>A high electron mobility of 1700 [cm2/Vs] was achieved in an AlN exclusion-layer HEMT. A similar electron mobility of 1650 [cm2/Vs] was achieved in a combination of a double heterojunction and exclusion-layer structure. The samples had approximately the same electron mobility but with a great difference: the exclusion-layer version gave a sheet carrier density of 1.58*1013 [electrons/cm2] while the combination of double heterojunction and exclusion-layer gave 1.07*1013 [electrons/cm2]. A second 2DEG was observed in most structures, but not all, but was not stable with time.</p><p>The structures we grew during this work were also simulated using a one-dimensional Poisson-Schrödinger solver and the simulated electron densities were in fairly good agreement with the experimentally obtained. III-nitride materials, the CVD concept, and the onedimensional solver are shortly explained.</p>

Point defects are an inherent part of crystalline materials and they influence important physical and chemical properties, such as diffusion, hardness, catalytic activity and phase stability. Increased understanding of point defects enables us to tailor the defect-related properties to the application at hand. Modeling and simulation have a prominent role in acquiring this knowledge. In this thesis thermodynamic and kinetic properties of point defects in metals and ceramics are studied using first-principles calculations based on density functional theory. Phenomenological models are used to translate the atomic level properties, obtained from the first-principles calculations, into functional materials properties. The next paragraph presents the particular problems under study. The formation and migration of vacancies and simple vacancy clusters in copper are investigated by calculating the energies associated with these processes. The structure, stability and electronic properties of the low-oxygen oxides of titanium, TiOx with 1/3 &lt; x &lt; 3/2, are studied and the importance of structural vacancies is demonstrated. We develop an integrated first-principles and Calphad approach to calculate phase diagrams in the titanium-carbon-nitrogen system, with particular focus on vacancy-induced ordering of the substoichiometric carbonitride phase, TiCxNy (x+y &lt; 1). The possibility of forming higher oxides of plutonium than plutonium dioxide is explored by calculating the enthalpies for nonstoichiometric defect-containing compounds and the analysis shows that such oxidation is only produced by strong oxidants. For ceria (CeO2) doped with trivalent ions from the lanthanide series we probe the connection between the choice of a dopant and the improvement of ionic conductivity by studying the oxygen-vacancy formation and migration properties. The significance of minimizing the dopant-vacancy interactions is highlighted. We investigate the redox thermodynamics of CeO2-MO2 solid solutions with M being Ti, Zr, Hf, Th, Si, Ge, Sn or Pb and show that reduction is facilitated by small solutes. The results in this thesis are relevant for the performance of solid electrolytes, which are an integral part of solid oxide fuel cells, oxygen storage materials in automotive three-way catalysts, nuclear waste materials and cutting tool materials. / QC 20100622