<p>JONSEN, DANIEL EVERETT. Experimental and Computational Studies of Carbon Sputtering with Application to Deposition of Tetrahedrally Bonded Amorphous Carbon Films. (Under the direction of Dr. Jerome J. Cuomo.) <p>In this work, amorphous carbon films are deposited on various substrates by ion beam sputtering of a graphite target. In addition, computational studies of the carbon sputtering process are performed using a molecular dynamics simulation program. In both cases, several process parameters are varied with the intent to find the optimum conditions for the sputter deposition of amorphous carbon films of high sp content amorphous carbon films.<P>

<p>The goals of this thesis were to synthesize nanocrystalline Zn, to study the mechanical properties of bulk nanocrystalline Zn and try to reveal the deformation mechanisms in nanocrystalline materials. Nanocrystalline Zn powder has been synthesized by a cryomilling method. The average grain size decreased exponentially with the cryomilling time and reached a minimum average grain size of around 17nm. Large numbers of small grains (2~6nm) have been found in the very early stages of cryomilling. Dynamic recrystallization (DRX) was used to explain the observed phenomena. Differential scanning calorimetry (DSC), x-ray diffraction and transmission electron microscopy (TEM) were used to study the structural changes and grain size distribution with milling time and subsequent annealing. Maxima in both stored enthalpy (for the low temperature DSC peak) and lattice strain on the Zn basal planes were observed at the same milling time. Dislocation density on the basal planes is proposed as a major source for lattice strain and the measured stored enthalpy. The released enthalpy that might be due to grain growth is very small. These cryomilled nanocrystalline Zn powders were consolidated into disks with a density of nearly theoretical density by uniaxial compression at room temperature. Cyclic variation of microhardness with milling time has been observed in cryomilled nanocrystalline Zn. Evidence from transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM) suggests that the variation of dislocation density and grain size distributions determine the hardness behavior. A model, based on a kinetic reaction-rate model for cyclic amorphous-to-crystalline phase transformations observed during ball milling, simulates the experimental results very well. The model confirms the effect of DRX on modulated cyclic variation of microhardness. Dislocation strain hardening and recrystallization effects are superposed linearly with the intrinsic grain boundary hardening during the simulation. A dislocation density on the order of 10/sup 16/m /sup -2/ is predicted to be necessary to trigger DRX from the model. This prediction is evidenced by HRTEM observation of dislocation density on the same order and consistent with the estimation from thermodynamic calculation. The activation energy for rate controlling step in DRX estimated from the model is around 50 kJ/mol. This estimation indicates that a grain boundary diffusion controlled mechanism could dominate in DRX. Ductility of cryomilled nanocrystalline Zn has been studied by MDBT. The yield strength obtained from MDBT shows modulated cyclic variations with cryomilling time. Three times yield strength is consistent with the microhardness values for the same Zn samples. Ductility of CM2h and CM4h samples are much better than other cryomilled samples as indicated by a much larger ratio of normalized displacement than other cryomilled nanocrystalline Zn samples. However, the ductility of all cryomilled Zn samples is poor or very limited. The poor ductility of cryomilled Zn is presumably due to the remaining flaws as a result of incomplete bonding between particles. The Young?s modulus measured from MDBT barely changes for all tested samples. Bulk (spherical balls) ultra-fine-grained (UFG) or nanostructured Zn via in situ consolidation of powders are produced by mechanical attrition at room temperature. The size of these spherical balls increased with the increase of ball milling time. The grain size decreased rapidly to around 80nm after 1h of ball milling and then increased to around 240nm at 3h. The grain size decreased gradually thereafter with the increase of milling time. An average gain size of around 23nm was achieved for Zn bulk samples ball milled for 25h. In situ consolidation of metal powders during mechanical attrition may be a promising method to produce bulk UFG or nanostructured materials with full density and less contamination. The hardness, yield stress measured from MDBT, and tensile tests are consistent with one another. The hardness increased almost linearly with the decrease of grain size. The positive Hall-Petch slope is much smaller compared to the slope for coarse-grained Zn. Except for BM1h Zn sample, all other samples possess good ductility as evidenced from miniaturized disk bend test (MDBT) results and from the observations of fracture surfaces studied by FESEM. A bulged hat shape sample is usually obtained after MDBT test. The Young?s modulus almost keeps the same as for conventional coarse-grained Zn. The low temperature ball milling proves to be more efficient in reducing the grain size. A maximum elongation of around 110% is achieved for UFG Zn (around 240nm) under uniaxial tension test, which discloses a superplastic deformation in UFG Zn at room temperature. The elongation of room temperature ball milled Zn decreases with the decrease of grain size. Around 20% elongation is observed for Zn with an average grain size of around 23nm. Tension tests at elevated temperature result in a reduction of yield stress. The significant drop of yield stress at 200 centigrade degree or above may be due to recovery or recrystallization as evidenced from FESEM images. A strain rate sensitivity value of around 0.14 is usually found for Zn tested at 20 centigrade degree - 40 centigrade degree. <P>

<p>High-density polyethylene (HDPE), ultrahigh molecular weight polyethylene (UHMWPE) and blends thereof are used to produce ternary and quaternary conductive polymer composites (CPCs) containing carbon black (CB), graphite (G), carbon fiber (CF) and selected mixtures thereof to discern if polymer blends and mixed fillers yield appreciable advantages over CPCs composed of single polymers and/or single fillers. The effects of polymer blend composition and filler type, concentration and composition on electrical conductivity, composite morphology, mechanical properties and thermal behavior have been examined and correlated to establish meaningful structure-property relationships that can facilitate the rational design of efficient CPCs. Enhanced conductivity due to double-percolation is observed in ternary CPCs containing CB or G, whereas the concept of bridged double percolation is proposed to explain substantial conductivity increases in quaternary composites.<P>

<p>&#09The energy distribution of electrons transported through intrinsic AlN films was directly measured as a function of the applied field and film thickness. The electron energy distribution featured kinetic energies higher than that of completely thermalized electrons. Transport through films thicker than 95 nm and applied field between 200 kV/cm - 350 kV/cm occurred as steady-state hot electron transport represented by a Fermi-Dirac/ Maxwellian energy distribution. At higher fields (470 kV/cm), intervalley scattering was evidenced by a second peak corresponding to the first satellite valley in AlN. Transport through 80 nm thick layers revealed the onset of quasi-ballistic transport.&#13 &#09 From these measurements, saturation velocities between 1.2 and 1.5x10 cm/s and a mean free path of 5.1 nm were determined under steady state conditions. Overshoots as high as five times the saturation velocity were observed and a transient length of less than 80 nm was deduced.&#13 &#09 Two field-emission states of single-walled carbon nanotubes were identified. The state yielding 10 times increased emission current was attributed to the presence of adsorbates on the nanotubes as confirmed by electron emission measurements at different background pressures. In the high current state, field-emitted electrons originated from states located up to 1 eV below the Fermi level, as determined by field-emission energy distribution measurements. This suggested that adsorbates introduced a resonant state on the surface which enhanced the tunneling probability of electrons. The adsorbed states were removed at high applied electric fields, presumably due to ohmic heating caused by large emission currents. This adsorption/desorption process was completely reversible.&#13 &#09 Using the Duke and Alferieff model, and a one-dimensional Fowler-Nordheim scheme, we demonstrated that adsorption enhances the field emission from single-walled carbon nanotubes through elastic resonance tunneling. As anticipated from this model, we observed FEED peak shifts towards lower energies and a symmetric peak shape in the energy distribution. The difference between the work function and the electronic binding energy of the non-perturbed state involved in the resonance was 0.3 eV ?± 0.2 eV, thus the state lied close to the Fermi level of the carbon nanotubes. <P>

Monolithic integration of optoelectronics on silicon is adream. This thesis deals with the studies on the heteroepitaxyof indium phosphide on silicon substrate towards making thatdream come true. Materials growth issues, characterization anddefect identification are addressed. Epitaxial lateral overgrowth (ELOG) technique is used togrow high quality epitaxial indium phosphide on a siliconsubstrate provided with a low quality indium phosphide seedlayer. Hydride vapor phase epitaxy is used for ELOG. The growthparameters were optimized first by carrying out ELOGexperiments on an InP substrate. The lateral growth rate isstrongly dependent on the orientation of the openings,thehighest growth rate being for the openings oriented at 30ºand 60º off [110]directions. But the vertical growth rateis relatively unaffected by the opening orientation. Theobservation of an inhomogeneous and orientation dependentdopant distribution within the same layer has been explained byinvoking the bonding configurations exposed to theincorporating dopant atoms in the different emergingplanes. When ELOG of InP is conducted on InP/Si, unlike that on InPsubstrates, the lateral growth is not symmetric on both sidesdue to the propagation of defects from the seed layer. Forexample, a higher concentration of threading dislocationsintersecting the surface of the {111}A emerging planes wouldcause a higher growth rate of these planes. The growth rate of{111}A planes with respect to the others can also be caused bythe vapor phase supersaturation as predicated byBurton-Cabrera-Frank model. The determined dislocation densityin the ELOG InP on InP/Si is ~ 4X107cm-2, which is nearly two magnitude lower than in theseed layer (~ 4X109cm-2). If the seed layer is of a better quality, theELOG layer will also be. Combination of high resolution x-raydiffraction reciprocal lattice mapping and low temperaturephotoluminescence indicates that the ELOG InP layer with highaspect ratio is nearly strain-free. When ELOG of sulfur doped InP is conducted on ring shapedopenings on InP/Si substrate instead of stripe openings,octahedral shaped ELOG InP templates with smooth surface areformed. Strain compensated InGaAsP 6 periods multi-quantumwells (MQW) at 1.5 μm wavelength (target value) were grownon these templates by metalorganic vapor phase epitaxy. RT-PLis indicative of a good quality ELOG layers. Optimized ELOG onring openings may become very attractive for heteroepitaxy ofIII-V compounds on silicon. As an extension of ELOG of InP on InP/Si, growth of InP isalso conducted on planar Focused-Ion-Beam (FIB)-modified (001)GaAs substrate. The impacts of the III/V ratio,crystallographic orientation of implanted lines andimplantation dose were explored. The choice of suitable growthconditions makes it possible to obtain continuous InP wiresaligned in all possible directions.

<p>Monolithic integration of optoelectronics on silicon is adream. This thesis deals with the studies on the heteroepitaxyof indium phosphide on silicon substrate towards making thatdream come true. Materials growth issues, characterization anddefect identification are addressed.</p><p>Epitaxial lateral overgrowth (ELOG) technique is used togrow high quality epitaxial indium phosphide on a siliconsubstrate provided with a low quality indium phosphide seedlayer. Hydride vapor phase epitaxy is used for ELOG. The growthparameters were optimized first by carrying out ELOGexperiments on an InP substrate. The lateral growth rate isstrongly dependent on the orientation of the openings,thehighest growth rate being for the openings oriented at 30ºand 60º off [110]directions. But the vertical growth rateis relatively unaffected by the opening orientation. Theobservation of an inhomogeneous and orientation dependentdopant distribution within the same layer has been explained byinvoking the bonding configurations exposed to theincorporating dopant atoms in the different emergingplanes.</p><p>When ELOG of InP is conducted on InP/Si, unlike that on InPsubstrates, the lateral growth is not symmetric on both sidesdue to the propagation of defects from the seed layer. Forexample, a higher concentration of threading dislocationsintersecting the surface of the {111}A emerging planes wouldcause a higher growth rate of these planes. The growth rate of{111}A planes with respect to the others can also be caused bythe vapor phase supersaturation as predicated byBurton-Cabrera-Frank model. The determined dislocation densityin the ELOG InP on InP/Si is ~ 4X10⁷cm^-2, which is nearly two magnitude lower than in theseed layer (~ 4X10⁹cm^-2). If the seed layer is of a better quality, theELOG layer will also be. Combination of high resolution x-raydiffraction reciprocal lattice mapping and low temperaturephotoluminescence indicates that the ELOG InP layer with highaspect ratio is nearly strain-free.</p><p>When ELOG of sulfur doped InP is conducted on ring shapedopenings on InP/Si substrate instead of stripe openings,octahedral shaped ELOG InP templates with smooth surface areformed. Strain compensated InGaAsP 6 periods multi-quantumwells (MQW) at 1.5 μm wavelength (target value) were grownon these templates by metalorganic vapor phase epitaxy. RT-PLis indicative of a good quality ELOG layers. Optimized ELOG onring openings may become very attractive for heteroepitaxy ofIII-V compounds on silicon.</p><p>As an extension of ELOG of InP on InP/Si, growth of InP isalso conducted on planar Focused-Ion-Beam (FIB)-modified (001)GaAs substrate. The impacts of the III/V ratio,crystallographic orientation of implanted lines andimplantation dose were explored. The choice of suitable growthconditions makes it possible to obtain continuous InP wiresaligned in all possible directions.</p>

Electrochemically formed passive layers on titanium and zirconium, and their optical, surface and corrosion properties are presented. With the use of higher applied AC voltages, the passive layers become thicker and more protective of the underlying metal, as determined from thickness measurements by scanning electron microscopy and focused ion beam instruments, as well as passive layer corrosion resistance measurements by electrochemical polarization curve and inductively coupled plasma mass spectrometry experiments. The surface morphology of all samples was studied with atomic force microscopy, profilometry, visible light microscopy, transmission electron microscopy, and finally electron backscattered diffraction experiments. The passive layers were found to be uniform in their surface structure with no cracks or fractures. However, the samples prepared at VAC = 60-80 V showed defects, which were increasingly prevalent at higher VAC. These defects are thought to be attributed to a process of localized electrochemical breakdown. The aforementioned increase in corrosion resistance is in spite of the defects, which were observed for the samples prepared at VAC = 60-80 V. Surface morphology, in relation to optical properties, was also investigated through reflectance spectroscopy measurements. A correlation between grain colouration and light reflected from the sample surface was observed through measurements using visible light microscopy as well as near infrared ultraviolet visible reflectance spectroscopy. These experiments showed a red-shift of wavelength maxima (λmax) values as voltages, and therefore thickness, were increased. This is the reason that different colours are seen for different thicknesses; the red shift causes different wavelengths to be reflected constructively and destructively. Overall, these passive layers are protective of an already remarkable metal and, with greater knowledge of their properties, their potential may be observed in a wide range of applications. / Thesis (Master, Chemistry) -- Queen's University, 2011-09-19 19:44:07.148

The loss and recovery of the surface hydrophobicity areimportant phenomena when highvoltage insulators, with a shedmaterial composed of polydimethylsiloxane (PDMS), are used. Theloss of hydrophobicity is mostly due to the oxidativecrosslinking which takes place on the PDMS surface duringexposure to electrical discharges, e. g. corona discharges. Thecrosslinking reaction leads to the formation of anoxygen-enriched, silica-like layer, which is brittle and henceprone to cracking, either spontaneously or upon mechanicaldeformation. Repetitive cracking leads to the propagation ofcracks into the core of the material, which is believed todeteriorate the insulator’s performance and reduce itsservice-life. Hence, an approach to make PDMS more resistant tothe build-up of the silica-like layer is beneficial for theperformance of PDMS in high voltage insulators. In this work the effect of antioxidative stabilizers on thecorona- and air-plasma-induced surface oxidation of PDMS isstudied. Three commercial stabilizers, a hindered phenol(Irganox® 1076), a hindered amine light stabilizer(Tinuvin® 770) and a bifunctional stabilizer withchainbreaking hindered phenol and secondary amine andhydroperoxide-decomposing sulfide moieties (Irganox® 565),have been used. Surface oxidation was achieved by exposure of amodel crosslinked PDMS to an air plasma or a corona discharge,and the surface characteristics of the exposed samples wereassessed by contact angle measurements, X-ray photoelectronspectroscopy, optical and scanning electron microscopy, andsurface profilometry before and after uniaxial stretching. A reliable rapid method for the assessment of stabilizerconcentration in PDMS was established. PDMS samples containingknown stabilizer concentrations of a phenolic antioxidant(Irganox® 1010) and a hindered amine stabilizer(Tinuvin® 144) were prepared. It was shown that thestabilizer concentration in PDMS could be determined by highperformance liquid chromatography (HPLC) of the microwaveassisted solvent extracts (MAE) of stabilized PDMS samplesusing acetone (a non-swelling solvent). This method wasemployed to measure the stabilizer concentration in PDMSsamples exposed to air plasma and corona discharges. Thestabilizer concentration in PDMS was varied by using diluteswelling solutions (0.005 wt% to 0.2 wt%) of the stabilizers inhexane. Samples stabilized with Irganox 565 showed stabilizerprecipitation on the surface after swelling in solutions with astabilizer concentration greater than 0.05 wt%. Samplescontaining Irganox 1076 and Tinuvin 770 showed no surfaceprecipitation except after swelling in a solution of 0.2 wt%stabilizer concentration. The air plasma and corona exposure time required for theformation of the silica-like surface layer increased,essentially, in a linear fashion with increasing stabilizerconcentration. Tinuvin 770 showed the strongest overallprotecting effect during, as well air plasma as coronaexposures, whereas Irganox 565 showed the strongest protectingeffect per mass fraction stabilizer during air plasmaexposures. Irganox 1076 was of moderate efficiency. The resultssuggest that efficient protection towards discharge-inducedsurface oxidation is achieved with hindered amine stabilizersor with stabilizers combining chain-breaking andhydroperoxide-decomposing functions. The diffusion of the stabilizers Irganox 1010 and Tinuvin144 from PDMS to water at elevated temperatures (75 °C and95 °C for Irganox 1010 and 95 °C for Tinuvin 144) wasstudied. For Irganox 1010 the diffusion constant (D), accordingto Fick’s second law for uni-dimensional penetrantdiffusion was assessed to 3.1 X 10-9cm2s-1at 95 °C and to 5.46 X 10-10cm2s-1at 75 °C. An estimate for the activationenergy for the diffusion of Irganox 1010 to the surroundingmedia was obtained (Ea=93 kJ mol-1), on the basis of the diffusion data. For Tinuvin144, no diffusion constant could be calculated due to poorseparation of the stabilizer peak from the impurities in theextract when using the HPLC method developed earlier.

<p>The loss and recovery of the surface hydrophobicity areimportant phenomena when highvoltage insulators, with a shedmaterial composed of polydimethylsiloxane (PDMS), are used. Theloss of hydrophobicity is mostly due to the oxidativecrosslinking which takes place on the PDMS surface duringexposure to electrical discharges, e. g. corona discharges. Thecrosslinking reaction leads to the formation of anoxygen-enriched, silica-like layer, which is brittle and henceprone to cracking, either spontaneously or upon mechanicaldeformation. Repetitive cracking leads to the propagation ofcracks into the core of the material, which is believed todeteriorate the insulator’s performance and reduce itsservice-life. Hence, an approach to make PDMS more resistant tothe build-up of the silica-like layer is beneficial for theperformance of PDMS in high voltage insulators.</p><p>In this work the effect of antioxidative stabilizers on thecorona- and air-plasma-induced surface oxidation of PDMS isstudied. Three commercial stabilizers, a hindered phenol(Irganox® 1076), a hindered amine light stabilizer(Tinuvin® 770) and a bifunctional stabilizer withchainbreaking hindered phenol and secondary amine andhydroperoxide-decomposing sulfide moieties (Irganox® 565),have been used. Surface oxidation was achieved by exposure of amodel crosslinked PDMS to an air plasma or a corona discharge,and the surface characteristics of the exposed samples wereassessed by contact angle measurements, X-ray photoelectronspectroscopy, optical and scanning electron microscopy, andsurface profilometry before and after uniaxial stretching.</p><p>A reliable rapid method for the assessment of stabilizerconcentration in PDMS was established. PDMS samples containingknown stabilizer concentrations of a phenolic antioxidant(Irganox® 1010) and a hindered amine stabilizer(Tinuvin® 144) were prepared. It was shown that thestabilizer concentration in PDMS could be determined by highperformance liquid chromatography (HPLC) of the microwaveassisted solvent extracts (MAE) of stabilized PDMS samplesusing acetone (a non-swelling solvent). This method wasemployed to measure the stabilizer concentration in PDMSsamples exposed to air plasma and corona discharges. Thestabilizer concentration in PDMS was varied by using diluteswelling solutions (0.005 wt% to 0.2 wt%) of the stabilizers inhexane. Samples stabilized with Irganox 565 showed stabilizerprecipitation on the surface after swelling in solutions with astabilizer concentration greater than 0.05 wt%. Samplescontaining Irganox 1076 and Tinuvin 770 showed no surfaceprecipitation except after swelling in a solution of 0.2 wt%stabilizer concentration.</p><p>The air plasma and corona exposure time required for theformation of the silica-like surface layer increased,essentially, in a linear fashion with increasing stabilizerconcentration. Tinuvin 770 showed the strongest overallprotecting effect during, as well air plasma as coronaexposures, whereas Irganox 565 showed the strongest protectingeffect per mass fraction stabilizer during air plasmaexposures. Irganox 1076 was of moderate efficiency. The resultssuggest that efficient protection towards discharge-inducedsurface oxidation is achieved with hindered amine stabilizersor with stabilizers combining chain-breaking andhydroperoxide-decomposing functions.</p><p>The diffusion of the stabilizers Irganox 1010 and Tinuvin144 from PDMS to water at elevated temperatures (75 °C and95 °C for Irganox 1010 and 95 °C for Tinuvin 144) wasstudied. For Irganox 1010 the diffusion constant (D), accordingto Fick’s second law for uni-dimensional penetrantdiffusion was assessed to 3.1 X 10^-9cm²s^-1at 95 °C and to 5.46 X 10^-10cm²s^-1at 75 °C. An estimate for the activationenergy for the diffusion of Irganox 1010 to the surroundingmedia was obtained (E_a=93 kJ mol^-1), on the basis of the diffusion data. For Tinuvin144, no diffusion constant could be calculated due to poorseparation of the stabilizer peak from the impurities in theextract when using the HPLC method developed earlier.</p>

Two classes of materials are investigated using ab intio methods based on density functional theory. The structural properties, electronic structure and thermodynamic properties of binary and ternary transition metal carbides are discussed in details. In addition, two actinide compounds will be presented. A new actinide monoxide, ThO, is predicted to be stable under pressure, and the weakly correlated UN is investigated as regards to its magnetic properties and electronic structure. The atomic and electronic structures of various types of single defects in TiC such as vacancies, interstitial defects, and antisite defects are investigated systematically. Both the C-poor and C-rich off-stoichiometric Ti1-cCc composition (0.49≤c≤0.51) have been studied. For the electronic structure, the difference of density of states (dDOS) is introduced to characterize the changes produced by the defects. Concerning the atomic structures, both interstitial defects and antisites are shown to induce the formation of C dumbbells or Ti dumbbells. To date, the Ti self-diffusion mechanism in TiC has not been fully understood, and particularly the Ti diffusion is much less studied in comparison with the C diffusion. Therefore, the self-diffusion of Ti in sub-stoichiometric TiC is studied, and the formation energies, migration barriers for Ti interstitials, dumbbells and dumbbell-vacancy clusters are reported. Some of the calculated activation energies are close to the experimental values, and the migration of Ti dumbbell terminated by C vacancies gives the lowest activation energy, which is in good agreement with the experimental data. These studies must be continued to obtain a full description (including phonon contributions, prefactors, etc.) of all the feasible diffusion mechanisms in TiC. The focus is then shifted from the light transition metal carbides to the heavy transition metal carbides. Various structures of Ru2C under ambient conditions are explored by using an unbiased swarm structure searching algorithm. The structures with R3m (one formula unit) and R-3m symmetry (two formula units) have been found to be lower in energy than the P-3m1 structure, and also to be dynamically stable at ambient conditions. The R-3m structure is characterized by emergence of the Ru-Ru metallic bonding, which has a crucial role in diminishing the hardness of this material. The study of correlation and relativistic effects in Ta2AlC is also presented. We have shown that going from a scalar relativity to a fully relativistic description does not have a significant effect on the computed electronic and mechanical properties of Ta2AlC. In addition, the calculations show that the structural and mechanical properties of Ta2AlC are strongly dependent on other details of theoretical treatment, such as the value of the Hubbard U parameter. The comparison between our results and experimental data point to that Ta2AlC is a weakly correlated system, which originates from that the 5d band is relatively wide in comparison with that of the 3d band. The existence of a rock salt Thorium monoxide (ThO) under high pressure is theoretically predicted. A chemical reaction between Th and ThO2 can produce a novel compound thorium monoxide under sufficient external pressure. To determine the pressure range where this reaction can be observed, we have identified two extreme boundaries by means of different theoretical approaches. The first one is given by a fully relativity DFT code in local density approximation (LDA). The second one is given by a scalar relativistic DFT code in generalized gradient approximation (GGA). It is found that ThO is energetically favored between 14 and 26 GPa. The f orbitals are filled at the expense of s and d electrons states of Th metal, under the action of pressure. The d-p hybridization leads to the stability of metallic ThO. Dynamical stability is also investigated by computing the phonon dispersions for the considered structures at high pressure. The electronic structure and magnetic properties of a promising nuclear fuel material, uranium mononitride (UN), are studied by means of density functional theory (DFT) and several extensions, such as dynamical mean-field theory (DMFT), disordered local moment (DLM) approach, and the GW method. The role of the relativistic corrections is analyzed for different levels of approximation. The importance of correlation effects is assessed through a detailed comparison between calculated electronic structure and measured photoemission spectrum, which helps to clarify the dual itinerant/localized nature of the 5f states of U in UN. Important effects are also observed for the 2p states of nitrogen, which are positioned at much lower energies that are difficult to be well treated in the conventional electronic structure calculations. / <p>QC 20141219</p>