An increasing number of fields would benefit from a single analytical probe that can characterise bulk objects that vary in morphology and/or material composition. These fields include security screening, medicine and material science. In this study the X-ray region is shown to be an effective probe for the characterisation of materials. The most prominent analytical techniques that utilise X-radiation are reviewed. The study then focuses on methods of amalgamating the three dimensional power of kinetic depth X-ray (KDFX) imaging with the materials discrimination of angular dispersive X-ray diffraction (ADXRD), thus providing KDEX with a much needed material specific counterpart. A knowledge of the sample position is essential for the correct interpretation of diffraction signatures. Two different sensor geometries (i.e. circumferential and linear) that are able to collect end interpret multiple unknown material diffraction patterns and attribute them to their respective loci within an inspection volume are investigated. The circumferential and linear detector geometries are hypothesised, simulated and then tested in an experimental setting with the later demonstrating a greater ability at discerning between mixed diffraction patterns produced by differing materials. Factors known to confound the linear diffraction method such as sample thickness and radiation energy have been explored and quantified with a possible means of mitigation being identified (i.e. via increasing the sample to detector distance). A series of diffraction patterns (following the linear diffraction appoach) were obtained from a single phantom object that was simultaneously interrogated via KDEX imaging. Areas containing diffraction signatures matched from a threat library have been highlighted in the KDEX imagery via colour encoding and match index is inferred by intensity. This union is the first example of its kind and is called diffraction enhanced KDEX imagery. Finally an additional source of information obtained from object disparity is explored as an alternative means of calculating sample loci. This offers a greater level of integration between these two complimentary techniques as object disparity could be used to reinforce the results produced by the linear diffraction geometry.

Filmes finos de BN foram depositados em uma ou duas camadas, em temperaturas entre a temperatura ambiente e 400oC, por deposição a vapor de átomos de boro sobre substratos de Si (111) ou Si (100), com irradiação simultânea de íons de argônio e/ou nitrogênio. A energia de íons variou de 400 a 1000 eV, e a razão de chegada ARR(N/A), definida pela razão do fluxo de partículas atômicas de nitrogênio relativa ao fluxo de átomos de boro transportados ao substrato, de 0,3 a 3,1. A pressão de gás na câmara de vácuo foi mantida a 1,6 x 10-2 Pa durante o processo de deposição. As amostras assim depositadas foram analisadas através de absorção no infravermelho, difração de raios-X e microscopia óptica. Todas as amostras apresentaram dois picos de BN hexagonal (h-BN) em 780 e 1370 cm-1 nos espectros de absorção e algumas, um pico de BN cúbico (c-BN) em 1070 cm-1. Estes picos foram analisados com os parâmetros de deposição, tais como temperatura de substrato, espessura nominal (En), momentum transferido por íons aos átomos depositados (MTA) e bombardeamento prévio do substrato com íons de argônio (BP). Foi verificado que a formação de c-BN nos filmes depende fortemente dos parâmetros En, MTA e BP. Os limiares da formação de c-BN encontrados para estes parâmetros são explicados em termos de: tensão compressiva, mobilidade de átomos no filme e rendimento de sputtering. / Thin BN films were deposited in one or two layers at temperatures from room temperature to 400oC, using boron vapor deposition on Si(111) or Si(100) substrates with simultaneous irradiation by nitrogen and/or argon ions (ion energy ranges from 400 to 1000 eV). The arrival rate ratio ARR(N/B), defined as the ratio of the flux of incident atomic nitrogen particles relative to the flux of evaporated boron atoms transported to the substrate, extends from 0.3 to 3.1. The gas pressure in the vacuum chamber was maintained at 1,6 x 10-2 Pa during the deposition. The samples deposited in this manner were analyzed through different characterization techniques such as infrared absorption, X-ray diffraction, and optical microscopy. Several samples presented two peaks of hexagonal BN (h-BN) at 780 and 1370 cm-1 in their IR spectra and a few samples, a peak of cubic BN (c-BN) at 1070 cm-1. These peaks were analyzed in terms of: substrate temperature, nominal thickness (En), momentum transferred from the ions to the boron atoms (MTA), and previous bombardment of the substrate by argon ions (BP). The formation of c-BN in those films was verified and it shows a strong relation onto depend strongly on the parameters En, MTA, and BP. The thresholds of the c-BN formation found for those parameters are explained in terms of compressive stress, atom mobility and sputtering efficiency.

Various experiments on Yb₂Ti₂O₇ have shown evidence of strange magnetic behaviour at low temperatures. Specific heat measurements on powder samples of Yb₂Ti₂O₇ show evidence of a sharp peak, indicating the occurence of a first order phase transition. Meanwhile, neutron scattering, Mössbauer absorption, and μSR measurements find no evidence of long range order below the temperature of this phase transition, leaving the nature of the low temperature phase a mystery. Quantifying the magnetic interactions in this material should allow us to better understand the low temperature behaviour of this material. In this study, we fit a symmetry allowed nearest-neighbour bilinear exchange model to quasi-elastic neutron scattering data collected well above the temperature of the experimentally observed phase transition. This neutron scattering data shows evidence of rods of scattering intensity along the ⟨111⟩ crystallographic directions. Neutron scattering probes the correlations between magnetic moments in a material, so fitting an interaction model to the neutron scattering is equivalent to fitting the interactions to the magnetic correlations. These correlations are driven by the interactions between the magnetic moments, so the neutron scattering should give us direct access to the form of these interactions. Using this method we successfully identify an anisotropic nearest-neighbour bilinear exchange model that reproduces the experimentally observed quasi-elastic neutron scattering. With this model we then proceed to compute real space correlation functions, finding that the rods of neutron scattering arise from the presence of strong correlations along nearest-neighbour chains. We also compute the bulk susceptibility and local susceptibility, obtaining very good fits to experiment with no variation of the model determined from the neutron scattering. The success of these calculations provides a further independent confirmation of the success of our interaction model in describing the magnetic interactions in Yb₂Ti₂O₇. Finally, we present a brief summary of ongoing work based on our anisotropic exchange model, including mean field calculations to determine the low temperature ground state of this model and classical Monte Carlo simulations to study the phase transition present in this model. We also discuss potential further studies of this and other models.

Various experiments on Yb₂Ti₂O₇ have shown evidence of strange magnetic behaviour at low temperatures. Specific heat measurements on powder samples of Yb₂Ti₂O₇ show evidence of a sharp peak, indicating the occurence of a first order phase transition. Meanwhile, neutron scattering, Mössbauer absorption, and μSR measurements find no evidence of long range order below the temperature of this phase transition, leaving the nature of the low temperature phase a mystery. Quantifying the magnetic interactions in this material should allow us to better understand the low temperature behaviour of this material. In this study, we fit a symmetry allowed nearest-neighbour bilinear exchange model to quasi-elastic neutron scattering data collected well above the temperature of the experimentally observed phase transition. This neutron scattering data shows evidence of rods of scattering intensity along the ⟨111⟩ crystallographic directions. Neutron scattering probes the correlations between magnetic moments in a material, so fitting an interaction model to the neutron scattering is equivalent to fitting the interactions to the magnetic correlations. These correlations are driven by the interactions between the magnetic moments, so the neutron scattering should give us direct access to the form of these interactions. Using this method we successfully identify an anisotropic nearest-neighbour bilinear exchange model that reproduces the experimentally observed quasi-elastic neutron scattering. With this model we then proceed to compute real space correlation functions, finding that the rods of neutron scattering arise from the presence of strong correlations along nearest-neighbour chains. We also compute the bulk susceptibility and local susceptibility, obtaining very good fits to experiment with no variation of the model determined from the neutron scattering. The success of these calculations provides a further independent confirmation of the success of our interaction model in describing the magnetic interactions in Yb₂Ti₂O₇. Finally, we present a brief summary of ongoing work based on our anisotropic exchange model, including mean field calculations to determine the low temperature ground state of this model and classical Monte Carlo simulations to study the phase transition present in this model. We also discuss potential further studies of this and other models.

Filmes finos de BN foram depositados em uma ou duas camadas, em temperaturas entre a temperatura ambiente e 400oC, por deposição a vapor de átomos de boro sobre substratos de Si (111) ou Si (100), com irradiação simultânea de íons de argônio e/ou nitrogênio. A energia de íons variou de 400 a 1000 eV, e a razão de chegada ARR(N/A), definida pela razão do fluxo de partículas atômicas de nitrogênio relativa ao fluxo de átomos de boro transportados ao substrato, de 0,3 a 3,1. A pressão de gás na câmara de vácuo foi mantida a 1,6 x 10-2 Pa durante o processo de deposição. As amostras assim depositadas foram analisadas através de absorção no infravermelho, difração de raios-X e microscopia óptica. Todas as amostras apresentaram dois picos de BN hexagonal (h-BN) em 780 e 1370 cm-1 nos espectros de absorção e algumas, um pico de BN cúbico (c-BN) em 1070 cm-1. Estes picos foram analisados com os parâmetros de deposição, tais como temperatura de substrato, espessura nominal (En), momentum transferido por íons aos átomos depositados (MTA) e bombardeamento prévio do substrato com íons de argônio (BP). Foi verificado que a formação de c-BN nos filmes depende fortemente dos parâmetros En, MTA e BP. Os limiares da formação de c-BN encontrados para estes parâmetros são explicados em termos de: tensão compressiva, mobilidade de átomos no filme e rendimento de sputtering. / Thin BN films were deposited in one or two layers at temperatures from room temperature to 400oC, using boron vapor deposition on Si(111) or Si(100) substrates with simultaneous irradiation by nitrogen and/or argon ions (ion energy ranges from 400 to 1000 eV). The arrival rate ratio ARR(N/B), defined as the ratio of the flux of incident atomic nitrogen particles relative to the flux of evaporated boron atoms transported to the substrate, extends from 0.3 to 3.1. The gas pressure in the vacuum chamber was maintained at 1,6 x 10-2 Pa during the deposition. The samples deposited in this manner were analyzed through different characterization techniques such as infrared absorption, X-ray diffraction, and optical microscopy. Several samples presented two peaks of hexagonal BN (h-BN) at 780 and 1370 cm-1 in their IR spectra and a few samples, a peak of cubic BN (c-BN) at 1070 cm-1. These peaks were analyzed in terms of: substrate temperature, nominal thickness (En), momentum transferred from the ions to the boron atoms (MTA), and previous bombardment of the substrate by argon ions (BP). The formation of c-BN in those films was verified and it shows a strong relation onto depend strongly on the parameters En, MTA, and BP. The thresholds of the c-BN formation found for those parameters are explained in terms of compressive stress, atom mobility and sputtering efficiency.

Topological insulators (TIs) are a class of quantum materials, which behave as insulators in the bulk, yet possess gapless spin-polarized surface states, which are robust against nonmagnetic impurities. The unique properties of TIs make them attractive not only for studying various fundamental phenomena in condensed matter and particle physics, but also as promising candidates for applications ranging from spintronics to quantum computation. Within the topological insulator realm, a great deal of focus has been placed on discovering new quantum materials, however, ideal multi-modal quantum materials have yet to be found. Here we study alpha-PdBi2, KFe2Te2, and DySb compounds including others within these families with high-resolution angle-resolved photoemission spectroscopy (ARPES) complimented by first principles calculations. We observe unique phase changes and phenomena across their transition temperatures. Our work paves a new direction in material discovery and application related to their unique electronic properties.

This is the first study comparing morphologies of CNT films on Kanthal wire, with their field emission properties, and as such offers ways to design better cylindrical emitter devices. A low turn-on field was achieved (0.35 V/µm), the field emission results have been explained using a simple model, and a fluorescent lamp was fabricated. Whilst previous work has been done on the link between “as grown” CNT films and their respective field emission properties on flat substrates, very little work has been done on linking morphology to emission performance on wire substrates, where the morphology can be very different. Microscopic structures such as towers, ridges and clumps consisting of many aligned or entangled CNTs were grown using an aerosol chemical vapour deposition (a-CVD) technique. Hydrogen added to the carrier gas resulted in a decrease in defect density in the growth of undoped CNTs, and an increase in defect density in the growth of nitrogen doped CNTs (N-CNTs) and boron doped CNTs (BCNTs). In-situ transmission electron microscopy (TEM) studies show that damage to CNT tips results in a significantly higher turn-on field compared to undamaged tips. This can be recovered by making the CNT emit current for several minutes which makes the tip recrystallize due to heat caused by the Nottingham effect. The field emission properties of the “as grown” CNT films are dominated by protruding CNTs found at the edges of ridge and tower microscopic structures. The field emission properties are also related to the dimensions of these structures with the longest ridges (hence those with the longest protruding CNTs) resulting in the lowest turn-on electric field. The ridge and tower structures act to accommodate protruding CNTs at their edges and their physical dimensions (mainly width) act to separate these emitters so that screening is minimised. This work shows that efficient emitters can be fabricated effectively from simple a-CVD techniques and microscopic structures act to improve, not degrade, field emission properties.

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.

Ce mémoire de thèse porte sur l'exploitation de l'effet Seebeck pour la caractérisation thermo-physique des matériaux thermoélectriques (TE) solides et liquides. Lors de travaux récents au sein du laboratoire, la technique photothermoélectrique (PTE) a été développée pour la caractérisation thermique de matériaux TE solides de faibles conductivités électriques. Dans ce travail, l'utilisation de cette technique a été généralisée à tous les matériaux TE solides (de faibles ou de hautes conductivités électriques). Cela est rendu possible par la prise en compte de la nature gaussienne de l'excitation thermique modulée à laquelle le matériau est soumis ainsi que par la compréhension des effets de couplage des mécanismes de transport thermique et électrique dans les matériaux TE. Dans cette thèse, plusieurs matériaux thermoélectriques solides ont été étudiés : le trisulfure de titane (TiS₃), les oxydes types Bi₂Ca₂Co₁,₇Oₓ, le séléniure du tellurure de bismuth (Bi₂Te₂,₄Se₀,₆). La tension auto-induite par effet Seebeck a été aussi exploitée pour la détection des transitions de phases que présentent certains matériaux thermoélectriques, ici le cas du séléniure de cuivre a été étudié. Une nouvelle procédure qui permet de déterminer l'évolution de la diffusivité thermique d'un matériau TE en fonction de la température est présentée. En plus des matériaux TE solides, la technique PTE a été étendue à l'étude des matériaux thermoélectriques liquides (LTE). Un modèle théorique qui décrit le signal délivré par un matériau LTE soumis à une excitation thermique périodique a été développé. Ensuite, une étude de l'évolution des propriétés thermiques d'un matériau LTE en fonction de la concentration d'un soluté a été réalisée. Enfin, l'approche dite de cavité résonnante d'ondes thermiques (TWRC) a été utilisée pour investiguer thermiquement des matériaux LTE. À notre connaissance, c'est la première fois que l'approche TWRC est utilisée pour l'analyse du signal généré par un liquide thermoélectrique. L'utilisation des LTE comme capteurs thermiques a été aussi abordée dans ce travail. / The use of the self-induced Seebeck effect in thermophysical characterization of solid and liquid thermoelectric (TE) materials is described in this manuscript. In previous works, the photothermoelectric technique (PTE) has been developed in our laboratory for the thermal characterization of solid TE materials having low electrical conductivities. In this work, we first generalized the use of the PTE technique to all solid thermoelectric materials (with high or low electrical conductivities). This is achieved by taking into account the Gaussian shape of the thermal source exciting the material as well as by the understanding of the coupling effects between thermal and electrical transport mechanisms when a TE material is submitted to a modulated thermal excitation. In this thesis, several solid thermoelectric materials were studied : Titanium trisulfide (TiS₃),Bi₂Ca₂Co₁,₇Oₓ oxydes and Bismuth Selenido-telluride (Bi₂Te₂,₄Se₀,₆). Then, the self-induced Seebeck voltage was used for the detection of phase transitions exhibited by certain thermoelectric materials. The case of the copper selenide (Cu₂Se) was studied. A new procedure allowing to follow the temperature dependance of the thermal diffusivity of solid TE materials is also presented. In this work, the PTE technique was extended to liquid thermoelectric (LTE) materials. Indeed, a theoretical model describing the signal delivered by a LTE material subject to a periodic thermal excitation has been developed. Then, a study of the evolution of the thermal properties of an electrolyte as function of a solute concentration was performed. Finally, the thermal-wave resonator cavity (TWRC) approach was used to characterize thermally LTE materials. As far as we know, this is the first method proposing a TWRC approach applied directly to the sensor itself. The use of LTE such as heat sensors was also addressed here.

STREAM is a 4-year multi-site training network that aims at career development of Early Stage Researchers (ESRs) on scientific design, construction manufacturing and of advanced radiation instrumentation. STREAM targets the development of innovative radiation-hard, smart CMOS sensor technologies for scientific and industrial applications. The platform technology developed within the project will be tested in the demanding conditions posed by the CERN LHC detectors' environment as well as European industry leaders in the field of CMOS imaging, electron microscopy and radiation sensors. This leveraging factor will allow to fine-tune the technology to meet the requirements of industrial application cases on demand such as electron microscopy and medical X-ray imaging, as well as pathway towards novel application fields such as satellite environments, industrial X-ray systems and near-infrared imaging. The project will train a new generation of creative, entrepreneurial and innovative early-stage researchers and widen their academic career and employment opportunities. The STREAM consortium is composed of 10 research organisations and 5 industrial partners; the network will provide training to 17 ESRs. STREAM structures the research and training in four scientific work-packages which span the whole value-chain from research to application: CMOS Technologies Assessment, Smart Sensor Design and Layout, Validation and Qualification, Technology Integration, and Valorization.