Growth and Structural Properties of Rare Earth Nitride Thin Films

<p>In this thesis aspects of the growth of rare earth nitride thin films and characterisation of the resulting structural, electronic and magnetic properties of the film are investigated. The rare earth nitrides are a class of materials which combine interesting electronic and magnetic properties with potential applications in novel spintronic device structures. We study the formation of a preferential orientation in polycrystalline thin films of GdN deposited by electron-beam physical vapour deposition. X-ray diffraction is used to characterise the crystalline structure of films of varying thickness to identify a preference to grow along the [111] crystal direction, understood in terms of an evolutionary selection process. Variations in the film microstructure as a result of growth parameter variation are also correlated to electronic and magnetic properties. Investigation of the epitaxial growth of SmN on AlN surfaces revealed a novel growth orientation transition, controllable only via the growth temperature. Epitaxial integration of rare earth nitrides with III-nitride surfaces has previously only resulted in (111)-oriented growth on the (0001) surface as is expected from matching of the close-packed planes in the different crystal structures. High growth temperatures (≥800 ℃) induce (001)-oriented growth of SmN on the same (0001) AlN surface. This unexpected cube-on-hexagon geometry is confirmed through ex situ x-ray and in situ electron diffraction, the latter for which a computational simulation tool was developed to model and understand. The viability of using Sm as a temporary capping layer for rare earth nitride thin film samples is investigated. Capping layers are required to passivate samples due to their high reactivity, limiting the range of ex situ characterisation techniques that can be performed on them. Elemental Sm is relatively volatile raising the possibility of removing a Sm cap in situ using moderate annealing temperatures (400 °C to 600 ℃). The ability to remove the capping layer would allow in situ characterisation techniques to be performed in ultra high vacuum systems not directly connected to the growth system. In situ electron diffraction is used to characterise the growth and thermal annealing of Sm grown on top of epitaxial GdN layers, and the effects of the thermal removal process on the structural, electronic and magnetic properties of the GdN layer are investigated.</p>

Growth and Structural Properties of Rare Earth Nitride Thin Films

<p>In this thesis aspects of the growth of rare earth nitride thin films and characterisation of the resulting structural, electronic and magnetic properties of the film are investigated. The rare earth nitrides are a class of materials which combine interesting electronic and magnetic properties with potential applications in novel spintronic device structures. We study the formation of a preferential orientation in polycrystalline thin films of GdN deposited by electron-beam physical vapour deposition. X-ray diffraction is used to characterise the crystalline structure of films of varying thickness to identify a preference to grow along the [111] crystal direction, understood in terms of an evolutionary selection process. Variations in the film microstructure as a result of growth parameter variation are also correlated to electronic and magnetic properties. Investigation of the epitaxial growth of SmN on AlN surfaces revealed a novel growth orientation transition, controllable only via the growth temperature. Epitaxial integration of rare earth nitrides with III-nitride surfaces has previously only resulted in (111)-oriented growth on the (0001) surface as is expected from matching of the close-packed planes in the different crystal structures. High growth temperatures (≥800 ℃) induce (001)-oriented growth of SmN on the same (0001) AlN surface. This unexpected cube-on-hexagon geometry is confirmed through ex situ x-ray and in situ electron diffraction, the latter for which a computational simulation tool was developed to model and understand. The viability of using Sm as a temporary capping layer for rare earth nitride thin film samples is investigated. Capping layers are required to passivate samples due to their high reactivity, limiting the range of ex situ characterisation techniques that can be performed on them. Elemental Sm is relatively volatile raising the possibility of removing a Sm cap in situ using moderate annealing temperatures (400 °C to 600 ℃). The ability to remove the capping layer would allow in situ characterisation techniques to be performed in ultra high vacuum systems not directly connected to the growth system. In situ electron diffraction is used to characterise the growth and thermal annealing of Sm grown on top of epitaxial GdN layers, and the effects of the thermal removal process on the structural, electronic and magnetic properties of the GdN layer are investigated.</p>

Hydrogen spillover and its relation to catalysis: observations on structurally defined single-atom sites

Hydrogen spillover, involving the transfer of H atoms from metal sites onto the catalyst support, is ubiquitous in chemical processes such as catalytic hydrogenation and hydrogen storage and is therefore of tremendous fundamental and technological interest. However, atomic level information concerning the kinetics of this process, the structural evolution of the catalysts during hydrogen spillover, as well as the nature of participation of the spilled over H in catalysis, remain vastly lacking. Here, we provide insights to those questions with the development of a solubilised polyoxometalate-supported single-atom catalyst which allows for the use of characterisation techniques generally inaccessible to study heterogeneous catalysis. Hydrogenation kinetics together with poisoning studies further reveal that hydrogen spillover can be either detrimental or beneficial for catalysis – the direction and magnitude of which depends predominantly on the nature of the reducible bond in the substrate. Similar trends were observed on one of the most prototypical hydrogen spillover catalysts, Pt/WO3, supporting the generalisability of the observations.

Nanomaterials for Biomedical Applications: Production, Characterisations, Recent Trends and Difficulties

Designing of nanomaterials has now become a top-priority research goal with a view to developing specific applications in the biomedical fields. In fact, the recent trends in the literature show that there is a lack of in-depth reviews that specifically highlight the current knowledge based on the design and production of nanomaterials. Considerations of size, shape, surface charge and microstructures are important factors in this regard as they affect the performance of nanoparticles (NPs). These parameters are also found to be dependent on their synthesis methods. The characterisation techniques that have been used for the investigation of these nanomaterials are relatively different in their concepts, sample preparation methods and obtained results. Consequently, this review article aims to carry out an in-depth discussion on the recent trends on nanomaterials for biomedical engineering, with a particular emphasis on the choices of the nanomaterials, preparation methods/instruments and characterisations techniques used for designing of nanomaterials. Key applications of these nanomaterials, such as tissue regeneration, medication delivery and wound healing, are also discussed briefly. Covering this knowledge gap will result in a better understanding of the role of nanomaterial design and subsequent larger-scale applications in terms of both its potential and difficulties.

Structural characterisation methods for supramolecular chemistry that go beyond crystallography

In this tutorial review, we present an introduction to structural characterisation techniques commonly used for non-crystalline supramolecular compounds and discuss their application based on recent case studies.

A novel characterisation approach to reveal the mechano–chemical effects of oxidation and dynamic distension on polypropylene surgical mesh

The application of novel SEM-based spectroscopical characterisation techniques reveals the mechano–chemical effects of oxidation and dynamic distension on polypropylene surgical mesh.