Robert Harrison

High energy x-ray photoelectron spectroscopy (HAXPES) measurements were carried out using a Scienta Omicron HAXPES instrument to provide reference spectra for depleted triuranium octoxide. Triuranium octoxide, as confirmed by x-ray diffraction, was synthesized by calcination of uranyl chloride at 1000 °C. The material was fixed on a double-sided carbon tape for the analysis with charge control measures in place. The expanded energy range, using a Ga Kα x-ray source, presents core-level photoelectrons not observed in traditional XPS. Included also is the region associated with MNN x-ray-induced Auger transitions, which can only be observed at energies achievable with HAXPES instrumentation. These reference spectra build on previous work by the authors on uranium dioxide, expanding the knowledge of the uranium/oxygen system by HAXPES and XPS analysis.

High energy x-ray photoelectron spectroscopy (HAXPES) measurements were carried out using a Scienta Omicron HAXPES instrument to provide reference spectra for depleted triuranium octoxide. Triuranium octoxide, as confirmed by x-ray diffraction, was synthesized by calcination of uranyl chloride at 1000 °C. The material was fixed on a double-sided carbon tape for the analysis with charge control measures in place. The expanded energy range, using a Ga Kα x-ray source, presents core-level photoelectrons not observed in traditional XPS. Included also is the region associated with MNN x-ray-induced Auger transitions, which can only be observed at energies achievable with HAXPES instrumentation. These reference spectra build on previous work by the authors on uranium dioxide, expanding the knowledge of the uranium/oxygen system by HAXPES and XPS analysis.

HAXPES measurements were carried out using a Scienta Omicron HAXPES instrument to provide reference spectra for depleted uranium dioxide. High purity uranium dioxide, as confirmed by trace elemental analysis and x-ray diffraction, was synthesized via the integrated dry route from uranium hexafluoride. The material was fixed on double sided carbon tape for the analysis with charge control measures in place. The expanded energy range, using a Ga Kα x-ray source, presents core level photoelectrons not observed in traditional XPS. In addition, a region associated with the x-ray induced Auger transitions MNN is evident at binding energies only achievable with HAXPES. The reference spectra presented here act as the first in a line of proposed investigations into the comparison of XPS and HAXPES from surface to bulk as well as a fundamental understanding of the electronic structure of uranium materials.

The self-organisation of void and gas bubbles in solids into superlattices is an intriguing nanoscale phenomenon. Despite the discovery of these lattices 45 years ago, the atomistics behind the ordering mechanisms responsible for the formation of these nanostructures are yet to be fully elucidated. Here we report on the direct observation via transmission electron microscopy of the formation of bubble lattices under He ion bombardment. By careful control of the irradiation conditions, it has been possible to engineer the bubble size and spacing of the superlattice leading to important conclusions about the significance of vacancy supply in determining the physical characteristics of the system. Furthermore, no bubble lattice alignment was observed in the <111> directions pointing to a key driving mechanism for the formation of these ordered nanostructures being the two-dimensional diffusion of self-interstitial atoms.

Oxidation of ZrN ceramics from 973–1373 K under static conditions reveals parabolic rate behavior, indicative of a diffusion‐controlled process. In‐situ high temperature powder XRD found the oxidation mechanism begins with destabilization of ZrN through formation of a ZrN_1−x phase with oxide peaks initially detected at around 773 K. The zirconium oxide layer was found to be monoclinic by in‐situ XRD with no evidence of tetragonal or cubic polymorphs present to 1023 K. Bulk ceramic samples oxidized at 1173 and 1273 K underwent slower oxidation than those oxidized at 973 and 1073 K. This change in oxidation rate and hence mechanism was due to formation of a denser c‐ZrO₂ polymorph stabilized by nitrogen defects. This N‐doped dense ZrO₂ layer acts as a diffusion barrier to oxygen diffusion. However, at an oxidation temperature of 1373 K this layer is no longer protective due to increased diffusion through it resulting in grain boundary oxidation.

During ion irradiation which is often used for the purposes of bandgap engineering, nanostructures can experience a phenomenon known as ion‐induced bending (IIB). The mechanisms behind this permanent deformation are the subject of debate. In this work, germanium nanowires are irradiated with 30 or 70 keV xenon ions to induce bending either away from or toward the ion beam. By comparing experimental results with Monte Carlo calculations, the direction of the bending is found to depend on the damage profile over the cross section of the nanowire. After irradiation, the nanowires are annealed at temperatures up to 440 °C triggering solid‐phase epitaxial growth (SPEG) causing further modification to the deformed nanowires. After IIB, it is observed that nanowires which had bent away from the ion beam then straighten during SPEG while those which had bent toward the ion beam bend even more. This is attributed to differences in the mechanisms responsible for the ion‐beam‐induced bending in opposite directions. Thus, the results reported here give insights into the mechanisms causing the IIB of nanowires and demonstrate how to predict the evolution of nanowires under irradiation and annealing. Finally, they show that, under certain conditions, the bending can even be removed via SPEG.

During ion irradiation which is often used for the purposes of bandgap engineering, nanostructures can experience a phenomenon known as ion‐induced bending (IIB). The mechanisms behind this permanent deformation are the subject of debate. In this work, germanium nanowires are irradiated with 30 or 70 keV xenon ions to induce bending either away from or toward the ion beam. By comparing experimental results with Monte Carlo calculations, the direction of the bending is found to depend on the damage profile over the cross section of the nanowire. After irradiation, the nanowires are annealed at temperatures up to 440 °C triggering solid‐phase epitaxial growth (SPEG) causing further modification to the deformed nanowires. After IIB, it is observed that nanowires which had bent away from the ion beam then straighten during SPEG while those which had bent toward the ion beam bend even more. This is attributed to differences in the mechanisms responsible for the ion‐beam‐induced bending in opposite directions. Thus, the results reported here give insights into the mechanisms causing the IIB of nanowires and demonstrate how to predict the evolution of nanowires under irradiation and annealing. Finally, they show that, under certain conditions, the bending can even be removed via SPEG.