Ultra-bright emission from hexagonal boron nitride defects as a new platform for bio-imaging and bio-labelling

Bio-imaging requires robust ultra-bright probes without causing any toxicity to the cellular environment, maintain their stability and are chemically inert. In this work we present hexagonal boron nitride (hBN) nanoflakes which exhibit narrowband ultra-bright single photon emitters1. The emitters are optically stable at room temperature and under ambient environment. hBN has also been noted to be noncytotoxic and seen significant advances in functionalization with biomolecules2,3. We further demonstrate two methods of engineering this new range of extremely robust multicolour emitters across the visible and near infrared spectral ranges for large scale sensing and biolabeling applications

Determining crystal structures through crowdsourcing and coursework

We show here that computer game players can build high-quality crystal structures. Introduction of a new feature into the computer game Foldit allows players to build and real-space refine structures into electron density maps. To assess the usefulness of this feature, we held a crystallographic model-building competition between trained crystallographers, undergraduate students, Foldit players and automatic model-building algorithms. After removal of disordered residues, a team of Foldit players achieved the most accurate structure. Analysing the target protein of the competition, YPL067C, uncovered a new family of histidine triad proteins apparently involved in the prevention of amyloid toxicity. From this study, we conclude that crystallographers can utilize crowdsourcing to interpret electron density information and to produce structure solutions of the highest quality

Doped Beam Very Low Energy Particle Induced X-Ray Emission

University of Technology Sydney. Faculty of Science.Particle Induced X-Ray Emission (PIXE) is a spectroscopic technique where characteristic X-Rays are generated from a sample by the impact of high energy particles. PIXE is typically performed with protons in a particle accelerator at energies in excess of 1MeV and is used for the detection of trace elements due to the lower background compared to complementary techniques such as Scanning Electron Microscope (SEM) Energy Dispersive Spectroscopy (EDS). PIXE performed at energies of less than 1MeV is sometimes used to enhance sensitivity to light elements, however very low energy PIXE (VLE-PIXE) performed at energies available to a commercial focused ion beam microscope of ≤30keV was considered impossible due to the extremely low X-Ray production at these energies. In this research, VLE-PIXE was made possible by doping a hydrogen focused ion beam with a small proportion of a heavier ion species such as Ar or Xe. The characteristic X-Ray signal was shown to increase dramatically, allowing trace element analysis in the low parts per million range, offering performance comparable to proton only PIXE performed at much higher energies. This thesis outlines the implementation, characterisation, and application of the doped beam VLEPIXE technique in a commercial focused ion beam microscope utilising available hardware and little to no modification to the instrument. An investigation into the beam doping technique led to an interpretive model which considers various physical mechanisms which may be responsible for the increased performance which includes: the formation of quasi-molecules between the heavy projectile ion and the target atom, the suppression of non-radiative transitions, and vacancy lifetime modification due to multiple ionisation. These mechanisms may arise from the coincident impact of protons and a heavy ion species upon the same region of the sample. The ions backscattering from the surface during VLE-PIXE analysis were also analysed to provide additional information regarding the sample thickness and composition. This leads to the possibility of several new techniques such as simultaneous doped beam VLE-PIXE and backscattered ion spectroscopy for real-time tomography, or endpointing during Focused Ion Beam (FIB) milling

Influence of Bound versus Non-Bound Stabilizing Molecules on the Thermal Stability of Gold Nanoparticles

Knowledge concerning the sintering behavior of gold nanoparticles (AuNPs) allows for improved nanomaterials for applications such as printed electronics, catalysis and sensing. In this study, we examined the ability of a range of compounds to stabilize AuNPs against thermal sintering and compared compounds with and without functional groups that anchor the molecules to the nanoparticle surface. Thermal stability was characterized in terms of the temperature of the sintering event (<i>T</i>_SE) as well as thermogravimetric analysis and scanning electron microscopy. We show that anchored stabilizing compounds with high thermal stability are effective at preventing the sintering of AuNPs until the decomposition of the compound. A <i>T</i>_SE of 390 °C was achieved using 1-pyrenebutanethiol as stabilizer. Of the unanchored stabilizers, which were combined with butanethiol-capped AuNPs, two were found to be particularly effective: oleylamine (<i>T</i>_SE ≈ 300 °C) and a perylenedicarboximide derivative (<i>T</i>_SE ≈ 540 °C), the latter conferring an unprecedented level of thermal stability on ligand-stabilized AuNPs. When selecting stabilizers without anchoring groups, our results demonstrate the importance of choosing those that have an affinity with the capping ligands on the AuNPs to ensure a uniform mixture of AuNPs and stabilizer within a film

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