ORCID Profile
0000-0002-4630-3803
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Atomic molecular and optical physics | Nanofabrication growth and self assembly | Astronomical instrumentation | Photonics optoelectronics and optical communications | Nonlinear optics and spectroscopy
Publisher: AIP Publishing
Date: 28-05-2007
DOI: 10.1063/1.2745264
Abstract: The authors investigate the effect of oxygen implantation and rapid thermal annealing in ZnO∕ZnMgO multiple quantum wells using photoluminescence. A blueshift in the photoluminescence is observed in the implanted s les. For a low implantation dose, a significant increase of activation energy and a slight increase of the photoluminescence efficiency are observed. This is attributed to the suppression of the point defect complexes and transformation between defect structures by implantation and subsequent rapid thermal annealing. A high dose of implantation leads to lattice damage and agglomeration of defects leading to large defect clusters, which result to an increase in nonradiative recombination.
Publisher: Springer Science and Business Media LLC
Date: 06-2016
Publisher: Elsevier BV
Date: 09-2013
DOI: 10.1016/J.JCIS.2013.02.030
Abstract: The particle size distribution (PSD) of a polydisperse or multimodal system can often be difficult to obtain due to the inherent limitations in established measurement techniques. For this reason, the resolution, accuracy and precision of three new and one established, commercially available and fundamentally different particle size analysis platforms were compared by measuring both in idual and a mixed s le of monodisperse, sub-micron (220, 330, and 410 nm - nominal modal size) polystyrene particles. The platforms compared were the qNano Tunable Resistive Pulse Sensor, Nanosight LM10 Particle Tracking Analysis System, the CPS Instruments's UHR24000 Disc Centrifuge, and the routinely used Malvern Zetasizer Nano ZS Dynamic Light Scattering system. All measurements were subjected to a peak detection algorithm so that the detected particle populations could be compared to 'reference' Transmission Electron Microscope measurements of the in idual particle s les. Only the Tunable Resistive Pulse Sensor and Disc Centrifuge platforms provided the resolution required to resolve all three particle populations present in the mixed 'multimodal' particle s le. In contrast, the light scattering based Particle Tracking Analysis and Dynamic Light Scattering platforms were only able to detect a single population of particles corresponding to either the largest (410 nm) or smallest (220 nm) particles in the multimodal s le, respectively. When the particle sets were measured separately (monomodal) each platform was able to resolve and accurately obtain a mean particle size within 10% of the Transmission Electron Microscope reference values. However, the broadness of the PSD measured in the monomodal s les deviated greatly, with coefficients of variation being ~2-6-fold larger than the TEM measurements across all four platforms. The large variation in the PSDs obtained from these four, fundamentally different platforms, indicates that great care must still be taken in the analysis of s les known to have complex PSDs. All of the platforms were found to have high precision, i.e. they gave rise to less than 5% variance in PSD shape descriptors over the replicate measurements.
Publisher: American Vacuum Society
Date: 22-07-2005
DOI: 10.1116/1.1991869
Abstract: We have employed synchrotron-based core level photoemission measurements and near-edge x-ray absorption fine structure spectroscopy to identify and characterize nitrogen interstitials in p-type GaN, created by nitrogen bombardment. From absorption measurements around the nitrogen K edge we have identified nitrogen interstitial levels within the band gap, in good agreement with theoretical predictions. The reduction in band bending determined from photoemission measurements was explained by the acceptor-like character of these defects. Argon bombardment produces nitrogen vacancies and the metallic Ga phase at the surface, which will produce the increased band bending and pinning of the surface Fermi level closer to the conduction band minimum.
Publisher: IOP Publishing
Date: 06-07-2007
Publisher: AIP Publishing
Date: 06-05-2004
DOI: 10.1063/1.1707232
Abstract: We have investigated compositional changes on GaN surfaces under low-energy Ar ion bombardment using synchrotron-based high-resolution core-level photoemission measurements and near-edge x-ray absorption fine-structure (NEXAFS) spectroscopy. The low-energy ion bombardment of GaN produces a Ga-rich surface layer which transforms into a metallic Ga layer at higher bombarding energies. At the same time, the photoemission spectra around the N 1s core level reveal the presence of both uncoordinated nitrogen and nitrogen interstitials, which we have analyzed in more detail by x-ray absorption measurements at the N K-edge. We have proposed a mechanism for the relocation and loss of nitrogen during ion bombardment, in agreement with some recent experimental and theoretical studies of defect formation in GaN. We have also demonstrated that photoemission spectroscopy and NEXAFS provide a powerful combination for studying compositional changes and the creation of point defects at GaN surface.
Publisher: Elsevier BV
Date: 03-2011
Publisher: Springer Science and Business Media LLC
Date: 22-07-2015
Publisher: Elsevier BV
Date: 02-2009
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3RA22727H
Publisher: AIP Publishing
Date: 11-05-2005
DOI: 10.1063/1.1929874
Abstract: The mechanical properties of zinc oxide epitaxial layers grown on a- and c-axis sapphire have been studied by spherical nanoindentation and cross-sectional transmission electron microscopy. As-grown threading dislocations, which are characteristic of epitaxial material, combined with the presence of the much harder, underlying substrate are found to have a significant effect on the mechanical behavior of ZnO epilayers as compared to bulk material. Epilayer material is found to be significantly harder than its bulk counterpart. For a-axis epilayers, analysis of load–unload data yields a hardness of 6.6±1.2GPa, and 5.75±0.8GPa for c-axis layers. We attribute this increased hardness to strain compensation via the presence of as-grown defects. These defects inhibit the slip mechanism responsible for relative softness of bulk single crystals. The absence of pop-in events from analyzed continuous-load nanoindentation data is further evidence for strain compensation by native defects within the epilayers. Large variations in the spread of collected data are indicative of inhomegenity in the epilayers.
Publisher: Elsevier BV
Date: 03-2006
Publisher: Elsevier BV
Date: 10-2019
DOI: 10.1016/J.JCIS.2019.07.016
Abstract: Supersaturation of dissolved gas is the most commonly reported method for generating long-lived bulk nanobubbles. However, these reports are treated with skepticism because of the lack of techniques that directly show that these particles are gas filled bubbles. Therefore, this work has tested the hypothesis that supersaturation obtained by a chemical reaction produces long-lived nanosized bubbles in bulk using an established protocol that relies on evaluating the density of nanoparticles and measuring their response to external pressure. Nanoparticles were generated using a chemical reaction between aqueous solutions of ammonium chloride and sodium nitrite. Standard nanoparticle sizing techniques, such as nanoparticle tracking analysis and dynamic light scattering, were utilized to determine the size and stability of the nanoparticles. Resonant mass measurement was used to measure the buoyant mass of the nanoparticles, and their compressibility was investigated by measuring their size under the application of external pressure. The formation of nanoparticles was consistent with the kinetics of nitrogen gas evolution produced in the reaction, where the nanoparticle size was shown to be dependent on the pH and concentration of the reactants. However, the chemical reaction was found to generate incompressible nanoparticles with a density larger than that of the solvent, confirming that these particles were not gas-filled bubbles.
Publisher: IOP Publishing
Date: 20-01-2006
Publisher: AIP Publishing
Date: 06-06-2016
DOI: 10.1063/1.4953210
Abstract: The results of systematic height measurements of polystyrene (PS) nanoparticles using intermittent contact litude modulation atomic force microscopy (IC-AM-AFM) are presented. The experimental findings demonstrate that PS nanoparticles deform during AFM imaging, as indicated by a reduction in the measured particle height. This deformation depends on the IC-AM-AFM imaging parameters, material composition, and dimensional properties of the nanoparticles. A model for nanoparticle deformation occurring during IC-AM-AFM imaging is developed as a function of the peak force which can be calculated for a particular set of experimental conditions. The undeformed nanoparticle height can be estimated from the model by extrapolation to zero peak force. A procedure is proposed to quantify and minimise nanoparticle deformation during IC-AM-AFM imaging, based on appropriate adjustments of the experimental control parameters.
Publisher: AIP Publishing
Date: 21-08-2006
DOI: 10.1063/1.2338552
Abstract: The influence of spherical nanoindentation on the band edge and deep level emission of single crystal c-axis ZnO has been studied by cathodoluminescence (CL) spectroscopy and monochromatic imaging. Excitonic emission is quenched at the indent site and defect emission in the range of 450–720nm is enhanced. Analysis of CL monochromatic images and spectra suggests that at least two different defect states are responsible for the broad defect emission band. Additionally, the indents result in a strong crystallographic dependence of the defect emission, producing a rosette feature with [112¯0] [21¯1¯0], and [12¯10] orientations that reflect the star-shaped luminescence quenching observed at the excitonic peak (390nm).
Publisher: IOP Publishing
Date: 22-03-2002
Publisher: American Chemical Society (ACS)
Date: 14-03-2023
Publisher: AIP Publishing
Date: 30-10-2006
DOI: 10.1063/1.2372747
Abstract: We have studied ZnO∕ZnMgO multiple quantum wells by spectrally resolved transient four-wave mixing with both one- and two-color excitations. The presence of an extended signal at negative interpulse delays in the two-color experiment is attributed to the two-photon coherence resulting from the generation of biexcitons. This technique provides a means to observe a transient four-wave mixing from biexcitons in the absence of any other signal, and thereby provides the first clear evidence that biexcitons are present in narrow ZnO∕ZnMgO quantum wells at room temperature. Dephasing times of the order of 100fs for the biexcitons are measured.
Publisher: American Physical Society (APS)
Date: 25-07-2008
Publisher: Elsevier BV
Date: 04-2006
Publisher: IOP Publishing
Date: 26-10-2017
Abstract: The estimation of nanoparticle number concentration in colloidal suspensions is a prerequisite in many procedures, and in particular in multi-stage, low-yield reactions. Here, we describe a rapid, non-destructive method based on optical extinction and dynamic light scattering (DLS), which combines measurements using common bench-top instrumentation with a numerical algorithm to calculate the particle size distribution (PSD) and concentration. These quantities were derived from Mie theory applied to measurements of the optical extinction spectrum of homogeneous, non-absorbing nanoparticles, and the relative PSD of a colloidal suspension. The work presents an approach to account for PSDs achieved by DLS which, due to the underlying model, may not be representative of the true s le PSD. The presented approach estimates the absolute particle number concentration of s les with mono-, bi-modal and broad size distributions with <50% precision. This provides a convenient and practical solution for number concentration estimation required during many applications of colloidal nanomaterials.
Publisher: Springer Science and Business Media LLC
Date: 02-2015
Publisher: IOP Publishing
Date: 14-01-2008
DOI: 10.1088/0957-4484/19/05/055205
Abstract: Strong suppression of the effects caused by the internal electric field in ZnO/ZnMgO quantum wells following ion-implantation and rapid thermal annealing, is revealed by photoluminescence, time-resolved photoluminescence, and band structure calculations. The implantation and annealing induces Zn/Mg intermixing, resulting in graded quantum well interfaces. This reduces the quantum-confined Stark shift and increases electron-hole wavefunction overlap, which significantly reduces the exciton lifetime and increases the oscillator strength.
Publisher: AIP Publishing
Date: 12-2005
DOI: 10.1063/1.2140481
Abstract: Zinc oxide single crystals implanted at room temperature with high-dose (1.4×1017cm−2) 300 keV As+ ions are annealed at 1000–1200 °C. Damage recovery is studied by a combination of Rutherford backscattering/channeling spectrometry (RBS/C), cross-sectional transmission electron microscopy (XTEM), and atomic force microscopy. Results show that such a thermal treatment leads to the decomposition and evaporation of the heavily damaged layer instead of apparent defect recovery and recrystallization that could be inferred from RBS/C and XTEM data alone. This study shows that heavily damaged ZnO has relatively poor thermal stability compared to as-grown ZnO which is a significant result and has implications for understanding results on thermal annealing of ion-implanted ZnO.
No related organisations have been discovered for Victoria Coleman.
Start Date: 2023
End Date: 12-2029
Amount: $34,948,820.00
Funder: Australian Research Council
View Funded Activity