ORCID Profile
0000-0002-7495-1349
Current Organisation
Monash University
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Metals and Alloy Materials | Condensed Matter Characterisation Technique Development | Materials Engineering | Functional Materials | Condensed Matter Physics
Expanding Knowledge in the Physical Sciences | Expanding Knowledge in the Chemical Sciences | Sheet Metal Products | Expanding Knowledge in Engineering | Structural Metal Products |
Publisher: IOP Publishing
Date: 02-07-2012
Publisher: American Physical Society (APS)
Date: 12-09-2011
Publisher: International Union of Crystallography (IUCr)
Date: 02-03-2010
DOI: 10.1107/S0021889810000749
Abstract: Measurements of electronic structure in solids by quantitative convergent-beam electron diffraction (QCBED) will not reach their ultimate accuracy or precision until the contribution of the background to the reflections in energy-filtered CBED patterns is fully accounted for. Apart from the well known diffuse background that arises from thermal diffuse scattering of electrons, there is a component that has a much higher angular frequency. The present work reports experimental evidence that this component mimics the angular distribution of the elastically scattered electrons within each reflection. A differential approach to QCBED is suggested as a means of quantitatively accounting for the background in energy-filtered CBED data.
Publisher: Elsevier BV
Date: 04-2023
Publisher: Elsevier BV
Date: 09-2011
Publisher: International Union of Crystallography (IUCr)
Date: 10-08-2016
DOI: 10.1107/S1600576716010657
Abstract: Voids can significantly affect the performance of materials and a key question is how voids form and evolve. Voids also provide a rare opportunity to study the fundamental interplay between surface crystallography and atomic diffusion at the nanoscale. In the present work, the shrinkage of voids in aluminium from 20 to 1 nm in diameter through in situ annealing is imaged in a transmission electron microscope. It is found that voids first shrink anisotropically from a non-equilibrium to an equilibrium shape and then shrink while maintaining their equilibrium shape until they collapse. It is revealed that this process maximizes the reduction in total surface energy per vacancy emitted. It is also observed that shrinkage is quantized, taking place one atomic layer and one void facet at a time. By taking the quantization and electron irradiation into account, the measured void shrinkage rates can be modelled satisfactorily for voids down to 5 nm using bulk diffusion kinetics. Continuous electron irradiation accelerates the shrinkage kinetics significantly however, it does not affect the energetics, which control void shape.
Publisher: American Chemical Society (ACS)
Date: 02-11-2017
Abstract: Recent advances in the ability to synthesize metallic nanoparticles with tailored geometries have led to a revolution in the field of plasmonics. However, studies of the important complementary system, an inverted nanostructure, have so far been limited to two-dimensional sphere-segment voids or holes. Here we reveal the localized surface plasmon resonances (LSPRs) of nanovoids that are topologically enclosed in three-dimensions: an "anti-nanoparticle". We combine this topology with the favorable plasmonic properties of aluminum to observe strongly localized field enhancements with LSPR energies in the extreme UV range, well beyond those accessible with noble metals or yet achieved with aluminum. We demonstrate the resonance tunability by tailoring the shape and size of the nanovoids, which are truncated octahedra in the 10-20 nm range. This system is pristine: the nanovoid cavity is free from any oxide or supporting substrate that would affect the LSPRs. We exploit this to infer LSPRs of pure, sub-20-nm Al nanoparticles, which have yet to be synthesized. Access to this extreme UV range will allow applications in LSPR-enhanced UV photoemission spectroscopy and photoionization.
Publisher: International Union of Crystallography (IUCr)
Date: 11-03-2019
DOI: 10.1107/S2053273319000354
Abstract: The rare earth hexaborides are known for their tendency towards very high crystal perfection. They can be grown into large single crystals of very high purity by inert gas arc floating zone refinement. The authors have found that single-crystal cerium hexaboride grown in this manner contains a significant number of inclusions of an impurity phase that interrupts the otherwise single crystallinity of this prominent cathode material. An iterative approach is used to unequivocally determine the space group and the lattice parameters of the impurity phase based on geometries of convergent-beam electron diffraction (CBED) patterns and the symmetry elements that they possess in their intensity distributions. It is found that the impurity phase has a tetragonal unit cell with space group P 4/ mbm and lattice parameters a = b = 7.23 ± 0.03 and c = 4.09 ± 0.02 Å. These agree very well with those of a known material, CeB 4 . Confirmation that this is indeed the identity of the impurity phase is provided by quantitative CBED (QCBED) where the very close match between experimental and calculated CBED patterns has confirmed the atomic structure. Further confirmation is provided by a density functional theory calculation and also by high-angle annular dark-field scanning transmission electron microscopy.
Publisher: MDPI AG
Date: 02-06-2021
DOI: 10.20944/PREPRINTS202106.0075.V1
Abstract: We introduce a number of techniques in quantitative convergent-beam electron diffraction under development by our group and discuss the basis for measuring interatomic electrostatic potentials (and therefore also electron densities), localised at sub-nanometre scales, with sufficient accuracy and precision to map chemical bonds in and around nanostructures in nanostructured materials. This has never before been possible as experimental measurements of bonding in quantum crystallography have hitherto always been restricted to homogeneous single-phased crystals.
Publisher: International Union of Crystallography (IUCr)
Date: 19-01-2005
DOI: 10.1107/S0108768104027739
Abstract: The single-crystal structure of a β′-copper vanadium bronze, Cu 0.63 V 2 O 5 , has been studied at room temperature and 9.6 K, and compared with that of the β-sodium vanadium bronze, Na 0.33 V 2 O 5 , structure. No convincing evidence to oppose an assignment of centrosymmetric C 2/ m symmetry to the structure was identified using the X-ray data. A subsequent convergent beam electron diffraction (CBED) experiment was performed and confirmed the C 2/ m space group. The oxygen–vanadium atom framework of Cu 0.63 V 2 O 5 is close to that of Na 0.33 V 2 O 5 . However, in the copper compound the Cu atoms are located in two positions: Cu1 in the 4( i ) position with x = 0.541, y = 0 and z = 0.345, and Cu2 in the 8( j ) position with x = 0.529, y = 0.038 and z = 0.357. The crystal structure changes little with temperature. Disorder of the Cu ion over two sites is seen at 9.6 K. This suggests that distribution of the Cu atoms over two sites is of a more static than dynamic nature.
Publisher: AIP Publishing
Date: 02-1999
DOI: 10.1063/1.369337
Abstract: The shift of the volume plasmon energy with particle size in cadmium sulphide nanoparticles was examined by energy filtered transmission electron microscopy. This technique allowed the plasmon energy of in idual, well-separated particles to be measured. The measured plasmon energy was found to increase with decreasing particle size, in general agreement with the theoretical approximation for plasmon shifting due to the quantum size effect. The nanoparticle diameters ranged between 1.5 and 3.8 nm and they were prepared by mechanochemical processing techniques and then electrophoretically deposited on the transmission electron microscope specimen grids.
Publisher: Elsevier BV
Date: 02-2003
DOI: 10.1016/S0304-3991(02)00250-4
Abstract: A new algorithm for determining the point spread function (PSF) of digital imaging systems is presented. The input is an image of an aperture whose shape need not be regular. The aperture shape is refined to an effective sub-pixel resolution and the PSF of the system is determined by de-convolution, assuming uniform illumination and a step function edge. The method has been tested on theoretical aperture images of varying shape and PSF, with and without noise. Depending on the degree of noise, a known PSF can be recovered to an accuracy of between 0.2 and 0.8%. Some typical results are given for a Gatan Image Filter with a 794 YAG multiscan camera on a Philips EM 430 transmission electron microscope at 200 and 300 kV. An ex le of a de-convoluted convergent beam electron diffraction pattern is included. The algorithm tolerates a small amount of de-focus.
Publisher: Elsevier BV
Date: 10-2023
Publisher: The Optical Society
Date: 08-03-2012
DOI: 10.1364/OL.37.001023
Publisher: Elsevier BV
Date: 10-2023
Publisher: Oxford University Press (OUP)
Date: 04-07-2014
Publisher: Proceedings of the National Academy of Sciences
Date: 12-08-2013
Abstract: A century has passed since Bragg solved the first atomic structure using diffraction. As with this first structure, all atomic structures to date have been deduced from the measurement of many diffracted intensities using iterative and statistical methods. We show that centrosymmetric atomic structures can be determined without the need to measure or even record a diffracted intensity. Instead, atomic structures can be determined directly and quickly from the observation of crystallographic phases in electron diffraction patterns. Furthermore, only a few phases are required to achieve high resolution. This represents a paradigm shift in structure determination methods, which we demonstrate with the moderately complex α-Al 2 O 3 . We show that the observation of just nine phases enables the location of all atoms with a resolution of better than 0.1 Å. This level of certainty previously required the measurement of thousands of diffracted intensities.
Publisher: Elsevier BV
Date: 07-2011
DOI: 10.1016/J.ULTRAMIC.2011.03.007
Abstract: Single defocused transmission electron microscope phase contrast images are used to reconstruct the projected thickness map of a single-material object. The algorithm is non-iterative and stable, and we extend it to account for the presence of spherical aberration in the objective optics. The technique can reconstruct the projected thickness map of general single-material objects in the strong phase/weak litude regime. It is sensitive to any excursions in the projected thickness from the average, and ideal for examining voids and free volume accumulation in amorphous/glassy materials at the nanometer scale. The resolution of the technique depends on the choice of defocus and the thickness of the specimen. In a certain regime, we demonstrate that variations in the transverse projected thickness with a lateral diameter of ∼ 0.25 nm may be detected. We use our algorithm to quantitatively reconstruct the projected thickness of latex sphere test specimens from single defocused electron micrographs. We demonstrate that the reconstruction has a large tolerance for error in the input parameters. Simulations confirm that the technique is quantitative, and demonstrate that the origin of low-frequency artifacts is an instability due to noise. We show that the autocorrelation of the projected thickness map may be used to measure the size of open structures in the object using both simulation and latex sphere data.
Publisher: Elsevier BV
Date: 2010
DOI: 10.1016/J.ULTRAMIC.2009.10.015
Abstract: Atomic-resolution transmission electron microscopy has largely benefited from the implementation of aberration correctors in the imaging part of the microscope. Though the dominant geometrical axial aberrations can in principle be corrected or suitably adjusted, the impact of higher-order aberrations, which are mainly due to the implementation of non-round electron optical elements, on the imaging process remains unclear. Based on a semi-empirical criterion, we analyze the impact of residual aperture aberrations on the quality of exit-plane waves that are retrieved from through-focal series recorded using an aberration-corrected and monochromated instrument which was operated at 300kV and enabled for an information transfer of approximately 0.05nm. We show that the impact of some of the higher-order aberrations in retrieved exit-plane waves can be balanced by a suitable adjustment of symmetry equivalent lower-order aberrations. We find that proper compensation and correction of 1st and 2nd order aberrations is critical, and that the required accuracy is difficult to achieve. This results in an apparent insensitivity towards residual higher-order aberrations. We also investigate the influence of the detector characteristics on the image contrast. We find that correction for the modulation transfer function results in a contrast gain of up to 40%.
Publisher: Elsevier BV
Date: 04-2012
Publisher: International Union of Crystallography (IUCr)
Date: 11-03-2005
DOI: 10.1107/S0021889805003900
Abstract: A new method that accounts for small but significant geometric distortions in quantitative convergent beam electron diffraction (QCBED) is briefly introduced. A summary of preliminary results obtained with this method shows an average three- to fourfold improvement in structure-factor measurement precision by QCBED. In the present work this method is applied to α-\\rm Al_{2}O_{3}, a benchmark compound for charge density studies. Experimental uncertainty is reduced to a level three times smaller than differences between density functional theory and periodic Hartree–Fock calculated structure factors.
Publisher: Oxford University Press (OUP)
Date: 31-07-2006
DOI: 10.1017/S1431927606069315
Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005
Publisher: Oxford University Press (OUP)
Date: 16-09-2003
DOI: 10.1017/S1431927603030356
Abstract: Current X-ray diffraction techniques intended for “ideally imperfect” specimens provide structure factors only on a relative scale and ever-present multiple scattering in strong low-angle Bragg reflections is difficult to correct. Multiple scattering is implicit in the quantitative convergent beam electron diffraction (QCBED) method, which provides absolutely scaled structure factors. Conventional single crystal X-ray diffraction has proved adequate in softer materials where crystal perfection is limited. In hard materials, the highly perfect nature of the crystals is often a difficulty, due to the inadequacy of the conventional corrections for multiple scattering (extinction corrections). The present study on α-Al 2 O 3 exploits the complementarity of synchrotron X-ray measurements for weak and medium intensities and QCBED measurement of the strong low-angle reflections. Two-dimensional near zone axis QCBED data from different crystals at various accelerating voltages, thicknesses, and orientations have been matched using Bloch-wave and multislice methods. The reproducibility of QCBED data is better than 0.5%. The low-angle strong QCBED structure factors were combined with middle and high-angle extinction-free data from synchrotron X-ray diffraction measurements. Static deformation charge density maps for α-Al 2 O 3 have been calculated from a multipole expansion model refined using the combined QCBED and X-ray data.
Publisher: American Physical Society (APS)
Date: 26-03-2010
Publisher: International Union of Crystallography (IUCr)
Date: 29-03-2017
DOI: 10.1107/S1600576717003260
Abstract: The effectiveness of tripod polishing and crushing as methods of mechanically preparing transmission electron microscopy specimens of hard brittle inorganic crystalline materials is investigated via the ex le of cerium hexaboride (CeB 6 ). It is shown that tripod polishing produces very large electron-transparent regions of very high crystal perfection compared to the more rapid technique of crushing, which produces crystallites with a high density of imperfections and significant mosaicity in the case studied here where the main crystallite facets are not along the natural {001} cleavage planes of CeB 6 . The role of specimen quality in limiting the accuracy of structure factor measurements by quantitative convergent-beam electron diffraction (QCBED) is investigated. It is found that the bonding component of structure factors refined from CBED patterns obtained from crushed and tripod-polished specimens varies very significantly. It is shown that tripod-polished specimens yield CBED patterns of much greater integrity than crushed specimens and that the mismatch error that remains in QCBED pattern matching of data from tripod-polished specimens is essentially nonsystematic in nature. This stands in contrast to QCBED using crushed specimens and lends much greater confidence to the accuracy and precision of bonding measurements by QCBED from tripod-polished specimens.
Publisher: Elsevier BV
Date: 04-2015
Publisher: Elsevier BV
Date: 02-2015
Publisher: Elsevier BV
Date: 06-2011
DOI: 10.1016/J.ULTRAMIC.2011.01.044
Abstract: The intensity distribution in three-beam CBED patterns from centrosymmetric crystals can be inverted analytically to enable the direct measurement of crystal structure litudes and three-phase invariants. The accuracy of the measurements depends upon the accuracy and precision with which specific loci within the discs can be identified. The present work exploits the equivalence in form of the intensity distribution along these loci to provide an algorithm for their automated location, enabling the rapid and unequivocal identification of their position. Moreover, it demonstrates how the loci can be used to determine directly the relative magnitudes of structure litudes with superior accuracy and without recourse to complex pattern-matching calculations.
Publisher: International Union of Crystallography (IUCr)
Date: 08-10-2018
DOI: 10.1107/S2052252518012216
Abstract: Under almost all circumstances, electron diffraction patterns contain information about the phases of structure factors, a consequence of the short wavelength of an electron and its strong Coulombic interaction with matter. However, extracting this information remains a challenge and no generic method exists. In this work, a set of simple analytical expressions is derived for the intensity distribution in convergent-beam electron diffraction (CBED) patterns recorded under three-beam conditions. It is shown that these expressions can be used to identify features in three-beam CBED patterns from which three-phase invariants can be extracted directly, without any iterative refinement processes. The octant, in which the three-phase invariant lies, can be determined simply by inspection of the indexed CBED patterns ( i.e. the uncertainty of the phase measurement is ±22.5°). This approach is demonstrated with the experimental measurement of three-phase invariants in two simple test cases: centrosymmetric Si and non-centrosymmetric GaAs. This method may complement existing structure determination methods by providing direct measurements of three-phase invariants to replace `guessed' invariants in ab initio phasing methods and hence provide more stringent constraints to the structure solution.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 25-03-2011
Abstract: Three techniques are used to probe the pseudogap state of cuprate high-temperature superconductors.
Publisher: American Physical Society (APS)
Date: 29-04-2021
Publisher: Elsevier BV
Date: 2009
Start Date: 09-2021
End Date: 08-2024
Amount: $390,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 03-2012
End Date: 06-2016
Amount: $601,225.00
Funder: Australian Research Council
View Funded ActivityStart Date: 07-2019
End Date: 06-2023
Amount: $490,000.00
Funder: Australian Research Council
View Funded Activity