ORCID Profile
0000-0002-8714-1484
Current Organisation
Monash University
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In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Materials Engineering Not Elsewhere Classified | Nanotechnology | Optical Physics | Nanotechnology | Condensed Matter Physics | Materials Engineering | Synchrotrons; Accelerators; Instruments and Techniques | Soft Condensed Matter | Electronic and Magnetic Properties of Condensed Matter; Superconductivity | Condensed Matter Physics—Electronic And Magnetic Properties; | Condensed Matter Imaging | Classical and Physical Optics | Condensed Matter Characterisation Technique Development | Condensed Matter Physics—Other
Expanding Knowledge in the Physical Sciences | Precious metals (e.g. refined bullion, wire and strip) | Other | Fabricated metal products not elsewhere classified | Expanding Knowledge in Engineering | Expanding Knowledge in the Biological Sciences | Integrated circuits and devices | Physical sciences | Expanding Knowledge in Technology |
Publisher: Elsevier BV
Date: 08-2008
DOI: 10.1016/J.ULTRAMIC.2008.01.001
Abstract: Through focus series of images are collected from MgO nano-cube crystals in the transmission electron microscope (TEM). The experimental data is used to solve the transport of intensity equation (TIE) to retrieve phase maps, which portray the morphology of the cubes and are quantified by the mean inner potential V(0). Particular attention is given to the practical difficulties associated with TIE phase retrieval of non-conducting polyhedron particles.
Publisher: Elsevier BV
Date: 10-2022
DOI: 10.1016/J.ULTRAMIC.2022.113580
Abstract: We propose a linear imaging theory for differential phase contrast under the weak-phase-weak- litude object approximation. Contrast transfer functions are defined for thin and thick weak objects, and they successfully describe several imaging characteristics of differential phase contrast. We discuss the defocus dependence of the contrast for several ex les: atomic resolution, a p-n junction, a heterointerface, and grain boundaries. Understanding the imaging characteristics helps in adjusting aberrations in DPC STEM.
Publisher: Springer International Publishing
Date: 2022
Publisher: Elsevier BV
Date: 07-2005
DOI: 10.1016/J.ULTRAMIC.2005.01.002
Abstract: In this paper a method for collecting electron diffraction patterns using a Gatan imaging filter is presented. The method enables high-quality diffraction data to be measured at scattering angles comparable to those that can be obtained using X-ray and neutron diffraction. In addition, the method offers the capability for examining small regions of s le in, for ex le, thin films and nano-structures. Using X-ray, neutron and electron diffraction data collected from the same s le, we demonstrate quantitative agreement between all three. We also present a novel method for obtaining the single scattering contribution to the total diffracted intensity by collecting data at various electron wavelengths. This approach allows pair distribution functions to be determined from electron diffraction in cases where there exists significant multiple scattering.
Publisher: American Physical Society (APS)
Date: 04-10-2013
Publisher: American Physical Society (APS)
Date: 03-10-2019
Publisher: Elsevier BV
Date: 03-2005
Publisher: Elsevier BV
Date: 2004
Publisher: Informa UK Limited
Date: 20-12-2002
Publisher: AIP Publishing
Date: 08-09-2008
DOI: 10.1063/1.2980505
Abstract: Quantitative phase maps from Au and polystyrene nanospheres were obtained using the transport of intensity equation approach for phase retrieval in the electron microscope. These were compared to surface plasmon maps, as generated by electron energy loss spectroscopy. Large phase excursions were observed in the vacuum regions surrounding the Au nanospheres, yet not near adjacent polystyrene nanospheres. It is proposed that these phase excursions are associated with surface plasmon excitation. These results suggest that phase retrieval offers an alternative means for sensing and interpreting the optical response of nanostructured metals.
Publisher: American Physical Society (APS)
Date: 18-09-2017
Publisher: Elsevier BV
Date: 03-2022
DOI: 10.1016/J.ULTRAMIC.2021.113457
Abstract: Quantitative differential phase contrast imaging of materials in atomic-resolution scanning transmission electron microscopy using segmented detectors is limited by various factors, including coherent and incoherent aberrations, detector positioning and uniformity, and scan-distortion. By comparing experimental case studies of monolayer and few-layer graphene with image simulations, we explore which parameters require the most precise characterisation for reliable and quantitative interpretation of the reconstructed phases. Coherent and incoherent lens aberrations are found to have the most significant impact. For images over a large field of view, the impact of noise and non-periodic boundary conditions are appreciable, but in this case study have less of an impact than artefacts introduced by beam deflections coupling to beam scanning (imperfect tilt-shift purity).
Publisher: Elsevier BV
Date: 11-2017
DOI: 10.1016/J.ULTRAMIC.2017.07.002
Abstract: Electric field mapping using segmented detectors in the scanning transmission electron microscope has recently been achieved at the nanometre scale. However, converting these results to quantitative field measurements involves assumptions whose validity is unclear for thick specimens. We consider three approaches to quantitative reconstruction of the projected electric potential using segmented detectors: a segmented detector approximation to differential phase contrast and two variants on ptychographical reconstruction. Limitations to these approaches are also studied, particularly errors arising from detector segment size, inelastic scattering, and non-periodic boundary conditions. A simple calibration experiment is described which corrects the differential phase contrast reconstruction to give reliable quantitative results despite the finite detector segment size and the effects of plasmon scattering in thick specimens. A plasmon scattering correction to the segmented detector ptychography approaches is also given. Avoiding the imposition of periodic boundary conditions on the reconstructed projected electric potential leads to more realistic reconstructions.
Publisher: AIP Publishing
Date: 05-06-2007
DOI: 10.1063/1.2743029
Abstract: Porous solids are very important from a scientific point of view as they provide a medium in which to study the behavior of confined fluids. Although some porous solids have a well defined pore geometry such as zeolites, many porous solids lack crystalline order and are usually described as amorphous. The description of the pore geometry in such structures is very difficult. The authors develop a modeling approach using a Monte Carlo algorithm to simulate porosity within amorphous systems based on constraints for the internal volume and surface area. To illustrate this approach, a model of microporous amorphous silicon is presented. Structural aspects of the porous model are then compared against hybrid reverse Monte Carlo simulations of nonporous amorphous silicon and published results from the literature. It is found that coordination defects are predominately located at the pore surface walls.
Publisher: American Physical Society (APS)
Date: 13-09-2005
Publisher: International Union of Crystallography (IUCr)
Date: 12-2017
Publisher: Wiley
Date: 04-08-2011
DOI: 10.1111/J.1365-2818.2011.03522.X
Abstract: Atom probe tomography is an accurate analytical and imaging technique which can reconstruct the complex structure and composition of a specimen in three dimensions. Despite providing locally high spatial resolution, atom probe tomography suffers from global distortions due to a complex projection function between the specimen and detector which is different for each experiment and can change during a single run. To aid characterization of this projection function, this work demonstrates a method for the reverse projection of ions from an arbitrary projection surface in 3D space back to an atom probe tomography specimen surface. Experimental data from transmission electron microscopy tilt tomography are combined with point cloud surface reconstruction algorithms and finite element modelling to generate a mapping back to the original tip surface in a physically and experimentally motivated manner. As a case study, aluminium tips are imaged using transmission electron microscopy before and after atom probe tomography, and the specimen profiles used as input in surface reconstruction methods. This reconstruction method is a general procedure that can be used to generate mappings between a selected surface and a known tip shape using numerical solutions to the electrostatic equation, with quantitative solutions to the projection problem readily achievable in tens of minutes on a contemporary workstation.
Publisher: Elsevier BV
Date: 08-2013
Publisher: Elsevier BV
Date: 04-2016
Publisher: The Optical Society
Date: 20-02-2018
DOI: 10.1364/OL.43.000975
Publisher: Elsevier BV
Date: 2003
Publisher: American Physical Society (APS)
Date: 03-06-2014
Publisher: The Optical Society
Date: 08-06-2012
DOI: 10.1364/OE.20.013947
Publisher: American Chemical Society (ACS)
Date: 29-05-2015
Abstract: Ab initio models of Ge(x)As10Se(90-x), and Ge(x)Sb10Se(90-x) glasses are constructed, and their bonding environments are characterized and compared against each other and to recent experimental studies of equivalent glasses at the same stoichiometry and density. A minimum in the linear refractive index is found to correlate with a maximum in the number of length-one, predominantly Se, atomic chains for both glass types. The threshold behavior difference between GeAsSe and GeSbSe is shown to be due to the appearance of As-As-Se2 structural units beyond the MCN = 2.67 threshold in the GeAsSe glasses.
Publisher: Elsevier BV
Date: 06-2022
DOI: 10.1016/J.ULTRAMIC.2022.113475
Abstract: The sensitive coherent interference of electron waves arising from a specimen is useful for revealing subtle structural information in electron micrographs, which can be important for minimising dose and for rapid imaging. In general, dynamical diffraction is expected due to the useful strong interactions of electrons with matter, which can create phase contrast that violates the requisite Radon projection assumption for tomography. It is for these reasons that incoherent imaging modalities such as high angle annular dark field have been favoured to date in electron tomography of crystalline specimens, to access a monotonic relationship between specimen thickness and micrograph intensity. Here we use a geometric approach to track topological features that are robust to perturbation of the imaging conditions, to enable 3D reconstructions from electron microscope tilt series under imaging conditions that violate the Radon projection assumption, with an emphasis on phase contrast. Invoking a sparsity assumption, we demonstrate that topological features can be reliably tracked in 3D using a differential geometric form of stereoscopy, to circumvent departures from the projection approximation and reduce noise by effecting segmentation of interest points from the outset. We demonstrate this approach on a variety of different specimen and data types, from polyhedral nanoparticles, to steel dislocation networks, cryo-EM cellular structures and 3D diffuse diffraction of a relaxor ferroelectric.
Publisher: American Physical Society (APS)
Date: 29-08-2014
Publisher: AIP Publishing
Date: 15-05-2009
DOI: 10.1063/1.3129310
Abstract: To adapt electron tomography for the specific study of specimen morphology, a novel reconstruction algorithm is proposed which treats strong intensity gradients in images as arising from the projected edges of surfaces. Images portraying scattering interfaces arising from absorption, elastic, or Fresnel diffraction processes are used to identify edge maps that define the abscissa of projected surface tangents. Differential geometry is used to calculate the shape of these surfaces by considering smooth variations of measured tangent abscissa to infer local tangent intersections. The approach outlined here is not restricted to convex shapes and is designed for cases where morphology is more important than retrieval of the three-dimensional scattering density. The proposed algorithm is tested on simulated data, experimental benchmark specimens of MgO nanoparticles and is then applied to a nanosized atom probe tip, for which the approach here was specifically developed.
Publisher: International Union of Crystallography (IUCr)
Date: 20-07-2012
Publisher: Informa UK Limited
Date: 11-04-2009
Publisher: American Physical Society (APS)
Date: 18-05-2016
Publisher: IEEE
Date: 12-2018
Publisher: Elsevier BV
Date: 03-2010
Publisher: Elsevier BV
Date: 11-2007
Publisher: IEEE
Date: 02-2010
Publisher: International Union of Crystallography (IUCr)
Date: 09-07-2015
DOI: 10.1107/S2053273315011845
Abstract: The interpretation of angular symmetries in electron nanodiffraction patterns from thin amorphous specimens is examined. It is found that in general there are odd symmetries in experimental electron nanodiffraction patterns. Using simulation, it is demonstrated that this effect can be attributed to dynamical scattering, rather than other ergences from the ideal experimental conditions such as probe-forming lens aberrations and camera noise. The departure of opposing diffracted intensities from Friedel's law in the phase grating formalism is calculated using a general structure factor for disordered materials. On the basis of this, a simple correction procedure is suggested to recover the kinematical angular symmetries, and thus readily interpretable information that reflects the symmetries of the original projected object. This correction is numerically tested using both the phase object and multislice calculations, and is demonstrated to fully recover all the kinematical diffracted symmetries from a simulated atomic model of a metallic glass.
Publisher: Informa UK Limited
Date: 21-08-2007
Publisher: American Physical Society (APS)
Date: 06-03-2019
Publisher: American Physical Society (APS)
Date: 18-04-2018
Publisher: Elsevier BV
Date: 05-2020
Publisher: American Physical Society (APS)
Date: 22-02-2018
Publisher: The Optical Society
Date: 12-10-2016
DOI: 10.1364/OE.24.024435
Publisher: Wiley
Date: 08-05-2020
Publisher: Elsevier BV
Date: 09-2019
DOI: 10.1016/J.MICRON.2019.102701
Abstract: For many soft-matter specimens, transmission electron microscopists face the double-bind of low contrast images, due to weakly-scattering specimens, alongside severe limits on the electron dose that can be used before the specimen is damaged by the electron beam. The combination of these effects causes the resultant micrographs to have very low signal-to-noise. It is well known that varying the defocus aberration can enhance image contrast in electron microscopy. For single-material objects where the variation of absorption and phase contrast are functions of one another, since both are governed by the variation in thickness profile, we show that the thickness profile can be reconstructed at very low dose. The algorithm, first established in X-ray imaging, requires some a priori information but only a single defocussed image of the region of interest, making it more dose efficient than either a conventional transport-of-intensity phase reconstruction (which would require two images and tends to lify noise), or an absorption-contrast analysis of a single in-focus image recorded at the same electron dose (which does not benefit from the significant signal-to-noise enhancement of the present algorithm). These findings are presented through both simulations and experimental data.
Publisher: Springer Science and Business Media LLC
Date: 04-01-2021
Publisher: Oxford University Press (OUP)
Date: 20-12-2022
Abstract: Segmented and pixelated detectors on scanning transmission electron microscopes enable the complex specimen transmission function to be reconstructed. Imaging the transmission function is key to interpreting the electric and magnetic properties of the specimen, and as such four-dimensional scanning transmission electron microscopy (4D-STEM) imaging techniques are crucial for our understanding of functional materials. Many of the algorithms used in the reconstruction of the transmission function rely on the multiplicative approximation and the (weak) phase object approximation, which are not valid for many materials, particularly at high resolution. Herein, we study the breakdown of simple phase imaging in thicker s les. We demonstrate the behavior of integrated center of mass imaging, single-side band ptychography, and Wigner distribution deconvolution over a thickness series of simulated GaN 4D-STEM datasets. We further give guidance as to the optimal focal conditions for obtaining a more interpretable dataset using these algorithms.
Publisher: Wiley
Date: 10-04-2017
DOI: 10.1002/JCC.24799
Abstract: Reverse Monte Carlo (RMC) simulations were performed to investigate the effectiveness of any combination of five experimentally motivated constraints on the reproduction of a test case, a ternary ab initio model. It was found that low energy structures fitting a variety of constraints commonly used in the RMC methodology could still provide an incorrect description of the chemical structural unit populations in multi-elemental systems. It is shown that the use of an elemental bond type constraint is an effective way to avoid this. © 2017 Wiley Periodicals, Inc.
Publisher: American Physical Society (APS)
Date: 18-10-2013
Publisher: IOP Publishing
Date: 18-09-2018
Publisher: IOP Publishing
Date: 15-04-2005
Publisher: American Physical Society (APS)
Date: 09-06-2016
Publisher: Wiley
Date: 14-07-2011
DOI: 10.1002/JEMT.21038
Publisher: Elsevier BV
Date: 11-2015
Publisher: Elsevier BV
Date: 03-2012
Publisher: IOP Publishing
Date: 25-08-2020
Publisher: AIP Publishing
Date: 28-11-2011
DOI: 10.1063/1.3663572
Publisher: Oxford University Press (OUP)
Date: 30-07-2020
Publisher: IOP Publishing
Date: 19-05-2016
Publisher: Proceedings of the National Academy of Sciences
Date: 13-09-2017
Abstract: Local structure and symmetry in amorphous materials and glasses may play a critical role in their formation and properties yet are notoriously hard to measure. Here, we demonstrate a direct method for measuring the proportions of polyhedra with different local point symmetries in amorphous colloidal packings, using small-volume transmission diffraction patterns. We show that local order is tuned by the interaction potential between microspheres and the method of preparation. This methodology can be readily applied to a broad range of disordered materials and packings to probe for universal features in their structure. It also has the potential to quantify local order in liquid, undercooled, and liquid–crystal systems approaching a phase transition.
Publisher: Oxford University Press (OUP)
Date: 28-11-2014
DOI: 10.1017/S1431927613013779
Abstract: High-resolution radial distribution functions of as-implanted and thermally relaxed amorphous silicon created by ion implantation were measured using tilted-illumination selected area electron diffraction at room temperature. The diffracted intensities were measured out to a maximum scattering vector 2 sin(θ)/λ of 3.3–3.7 Å −1 . The volume-averaged pair-correlation statistics of as-implanted and relaxed ion-implanted amorphous silicon are virtually indistinguishable with coordination numbers of 3.7 ± 0.3 and 3.9 ± 0.3 (for neighbors closer than 3 Å) and average bond angles of 109 ± 0.5° and 110 ± 0.6°, respectively. The atomic rearrangements in ion-implanted amorphous silicon due to a low temperature anneal are subtle.
Publisher: Informa UK Limited
Date: 26-08-2016
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2020
Publisher: American Association for the Advancement of Science (AAAS)
Date: 18-03-2022
Abstract: The mechanical properties of crystals are controlled by the translational symmetry of their structures. But for glasses with a disordered structure, the link between the symmetry of local particle arrangements and stability is not well established. In this contribution, we provide experimental verification that the centrosymmetry of nearest-neighbor polyhedra in a glass strongly correlates with the local mechanical stability. We examine the distribution of local stability and local centrosymmetry in a glass during aging and deformation using microbeam x-ray scattering. These measurements reveal the underlying relationship between particle-level structure and larger-scale behavior and demonstrate that spatially connected, coordinated local transformations to lower symmetry structures are fundamental to these phenomena. While glassy structures lack obvious global symmetry breaking, local structural symmetry is a critical factor in predicting stability.
Publisher: Elsevier BV
Date: 08-2020
Publisher: Oxford University Press (OUP)
Date: 30-07-2020
Publisher: Springer Science and Business Media LLC
Date: 26-09-2018
Publisher: Elsevier BV
Date: 08-2007
DOI: 10.1016/J.ULTRAMIC.2006.12.005
Abstract: Phase retrieval, in principle, can be performed in a transmission electron microscope (TEM) using arbitrary aberrations of electron waves provided that the aberrations are well-characterised and known. For ex le, the transport of intensity equation (TIE) can be used to infer the phase from a through-focus series of images. In this work an "astigmatic intensity equation" (AIE) is considered, which relates phase gradients to intensity variations caused by TEM objective lens focus and astigmatism variations. Within the paraxial approximation, it is shown that an exact solution of the AIE for the phase can be obtained using efficient Fourier transform methods. Experimental requirements for using the AIE are the measurement of a through-focus derivative and another intensity derivative, which is taken with respect to objective lens astigmatism variation. Two quasi-experimental investigations are conducted to test the validity of the solution.
Publisher: Elsevier BV
Date: 2007
Publisher: The Optical Society
Date: 28-01-2016
DOI: 10.1364/OE.24.002259
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8CP06649C
Abstract: The crystalline structural stability and threshold of amorphisation of carbon, silicon and silicon carbide is investigated via vacancy removal and Monte Carlo annealing simulations.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 06-2014
Publisher: The Optical Society
Date: 19-09-2016
DOI: 10.1364/OE.24.022366
Publisher: Elsevier BV
Date: 06-2014
Publisher: IOP Publishing
Date: 27-05-2016
Publisher: American Physical Society (APS)
Date: 25-10-2017
Publisher: American Physical Society (APS)
Date: 14-01-2013
Publisher: Elsevier BV
Date: 12-2020
Publisher: Elsevier BV
Date: 05-2011
DOI: 10.1016/J.ULTRAMIC.2011.01.024
Abstract: One major concern since the development of the field ion microscope is the mechanical strength of the specimens. The macroscopic shape of the imaging tip greatly influences field-induced stresses and there is merit in further study of this phenomenon from a classical perspective. Understanding the geometrical, as opposed to localized electronic, factors that affect the stress might improve the quality and success rate of atom probe experiments. This study uses macroscopic electrostatic principles and finite element modelling to investigate field-induced stresses in relation to the shape of the tip. Three two-dimensional idealized models are considered, namely hyperbolic, parabolic and sphere-on-orthogonal-cone the shapes of which are compared to experimental tips prepared by electro-polishing. Three dimensional morphologies of both a nano-porous and single-crystal aluminium tip are measured using electron tomography to quantitatively test the assumption of cylindrical symmetry for electro-polished tips. The porous tip was prepared and studied to demonstrate a fragile specimen for which such finite element studies could determine potential mechanical failure, prior to any exhaustive atom probe investigation.
Start Date: 2007
End Date: 12-2011
Amount: $420,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 02-2008
End Date: 02-2013
Amount: $300,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 05-2016
End Date: 12-2021
Amount: $399,800.00
Funder: Australian Research Council
View Funded ActivityStart Date: 06-2019
End Date: 10-2023
Amount: $350,000.00
Funder: Australian Research Council
View Funded Activity