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2. Ultrafast Spin-To-Charge Conversion at the Surface of Topological Insulator Thin Films

Author

Wang, Xinbo, Cheng, Liang, Zhu, Dapeng, Wu, Yang, Chen, Mengji, Wang, Yi, Zhao, Daming, Boothroyd, Chris B., Lam, Yeng Ming, Zhu, Jian-Xin, Battiato, Marco, Song, Justin C. W., Yang, Hyunsoo, and Chia, Elbert E. M.

Subjects
Condensed Matter - Materials Science
Abstract

Strong spin-orbit coupling, resulting in the formation of spin-momentum-locked surface states, endows topological insulators with superior spin-to-charge conversion characteristics, though the dynamics that govern it have remained elusive. Here, we present an all-optical method that enables unprecedented tracking of the ultrafast dynamics of spin-to-charge conversion in a prototypical topological insulator Bi$_2$Se$_3$/ferromagnetic Co heterostructure, down to the sub-picosecond timescale. Compared to pure Bi$_2$Se$_3$ or Co, we observe a giant terahertz emission in the heterostructure than originates from spin-to-charge conversion, in which the topological surface states play a crucial role. We identify a 0.12-picosecond timescale that sets a technological speed limit of spin-to-charge conversion processes in topological insulators. In addition, we show that the spin-to-charge conversion efficiency is temperature independent in Bi$_2$Se$_3$ as expected from the nature of the surface states, paving the way for designing next-generation high-speed opto-spintronic devices based on topological insulators at room temperature., Comment: 19 pages, 4 figures

Published
2018
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4. Geometric reconstruction methods for electron tomography

Author

Alpers, Andreas, Gardner, Richard J., König, Stefan, Pennington, Robert S., Boothroyd, Chris B., Houben, Lothar, Dunin-Borkowski, Rafal E., and Batenburg, Kees Joost

Subjects
Mathematical Physics, Condensed Matter - Materials Science
Abstract

Electron tomography is becoming an increasingly important tool in materials science for studying the three-dimensional morphologies and chemical compositions of nanostructures. The image quality obtained by many current algorithms is seriously affected by the problems of missing wedge artefacts and nonlinear projection intensities due to diffraction effects. The former refers to the fact that data cannot be acquired over the full $180^\circ$ tilt range; the latter implies that for some orientations, crystalline structures can show strong contrast changes. To overcome these problems we introduce and discuss several algorithms from the mathematical fields of geometric and discrete tomography. The algorithms incorporate geometric prior knowledge (mainly convexity and homogeneity), which also in principle considerably reduces the number of tilt angles required. Results are discussed for the reconstruction of an InAs nanowire.

Published
2012
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9. Counting vacancies and nitrogen-vacancy centers in detonation nanodiamond† †Electronic supplementary information (ESI) available: (1) DND synthesis; (2) HRTEM and EELS characterization methods; (3) EELS simulation method; (4) supporting figures of EELS simulations; (5) soft-X-ray K-edge spectra of the DND; and (6) ab initio N-V center modeling method. See DOI: 10.1039/C6NR01888B Click here for additional data file

Author

Chang, Shery L. Y., Barnard, Amanda S., Dwyer, Christian, Boothroyd, Chris B., Hocking, Rosalie K., Ōsawa, Eiji, and Nicholls, Rebecca J.

Subjects
Chemistry
Abstract

Vacancies and Nitrogen-vacancy centers in detonation nanodiamond particles can be detected and quantified., Detonation nanodiamond particles (DND) contain highly-stable nitrogen-vacancy (N-V) centers, making it important for quantum-optical and biotechnology applications. However, due to the small particle size, the N-V concentrations are believed to be intrinsically very low, spawning efforts to understand the formation of N-V centers and vacancies, and increase their concentration. Here we show that vacancies in DND can be detected and quantified using simulation-aided electron energy loss spectroscopy. Despite the small particle size, we find that vacancies exist at concentrations of about 1 at%. Based on this experimental finding, we use ab initio calculations to predict that about one fifth of vacancies in DND form N-V centers. The ability to directly detect and quantify vacancies in DND, and predict the corresponding N-V formation probability, has a significant impact to those emerging technologies where higher concentrations and better dispersion of N-V centres are critically required.

Published
2016

10. Correction for Keogh et al., “Extracellular Electron Transfer Powers Enterococcus faecalis Biofilm Metabolism”

Author

Keogh, Damien, primary, Lam, Ling Ning, additional, Doyle, Lucinda E., additional, Matysik, Artur, additional, Pavagadhi, Shruti, additional, Umashankar, Shivshankar, additional, Low, Pui Man, additional, Dale, Jennifer L., additional, Song, Yiyang, additional, Ng, Sean Pin, additional, Boothroyd, Chris B., additional, Dunny, Gary M., additional, Swarup, Sanjay, additional, Williams, Rohan B. H., additional, Marsili, Enrico, additional, and Kline, Kimberly A., additional

Published
2019
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11. Ultrafast Spin‐to‐Charge Conversion at the Surface of Topological Insulator Thin Films

Author

Wang, Xinbo, primary, Cheng, Liang, additional, Zhu, Dapeng, additional, Wu, Yang, additional, Chen, Mengji, additional, Wang, Yi, additional, Zhao, Daming, additional, Boothroyd, Chris B., additional, Lam, Yeng Ming, additional, Zhu, Jian‐Xin, additional, Battiato, Marco, additional, Song, Justin C. W., additional, Yang, Hyunsoo, additional, and Chia, Elbert E. M., additional

Published
2018
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12. Extracellular Electron Transfer Powers Enterococcus faecalis Biofilm Metabolism

Author

Keogh, Damien, primary, Lam, Ling Ning, additional, Doyle, Lucinda E., additional, Matysik, Artur, additional, Pavagadhi, Shruti, additional, Umashankar, Shivshankar, additional, Low, Pui Man, additional, Dale, Jennifer L., additional, Song, Yiyang, additional, Ng, Sean Pin, additional, Boothroyd, Chris B., additional, Dunny, Gary M., additional, Swarup, Sanjay, additional, Williams, Rohan B. H., additional, Marsili, Enrico, additional, and Kline, Kimberly A., additional

Published
2018
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13. Experimental realization of the Ehrenberg-Siday thought experiment

Author

Pozzi, Giulio, Boothroyd, Chris B., Tavabi, Amir H., Yucelen, Emrah, Rafal Dunin-Borkowski, Frabboni, Stefano, and Gazzadi, Gian Carlo

Subjects
electron interference, quantum mechanics, quantum mechanics, electron interference, Physics::Optics, ddc:530
Abstract

In 1949, at the end of a paper dedicated to the concept of the refractive index in electron optics, Ehrenberg and Siday noted that wave-optical effects will arise from an isolated magnetic field even when the rays themselves travel in magnetic-field-free space. They proposed a two-slit experiment, in which a magnetic flux is enclosed between interfering electron beams. Now, through access to modern nanotechnology tools, we used a focused ion beam to open two nanosized slits in a gold-coated silicon nitride membrane and focused electron beam induced deposition to fabricate a thin magnetic bar between the two slits. We then performed Fraunhofer experiments in a transmission electron microscope equipped with a field emission gun and a Lorentz lens. By tilting the specimen in the objective lens field of the electron microscope, the magnetization of the bar could be reversed and the corresponding change in the phase of the electron wave observed directly in the form of a shift in the interference fringe pattern.

Published
2016

14. One-pot synthesis of new-phase AgInSe2 nanorods

Author

Ng, Meng T., Boothroyd, Chris B., and Vittal, Jagadese J.

Subjects
Silver compounds -- Chemical properties, Indium -- Chemical properties, Selenium compounds -- Chemical properties, Nanorods -- Chemical properties, Chemistry
Abstract

A novel one-pot synthesis of close to monodispersed, one-dimensional (1D) AgInSe2 nanorods is reported, where the single-source precursor is thermally decomposed in mixed amine and thiol solution. The results have shown that perfect matching of two or more surfactants might be the key to obtaining high-quality nanocrystals for many novel materials.

Published
2006

16. Extracellular Electron Transfer Powers Enterococcus faecalis Biofilm Metabolism

Author

Keogh, Damien, primary, Lam, Ling Ning, additional, Doyle, Lucinda E., additional, Matysik, Artur, additional, Pavagadhi, Shruti, additional, Umashankar, Shivshankar, additional, Dale, Jennifer L., additional, Boothroyd, Chris B., additional, Dunny, Gary M., additional, Swarup, Sanjay, additional, Williams, Rohan B. H., additional, Marsili, Enrico, additional, and Kline, Kimberly A., additional

Published
2017
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18. Synthesis and characterization of carbon nanofibers produced by the floating catalyst method

Author

Singh, Charanjeet, Abou-Kandil, Ahmed I., Windle, Alan H., Quested, Tom, Boothroyd, Chris B., Thomas, Paul, and Kinloch, Ian A.

Subjects
Thiophene -- Chemical properties, Carbon -- Chemical properties, Chemicals, plastics and rubber industries
Abstract

A novel method is presented to synthesize herringbone-stacked carbon nanofibers in high selectivity using cobaltocene as the catalytic precursor. Selectivity close to 100% was achieved using cobaltocene, thiophene, and hydrogen reacted at 1100 degrees Celsius.

Published
2002

22. Anomalous Particle Size Dependence of Magnetic Relaxation Phenomena in Goethite Nanoparticles

Author

Frandsen, Cathrine, Madsen, Daniel Esmarch, Boothroyd, Chris B., Mørup, Steen, Frandsen, Cathrine, Madsen, Daniel Esmarch, Boothroyd, Chris B., and Mørup, Steen

Abstract

By use of Mossbauer spectroscopy we have studied the magnetic properties of samples of goethite nanoparticles with different particle size. The spectra are influenced by fluctuations of the magnetization directions, but the size dependence is not in accordance with the Neel-Brown expression for superparamagnetic relaxation of the magnetization vectors of the particles as a whole. The data suggest that the magnetic fluctuations can be explained by fluctuations of the magnetization directions of small interacting grains within the particles.

Published
2015

24. Influence of Particle Velocity When Propelled Using N2 or N2-He Mixed Gas on the Properties of Cold-Sprayed Ti6Al4V Coatings.

Author

Wei-Yee Tan, Adrian, Jun Yan Lek, Wen Sun, Bhowmik, Ayan, Marinescu, Iulian, Xu Song, Wei Zhai, Feng Li, Zhili Dong, Boothroyd, Chris B., and Liu, Erjia

Subjects
SURFACE coatings, LOW temperatures, POROSITY
Abstract

Cold-spraying is a relatively new low-temperature coating technology which produces coatings by the deposition of metallic micro-particles at supersonic speed onto target substrate surfaces. This technology has the potential to enhance or restore damaged parts made of light metal alloys, such as Ti6Al4V (Ti64). Particle deposition velocity is one of the most crucial parameters for achieving high-quality coatings because it is the main driving force for particle bonding and coating formation. In this work, studies were conducted on the evolution of the properties of cold-sprayed Ti64 coatings deposited on Ti64 substrates with particle velocities ranging from 730 to 855 m/s using pure N2 and N2-He mixture as the propellant gases. It was observed that the increase in particle velocity significantly reduced the porosity level from about 11 to 1.6% due to greater densification. The coatings' hardness was also improved with increased particle velocity due to the intensified grain refinement within the particles. Interestingly, despite the significant differences in the coating porosities, all the coatings deposited within the velocity range (below and above critical velocity) achieved a high adhesion strength exceeding 60 MPa. The fractography also showed changes in the degree of dimple fractures on the particles across the deposition velocities. Finite element modelling was carried out to understand the deformation behaviour of the impacting particles and the evolutions of strain and temperature in the formed coatings during the spraying process. This work also showed that the N2-He gas mixture was a cost-effective propellant gas (up to 3-times cheaper than pure He) to deliver the high-quality Ti64 coatings. [ABSTRACT FROM AUTHOR]

Published
2018
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25. Hybrid Electron Holography

Author

Ozsoy-Keskinbora, Cigdem, primary, Boothroyd, Chris B., additional, Dunin-Borkowski, Rafal E., additional, van Aken, Peter A., additional, and Koch, Christoph T., additional

Published
2015
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32. Geometric reconstruction methods for electron tomography

Author

Alpers, Andreas, primary, Gardner, Richard J., additional, König, Stefan, additional, Pennington, Robert S., additional, Boothroyd, Chris B., additional, Houben, Lothar, additional, Dunin-Borkowski, Rafal E., additional, and Joost Batenburg, Kees, additional

Published
2013
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40. Cover Picture

Author

Whitby, Raymond L. D., primary, Hsu, Wen Kuang, additional, Boothroyd, Chris B., additional, Fearon, Peter K., additional, Kroto, Harold W., additional, and Walton, David R. M., additional

Published
2001
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41. Prospects for quantitative and time-resolved double and continuous exposure off-axis electron holography

Author

Migunov, Vadim, Dwyer, Christian, Boothroyd, Chris B., Pozzi, Giulio, and Dunin-Borkowski, Rafal E.

Subjects
Off-axis electron holography, Continuous exposure electron holography, ddc:570, Physics::Optics, Double exposure electron holography, Instrumentation, Atomic and Molecular Physics, and Optics, Transmission electron microscopy, Electronic, Optical and Magnetic Materials
Abstract

The technique of double exposure electron holography, which is based on the superposition of two off-axis electron holograms, was originally introduced before the availability of digital image processing to allow differences between electron-optical phases encoded in two electron holograms to be visualised directly without the need for holographic reconstruction. Here, we review the original method and show how it can now be extended to permit quantitative studies of phase shifts that oscillate in time. We begin with a description of the theory of off-axis electron hologram formation for a time-dependent electron wave that results from the excitation of a specimen using an external stimulus with a square, sinusoidal, triangular or other temporal dependence. We refer to the more general method as continuous exposure electron holography, present preliminary experimental measurements and discuss how the technique can be used to image electrostatic potentials and magnetic fields during high frequency switching experiments.

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44. Extracellular Electron Transfer Powers Enterococcus faecalisBiofilm Metabolism

Author

Keogh, Damien, Lam, Ling Ning, Doyle, Lucinda E., Matysik, Artur, Pavagadhi, Shruti, Umashankar, Shivshankar, Low, Pui Man, Dale, Jennifer L., Song, Yiyang, Ng, Sean Pin, Boothroyd, Chris B., Dunny, Gary M., Swarup, Sanjay, Williams, Rohan B. H., Marsili, Enrico, and Kline, Kimberly A.

Abstract

ABSTRACTEnterococci are important human commensals and significant opportunistic pathogens. Biofilm-related enterococcal infections, such as endocarditis, urinary tract infections, wound and surgical site infections, and medical device-associated infections, often become chronic upon the formation of biofilm. The biofilm matrix establishes properties that distinguish this state from free-living bacterial cells and increase tolerance to antimicrobial interventions. The metabolic versatility of the enterococci is reflected in the diversity and complexity of environments and communities in which they thrive. Understanding metabolic factors governing colonization and persistence in different host niches can reveal factors influencing the transition to biofilm pathogenicity. Here, we report a form of iron-dependent metabolism for Enterococcus faecaliswhere, in the absence of heme, extracellular electron transfer (EET) and increased ATP production augment biofilm growth. We observe alterations in biofilm matrix depth and composition during iron-augmented biofilm growth. We show that the ldhgene encoding l-lactate dehydrogenase is required for iron-augmented energy production and biofilm formation and promotes EET.IMPORTANCEBacterial metabolic versatility can often influence the outcome of host-pathogen interactions, yet causes of metabolic shifts are difficult to resolve. The bacterial biofilm matrix provides the structural and functional support that distinguishes this state from free-living bacterial cells. Here, we show that the biofilm matrix can immobilize iron, providing access to this growth-promoting resource which is otherwise inaccessible in the planktonic state. Our data show that in the absence of heme, Enterococcus faecalisl-lactate dehydrogenase promotes EET and uses matrix-associated iron to carry out EET. Therefore, the presence of iron within the biofilm matrix leads to enhanced biofilm growth.

Published
2018
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45. One-Pot Synthesis of New-Phase AgInSe2 Nanorods.

Author

Ng, Meng T., Boothroyd, Chris B., and Vittal, Jagadese J.

Subjects
*SEMICONDUCTORS, *NANOPARTICLES, *NANOCRYSTALS, *AMINES, *THIOLS, *CHEMISTRY
Abstract

The article reports on a novel one-pot synthesis of close to monodispersed, one-dimensional (1D) semiconductor AgInSe2 nanorods. The single-source precursor is thermally decomposed in mixed amine and thiol solution. The novel properties of the material may be studied using the good solubility of the synthesized nanorods.

Published
2006
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