I am currently an Associate Professor in the School of Mathematical and Physical sciences, University of Technology Sydney. I have previously held positions as a consultant and senior scientist at FEI company (now part of Thermo Fisher), as a senior editor of Nature Materials, and held a postdoctoral research position at Cambridge University. My current research is in experimental studies and modeling of electron beam induced deposition and etching processes, fabrication of optoelectronic grade materials, and characterization of nanostructured materials. My expertise in nanofabrication by electron beam and chemical vapour deposition has been recognized by extensive peer citations (>2800 citations with a H index of 22). I am co-investigator on a number of ARC grants, have several international patents and have published over 60 refereed journal and conference papers.
I am currently recruiting PhD students for a recently funded Linkage Project. See the details on the UTS website: https://www.uts.edu.au/future-students/science/science-courses/research-courses/phd-scholarships/development-2d-material
Can supervise: YES
Growth and functionalization of nanostructures (nanowires, nanotubes, quantum dots, etc).
Computational modelling of nanostructure growth dynamics.
Electron beam induced nanostructure fabrication.
Visit the Materials Physics and Nanophotonics website for more details.
Vapour and electron beam induced deposition methods and process modelling (Honours course)
Nanomaterials (2nd/3rd year subject in Physics and Nanotechnology degrees)
Introduction to Materials (1st year subject in Nanotechnology degree)
Advanced mathematics and physics (2nd/3rd year subject in Electrical Engineering degree)
Kianinia, M., Bradac, C., Sontheimer, B., Wang, F., Tran, T.T., Nguyen, M., Kim, S., Xu, Z.-.Q., Jin, D., Schell, A.W., Lobo, C.J., Aharonovich, I. & Toth, M. 2018, 'All-optical control and super-resolution imaging of quantum emitters in layered materials.', Nature communications, vol. 9, no. 1, p. 874.View/Download from: UTS OPUS or Publisher's site
Layered van der Waals materials are emerging as compelling two-dimensional platforms for nanophotonics, polaritonics, valleytronics and spintronics, and have the potential to transform applications in sensing, imaging and quantum information processing. Among these, hexagonal boron nitride (hBN) is known to host ultra-bright, room-temperature quantum emitters, whose nature is yet to be fully understood. Here we present a set of measurements that give unique insight into the photophysical properties and level structure of hBN quantum emitters. Specifically, we report the existence of a class of hBN quantum emitters with a fast-decaying intermediate and a long-lived metastable state accessible from the first excited electronic state. Furthermore, by means of a two-laser repumping scheme, we show an enhanced photoluminescence and emission intensity, which can be utilized to realize a new modality of far-field super-resolution imaging. Our findings expand current understanding of quantum emitters in hBN and show new potential ways of harnessing their nonlinear optical properties in sub-diffraction nanoscopy.
Bishop, J., Fronzi, M., Elbadawi, C., Nikam, V., Pritchard, J., Fröch, J.E., Duong, N.M.H., Ford, M.J., Aharonovich, I., Lobo, C.J. & Toth, M. 2018, 'Deterministic Nanopatterning of Diamond Using Electron Beams.', ACS nano, vol. 12, no. 3, pp. 2873-2882.View/Download from: UTS OPUS or Publisher's site
Diamond is an ideal material for a broad range of current and emerging applications in tribology, quantum photonics, high-power electronics, and sensing. However, top-down processing is very challenging due to its extreme chemical and physical properties. Gas-mediated electron beam-induced etching (EBIE) has recently emerged as a minimally invasive, facile means to dry etch and pattern diamond at the nanoscale using oxidizing precursor gases such as O2 and H2O. Here we explain the roles of oxygen and hydrogen in the etch process and show that oxygen gives rise to rapid, isotropic etching, while the addition of hydrogen gives rise to anisotropic etching and the formation of topographic surface patterns. We identify the etch reaction pathways and show that the anisotropy is caused by preferential passivation of specific crystal planes. The anisotropy can be controlled by the partial pressure of hydrogen and by using a remote RF plasma source to radicalize the precursor gas. It can be used to manipulate the geometries of topographic surface patterns as well as nano- and microstructures fabricated by EBIE. Our findings constitute a comprehensive explanation of the anisotropic etch process and advance present understanding of electron-surface interactions.
Walia, S., Balendhran, S., Ahmed, T., Singh, M., El-Badawi, C., Brennan, M.D., Weerathunge, P., Karim, M.N., Rahman, F., Rassell, A., Duckworth, J., Ramanathan, R., Collis, G.E., Lobo, C.J., Toth, M., Kotsakidis, J.C., Weber, B., Fuhrer, M., Dominguez-Vera, J.M., Spencer, M.J.S., Aharonovich, I., Sriram, S., Bhaskaran, M. & Bansal, V. 2017, 'Ambient Protection of Few-Layer Black Phosphorus via Sequestration of Reactive Oxygen Species.', Advanced Materials, vol. 29, no. 27, pp. 1-8.View/Download from: UTS OPUS or Publisher's site
Few-layer black phosphorous (BP) has emerged as a promising candidate for next-generation nanophotonic and nanoelectronic devices. However, rapid ambient degradation of mechanically exfoliated BP poses challenges in its practical deployment in scalable devices. To date, the strategies employed to protect BP have relied upon preventing its exposure to atmospheric conditions. Here, an approach that allows this sensitive material to remain stable without requiring its isolation from the ambient environment is reported. The method draws inspiration from the unique ability of biological systems to avoid photo-oxidative damage caused by reactive oxygen species. Since BP undergoes similar photo-oxidative degradation, imidazolium-based ionic liquids are employed as quenchers of these damaging species on the BP surface. This chemical sequestration strategy allows BP to remain stable for over 13 weeks, while retaining its key electronic characteristics. This study opens opportunities to practically implement BP and other environmentally sensitive 2D materials for electronic applications.
Choi, S., Tran, T.T., Elbadawi, C., Lobo, C., Wang, X., Juodkazis, S., Seniutinas, G., Toth, M. & Aharonovich, I. 2016, 'Engineering and Localization of Quantum Emitters in Large Hexagonal Boron Nitride Layers', ACS APPLIED MATERIALS & INTERFACES, vol. 8, no. 43, pp. 29642-29648.View/Download from: Publisher's site
Tran, T.T., Elbadawi, C., Totonjian, D., Lobo, C.J., Grosso, G., Moon, H., Englund, D.R., Ford, M.J., Aharonovich, I. & Toth, M. 2016, 'Robust Multicolor Single Photon Emission from Point Defects in Hexagonal Boron Nitride.', ACS nano, vol. 10, no. 8, pp. 7331-7338.View/Download from: UTS OPUS or Publisher's site
Hexagonal boron nitride (hBN) is an emerging two-dimensional material for quantum photonics owing to its large bandgap and hyperbolic properties. Here we report two approaches for engineering quantum emitters in hBN multilayers using either electron beam irradiation or annealing and characterize their photophysical properties. The defects exhibit a broad range of multicolor room-temperature single photon emissions across the visible and the near-infrared spectral ranges, narrow line widths of sub-10 nm at room temperature, and a short excited-state lifetime, and high brightness. We show that the emitters can be categorized into two general groups, but most likely possess similar crystallographic structure. Remarkably, the emitters are extremely robust and withstand aggressive annealing treatments in oxidizing and reducing environments. Our results constitute a step toward deterministic engineering of single emitters in 2D materials and hold great promise for the use of defects in boron nitride as sources for quantum information processing and nanophotonics.
Elbadawi, C., Tran, T.T., Kolíbal, M., Šikola, T., Scott, J., Cai, Q., Li, L.H., Taniguchi, T., Watanabe, K., Toth, M., Aharonovich, I. & Lobo, C. 2016, 'Electron beam directed etching of hexagonal boron nitride.', Nanoscale, vol. 8, no. 36, pp. 16182-16186.View/Download from: UTS OPUS or Publisher's site
Hexagonal boron nitride (hBN) is a wide bandgap van der Waals material with unique optical properties that make it attractive for two dimensional (2D) photonic and optoelectronic devices. However, broad deployment and exploitation of hBN is limited by alack of suitable material and device processing and nano prototyping techniques. Here we present a high resolution, single step electron beam technique for chemical dry etching of hBN. Etching is achieved using H2O as a precursor gas, at both room temperature and elevated hBN temperatures. The technique enables damage-free, nano scale, iterative patterning of supported and suspended 2D hBN, thus opening the door to facile fabrication of hBN-based 2D heterostructures and devices.
Scott, J.A., Totonjian, D., Martin, A.A., Tran, T.T., Fang, J., Toth, M., McDonagh, A.M., Aharonovich, I. & Lobo, C.J. 2016, 'Versatile method for template-free synthesis of single crystalline metal and metal alloy nanowires.', Nanoscale, vol. 8, no. 5, pp. 2804-2810.View/Download from: UTS OPUS or Publisher's site
Metal and metal alloy nanowires have applications ranging from spintronics to drug delivery, but high quality, high density single crystalline materials have been surprisingly difficult to fabricate. Here we report a versatile, template-free, self-assembly method for fabrication of single crystalline metal and metal alloy nanowires (Co, Ni, NiCo, CoFe, and NiFe) by reduction of metal nitride precursors formed in situ by reaction of metal salts with a nitrogen source. Thiol reduction of the metal nitrides to the metallic phase at 550-600 °C results in nanowire growth. In this process, sulfur acts as a uniaxial structure-directing agent, passivating the surface of the growing nanowires and preventing radial growth. The versatility of the method is demonstrated by achieving nanowire growth from gas-phase, solution-phase or a combination of gas- and solution-phase precursors. The fabrication method is suited to large-area CVD on a wide range of solid substrates.
Bray, K., Sandstrom, R., Elbadawi, C., Fischer, M., Schreck, M., Shimoni, O., Lobo, C., Toth, M. & Aharonovich, I. 2016, 'Localization of Narrowband Single Photon Emitters in Nanodiamonds.', ACS applied materials & interfaces, vol. 8, no. 11, pp. 7590-7594.View/Download from: UTS OPUS or Publisher's site
Diamond nanocrystals that host room temperature narrowband single photon emitters are highly sought after for applications in nanophotonics and bioimaging. However, current understanding of the origin of these emitters is extremely limited. In this work, we demonstrate that the narrowband emitters are point defects localized at extended morphological defects in individual nanodiamonds. In particular, we show that nanocrystals with defects such as twin boundaries and secondary nucleation sites exhibit narrowband emission that is absent from pristine individual nanocrystals grown under the same conditions. Critically, we prove that the narrowband emission lines vanish when extended defects are removed deterministically using highly localized electron beam induced etching. Our results enhance the current understanding of single photon emitters in diamond and are directly relevant to fabrication of novel quantum optics devices and sensors.
Kianinia, M., Shimoni, O., Bendavid, A., Schell, A.W., Randolph, S.J., Toth, M., Aharonovich, I. & Lobo, C.J. 2016, 'Robust, directed assembly of fluorescent nanodiamonds.', Nanoscale, vol. 8, no. 42, pp. 18032-18037.View/Download from: UTS OPUS or Publisher's site
Arrays of fluorescent nanoparticles are highly sought after for applications in sensing, nanophotonics and quantum communications. Here we present a simple and robust method of assembling fluorescent nanodiamonds into macroscopic arrays. Remarkably, the yield of this directed assembly process is greater than 90% and the assembled patterns withstand ultra-sonication for more than three hours. The assembly process is based on covalent bonding of carboxyl to amine functional carbon seeds and is applicable to any material, and to non-planar surfaces. Our results pave the way to directed assembly of sensors and nanophotonics devices.
Cullen, J., Bahm, A., Lobo, C.J., Ford, M.J. & Toth, M. 2015, 'Localized probing of gas molecule adsorption energies and desorption attempt frequencies', Journal of Physical Chemistry C, vol. 119, no. 28, pp. 15948-15953.View/Download from: UTS OPUS or Publisher's site
© 2015 American Chemical Society. Gas-mediated electron beam induced etching (EBIE) and deposition (EBID) can be used to measure activation energies that are interpreted as the adsorption energies of surface-adsorbed precursor molecules. However, the measured quantities often disagree with adsorption energies measured by conventional analysis techniques such as thermally programmed desorption and have anomalous dependencies on parameters such as the electron beam current used to perform EBID. Here, we use the theory of EBIE and EBID rate kinetics to explain this behavior and identify conditions under which the activation energies and the associated pre-exponential factors correspond to gas molecule adsorption energies and desorption attempt frequencies, respectively. Under these conditions, EBIE and EBID can be used as robust, nanoscale techniques for the analysis of adsorbates.
Cullen, J., Lobo, C.J., Ford, M.J. & Toth, M. 2015, 'Electron-Beam-Induced Deposition as a Technique for Analysis of Precursor Molecule Diffusion Barriers and Prefactors.', ACS applied materials & interfaces, vol. 7, no. 38, pp. 21408-21415.View/Download from: UTS OPUS or Publisher's site
Electron-beam-induced deposition (EBID) is a direct-write chemical vapor deposition technique in which an electron beam is used for precursor dissociation. Here we show that Arrhenius analysis of the deposition rates of nanostructures grown by EBID can be used to deduce the diffusion energies and corresponding preexponential factors of EBID precursor molecules. We explain the limitations of this approach, define growth conditions needed to minimize errors, and explain why the errors increase systematically as EBID parameters diverge from ideal growth conditions. Under suitable deposition conditions, EBID can be used as a localized technique for analysis of adsorption barriers and prefactors.
Toth, M., Lobo, C., Friedli, V., Szkudlarek, A. & Utke, I. 2015, 'Continuum models of focused electron beam induced processing', Beilstein Journal of Nanotechnology, vol. 6, no. 1, pp. 1518-1540.View/Download from: UTS OPUS or Publisher's site
© 2015 Toth et al. Focused electron beam induced processing (FEBIP) is a suite of direct-write, high resolution techniques that enable fabrication and editing of nanostructured materials inside scanning electron microscopes and other focused electron beam (FEB) systems. Here we detail continuum techniques that are used to model FEBIP, and release software that can be used to simulate a wide range of processes reported in the FEBIP literature. These include: (i) etching and deposition performed using prec ursors that interact with a surface through physisorption and activated chemisorption, (ii) gas mixtures used to perform simultaneous focused electron beam induced etching and deposition (FEBIE and FEBID), and (iii) etch processes that proceed through multiple reaction pathways and generate a number of reaction products at the substrate surface. We also review and release software for Monte Carlo modeling of the precursor gas flux which is needed as an input parameter for continuum FEBIP models.
Elbadawi, C., Toth, M. & Lobo, C. 2013, 'Pure Platinum Nanostructures Grown by Electron Beam Induced Deposition', ACS Applied Materials & Interfaces, vol. 5, no. 19, pp. 9372-9376.View/Download from: UTS OPUS or Publisher's site
Platinum has numerous applications in catalysis, nanoelectronics, and sensing devices. Here we report a method for localized, mask-free deposition of high-purity platinum that employs a combination of room-temperature, direct-write electron beam induced deposition (EBID) using the precursor Pt(PF3)4, and low temperature (=400 °C) postgrowth annealing in H2O. The annealing treatment removes phosphorus contaminants through a thermally activated pathway involving dissociation of H2O and the subsequent formation of volatile phosphorus oxides and hydrides that desorb during annealing. The resulting Pt is indistinguishable from pure Pt films by wavelength dispersive X-ray spectroscopy (WDS).
Bishop, J., Toth, M., Phillips, M. & Lobo, C. 2012, 'Effects of oxygen on electron beam induced deposition of SiO2 using physisorbed and chemisorbed tetraethoxysilane', Applied Physics Letters, vol. 101, p. 211605.View/Download from: UTS OPUS or Publisher's site
Electron beam induced deposition (EBID) is limited by low throughput and purity of as-grown material. Co-injection of O2 with the growth precursor is known to increase both the purity and deposition rate of materials such as SiO2 at room temperature. Here, we show that O2 inhibits rather than enhances EBID from tetraethoxysilane (TEOS) precursor at elevated temperatures. This behavior is attributed to surface site competition between chemisorbates at elevated temperature, and TEOS decomposition by atomic oxygen produced through electron dissociation of physisorbed O2 at room temperature.
Bishop, J.D., Lobo, C., Martin, A.A., Ford, M., Phillips, M. & Toth, M. 2012, 'Role of activated chemisorption in gas-mediated electron beam induced deposition', Physical Review Letters, vol. 109, p. 146103.View/Download from: UTS OPUS or Publisher's site
Models of adsorbate dissociation by energetic electrons are generalized to account for activated sticking and chemisorption, and used to simulate the rate kinetics of electron beam induced chemical vapor deposition (EBID). The model predicts a novel temperature dependence caused by thermal transitions from physisorbed to chemisorbed states that govern adsorbate coverage and EBID rates at elevated temperatures. We verify these results by experiments that also show how EBID can be used to deposit high purity materials and characterize the rates and energy barriers that govern adsorption.
Lobo, C., Martin, A.A., Phillips, M. & Toth, M. 2012, 'Electron beam induced chemical dry etching and imaging in gaseous NH3 environments', Nanotechnology, vol. 23, pp. 375302-375302.View/Download from: UTS OPUS or Publisher's site
We report the use of ammonia (NH3) vapor as a new precursor for nanoscale electron beam induced etching (EBIE) of carbon, and an efficient imaging medium for environmental scanning electron microscopy (ESEM). Etching is demonstrated using amorphous carbonaceous nanowires grown by electron beam induced deposition (EBID). It is ascribed to carbon volatilization by hydrogen radicals generated by electron dissociation of NH3 adsorbates. The volatilization process is also effective at preventing the buildup of residual hydrocarbon impurities that often compromise EBIE, EBID and electron imaging. We also show that ammonia is a more efficient electron imaging medium than H2O, which up to now has been the most commonly used ESEM imaging gas.
Steven, R., Toth, M., Cullen, J.C., Chandler, O. & Lobo, C. 2011, 'Kinetics of gas mediated electron beam induced etching', Applied Physics Letters, vol. 99, no. 21, pp. 213103-213105.View/Download from: UTS OPUS or Publisher's site
Electron beam induced etching (EBIE) is a high resolution, direct write, chemical dry etch process in which surface-adsorbed precursor molecules are activated by an electron beam. We show that nanoscale EBIE is rate limited through at least two mechanisms ascribed to adsorbate depletion and the transport of gaseous precursor molecules into an etch pit during etching, respectively. The latter has, to date, not been accounted for in models of EBIE and is needed to reproduce etch kinetics which govern the time-evolution of etch pits, EBIE throughput, and spatial resolution.
Toth, M., Lobo, C.J., Lysaght, M.J., Vladar, A.E. & Postek, M.T. 2009, 'Contamination-free imaging by electron induced carbon volatilization in environmental scanning electron microscopy', Journal Of Applied Physics, vol. 106, pp. 034306-034306.
Many ultraviolet, x-ray and charged particle beam techniques are inhibited by the growth of carbonaceous films caused by cross linking of hydrocarbon contaminant adsorbates. In electron microscopy, such films obscure surface features and reduce resolution. We demonstrate how resolution degradation can be alleviated using a H2O environment via gas mediated, electron beam induced carbon volatilization, a process that competes with film growth. Net behavior is a function of electron flux, which provides control over growth kinetics during imaging. Under optimized conditions, film growth can be eliminated, removing contamination as a factor limiting image information content and resolution.
Lobo, C.J., Toth, M., Wagner, R., Thiel, B.L. & Lysaght, M. 2008, 'High resolution radially symmetric nanostructures from simultaneous electron beam induced etching and deposition', Nanotechnology, vol. 19, pp. 025303-025303.
Electron beam induced etching (EBIE) and deposition (EBID) are promising fabrication techniques in which an electron beam is used to dissociate surface-adsorbed precursor molecules to achieve etching or deposition. Spatial resolution is normally limited by the electron flux distribution at the substrate surface. Here we present simultaneous EBIE and EBID (EBIED) as a method for surpassing this resolution limit by using adsorbate depletion to induce etching and deposition in adjacent regions within the electron flux profile. Our simulation results indicate the possibility of growth control of radially symmetric nanostructures at the sub-1 nm length scale on bulk substrates. The technique is well suited to the fabrication of ring-shaped nanostructures such as those employed in plasmonics, sensing devices, magneto-optics and magnetoelectronics.
Li, J., Toth, M., Tileli, V., Dunn, K.A., Lobo, C.J. & Thiel, B.L. 2008, 'Evolution of the nanostructure of deposits grown by electron beam induced deposition', Applied Physics Letters, vol. 93, pp. 023130-023130.
Environmental scanning electron microscopy (ESEM) was used to perform electron beam induced deposition (EBID) using a WF6 precursor. The deposits consist of WO3 nanocrystals embedded in an amorphous matrix. Oxide formation is attributed to residual oxidizers present in the ESEM chamber during EBID. Under conditions of fixed low electron flux, the WO3 grain size and the degree of deposit crystallinity increase with time. These changes correlate with the degree of electron energy deposition into the material during growth, indicating that electron beam induced modification of as-grown material is significant in controlling the nanostructure and functionality of materials fabricated by EBID. (C) 2008 American Institute of Physics.
Lobo, C.J., Toth, M., Wagner, R., Thiel, B.L. & Lysaght, M. 2008, 'High resolution radially symmetric nanostructures from simultaneous electron beam induced etching and deposition', Nanotechnology, vol. 19, pp. 025303-025303.View/Download from: UTS OPUS
Toth, M., Lobo, C.J., Hartigan, G. & Knowles, W.R. 2007, 'Electron flux controlled switching between electron beam induced etching and deposition', Journal Of Applied Physics, vol. 101, pp. 054309-054309.
Electron beam induced deposition (EBID) and etching (EBIE) are promising methods for the fabrication of three-dimensional nanodevices, wiring of nanostructures, and repair of photolithographic masks. Here, we study simultaneous EBID and EBIE, and demonstrate an athermal electron flux controlled transition between material deposition and etching. The switching is observed when one of the processes has both a higher efficiency and a lower precursor partial pressure than the other. This is demonstrated in two technologically important systems: during XeF2-mediated etching of chrome on a photolithographic mask and during deposition and etching of carbonaceous films on a semiconductor surface. Simultaneous EBID and EBIE can be used to enhance the spatial localization of etch profiles. It plays a key role in reducing contamination buildup rates during low vacuum electron imaging and deposition of high purity nanostructures in the presence of oxygen-containing gases. (c) 2007 American Institute of Physics.
Toth, M., Lobo, C.J., Knowles, W.R., Phillips, M.R., Postek, M.T. & Vladar, A.E. 2007, 'Nanostructure fabrication by ultra-high-resolution environmental scanning electron microscopy', Nano Letters, vol. 7, pp. 525-530.View/Download from: UTS OPUS
Electron beam induced deposition (EBID) is a maskless nanofabrication technique capable of surpassing the resolution limits of resist-based lithography. However, EBID fabrication of functional nanostructures is limited by beam spread in bulk substrates, substrate charging, and delocalized film growth around deposits. Here, we overcome these problems by using environmental scanning electron microscopy (ESEM) to perform EBID and etching while eliminating charging artifacts at the nanoscale. Nanostructure morphology is tailored by slimming of deposits by ESEM imaging in the presence of a gaseous etch precursor and by pre-etching small features into a deposit (using a stationary or a scanned electron beam) prior to a final imaging process. The utility of this process is demonstrated by slimming of nanowires deposited by EBID, by the fabrication of gaps (between 4 and 7 nm wide) in the wires, and by the removal of thin films surrounding such nanowires. ESEM imaging provides a direct view of the slimming process, yielding process resolution that is limited by ESEM image resolution (similar to 1 nm) and surface roughening occurring during etching.
Shields, A.J., Stevenson, R.M., Thompson, R.M., Ward, M.B., Yuan, Z., Kardynal, B.E., See, P., Farrer, I., Lobo, C., Cooper, K. & Ritchie, D.A. 2003, 'Self-assembled quantum dots as a source of single photons and photon pairs', Physica Status Solidi (B) Basic Research, vol. 238, pp. 353-359.
Leon, R., Marcinkevicius, S., Siegert, J., Cechavicius, B., Magness, B., Taylor, W. & Lobo, C. 2002, 'Effects of proton irradiation on luminescence emission and carrier dynamics of self-assembled III-V quantum dots', IEEE Transactions on Nuclear Science, vol. 49 I, pp. 2844-2851.
Marcinkevicius, S., Siegert, J., Leon, R., Cechavicius, B., Magness, B., Taylor, W. & Lobo, C. 2002, 'Changes in luminescence intensities and carrier dynamics induced by proton irradiation in InxGa1-xAs/GaAs quantum dots', Physical Review B - Condensed Matter and Materials Physics, vol. 66, pp. 2353141-2353146.
Marcinkevičius, S., Siegert, J., Leon, R., Čechavičius, B., Magness, B., Taylor, W. & Lobo, C. 2002, 'Changes in luminescence intensities and carrier dynamics induced by proton irradiation in (formula presented) quantum dots', Physical Review B - Condensed Matter and Materials Physics, vol. 66, no. 23, pp. 1-6.View/Download from: Publisher's site
The effects of proton irradiation (1.5 MeV) on photoluminescence intensities and carrier dynamics were compared between InGaAs/GaAs quantum dots and similar quantum well structures. A significant enhancement in radiation tolerance is seen with three-dimensional quantum confinement. Measurements were carried out in different quantum dot structures varying in dot surface density (formula presented) and substrate orientation [(100) and (formula presented). Similar trends were observed for all quantum dot samples. A slight increase in photoluminescence emission intensity after low to intermediate proton doses is observed in InGaAs/GaAs (100) quantum dot structures. The latter is explained in terms of more efficient carrier transfer from the wetting layer via radiation-induced defects. © 2002 The American Physical Society.
Stevenson, R.M., Thompson, R.M., Shields, A.J., Farrer, I., Lobo, C.J., Ritchie, D.A., Leadbeater, M.L. & Pepper, M. 2002, 'Exciton complexes in individual quantum dots as a single-photon source', Physica E: Low-Dimensional Systems and Nanostructures, vol. 13, pp. 423-426.
Yuan, Z., Kardynal, B.E., Stevenson, R.M., Shields, A.J., Lobo, C.J., Cooper, K., Beattie, N.S., Ritchie, D.A. & Pepper, M. 2002, 'Electrically driven single-photon source', Science, vol. 295, pp. 102-105.
Thompson, R.M., Stevenson, R.M., Shields, A.J., Farrer, I., Lobo, C.J., Ritchie, D.A., Leadbeater, M.L. & Pepper, M. 2001, 'Single-photon emission from exciton complexes in individual quantum dots', Physical Review B - Condensed Matter and Materials Physics, vol. 64, pp. 2013021-2013024.
Lobo, C., Perret, N., Morris, D., Zou, J., Cockayne, D.J.H., Johnston, M.B., Gal, M. & Leon, R. 2000, 'Carrier capture and relaxation in Stranski-Krastanow InxGa1-xAs/GaAs(311)B quantum dots', Physical Review B - Condensed Matter and Materials Physics, vol. 62, pp. 2737-2742.
Babinski, A., Tomaszewicz, T., Wysmolek, A., Baranowski, J.M., Lobo, C., Leon, R. & Jagadish, C. 1999, 'Optical properties of self-organized InGaAs/GaAs quantum dots in field-effect structures', Materials Research Society Symposium - Proceedings, vol. 536, pp. 269-274.
Leon, R., Lobo, C., Liao, X.Z., Zou, J., Cockayne, D.J.H. & Fafard, S. 1999, 'Island shape instabilities and surfactant-like effects in the growth of InGaAs/GaAs quantum dots', Thin Solid Films, vol. 357, pp. 40-45.
Liao, X.Z., Zou, J., Cockayne, D.J.H., Leon, R. & Lobo, C. 1999, 'Indium segregation and enrichment in coherent InxGa1-xAs/GaAs quantum dots', Physical Review Letters, vol. 82, pp. 5148-5151.
Liao, X.Z., Zou, J., Duan, X.F., Cockayne, D.J.H., Leon, R. & Lobo, C. 1999, 'Transmission electron microscopy determination of quantum dot profile', Conference on Optoelectronic and Microelectronic Materials and Devices, Proceedings, COMMAD, pp. 106-108.
Lobo, C., Leon, R., Marcinkeviƒ c cius, S., Yang, W., Sercel, P.C., Liao, X.Z., Zou, J. & Cockayne, D.J.H. 1999, 'Inhibited carrier transfer in ensembles of isolated quantum dots', Physical Review B - Condensed Matter and Materials Physics, vol. 60, pp. 16647-16651.
Leon, R., Okuno, J.O., Lawton, R.A., Stevens-Kalceff, M., Phillips, M.R., Zou, J., Cockayne, D.J.H. & Lobo, C. 1999, 'Dislocation-induced changes in quantum dots: Step alignment and radiative emission', Applied Physics Letters, vol. 74, pp. 2301-2303.
Babinski, A., Wysmolek, A., Tomaszewicz, T., Baranowski, J.M., Leon, R., Lobo, C. & Jagadish, C. 1998, 'Electrically modulated photoluminescence in self-organized InGaAs/GaAs quantum dots', Applied Physics Letters, vol. 73, pp. 2811-2813.
Leon, R., Lobo, C., Chin, T.P., Woodall, J.M., Fafard, S., Ruvimov, S., Liliental-Weber, Z. & Stevens Kalceff, M.A. 1998, 'Self-forming InAs/GaP quantum dots by direct island growth', Applied Physics Letters, vol. 72, pp. 1356-1358.
Leon, R., Lobo, C., Clark, A., Bozek, R., Wysmolek, A., Kurpiewski, A. & Kaminska, M. 1998, 'Different paths to tunability in III-V quantum dots', Journal of Applied Physics, vol. 84, pp. 248-254.
Leon, R., Lobo, C., Zou, J., Romeo, T. & Cockayne, D.J.H. 1998, 'Stable and metastable InGaAs/GaAs island shapes and surfactantlike suppression of the wetting transformation', Physical Review Letters, vol. 81, pp. 2486-2489.
Liao, X.Z., Zou, J., Duan, X.F., Cockayne, D.J.H., Leon, R. & Lobo, C. 1998, 'Transmission-electron microscopy study of the shape of buried InxGa1-xAs/GaAs quantum dots', Physical Review B - Condensed Matter and Materials Physics, vol. 58, pp. R4235-R4237.
Lobo, C. & Leon, R. 1998, 'InGaAs island shapes and adatom migration behavior on (100), (110), (111), and (311) GaAs surfaces', Journal of Applied Physics, vol. 83, pp. 4168-4172.
Lobo, C., Leon, R., Fafard, S. & Piva, P.G. 1998, 'Intermixing induced changes in the radiative emission from III-V quantum dots', Applied Physics Letters, vol. 72, pp. 2850-2852.
Withers, R.L., Lobo, C., Thompson, J.G., Schmid, S. & Stranger, R. 1997, 'A Modulation Wave Approach to the Structural Characterization of Three New Cristobalite-Related Sodium Magnesiosilicates', Acta Crystallographica Section B: Structural Science, vol. 53, pp. 203-220.
Schmid, S., Lobo, C., Withers, R.L. & Thompson, J.G. 1996, 'A TEM and powder XRD study of new fluorite and perovskite-related phases in the CaO-ZrO2-Ta2O5 system', Journal of Solid State Chemistry, vol. 127, pp. 82-86.
Thompson, J.G., Dougherty, J., Melnitchenko, A., Lobo, C. & Withers, R.L. 1996, 'Sodalite-type Na8Mg3Si9O24(OH)2 and Na8Mg3Si9O24(OH,Cl)2: Novel framework magnesiosilicates', Journal of Materials Chemistry, vol. 6, pp. 1933-1937.
Kianinia, M., Bradac, C., Wang, F., Sontheimer, B., Tran, T.T., Nguyen, M., Kim, S., Xu, Z.-.Q., Jin, D., Schell, A.W., Lobo, C.J., Aharonovich, I. & Toth, M., 'Super-resolution imaging of quantum emitters in layered materials'.View/Download from: UTS OPUS or Publisher's site
Layered van der Waals materials are emerging as compelling two-dimensional
(2D) platforms for studies of nanophotonics, polaritonics, valleytronics and
spintronics, and have the potential to transform applications in sensing,
imaging and quantum information processing. Amongst these, hexagonal boron
nitride (hBN) is unique in that it hosts ultra-bright, room temperature single
photon emitters (SPEs). However, an outstanding challenge is to locate SPEs in
hBN with high precision, a task which requires breaking the optical diffraction
limit. Here, we report the imaging of SPEs in layered hBN with a spatial
resolution of 63 nm using ground state depletion (GSD) nanoscopy. Furthermore,
we show that SPEs in hBN possess nonlinear photophysical properties which can
be used to realize a new variant of GSD that employs a coincident pair of
doughnut-shaped lasers to reduce the laser power that is needed to achieve a
given resolution target. Our findings expand the current understanding of the
photophysics of quantum emitters in layered hBN and demonstrate the potential
for advanced nanophotonic and bio-imaging applications which require
localization of individual emitters with super-resolution accuracy.
Lobo, C. & Toth, M. 2012, 'Continuum modeling of electron beam induced processes' in Utke, I., Moshkalev, S.A. & Russell, P. (eds), Nanofabrication Using Focused Ion and Electron Beams: Principles and Applications, Oxford University Press, New York, USA, pp. 286-320.View/Download from: UTS OPUS
Gas-mediated focused electron beam induced etching (FEBIE) and deposition (FEBID), collectively referred to here as FEBIED, permit nanoscale modification of surface material via chemical reactions involving electron-dissociated precursor molecules. Electrons crossing the solid-vacuum interface usually possess a wide range of energies, are capable of breaking most bonds in typical precursor adsorbates and dissociation products, and can therefore generate a wide range of mobile, chemically active species. Adsorption, desorption, diffusion, and dissociation of these species all contribute to the development of nanostructures fabricated by FEBIED processes. Furthermore, these nanostructures are often electron-sensitive, and thus their structure evolves during deposition. The wide range of processes behind FEBIED yields very complex behavior that is yet to be modeled realistically fifty years after Christy first proposed a simple analytical model of deposition induced by a broad (defocused) electron beam . A complete description of FEBIED requires a realistic model of electron-gas and electron-solid interactions, the spatial and energy distributions of secondary and backscattered electrons, electron interactions with adsorbates, and the behavior of adsorbates and dissociation products at the solid-vacuum interface.
Elbadawi, C., Tran, T.T., Shimoni, O., Totonjian, D., Lobo, C.J., Grosso, G., Moon, H., Englund, D.R., Ford, M.J., Aharonovich, I. & Toth, M. 2016, 'Ultra-bright emission from hexagonal boron nitride defects as a new platform for bio-imaging and bio-labelling', Proceedings of SPIE - The International Society for Optical Engineering.View/Download from: UTS OPUS or Publisher's site
© 2016 SPIE. 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.
Lobo, C.J., Elbadawi, C. & Toth, M. 2014, 'Localized deposition of pure platinum nanostructures', 2014 Conference on Optoelectronic and Microelectronic Materials and Devices, COMMAD 2014, Conference on Optoelectronic and Microelectronic Materials and Devices, IEEE, Perth, Western Australia, Australia, pp. 15-16.View/Download from: UTS OPUS or Publisher's site
© 2014 IEEE. Localized deposition of pure platinum nanostructures was achieved using a combination of focused electron beam induced processing (FEBID) of an inorganic platinum precursor and low temperature annealing in water vapour. This technique enables fabrication of Pt nanostructures with high spatial resolution and purity, for applications in nanoelectronics, sensing devices and catalysis.
Lobo, C.J., Martin, A.A., Elbadawi, C., Bishop, J., Aharonovich, I. & Toth, M. 2014, 'Gas-mediated charged particle beam processing of nanostructured materials', Proceedings of SPIE - The International Society for Optical Engineering, The International Society for Optical Engineering Conference, SPIE-INT SOC OPTICAL ENGINEERING, San Francisco, CA.View/Download from: UTS OPUS or Publisher's site
Gas mediated processing under a charged particle (electron or ion) beam enables direct-write, high resolution surface functionalization, chemical dry etching and chemical vapor deposition of a wide range of materials including catalytic metals, optoelectronic grade semiconductors and oxides. Here we highlight three recent developments of particular interest to the optical materials and nanofabrication communities: fabrication of self-supporting, three dimensional, fluorescent diamond nanostructures, electron beam induced deposition (EBID) of high purity materials via activated chemisorption, and post-growth purification of nanocrystalline EBID-grown platinum suitable for catalysis applications. © 2014 SPIE.
Toth, M., Knowles, W.R., Hartigan, G. & Lobo, C.J. 2006, 'Electron flux controlled switching between electron beam induced etching and deposition', Microscopy and Microanalysis, pp. 168-169.View/Download from: Publisher's site
Stevenson, R.M., Yuan, Z.L., Ward, M.B., Thompson, R.M., See, P., Kardynal, B.E., Shields, A.J., Farrer, I., Lobo, C.J., Cooper, K. & Ritchie, D.A. 2002, 'Generation of single photons and photon pairs using quantum dots', QUANTUM COMMUNICATION, MEASUREMENT AND COMPUTING, PROCEEDINGS, 6th International Conference on Quantum Communication, Measurement and Computing (QCMC 02), RINTON PRESS, INC, MIT, CAMBRIDGE, MA, pp. 532-535.
Marcinkevicius, S., Leon, R., Cechavius, B., Siegert, J., Lobo, C., Magness, B. & Taylor, W. 2002, 'Changes in carrier dynamics induced by proton irradiation in quantum dots', Physica B: Condensed Matter, pp. 203-206.
Yuan, Z., Kardynal, B.E., Stevenson, R.M., Ward, M.B., Shields, A.J., Lobo, C.J., Cooper, K., Ritchie, D.A. & Pepper, M. 2002, 'Single photon emitting diode using semiconductor quantum dot', Conference on Quantum Electronics and Laser Science (QELS) - Technical Digest Series, pp. 96-97.
Leon, R., Stevens-Kalceff, M., Zou, J., Lobo, C. & Cockayne, D.J.H. 1998, 'Ordering, tunability, and stability in the formation of semiconductor quantum dots', ELECTRON MICROSCOPY 1998, VOL 3, 14th International Congress on Electron Microscopy, IOP PUBLISHING LTD, CANCUN, MEXICO, pp. 377-378.
Marcinkevicius, S., Leon, R., Lobo, C., Magness, B. & Taylor, W., 'Time resolved studies of proton irradiated quantum dots', Materials Research Society Symposium - Proceedings, pp. 337-342.
Ward, M.B., Yuan, Z., Stevenson, R.M., Kardynal, B.E., Lobo, C.J., Cooper, K., Ritchie, D.A. & Shields, A.J., 'A single photon emitting diode', Proceedings of SPIE - The International Society for Optical Engineering, pp. 466-473.