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Professor Mike Ford

Biography

Mike Ford is Professor of Physics and Associate Dean, Research and Development, Faculty of Science

Mike Ford is originally from the UK where he undertook his doctoral studies at Southampton University. He first arrived in Australia in 1989 as a senior tutor at the University of Western Australia, then spent 4 years in the US as a research fellow jointly between Johns Hopkins University and University of Maryland, returning to Australia in 1996 to take up an academic appointment at Flinders. With the lure of the big city and the chance to pioneer nanotechnology education in Sydney, he moved to UTS in mid 2002. At Flinders University Mike co-founded the first nanotechnology undergraduate degree in Australia, and as Associate Director of the Institute his primary responsibility was the development of nanotechnology education initiatives at UTS. From 2006 to 2011 Mike was Head of School, Physics and Advanced Materials and is now the Director of the Materials and Technology for Energy Efficiency research strength.

Mike's research interests are in materials physics and most recently using quantum mechanical computer simulations to understand the electronic properties of materials.  In the past he has been known to undertake experimental work using electron beams to measure properties of atoms, molecules and solid materials.  In his spare time he rides push bikes and clings to rocks.

Image of Mike Ford
Associate Dean (Research), Faculty of Science
Education Consultant, Institute for Nanoscale Technology
Member, Research Centre for Clean Energy Technology
Core Member, MTEE - Materials and Technology for Energy Efficiency
BSc (Hons) (Southampton), PhD (Southampton)
Member, Australian Institute of Physics
 
Phone
+61 2 9514 7574

Research Interests

My research interests across my career have centered on the electron properties of materials using experimental and computational methods.

Over the past 12 years or so I have developed expertise in quantum chemical calculations to understand the properties of materials, in particular the application of density functional theory for understanding and predicting the properties of nanostructures, such as surface processes and optical properties. These are challenging problems that require very large scale calculations.

We have implemented a linear scaling method within the SIESTA DFT code that can be applied to nanostructures containing upwards of 10,000 atoms. This means that these first principles techniques can now be applied to entire nanoparticles for example rather than reducing the nanostructure to a smaller, idealised structure. A 7 nm gold nanoparticle, for example contains around 10,000 atoms. We access the high performance computing facilities at the National Computational Infrastructure to run these calculations.

Over the past few years we have been particularly interested in using DFT based methods to calculate the optical response of materials from first principles and developed a methodology for calculating the entire dielectric response function without any empirical parameters.

The motivation for this work was to identify new materials for plasmonics applications. Gold is commonly use, but is quite 'lossy' and therefore not ideal. We use our methods to calculate, for the first time, the optical properties of a range of intermetallic compounds in order to identify new promising materials.

Can supervise: Yes

I teach into the Applied Physics and Nanotechnology undergraduate majors. Currently I am teaching subjects on Computational Physics and Quantum Physics.

Chapters

Ford, M.J. 2011, 'SIESTA: Properties and Applications' in Computational Methods for Large Systems: Electronic Structure Approaches for Biotechnology and Nanotechnology, pp. 367-395.
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In this chapter a number of these properties are discussed through examples relevant to nanoscience and technology. The SIESTA methodology in detail in Chapter 2; the present chapter is intended as an accompaniment. The first three examples illustrate the general capabilities of the SIESTA code for problems containing relatively small numbers of atoms and that are amenable to standard diagonalization to solve the self-consistent problem. The last example illustrates the divide-and-conquer linear-scaling capabilities to tackle problems containing large numbers of atoms. © 2011 John Wiley & Sons, Inc.
Blaber, M.G., Ford, M. & Cortie, M.B. 2010, 'The Physics and Optical Properties of Gold' in Corti, C. & Holliday, R. (eds), Gold Science and Applications, CRC Press, Boca Raton, Florida, pp. 13-30.
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Although gold is well down on the periodic table, at position 79, it was the first of the metals to be discovered and exploited by humans. This was almost certainly as a result of it possessing four unique attributes: a bright metallic yellow color, excellent resistance to corrosion, considerable malleability, and a high density (19.32 g/cm3). The high corrosion resistance and density facilitated the concentration of native gold nuggets and powders in the beds of streams, while the yellow color and malleability made it very suitable for the production of jewelry or religious artifacts. A few other metallic elements-such as silver, copper, or platinum-possess color and/or corrosion resistance and/or ductility and/or density, but none to the simultaneous degree exhibited by gold. What are the reasons for this unusual cluster of interesting properties in element 79?

Conferences

Tran, T.T., Bray, K., Ford, M.J., Toth, M. & Aharonovich, I. 2016, 'Quantum emission from hexagonal boron nitride monolayers', 2016 Conference on Lasers and Electro-Optics, CLEO 2016.
© 2016 OSA.We demonstrate first room temperature, and ultrabright single photon emission from a color center in two-dimensional multilayer hexagonal boron nitride. Density Functional Theory calculations indicate that vacancy-related centers are a likely source of the emission.
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.
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© 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.
Cortie, M.B., Barnett, M.W. & Ford, M. 2007, 'Active control of the optical properties of nanoscale coatings using 'smart' nanoparticles', Nanocoatings. Proceedings of SPIE vol 6647, SPIE, SPIE, San Diego, USA, pp. 1-4.
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Coatings that can self-modulate their optical properties as a function of an external stimulus are of significant technological interest. In this regard, the possibilities for thermo- or electrochromic materials such as VO2 and WO3 are already comparatively well-known. Here, however, we explore a new kind of 'smart' coating, based on the active control of a plasmon resonance in nanoparticles. One possible system is based on the modulation of the plasmon resonance of a precious metal nanorod or nanosphere by an active dielectric shell. The active dielectric undergoes an insulator-to-metal transition on increase of temperature which modulates the plasmon resonance of the underlying precious metal nanoparticle, thereby changing the wavelength at which its optical extinction is maximum. In the case of nanorods, the absorption maximum of the longitudinal plasmon is particularly sensitive to the aspect ratio of the nanoparticle and the dielectric properties of the environment, and may be readily tuned across the visible and near-infrared portions of the spectrum. In addition, nanoparticles of certain thermochromic dielectrics, such as VO2, are expected to have a plasmon resonance of their own which can be switched on or off by control of the temperature. We consider some of the possibilities, using both the discrete dipole approximation and the exact analytical solution due to Mie to calculate the optical properties.
Cankurtaran, B.O., Ford, M. & Cortie, M.B. 2006, 'Local electromagnetic fields surrounding gold nano-cap particles', 2006 International Conference on Nanoscience and Nanotechnology, ICONN, IEEE Publishing Company, Brisbane, Australia, pp. 1-4.
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Using the discrete dipole approximation (DDA) the local electromagnetic fields surrounding gold nano-cap particles are investigated. Suitable k-vectors and polarization vectors of the incident light are used to determine the largest local electric field enhancement. The largest enhancement can be found for the 864 nm dipole resonance; where the field enhancement is approximately 30000 times the applied field. The electric field contours surounding the particle are used to assign the order of the surface plasmon resonance.
Blaber, M.G., Harris, N., Ford, M. & Cortie, M.B. 2006, 'Optimisation of absorption efficiency for varying dielectric spherical nanoparticles', ICONN2006, International Conference on Nanoscience and nanotehcnology, IEEE, Brisbane, QLD Australia, pp. 556-559.
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In this paper we compare tje optical absorption for nanospheres made from a range of transition and alkali metals from li (A=3) to Au (A=79). numerical solutions to Mie theory were used to claculate the absorption efficiency for nanospheres varying in radii between 5nm and 100 nm in vacuum. We show that although gold is the most commonly used nanoparicle material, its absorption efficiency at the lasmon resonance is not as strong as materials such as the alkali metals. Of all the materials tried, potassium spheres with a radius of 21 nm have an optimum absorption efficiency of 14.7. in addition we also show that, unlike gold, the wavelength of the plasmon peak in other materials is sensitive to the sphere radius. In potassium the peaporition shifts by 100 nm for spheres ranging from 5 nm to 65 nm, the shift is less than 10 nm for gold spheres.
Hoft, R.C., Ford, M. & Cortie, M.B. 2006, 'Effect of dipole moment on current-voltage characteristics of single molecules', ICONN2006, International Conference on Nanoscience and nanotechnology, IEEE, Brisbane, QLD Australia, pp. 395-398.
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We perform emperical calculations of the tunneling current through various small organic molecules sandwiched between gold electrodes by using the Wenzel-Kramers-Brillouin (WKB) approximation. The barrierto tunneling is taken to eb the work function of gold and calculated from a first principles electronic structure code. The current-voltage characteristics of these molecules are compared in the context of exisiting first principles and experimental results. In this model the surface dipole moment, induced by the adsorbed molecule can have asignificant effect on the current and hence dipole moments may be an important property for prediction of the conductance chracteristics of a molecule.
Ford, M., Hoft, R.C., Gale, J.D. & McDonagh, A.M. 2007, 'A new class of self-assembled monolayers on gold using an alkynyl group as linker', Proceedings of the 2006 International Conference on Nanoscience and Nanotechnology, ICONN, IEEE, Brisbane QLD, Australia, pp. 645-648.
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The geometry and energetics for adsorption of ethynylbenzene on au(!!!) have been studied using Density Functional Theory. The alkynyl group, following removal of the terminal H atom, adsorbs covalently to the surface in the fcc hollow site with a bond energy of about 70 kcal.mol-1. Intermediate adsorption states are also possible via a hydrogen 1,2 shoft to form a surface-bound vinylidene, or through the opening o the c-c triple bond without removing the hydrogen atom.
Hoft, R.C., Liu, J., Cortie, M.B. & Ford, M. 2005, 'Electron tunneling through alkanedithiol molecules - art. no. 603603', Biomems And Nanotechnology Ii, Conference on BioMEMS and Nanotechnology II, Spie-Int Society Optical Engineering, Brisbane, AUSTRALIA, pp. 3603-3603.
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We report on first principles calculations of the tunneling current across n-alkanedithiol molecules (n = 4,6,8,10,12) sandwiched between two Au {111} electrodes. The conductance drops exponentially with increased chain length with decay parameter beta(n
Ford, M., Kirkup, L., Gentle, A.R., Zareie, H.M. & Cortie, M.B. 2005, 'How reliable are scanning tunneling microscopy measurements of electron transport in molecules? - art. no. 603604', Biomems And Nanotechnology Ii, Conference on BioMEMS and Nanotechnology II, Spie-Int Society Optical Engineering, Brisbane, AUSTRALIA, pp. 3604-3604.
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Scanning tunneling microscopy measurements of tunneling through molecules adsorbed on a surface have been simulated using a standard empirical model based upon the Wentzel-Kramer-Brillouin method applied to tunneling through a barrier. The Gaussian noise
Hoft, R.C., Ford, M.J., Cortie, M.B. & IEEE 2006, 'Effect of dipole moment on current-voltage characteristics of single molecules', 2006 INTERNATIONAL CONFERENCE ON NANOSCIENCE AND NANOTECHNOLOGY, VOLS 1 AND 2, pp. 77-80.
Blaber, M.G., Harris, N., Ford, M.J., Cortie, M.B. & IEEE 2006, 'Optimisation of absorption efficiency for varying dielectric spherical nanoparticles', 2006 INTERNATIONAL CONFERENCE ON NANOSCIENCE AND NANOTECHNOLOGY, VOLS 1 AND 2, pp. 61-64.
Ford, M.J., Hoft, R.C., Gale, J.D., McDonagh, A.M. & IEEE 2006, 'A new class of self-assembled monolayers on gold using an alkynyl group as a linker', 2006 INTERNATIONAL CONFERENCE ON NANOSCIENCE AND NANOTECHNOLOGY, VOLS 1 AND 2, pp. 11-14.
Cankurtaran, B., Ford, M.J., Cortie, M. & IEEE 2006, 'Local electromagnetic fields surrounding gold nano-cap particles', 2006 INTERNATIONAL CONFERENCE ON NANOSCIENCE AND NANOTECHNOLOGY, VOLS 1 AND 2, pp. 15-18.
Cortie, M.B., Zareie, H.M., Liu, J., Muller, K.H. & Ford, M. 2004, 'Modelling and verification of the electrical properties of organic dielectric monolayers in capacitive configurations', Proceedings Of The Society Of Photo-Optical Instrumentation Engineers (SPIE) Vol 5649, Conference on Smart Structures, Devices, and Systems II, International Society for Optical Engineering (SPIE), Sydney, Australia, pp. 316-322.
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The possible role of self-assembled monolayers (SAMs) as the dielectric component of nanoscale capacitors is considered. SAMs of two rather different molecules, á,á′-p-xylyldithiol (′ XYL′) and dodecanedithiol (′ C12&P
Killen, C.P. & Ford, M. 2005, 'Innovation in Cross-Faculty Education: Engineering and Science', Proceedings of 4th ASEE/AaeE Global Colloquium on Engineering Education, ASEE Global Colloquium of Engineering Education, University of Queensland, Sydney, Australia, pp. 1-10.
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Maclurcan, D., Ford, M., Cortie, M.B. & Ghosh, D. 2003, 'Medical Nanotechnology and Developing Nations', Proceedings of the Asia Pacific Nanotechnology Forum 2003, Oz Nano, World Scientific Publishing Co, Cairns, Australia, pp. 165-172.
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Shapter, J.G., Hale, P., Maddox, L.M., Ford, M.J. & Waclawik, E.R. 2004, 'Teaching undergraduates nanotechnology', Materials Research Society Symposium Proceedings, pp. 6-16.
One of the first nanotechnology undergraduate degrees in the world was established at Flinders University in 2000. In this paper we present our experience of developing and delivering this degree in a climate where 'traditional' physical sciences are under considerable strain. We will discuss the motivation for this initiative, structure of the established course and educational issues relating to its development. © 2004 Materials Research Society.
Mikajlo, E.A., Sashin, V.A., Nixon, K.L., Soule, D.B.B.J., Dorsett, H.E. & Ford, M. 2003, 'Band sturctures of the group I and group II oxides: using EMS measurements as a test of theoretical models', Proceedings of the 27th Annual A&NZIP Condenced Matter and Materials Meeting, Annual Australia and New Zealand Institute of Physics COndenced Matter and Materials Meeting, Australian Institute of Physics, Wagga Wagga, Australia, pp. 1-3.
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Ekanayake, S.R., Rodanski, B., Cortie, M.B. & Ford, M. 2003, 'Quantum electrical characterisatic of nanocapacitors', 2003 Third IEEE Conference on Nanotechnology, IEEE-Nano 2003, IEEE Conference on Nanotechnology, IEEE, San Franscisco, USA, pp. 756-759.
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Current integrated circuit miniaturization will soon require device sizes at atomic scale. Recent work has proposed many Coulomb blockade, and tunneling devices as active devices. However, among passive components, capacitors are extremely critical circuit elements in all electronic circuits with wide range applications. In this work, we present the operational criteria that will govern the feasibility of nanocapacitors for future nanoelectronic circuits.
Mikajlo, E.A., Nixon, K.L., Soule, D.B.B.J., Dorsett, H.E. & Ford, M. 2002, 'Electron Momentum Spectroscopy of Group I and II Oxides', Proceedings of the 15th National Congress of the AIP, Causal / AIP, Sydney, Australia.
Brunger, M.J., Adcock, W., Mackenzie-Ross, H., Nixon, K.L., Drury, W., Ford, M., Campbell, L., Shaw, R., Lawrance, W., Wang, F. & Winkler, D. 2001, 'High resolution electron momentum spectroscopy of molecules', Proceedings of the Photonic, Electronic and Atomic Collisions: XXII International Conference, Photonic, Electronic and Atomic Collisions: XXII International Conference, Rinton Press, Santa Fe, USA, pp. 369-380.
Moore, J.H., Ford, M.J., Coplan, M.A., Cooper, J.W. & Doering, J.P. 1997, 'Partitioning of momentum in electron-impact double ionization', COINCIDENCE STUDIES OF ELECTRON AND PHOTON IMPACT IONIZATION, pp. 85-92.
FORD, M.J., DOERING, J.P., COOPER, J.W., COPLAN, M.A. & MOORE, J.H. 1993, 'ELECTRON-IMPACT DOUBLE-IONIZATION OF NEON', JOURNAL DE PHYSIQUE IV, pp. 117-123.
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Ford, M.J. 1981, 'EXPERIENCES WITH A FULLY AUTOMATED HIGH SPEED WRAPPING SYSTEM.', Paper Finishing and Converting Conference, Proceedings of the Technical Association of the Pulp an, pp. 125-129.

Journal articles

Kianinia, M., Regan, B., Tawfik, S.A., Tran, T.T., Ford, M.J., Aharonovich, I. & Toth, M. 2017, 'Robust Solid-State Quantum System Operating at 800 K', ACS Photonics, vol. 4, no. 4, pp. 768-773.
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© 2017 American Chemical Society.Realization of quantum information and communications technologies requires robust, stable solid-state single-photon sources. However, most existing sources cease to function above cryogenic or room temperature due to thermal ionization or strong phonon coupling, which impedes their emissive and quantum properties. Here we present an efficient single-photon source based on a defect in a van der Waals crystal that is optically stable and operates at elevated temperatures of up to 800 K. The quantum nature of the source and the photon purity are maintained upon heating to 800 K and cooling back to room temperature. Our report of a robust high-temperature solid-state single photon source constitutes a significant step toward practical, integrated quantum technologies for real-world environments.
Zhu, L., Lem, L.L.C., Nguyen, T.P., Fair, K., Ali, S., Ford, M.J., Phillips, M.R. & Ton-That, C. 2017, 'Indirect excitons in hydrogen-doped ZnO', Journal of Physics D: Applied Physics, vol. 50, no. 11.
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© 2017 IOP Publishing Ltd.We present a correlative experimental and theoretical study of bound excitons in hydrogen-doped ZnO, with a particular focus on the dynamics of their metastable state confined in the sub-surface region, using a combination of surface-sensitive characterisation techniques and density functional theory calculations. A metastable sub-surface emission at 3.31 eV found in H-doped ZnO is attributed to the radiative recombination of indirect excitons localised at basal plane stacking faults (BSFs) where the excitonic transition involves electrons bound to bond-centre hydrogen donors in the potential well of the BSF. Additionally, our work shows the electrical transport of ZnO Schottky junctions is dominated by electrons confined at BSFs in the near-surface region.
Reimers, J.R., Ford, M.J. & Goerigk, L. 2016, 'Problems, successes and challenges for the application of dispersion-corrected density-functional theory combined with dispersion-based implicit solvent models to large-scale hydrophobic self-assembly and polymorphism', Molecular Simulation, vol. 42, no. 6-7, pp. 494-510.
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© 2015 Taylor & Francis.The recent advent of dispersion-corrected density-functional theory (DFT) methods allows for quantitative modelling of molecular self-assembly processes, and we consider what is required to develop applications to the formation of large self-assembled monolayers (SAMs) on hydrophobic surfaces from organic solution. Focus is on application of the D3 dispersion correction of Grimme combined with the solvent dispersion model of Floris, Tomasi and Pascual-Ahuir to simulate observed scanning-tunnelling microscopy (STM) images of various polymorphs of tetraalkylporphyrin SAMs on highly oriented pyrolytic graphite surfaces. The most significant problem is identified as the need to treat SAM structures that are incommensurate with those of the substrate, providing a challenge to the use of traditional periodic-imaging boundary techniques. Using nearby commensurate lattices introduces non-systematic errors into calculated lattice constants and free energies of SAM formation that are larger than experimental uncertainties and polymorph differences. Developing non-periodic methods for polymorph interface simulation also remains a challenge. Despite these problems, existing methods can be used to interpret STM images and SAM atomic structures, distinguishing between multiple feasible polymorph types. They also provide critical insight into the factors controlling polymorphism. All this stems from a delicate balance that the intermolecular D3 and solvent Floris, Tomasi and Pascual-Ahuir corrections provide. Combined optimised treatments should yield fully quantitative approaches in the future.
Tran, T.T., Bray, K., Ford, M.J., Toth, M. & Aharonovich, I. 2016, 'Quantum emission from hexagonal boron nitride monolayers.', Nature nanotechnology, vol. 11, no. 1, pp. 37-41.
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Artificial atomic systems in solids are widely considered the leading physical system for a variety of quantum technologies, including quantum communications, computing and metrology. To date, however, room-temperature quantum emitters have only been observed in wide-bandgap semiconductors such as diamond and silicon carbide, nanocrystal quantum dots, and most recently in carbon nanotubes. Single-photon emission from two-dimensional materials has been reported, but only at cryogenic temperatures. Here, we demonstrate room-temperature, polarized and ultrabright single-photon emission from a colour centre in two-dimensional hexagonal boron nitride. Density functional theory calculations indicate that vacancy-related defects are a probable source of the emission. Our results demonstrate the unprecedented potential of van der Waals crystals for large-scale nanophotonics and quantum information processing.
Reimers, J.R., Panduwinata, D., Visser, J., Chin, Y., Tang, C., Goerigk, L., Ford, M.J., Baker, M., Sum, T.J., Coenen, M.J.J., Hendriksen, B.L.M., Elemans, J.A.A.W., Hush, N.S. & Crossley, M.J. 2016, 'From chaos to order: Chain-length dependence of the free energy of formation of meso-tetraalkylporphyrin self-assembled monolayer polymorphs', Journal of Physical Chemistry C, vol. 120, no. 3, pp. 1739-1748.
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© 2016 American Chemical Society.We demonstrate that systematic errors can be reduced and physical insight gained through investigation of the dependence of free energies for meso-tetraalkylporphyrin self-assembled monolayers (SAMs) polymorphism on the alkyl chain length m. These SAMs form on highly ordered pyrolytic graphite (HOPG) from organic solution, displaying manifold densities and atomic structures. SAMs with m = 11-19 are investigated experimentally while those with m = 6-28 are simulated using density-functional theory (DFT). It is shown that, for m = 15 or more, the alkyl chains crystallize to dominate SAM structure. Meso-tetraalkylporphyrin SAMs of length less than 11 have never been observed, a presumed effect of inadequate surface attraction. Instead, we show that free energies of SAM formation actually enhance as the chain length decreases. The inability to image regular SAMs stems from the appearance of many polymorphic forms of similar free energy, preventing SAM ordering. We also demonstrate a significant odd/even effect in SAM structure arising from packing anomalies. Comparison of the chain-length dependence of formation free energies allows the critical dispersion interactions between molecules, solvent, and substrate to be directly examined. Interpretation of the STM data combined with measured enthalpies indicates that Grimme's D3 explicit-dispersion correction and the implicit solvent correction of Floris, Tomasi and Pascual Ahuir are both quantitatively accurate and very well balanced to each other.
Reimers, J.R., Ford, M.J., Halder, A., Ulstrup, J. & Hush, N.S. 2016, 'Gold surfaces and nanoparticles are protected by Au(0)-thiyl species and are destroyed when Au(I)-thiolates form.', Proceedings of the National Academy of Sciences of the United States of America, vol. 113, no. 11, pp. E1424-E1433.
The synthetic chemistry and spectroscopy of sulfur-protected gold surfaces and nanoparticles is analyzed, indicating that the electronic structure of the interface is Au(0)-thiyl, with Au(I)-thiolates identified as high-energy excited surface states. Density-functional theory indicates that it is the noble character of gold and nanoparticle surfaces that destabilizes Au(I)-thiolates. Bonding results from large van der Waals forces, influenced by covalent bonding induced through s-d hybridization and charge polarization effects that perturbatively mix in some Au(I)-thiolate character. A simple method for quantifying these contributions is presented, revealing that a driving force for nanoparticle growth is nobleization, minimizing Au(I)-thiolate involvement. Predictions that Brust-Schiffrin reactions involve thiolate anion intermediates are verified spectroscopically, establishing a key feature needed to understand nanoparticle growth. Mixing of preprepared Au(I) and thiolate reactants always produces Au(I)-thiolate thin films or compounds rather than monolayers. Smooth links to O, Se, Te, C, and N linker chemistry are established.
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.
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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.
Reimers, J.R., Chi, Q., Ford, M.J., Halder, A., Hush, N.S., Ulstrup, J. & Zhang, J. 2016, 'En ny historie om guld og svovl', Dansk Kemi, vol. 97, no. 8, pp. 20-23.
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- guld-svovlbindingen i thiolers adsorption på guldnanopartikler og plane guldoverflader En netop publiceret større australsk-dansk undersøgelse giver ny indsigt i, hvordan thioldækkede Au-overflader er opbygget. Det har betydning for design, syntese og dannelsesmekanismer for Au-nanopartikler og Au-overflader med skræddersyede fysiske og kemiske egenskaber
Jiang, T., Xue, Z., Ford, M., Shaw, J., Cao, X., Tao, Y., Hu, Y. & Huang, W. 2016, 'An ultra-low bandgap diketopyrrolopyrrole (DPP)-based polymer with balanced ambipolar charge transport for organic field-effect transistors', RSC Advances, vol. 6, no. 82, pp. 78720-78726.
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© 2016 The Royal Society of Chemistry.A new A1-A2 type polymer pDTDPP-TTF containing diketopyrrolopyrrole (DPP) and 2-ethylhexyl-3-fluorothieno[3,4-b]thiophene-2-carboxylate (TTF) as the main electron-accepting building blocks has been synthesized via Suzuki cross-coupling polycondensation. The introduction of TTF as an additional electron-deficient unit significantly lowers the LUMO energy level of this DPP containing polymer to -4.37 eV which is beneficial for efficient electron injection and transport. The pDTDPP-TTF polymer shows an ultra narrow optical bandgap of 1.06 eV with a broad absorption spectra covering the visible to near infrared region of up to 1300 nm. Solution-processed OFET devices with pDTDPP-TTF as the active semiconducting layer have been fabricated with the configurations of both bottom-gate bottom-contact (BG-BC) and top-gate bottom-contact (TG-BC). The BG-BC devices with SiO2 as a dielectric exhibit ambipolar behavior with a hole and electron mobility of 1.85 10-4 and 3.55 10-5 cm2 V-1 s-1, respectively. Improved OFET performance has been achieved in TG-BC devices by using PMMA as the dielectric; balanced ambipolar charge transport is obtained with a hole and electron mobility of 6.17 10-3 cm2 V-1 s-1 and 3.13 10-3 cm2 V-1 s-1, respectively. To the best of our knowledge, our work is among the very few examples of ultra-low bandgap semiconducting polymers with balanced ambipolar charge transport properties.
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.
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© 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.
Fair, K.M. & Ford, M.J. 2015, 'Phase transitions and optical properties of the semiconducting and metallic phases of single-layer MoS2', Nanotechnology, vol. 26, no. 43.
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We report density functional theory calculations for single layer MoS2 in its 2H, semiconducting and 1T metallic phases in order to understand the relative stability of these two phases and transition between them in the presence of adsorbed lithium atoms and under compressive strain. We have determined the diffusion barriers between the two phases and demonstrate how the presence of Li adatoms or strain can significantly reduce these barriers. We show that the 2H and 1T structures have the same energy under 15% biaxial, compressive strain. This is the same strain value posited by Lin et al (2014 Nat. Nanotechnology 9 391–396) for their intermediate phase. Calculations of the 1T and 2H permittivity and electron energy loss spectrum are also performed and characterized.
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.
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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.
Reimers, J.R., Panduwinata, D., Visser, J., Chin, Y., Tang, C., Goerigk, L., Ford, M.J., Sintic, M., Sum, T.J., Coenen, M.J.J., Hendriksen, B.L.M., Elemans, J.A.A.W., Hush, N.S. & Crossley, M.J. 2015, 'A priori calculations of the free energy of formation from solution of polymorphic self-assembled monolayers', Proceedings of the National Academy of Sciences of the United States of America, vol. 112, no. 45, pp. E6101-E6110.
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First-principles free energy calculations, characterizing polymorphism of self-assembled monolayers (SAMs) of porphyrin molecules formed from solution onto graphite, are performed using efficient methods previously applied only to small-molecule reactivity. SAM structures are typically optimized in the absence of solvent using density functional theory embodying explicit dispersion corrections. Added then are dispersion-dominated implicit solvation energies and SAM formation entropies derived from both molecular and phonon vibration frequencies. Scanning tunneling microscopy (STM) images are measured, and polymorph formation free energies are approximated. Close parallels between experiment and theory support the hypothesis that the first seconds of SAM formation are under thermodynamic control, despite formed SAMs being kinetically trapped. Polymorphism is associated with large opposing changes to entropy and substratemolecule and solventmolecule interaction energies.
Fair, K., Arnold, M.D. & Ford, M. 2014, 'Determination of the elastic properties of graphene by indentation and the validity of classical models of indentation', Journal Of Physics: Condensed Matter, vol. 26, p. 015307.
Arnold, M.D., Blaber, M.G. & Ford, M. 2014, 'Local plasmon resonances of metal-in-metal core-shells', Optics Express, vol. 22, no. 3, p. 3186.
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Callsen, G., Wagner, M.R., Reparaz, J.S., Nippert, F., Kure, T., Kalinowski, S., Hoffmann, A., Ford, M.J., Phillips, M.R., Dalmau, R.F., Schlesser, R., Collazo, R. & Sitar, Z. 2014, 'Phonon pressure coefficients and deformation potentials of wurtzite AlN determined by uniaxial pressure-dependent Raman measurements', PHYSICAL REVIEW B, vol. 90, no. 20.
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Fair, K., Cui, X., Li, L., Shieh, C., Zheng, R., Liu, Z., Delley, B., Ford, M., Ringer, S.P. & Stampfl, C.M. 2013, 'Hydrogen Adsorption Capacity Of Adatoms On Double Carbon Vacancies Of Graphene: A Trend Study From First Principles', Physical Review B, vol. 87, no. 1, pp. 1-7.
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Structural stability and hydrogen adsorption capacity are two key quantities in evaluating the potential of metal-adatom decorated graphene for hydrogen storage and related devices. We have carried out extensive density functional theory calculations for the adsorption of hydrogen molecules on 12 different adatom (Ag, Au, Ca, Li, Mg, Pd, Pt, Sc, Sr, Ti, Y, and Zr) decorated graphene surfaces where the adatoms are found to be stabilized on double carbon vacancies, thus overcoming the clustering problem that occurs for adatoms on pristine graphene. Ca and Sr are predicted to bind the greatest number, namely six, of H2 molecules. We find an interesting correlation between the hydrogen capacity and the change of charge distribution with increasing H2 adsorption, where Ca, Li, Mg, Sc, Ti, Y, Sr, and Zr adatoms are partial electron donors and Ag, Au, Pd, and Pt are partial electron acceptors. The 18-electron rule for predicting maximum hydrogen capacity is found not to be a reliable indicator for these systems
Setiadi, J., Arnold, M.D. & Ford, M. 2013, 'Li-ion adsorption and diffusion on 2D Silicon with defects: a first principles study', ACS Applied Materials & Interfaces, vol. 5, no. 21, pp. 10690-10695.
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Using first principles calculations we investigate the binding and diffusion of Li on silicene and evaluate the prospects for application to Li-ion batteries. We find that the defect formation energy for silicene is half that of graphene, showing that silicene is more likely to contain defects. The overall lithium adsorption energy on silicene with defects is greater than the bulk cohesive energy of lithium giving stability for use in storage. Our results predict high mobility for lithium atoms on the surface of silicene with energy barriers in the range of 0.280.30 eV. Further, we find that the diffusion barrier through silicene is significantly lower than the diffusion barrier through graphene, with a value of 0.05 eV for the double vacancy and 0.88 eV for the single vacancy. The low diffusion barriers, both on the surface and through the hollow site, suggest a suitable material for use in Li-ion batteries.
Scheurer, M.S., Arnold, M.D., Setiadi, J. & Ford, M. 2012, 'Damping of plasmons of closely coupled sphere chains due to disordered gaps', Journal of Physical Chemistry C, vol. 116, no. 1, pp. 1335-1343.
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The damping of plasmons due to structural disorder may have important practical consequences. Here, we use spherical harmonic expansions to quantify the damping of plasmons of ensembles of closely coupled sphere chains with moderately disordered gaps. We show that the quadratic shift of average resonance position due to disorder is maintained in the transition from weak to close coupling, but the sensitivity to disorder increases. Further, we find that although the main peak is most often damped and broadened by disorder, it is possible for the optical extinction of disordered gold chains to increase slightly due to red-skew into a region with more favorable metal properties.
Su, D., Ford, M. & Wang, G. 2012, 'Mesoporous NiO crystals with dominantly exposed {110} reactive facets for ultrafast lithium storage', Scientific Report, vol. 2, p. 924.
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Faceted crystals with exposed highly reactive planes have attracted intensive investigations for applications such as hydrogen production, enhanced catalytic activity, and electrochemical energy storage and conversion. Herein, we report the synthesis of mesoporous NiO crystals with dominantly exposed {110} reactive facets by the thermal conversion of hexagonal Ni(OH)2 nanoplatelets. When applied as anode materials in lithium-ion batteries, mesoporous NiO crystals exhibit a high reversible lithium storage capacity of 700âmAh gâ1 at 1 C rate in 100âcycles and an excellent cyclability. In particular, the dominantly exposed {110} reactive facets and mesoporous nanostructure of NiO crystals lead to ultrafast lithium storage, which mimics the high power delivery of supercapacitors.
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.
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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.
Jamting, A., Cullen, J.C., Coleman, V., Lawn, M., Herrmann, J., Miles, J. & Ford, M. 2011, 'Systematic Study Of Bimodal Suspensions Of Latex Nanoparticles Using Dynamic Light Scattering', Advanced Powder Technology, vol. 22, no. 2, pp. 290-293.
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Determining the size of nanoparticles accurately, quickly and easily is becoming more and more important as the use of such particles increases. One of the common techniques for measuring the size of particles in suspension is dynamic light scattering (D
Blaber, M.G., Arnold, M.D. & Ford, M. 2010, 'Designing materials for plasmonic systems: the alkali-noble intermetallics', Journal Of Physics: Condensed Matter, vol. 22, no. 9, pp. 1-8.
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We use electronic structure calculations based upon density functional theory to search for ideal plasmonic materials among the alkalinoble intermetallics. Importantly, we use density functional perturbation theory to calculate the electronphonon interaction and from there use a first order solution to the Boltzmann equation to estimate the phenomenological damping frequency in the Drude dielectric function. We discuss the necessary electronic features of a plasmonic material and investigate the optical properties of the alkalinoble intermetallics in terms of some generic plasmonic system quality factors. We conclude that at low negative permittivities, KAu, with a damping frequency of 0.0224 eV and a high optical gap to bare plasma frequency ratio, outperforms gold and to some extent silver as a plasmonic material. Unfortunately, a low plasma frequency (1.54 eV) reduces its utility in modern plasmonics applications. We also discuss, briefly, the effect of local fields on the optical properties of these materials.
Arnold, M.D., Blaber, M.G., Ford, M. & Harris, N. 2010, 'Universal scaling of local plasmons in chains of metal spheres', Optics Express, vol. 18, no. 7, pp. 7528-7542.
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The position, width, extinction, and electric field of localized plasmon modes in closely-coupled linear chains of small spheres are investigated. A dipole-like model is presented that separates the universal geometric factors from the specific metal permittivity. An electrostatic surface integral method is used to deduce universal parameters that are confirmed against results for different metals (bulk experimental Ag, Au, Al, K) calculated using retarded vector spherical harmonics and finite elements. The mode permittivity change decays to an asymptote with the number of particles in the chain, and changes dramatically from 1/f3 to 1/f1/2 as the gap fraction (ratio of gap between spheres to their diameter), f, gets smaller. Scattering increases significantly with closer coupling. The mode sharpness, strength and electric field for weakly retarded calculations are consistent with electrostatic predictions once the effect of radiative damping is accounted for.
Denisyuk, A.I., Adamo, G., MacDonald, K.F., Edgar, J.A., Arnold, M.D., Myroshnychenko, V., Ford, M., Javier, G.D.A.F. & Zheludev, N.I. 2010, 'Transmitting Hertzian Optical Nanoantenna with Free-Electron Feed', Nano Letters, vol. 10, no. 9, pp. 3250-3252.
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A pair of coupled gold nanorods excited by a beam of free electrons acts as a transmitting Hertzian antenna in the optical part of the spectrum. Significantly enhanced resonant emission is observed from the antenna when the electron beam is injected around the junction between the rods, where the local density of electromagnetic states is elevated.
Blaber, M.G., Arnold, M.D. & Ford, M.J. 2010, 'A review of the optical properties of alloys and intermetallics for plasmonics', JOURNAL OF PHYSICS-CONDENSED MATTER, vol. 22, no. 14.
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Blaber, M.G., Arnold, M.D. & Ford, M. 2009, 'Search for the ideal plasmonic nanoshell: the effects of surface scattering and alternatives to gold and silver', Journal of Physical Chemistry C, vol. 113, no. 8, pp. 3041-3045.
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Blaber, M.G., Arnold, M.D. & Ford, M. 2009, 'Optical properties of intermetallic compounds from first principles calculations: a search for the ideal plasmonic material', Journal Of Physics: Condensed Matter, vol. 21, pp. 144211-144218.
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First principles calculations have been used to predict the optical properties for a range of intermetallic compounds for which little or no experimental optical data are currently available. Density functional theory combined with the random phase approximation is used to calculate the dielectric functions for these compounds. The aim of this work is to investigate how the band edge and plasma frequency vary with composition in order to identify materials with promising plasmonic properties. Towards this end the intermetallic compounds chosen are composed of elements which on their own have reasonable optical properties for plasmonic applications. The position of the band edge relative to the plasma frequency is most favourable in the simple binary compounds formed from the alkali plus noble metals NaAu, KAu and KAg. In particular, for KAu the band edge and plasma frequency occur at almost the same frequency, and hence the imaginary part of the dielectric function is practically zero for frequencies below the plasma frequency. In addition, the plasma frequency in this compound is at relatively low frequency, promising a material with strong plasmon response in the infrared.
Coutts, M.J., Cortie, M.B., Ford, M. & McDonagh, A.M. 2009, 'Rapid and Controllable Sintering of Gold Nanoparticle Inks at Room Temperature Using a Chemical Agent', Journal of Physical Chemistry C, vol. 113, no. 4, pp. 1325-1328.
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We show that oxidation of protective thiol ligands and the exothermic reduction of surface area are important factors in the sintering of thiol-stabilized gold nanoparticle films. We also present a chemical treatment to achieve sintering of gold nanoparticles at room temperature. The process is facilitated by the remarkable enthalpy of reaction arising from the reduction of the surface area of the nanoparticles.
Ford, M., Russo, S. & Gale, J.D. 2009, 'Proceedings of the International Conference on Nanoscience and Nanotechnology (Melbourne, 25-29 February 2008) PREFACE', Journal Of Physics: Condensed Matter, vol. 21, no. 14, p. 140301.
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The International Conference on Nanoscience and Nanotechnology is held bi-annually in Australia, supported by the Australian Research Council and Australian Nanotechnology Network. The purpose of the conference is to provide a forum for discussion about all aspects of nanoscience and nanotechnology, to enable young Australian researchers a chance to meet and engage with leading global scientists in the field, and to set up the exchange mechanisms and collaborations that will enable the field to continue to develop and flourish.
Harris, N., Arnold, M.D., Blaber, M.G. & Ford, M. 2009, 'Plasmonic resonances of closely coupled gold nanosphere chains', Journal of Physical Chemistry C, vol. 113, no. 7, pp. 2784-2791.
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The optical properties of an ordered array of gold nanospheres have been calculated using the T-matrix method in the regime where the near-fields of the particles are strongly coupled. The array consists of a one-dimensional chain of spheres of 15 nm diameter where the number of spheres in the chain and interparticle spacing is varied. Calculations have been performed with chains up to 150 particles in length and with an interparticle spacing between 0.5 and 30 nm. Incident light polarized along the axis of the chain (longitudinal) and perpendicular (transverse) to it are considered, and in the latter case for wavevectors along and perpendicular to the chain axis. For fixed chain length the longitudinal plasmon resonance red shifts, relative to the resonance of an isolated sphere, as the interparticle spacing is reduced. The shift in the plasmon resonance does not appear to follow an exponential dependence upon gap size for these extended arrays of particles. The peak shift is inversely proportional to the distance, a result that is consistent with the van der Waals attraction between two spheres at short range, which also varies as 1/d. The transverse plasmon resonance shifts in the opposite direction as the interparticle gap is reduced; this shift is considerably smaller and approaches 500 nm as the gap tends to zero. Increasing the number of particles in the chain for a fixed gap has a similar effect on the longitudinal and transverse plasmon. In this case, however, the longitudinal plasmon tends toward an asymptotic value with increasing chain length, with the asymptotic value determined by the interparticle spacing. Here, the approach to the asymptote is exponential with a characteristic length of approximately two particles, at small interparticle spacings. This approach to an asymptote as the chain length becomes infinite has been verified in a finite element calculation with periodic boundary conditions.
Harris, N., Arnold, M.D., Blaber, M.G. & Ford, M.J. 2009, 'Plasmonic resonances of closely coupled gold nanosphere chains', Journal of Physical Chemistry C, vol. 113, no. 7, pp. 2784-2791.
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The optical properties of an ordered array of gold nanospheres have been calculated using the T-matrix method in the regime where the near-fields of the particles are strongly coupled. The array consists of a one-dimensional chain of spheres of 15 nm diameter where the number of spheres in the chain and interparticle spacing is varied. Calculations have been performed with chains up to 150 particles in length and with an interparticle spacing between 0.5 and 30 nm. Incident light polarized along the axis of the chain (longitudinal) and perpendicular (transverse) to it are considered, and in the latter case for wavevectors along and perpendicular to the chain axis. For fixed chain length the longitudinal plasmon resonance red shifts, relative to the resonance of an isolated sphere, as the interparticle spacing is reduced. The shift in the plasmon resonance does not appear to follow an exponential dependence upon gap size for these extended arrays of particles. The peak shift is inversely proportional to the distance, a result that is consistent with the van der Waals attraction between two spheres at short range, which also varies as 1/d. The transverse plasmon resonance shifts in the opposite direction as the interparticle gap is reduced; this shift is considerably smaller and approaches 500 nm as the gap tends to zero. Increasing the number of particles in the chain for a fixed gap has a similar effect on the longitudinal and transverse plasmon. In this case, however, the longitudinal plasmon tends toward an asymptotic value with increasing chain length, with the asymptotic value determined by the interparticle spacing. Here, the approach to the asymptote is exponential with a characteristic length of approximately two particles, at small interparticle spacings. This approach to an asymptote as the chain length becomes infinite has been verified in a finite element calculation with periodic boundary conditions. © 2009 American Chemical Society.
Hoft, R.C., Ford, M., Garcia-Suarez, V.M., Lambert, C.J. & Cortie, M.B. 2008, 'The effect of stretching thiyl and ethynyl-Au molecular junctions', Journal of Physics: Condensed Matter, vol. 20, no. 2, pp. 1-9.
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We perform density functional theory (DFT) calculations of the stretching of Au(111)XAu(111) molecular junctions where X is either a thiyl or ethynyl biradical. The equilibrium geometries for the radicals adsorbing on the surface are first calculated and the radicals then placed in the junction geometry. The unit cell is stepwise increased in length and the geometry relaxed at each step. When stretching the ethynyl junction, a single gold atom is detached from the rest of the surface and the goldcarbon bond does not break. In contrast, the goldsulfur bond in the thiyl junction breaks without detaching any gold atoms. This behaviour can be attributed to the enhanced strength of the AuC interaction over the AuS interaction. In both junctions the conductance calculated using the non-equilibrium Green's function formalism (NEGF) decreases as the junction is stretched. After breakage of the AuS bond, the thiyl radical contains an unpaired electron on the sulfur atom and the system is in a spin doublet state. Transmission spectra were calculated for the spin-unpolarized case only; evaluation of the spin-polarized density of states suggests that an enhanced conductance for electrons of one spin type may be observed after the AuS bond is broken.
Ford, M., Hoft, R.C., McDonagh, A.M. & Cortie, M.B. 2008, 'Rectification in Donor-Acceptor Molecular Junctions', Journal Of Physics: Condensed Matter, vol. 20, no. 37, pp. 1-8.
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We perform density functional theory (DFT) calculations on molecular junctions consisting of a single molecule between two Au(111) electrodes. The molecules consist of an alkane or aryl bridge connecting acceptor, donor or thiol endgroups in various combinations. The molecular geometries are optimized and wavefunctions and eigenstates of the junction calculated using the DFT method, and then the electron transport properties for the junction are calculated within the non-equilibrium Green's function (NEGF) formalism. The currentvoltage or i(V) characteristics for the various molecules are then compared. Rectification is observed for these molecules, particularly for the donorbridgeacceptor case where the bridge is an alkane, with rectification being in the same direction as the original findings of Aviram and Ratner (1974 Chem. Phys. Lett. 29 27783), at least for relatively large negative and positive applied bias. However, at smaller bias rectification is in the opposite direction and is attributed to the lowest unoccupied orbital associated with the acceptor group.
Harris, N., Ford, M., Mulvaney, P. & Cortie, M.B. 2008, 'Tunable infrared absorption by metal nanoparticles: The case for gold rods and shells', Gold Bulletin, vol. 41, no. 1, pp. 5-14.
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Nanoparticles of elements such as Au, Al or Ag have optical extinction cross-sections that considerably surpass their geometric cross-sections at certain wavelengths of light. While the absorption and scattering maxima for nanospheres of these elements are relatively insensitive to particle diameter, the surface plasmon resonance of Au nanoshells and nanorods can be readily tuned from the visible into the infrared by changing the shape of the particle. Here we compare nanoshells and nanorods in terms of their ease of synthesis, their optical properties, and their longer term technological prospects as tunable plasmonic absorbers. While both particle types are now routinely prepared by wet chemistry, we submit that it is more convenient to prepare rods. Furthermore, the plasmon resonance and peak absorption efficiency in nanorods may be readily tuned into the infrared by an increase of their aspect ratio, whereas in nanoshells such tuning may require a decrease in shell thickness to problematic dimensions.
Vijayakumar, R., Shivaramu, G., Ramamurthy, N. & Ford, M. 2008, 'Compton scattering study of electron momentum distribution in lithium fluoride using 662 keV gamma radiations', Physica B: Condensed Matter, vol. 403, no. 23-24, pp. 4309-4313.
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Here we report the first ever 137Cs Compton spectroscopy study of lithium fluoride. The spherical average Compton profiles of lithium fluoride are deduced from Compton scattering measurements on poly crystalline sample at gamma ray energy of 662 keV. To compare the experimental data, we have computed the spherical average Compton profiles using self-consistent HartreeFock wave functions employed on linear combination of atomic orbital (HF-LCAO) approximation. The directional Compton profiles and their anisotropic effects are also calculated using the same HF-LCAO approximation. The experimental spherical average profiles are found to be in good agreement with the corresponding HF-LCAO calculations and in qualitative agreement with HartreeFock free atom values. The present experimental isotropic and calculated directional profiles are also compared with the available experimental isotropic and directional Compton profiles using 59.54 and 159 keV gamma-rays.
Cankurtaran, B.O., Gale, J.D. & Ford, M. 2008, 'First principles calculations using density matrix divide-and-conquer within the SIESTA methodology', Journal Of Physics: Condensed Matter, vol. 20, no. 29, pp. 1-12.
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The density matrix divide-and-conquer technique for the solution of KohnSham density functional theory has been implemented within the framework of the SIESTA methodology. Implementation details are provided where the focus is on the scaling of the computation time and memory use, in both serial and parallel versions. We demonstrate the linear-scaling capabilities of the technique by providing ground state calculations of moderately large insulating, semiconducting and (near-) metallic systems. This linear-scaling technique has made it feasible to calculate the ground state properties of quantum systems consisting of tens of thousands of atoms with relatively modest computing resources. A comparison with the existing order-N functional minimization (KimMauriGalli) method is made between the insulating and semiconducting systems.
Ford, M.J., Hoft, R.C., McDonagh, A.M. & Cortie, M.B. 2008, 'Rectification in donor-acceptor molecular junctions', JOURNAL OF PHYSICS-CONDENSED MATTER, vol. 20, no. 37.
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McDonagh, A.M., Zareie, H.M., Ford, M., Barton, C., Ginic-markovic, M. & Matisons, J. 2007, 'Ethynylbenzene monolayers on gold A metal-molecule binding motif derived from a hydrocarbon', Journal Of The American Chemical Society, vol. 129, no. 12, pp. 3533-3538.
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Exposure of a Au(111) surface to ethynylbenzene in solution leads to the formation of a bound monolayer. A chemisorption process occurs to give a stable layer consisting of oxygen-containing hydrocarbon species. Ethynylbenzene itself does not oxidize under the deposition conditions indicating that the gold surface facilitates the oxidation process. Calculations show that ethynylbenzene and its oxidation products phenylacetic acid and phenylxirane have positive bending energies to the gold surface. 1,4- Diethynylbenzene also bind to Au (111) and anchors gold nanoparticles deposited from solution to form dense, semiregular arrays.
Cortie, M.B., Harris, N. & Ford, M. 2007, 'Plasmonic heating and its possible exploitation in nanolithography', Physica B: Condensed Matter, vol. 394, no. 2, pp. 188-192.
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Gold nanoparticles manifest one or more plasmon resonances, resulting in enhanced absorption and scattering of light at the resonant frequencies. The absorbed light is converted to heat. Here we analyze how the resulting localized heat generation might be exploited to generate nanoscale polymer artifacts
Armstrong, N.G., Hoft, R.C., McDonagh, A.M., Cortie, M.B. & Ford, M. 2007, 'Exploring The Performance Of Molecular Rectifiers Limitations And Factors Affecting Molecular Rectification', Nano Letters, vol. 7, no. 10, pp. 3018-3022.
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There has been significant work investigating the use of molecules as nanoscale rectifiers in so-called molecular electronics. However, less attention has been paid to optimizing the design parameters of molecular rectifiers or to their inherent limitati
Cortie, M.B. & Ford, M. 2007, 'A Plasmon-induced Current Loop In Gold Semi-shells', Nanotechnology, vol. 18, no. 23, pp. 1-6.
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We perform a computational investigation of the optical properties of nanoscale gold semi-shells and show how additional plasmon resonances develop as the shape is successively mutated from nanoshell to nano-cup, half-shell and finally to nano-cap. The e
Krishnamurty, S., Shafai, G., Kanhere, D.G., Soule, D.B.B.J. & Ford, M. 2007, 'Ab initio molecular dynamical investigation of the finite temperature behavior of the tetrahedral Au19 and Au20 clusters', Journal of Physical Chemistry A, vol. 111, no. 42, pp. 10769-10775.
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Density functional molecular dynamics simulations have been carried out to understand the finite temperature behavior of Au19 and Au20 clusters. Au20 has been reported to be a unique molecule having tetrahedral geometry, a large HOMO-LUMO energy gap, and an atomic packing similar to that of the bulk gold (Li, J.; et al. Science 2003, 299, 864). Our results show that the geometry of Au19 is exactly identical with that of Au20 with one missing corner atom (called a vacancy). Surprisingly, our calculated heat capacities for this nearly identical pair of gold clusters exhibit dramatic differences. Au20 undergoes a clear and distinct solid-like to liquid-like transition with a sharp peak in the heat capacity curve around 770 K. On the other hand, Au19 has a broad and flat heat capacity curve with continuous melting transition. This continuous melting transition turns out to be a consequence of a process involving a series of atomic rearrangements along the surface to fill in the missing corner atom. This results in a restricted diffusive motion of atoms along the surface of Au19 between 650 to 900 K during which the shape of the ground state geometry is retained. In contrast, the tetrahedral structure of Au20 is destroyed around 800 K, and the cluster is clearly in a liquid-like state above 1000 K. Thus, this work clearly demonstrates that (i) the gold clusters exhibit size sensitive variations in the heat capacity curves and (ii) the broad and continuous melting transition in a cluster, a feature that has so far been attributed to the disorder or absence of symmetry in the system, can also be a consequence of a defect (absence of a cap atom) in the structure.
Hoft, R.C., Ford, M. & Cortie, M.B. 2007, 'Electron tunneling in the presence of adsorbed molecules', Surface Science, vol. 601, no. 24, pp. 5715-5720.
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We perform ab initio density functional theory calculations of the tunneling current through an electrodemoleculeelectrode system with four different small organic molecules, benzenedithiol (BDT), benzenedimethanethiol (XYL), diethynylbenzene (DEB) and dodecanethiol (C12), sandwiched between two gold (111) electrodes. For the XYL molecule, we test the effect of alternate bonding types and sites. Although this reduces the current considerably, it does not account for the orders of magnitude differences between experimental and theoretical results in the literature. We also model a typical STM experimental setup with a gold nanoparticle absorbed on a selfassembled monolayer (SAM) of the molecule with a gap between the nanoparticle and probing tip and show that such a gap could account for these differences. Finally, we describe the effect that the gap has on the ability of STS measurements to distinguish between the i(V) characteristics and thicknesses of self-assembled monolayers of different molecules.
Hoft, R.C., Ford, M. & Cortie, M.B. 2007, 'The effect of reciprocal-space sampling and basis set quality on the calculated conductance of a molecular junction', Molecular Simulation, vol. 33, no. 11, pp. 897-904.
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We perform density functional theory and non-equilibrium Green's function calculations of the conductance of a gold wire and a 1,4-phenylenedimethanethiol (XYL) molecule adsorbed between Au(111) electrodes using the TranSIESTA software package. The effect of varying different computational parameters is investigated. We find that the conductance is more sensitive to the reciprocal-space sampling grid than the quality of the basis set employed. The conductance can vary up to a factor of five as a result of the choice of computational parameters. We report a set of computational parameters that yields a well-converged conductance value.
Ford, M., Soule, D.B.B.J. & Cortie, M.B. 2007, 'Stability of the tetrahedral motif for small gold clusters in the size range 16-24 atoms', Materials Science and Engineering B: Solid State Materials for Advanced Technology, vol. 140, no. 3, pp. 177-181.
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The tetrahedral 20-atom gold cluster is surprisingly stable, and is believed to be the ground state structure as evidenced both by ab initio calculations [1-3] and experiment [3]. This sturcture is very orderd, has no internal atoms and is essentially a small section of fcc-bulk gold cut along four intersecting close-packed (111) planes. We have previously shown that it is at least 0.5eV more stable than the tetrahedral structure represents a deep minimum in the potential energy surface that is isolated from its isomers, gives rise to a well-defined melting point with a melting temperature comparable to bulk gold [4].
Harris, N., Ford, M., Cortie, M.B. & McDonagh, A.M. 2007, 'Laser-induced Assembly Of Gold Nanoparticles Into Colloidal Crystals', Nanotechnology, vol. 18, no. 36, pp. 1-4.
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Micron-sized colloidal crystals comprised of gold nanospheres have been synthesized directly from a gold nanoparticlepermethyl methacrylate colloid by application of a 514 nm laser at 500 mW. An array of colloidal crystals can be created by translation o
Hoft, R.C., Armstrong, N.G., Ford, M. & Cortie, M.B. 2007, 'Ab Initio And Empirical Studies On The Asymmetry Of Molecular Current-voltage Characteristics', Journal of Physics: Condensed Matter, vol. 19, no. 21, pp. 1-14.
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We perform theoretical calculations of the tunnelling current through various small organic molecules sandwiched between gold electrodes by using both a tunnel barrier model and an ab initio transport code. The height of the tunnelling barrier is taken t
Hoft, R.C., Ford, M., McDonagh, A.M. & Cortie, M.B. 2007, 'Adsorption Of Amine Compounds On The Au(111) Surface: A Density Functional Study', Journal Of Physical Chemistry C, vol. 111, no. 37, pp. 13886-13891.
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A Density Functional Theory study of the adsorption energetics of various amine compounds on the gold(111) surface revealed that preferential binding occurs in under-coordinated sites. The largest binding energy is obtained when a gold adatom is placed i
Blaber, M.G., Arnold, M.D., Harris, N., Ford, M. & Cortie, M.B. 2007, 'Plasmon Absorption In Nanospheres: A Comparison Of Sodium, Potassium, Aluminium, Silver And Gold', Physica B: Condensed Matter, vol. 394, no. 2, pp. 184-187.
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The optical absorption for nanospheres made from Na, K, At, Ag and An are compared as a precursor to choosing the ideal metal for use in a negative permittivity (NP) near-field superlens. The relationship between optical absorption of the metal nanospher
Cortie, M.B., Dowd, A., Harris, N. & Ford, M.J. 2007, 'Core-shell nanoparticles with self-regulating plasmonic functionality', PHYSICAL REVIEW B, vol. 75, no. 11.
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Nixon, K.L., Vos, M., Bowles, C. & Ford, M. 2006, 'Measuring the electronic structure of disordered overlayers by electron momentum spectroscopy the CuSi interface', Surface And Interface Analysis, vol. 38, no. 8, pp. 1236-1241.
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The Cu-Si interface was studied by electron momentum spectroscopy. A thick disordered interface is formed if one material is deposited on the other. Electron momentum spectroscopy measures intensity as a function of binding energy and target electron mom
Zareie, H.M., McDonagh, A.M., Edgar, J.A., Ford, M., Cortie, M.B. & Phillips, M. 2006, 'Controlled assembly of 1,4-phenylenedimethanethiol molecular nanostructures', Chemistry Of Materials, vol. 18, no. 9, pp. 2376-2380.
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We present here the first high-resolution scanning tunneling microscope images showing that 1,4phenylenedimethanethiol forms mono- and multilayers on gold(1 11) substrates under particular solution-deposition conditions. The high-resolution images show t
Harris, N., Ford, M. & Cortie, M.B. 2006, 'Optimization of plasmonic heating by gold nanospheres and nanoshells', Journal Of Physical Chemistry B, vol. 110, no. 22, pp. 10701-10707.
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Gold nanoparticles have strong and tunable absorption peaks in their optical extinction spectra, a phenomenon that has recently been exploited to generate localized heating in the vicinity of these particles. However the optimum particle geometry and ill
Bilic, A., Reimers, J.R., Hush, N., Hoft, R.C. & Ford, M. 2006, 'Adsorption Of Benzene On Copper, Silver, And Gold Surfaces', Journal Of Chemical Theory And Computation, vol. 2, no. 4, pp. 1093-1105.
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Cortie, M.B., Xu, X. & Ford, M. 2006, 'Effect of composition and packing configuration on the dichroic optical properties of coinage metal nanorods', Physical Chemistry Chemical Physics, vol. 8, no. 30, pp. 3520-3527.
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When nanorods of Au, Ag and some other elements are aligned with a preferred orientation with respect to light, their optical extinction characteristics become dependent on the polarization and angle of incidence of the light. This effect is explored her
Hoft, R.C., Gale, J.D. & Ford, M. 2006, 'Implementation of a Z-matrix approach within the SIESTA periodic boundary conditions code and its application to surface adsorption', Molecular Simulation, vol. 32, no. 8, pp. 595-600.
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We implement a flexible Z-matrix approach in the density functional theory (DFT) periodic boundary conditions code, SIESTA. This allows a mixture of Z-matrix and Cartesian coordinates to be used for geometry specification and optimisation. In addition, g
Ford, M., Hoft, R.C. & Gale, J.D. 2006, 'Adsorption and dimerisation of thiol molecules on Au(111) using a Z-matrix approach in density functional theory', Molecular Simulation, vol. 32, no. 15, pp. 1219-1225.
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Th adsorption energies of methanethiolate on Au(111) have been calculated using periodic density functional theory (DFT), based on the SIESTA methodology, with an internal coordination implementation for geometry input and sturcture optimisation. Both molecules are covalently boudn with interaction energies of 1.85 and 1.43 eV for methanethiolate and benzenethiolate, respectively. The preferred binding site is slightly offset from the bridge sire i both cases towards the fcc-hollow. The potential energy durfacces (PES) have depths of 0.36 and 0.22 eV, the hollow sites are local maxima in both cases, and there is not barrier to diffusion ofthe molecule at the bridge site. The corresponding dimers are weakly bound for methanethiolate and benzenthiolate, with binding energies of 0.38 and 0.16eV, respectively, and the preferred binding geometry is with the two sulphur atoms close to adjacent atop sites. The barrier to dissociation of the dimer dimethyl disulphide is estimated to like between 0.3 and 0.35eV.
Ford, M., Masens, C.D. & Cortie, M.B. 2006, 'The application of gold surfaces and particles in nanotechnology', Surface Review Letters, vol. 12, no. 2-3, pp. 297-307.
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Gold is widely used in nanotechnology, for example as a substrate in forming self-assembled monolayers or as nanoparticles for their unique optical and chemical properties. In this paper we give an overview of the properties of gold relevant to its potential application in molecular-scale devices and present some of our recent computational predictions. Density functional calculations of molecular adsorption onto gold surfaces were used to investigate the effect of surface symmetry and identify new linking schemes for self-assembled monolayers. Adsorption energies of methythiolate (SCH3) onto the (111), 9100) and (110) surfaces of gold are predicted to be 39.3, 48.4 and 51.1 kcal/mol respectively and demonstrate that selective functionalisation of the surfaces is possible. Phosphine molecules with at least two hydrogen atoms substituted for methyl groups are predicted to form Au-P surface bonds with energies of about 13-20 kcal/mol.
Soule, D.B.B.J., Ford, M. & Cortie, M.B. 2006, 'Melting in small gold clusters: a density functional molecular dynamics study', Journal of Physics: Condensed Matter, vol. 18, no. 1, pp. 55-74.
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Molecular dynamics simulations of the thermal behaviour of gold clusters containing 7, 13 and 20 atoms have been performed. Total energies and forces at each step of the simulation are calculated from first principles using density functional theory. Ion trajectories are then calculated classically from these forces. In each case the global minimum energy structure and a low-lying isomer are used as the starting structures. In most cases, the clusters do not exhibit a sharp transition from a solid-like phase to a liquid-like phase, but rather pass through a region of transformation between structural isomers that extends over a considerable temperature range. Solid-like behaviour is observed in the atomic trajectories of ther simulation at temperatures up to, or above, the bulk melting point. The 20-atom tetrahedral structure is the one exception, showing a sharo transition between solid-like and liquid-like phases at about 1200 K. The starting sturcture used in the simulation is shown to have a considerable effect upon the subsequent thermal behaviour.
Liu, J., Cankurtaran, B.O., Wieczorek, L., Ford, M. & Cortie, M.B. 2006, 'Anisotropic optical properties of semitransparent coatings of gold nanocaps', Advanced Functional Materials, vol. 16, no. 11, pp. 1457-1461.
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An ordered array of cap-shaped gold nanoparticles has been prepared by vapor deposition onto polystyrene nanospheres supported on a glass substrate, The method of fabrication used imparts a significant anisotropy to the geometric and optical properties o
Hoft, R.C., Ford, M. & Cortie, M.B. 2006, 'Prediction of increased tunneling current by bond length stretch in molecular break junctions', Chemical Physics Letters, vol. 429, no. 4-6, pp. 503-506.
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We use ab initio calculations of the tunneling current through a 1,4-phenylenedimethanethiol (XYL) molecule adsorbed between Au(111) electrodes to show that there are circumstances under which tunneling currents can be increased by bond stretching. The e
Ford, M., Cortie, M.B., Maclurcan, D. & Martin, D.K. 2006, 'Real world nanotechnology', Materials Australia, vol. 39, no. 3, pp. 10-12.
There is a degree of uncertainty in the public mind concerning the exact subject matter of nanotechnology. Novels such as Michael Crichtons Prey and the movie Agent Codie Banks have primed many to believe that nanotechnology is about tiny (and rather dangerous) nano-robots. Of course, most technically savvy individuals know better, but because this misconception exists there is an obligation on researchers in this field to communicate a more accurate understanding of the topic to the wider community. The Institute for Nanoscale Technology at the University of Technology, Sydney (UTS) has sought to bridge this gap in understanding.
Ford, M.J., Masens, C. & Cortie, M.B. 2006, 'The application of gold surfaces and particles in nanotechnology', SURFACE REVIEW AND LETTERS, vol. 13, no. 2-3, pp. 297-307.
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Cortie, M.B., Zareie, H.M., Ekanayake, S.R. & Ford, M. 2005, 'Conduction, storage, and leakage in particle-on-SAM nanocapacitors', IEEE Transactions On Nanotechnology, vol. 4, no. 4, pp. 406-414.
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Individual gold nanoparticles exhibit discrete capacitances of the order of 1 aF, and they can be tethered to a conductive substrate using a bi-functional monolayer of a suitable organic molecule. However the conduction, retention and leakage of charge b
Vijayakumar, R., Shivaramu, G., Rajasekaran, L., Ramamurthy, N. & Ford, M. 2005, 'Compton profile of polycrystalline sodium chloride and sodium fluoride', Nuclear Instruments & Methods In Physics Research Section B-Beam Interactions With Materials And Atoms, vol. 234, no. 3, pp. 185-193.
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We present here the Compton profile (CP) of polycrystalline sodium chloride and sodium fluoride. Our results consists of spherical average Compton profile based on measurements and calculation of spherical average Compton profile, directional Compton pro
Hale, P.S., Maddox, L.M., Shapter, J., Voelcker, N., Ford, M. & Waclawik, E.R. 2005, 'Growth kinetics and modeling of ZnO nanoparticles', Journal Of Chemical Education, vol. 82, no. 5, pp. 775-778.
This article describes a method to measure the growth kinetics of a zinc oxide colloid. Using common instrumentation such as UVvis spectroscopy, the cut-off wavelength can be determined and hence, the particle size can be estimated. Using existing models of colloidal nanoparticle properties, the absorbance is modeled and compared to the experimental curves. The effect of different parameters in the model such as particle size, refractive index, and solvent type are investigated and conclusions drawn about the nature of nanoparticulate systems.
Liu, J., McCredie, G., Ford, M., Wieczorek, L. & Cortie, M.B. 2005, 'Investigation of the optical properties of hollow aluminium 'nano-caps'', Nanotechnology, vol. 16, no. 12, pp. 3023-3028.
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A colloidal suspension of hollow aluminium, cap-shaped nanoparticles ('nano-caps'_ can be conveniently produced by evaporation of aluminium onto a spin-coated layer of polystyrene nanoparticles (PSNPs), followed by sonication and dissolution of the polymer template. Although ordinary spherical aluminium nanoparticles have a plasmon resonance in the ultra-violet, the 'nano-caps' show plasmon absorption between 700 and 1200 nm due to their geometry. The position of their extinction peaks can be tuned by varying the thickness of the aluminium and the shape of the nano-cap. The optical properties of these shapes were modelled using the discrete dipole approximation method, which confirmed that the 'caps'have very significantly red-shifted absorbance and scattering compared to spheres. This finding suggests that aluminium nano-caps might compete with gold and silver nanoparticles in applciations requiring absorption in the near infrared.
Masens, C.D., Ford, M. & Cortie, M.B. 2005, 'The effect of surface symmetry on the adsorption energetics of SCH3 on gold surfaces studied using Density Functional Theory', Surface Science, vol. 580, no. 1-3, pp. 19-29.
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Adsorption of methanethiol onto the three, high symmetry gold surfaces has been studied at the density functional level using a linear combination of atomic orbitals approach. In all three cases the bond energy between the thiolate radical and surface is
Ford, M., Hoft, R.C. & McDonagh, A.M. 2005, 'Theoretical study of ethynylbenzene adsorption on Au(111) and implications for a new class of self-assembled monolayer', Journal Of Physical Chemistry B, vol. 109, no. 43, pp. 20387-20392.
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Density functional calculations of the adsorption of ethynylbenzene on the Au(I 11) surface show that, after cleavage of the C-H bond, the terminal carbon makes a strong covalent bond to the surface. The bond energy is shown to be about 70 kcal(.)mol(-1)
Rogers, B.L., Shapter, J. & Ford, M. 2004, 'Ab initio study of benzene adsorption on the Cu(110) surface and simulation of STM images', Surface Science, vol. 548, no. 1-3, pp. 29-40.
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The adsorption of benzene molecules onto the Cu(1 1 0) surface has been studied using a crystalline linear combination of atomic orbitals approximation (LCAO). Adsorption energetics have been modelled at both the HartreeFock (HF) and density functional theory (DFT) level, and scanning tunneling microscope (STM) images generated for the preferred adsorption geometry. The calculated binding energies are strongly dependent upon basis set superposition errors (BSSE). As expected HF provides a relatively poor description of this loosely bound system, and is found to be unbound when BSSE is taken into account. Inclusion of electron correlation through DFT methods gives an optimised binding energy of 106 kJ mol-1 with the benzene molecule occupying a bridging site between the rows of surface copper atoms and an adsorption height of approximately 2 Å. This figure takes account of relaxation of benzene upon adsorption with the hydrogen atoms tilting away from the surface. Our predicted energetics compare favourably with previous theoretical studies using cluster methods and experimental binding energies determined from temperature programmed desorption (TPD). We have also simulated scanning tunneling microscope (STM) images using the Tersoff and Hamann method and compare our results with recent experimental measurements. Our simulation suggests the experimental image results from a benzene dimer rather than an isolated molecule.
Maclurcan, D., Ford, M. & Cortie, M.B. 2004, 'The confusion surrounding nanotechnology', Materials Australia, vol. 37, no. 2, pp. 24-25.
Maclurcan, D., Ford, M. & Cortie, M.B. 2004, 'Rectifying Nanotechnology Confusion and Redirecting Focus', The Physicist, vol. 41, no. 3, pp. 84-85.
Bolorizadeh, M.A., Sashin, V.A., Kheifets, A.S. & Ford, M. 2004, 'Electronic Band structure of calcium oxide', Journal of Electron Spectroscopy, vol. 141, no. 1, pp. 27-38.
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We employed electron momentum spectroscopy (EMS) to measure the bulk electronic structure of calcium oxide. We extracted the electron momentum density (EMD), density of occupied states (DOS), band dispersions, bandwidths and intervalence bandgaps from the data. The results are compared with calculations based on the full potential linear muffin-tin orbital (FP-LMTO) approximation. While the bandwidths of 0.6 ± 0.2 and 1.2 ± 0.1 eV for the s- and p-bands, respectively, and their dispersions agree well with the LMTO calculation, the relative intensity of the two bands is at odds with the theory. The measured intervalence bandgap at the ?-point of 16.5 ± 0.2 eV is larger by 2.1 eV than that from the LMTO calculation. The experimental bandwidth of the Ca 3p semi-core level of 0.7 ± 0.1 eV agrees with the LMTO prediction. The measured bandgap between this level and the s-band is 3.6 ± 0.2 eV. The Ca 3s3p level splitting is in excellent agreement with the literature.
Ekanayake, S.R., Ford, M. & Cortie, M.B. 2004, 'Metal-insulator-metal (MIM) nanocapacitors and effects of material properties on their operation', Materials Forum, vol. 27, pp. 15-20.
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Rogers, B.L., Shapter, J. & Ford, M. 2004, 'Absorption energetics and simulation of STM images for fluorobenzene on the Cu(110) surface', Modelling Simulation in Materials Science and Engineering, vol. 12, pp. 1109-1120.
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Smith, G., Ford, M., Masens, C.D. & Muir, J.G. 2004, 'Energy-efficient coatings in the nanohouse initiative', Current Applied Physics, vol. 4, no. 2-4, pp. 381-384.
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The University of Technology Sydney (UTS), in collaboration with CSIRO has created the NanohouseTM Initiative, a concept that serves as the conceptual framework for various pedagogical, scientific, architectural and engineering activities at the University. Housing is a significant item in both personal and regional budgets, and the NanohouseTM therefore serves as a powerful vehicle for demonstrating nanotechnologies. One of the major energy-efficient components of the NanohouseTM are nanoengineered coatings and films for transparent and translucent surfaces that modify their optical properties. These nanostructured materials can provide wavelength-selective control of reflection, absorption and transmission of light as well as angular selectivity for directional control, making it possible to design houses that have very large windows and skylights, but which nevertheless remain cool in summer and warm in winter. We have already made significant progress towards the development of these nanotechnologies. In this paper will be discuss the design and performance of these optically controllable nanocoatings and their application to the Nanohouse
Ford, M. & Cortie, M.B. 2004, 'Nanotechnology, nanoscience and nanohype', Chemistry in Australia, vol. 73, no. 3, p. 2.
Ekanayake, S.R., Cortie, M.B. & Ford, M. 2004, 'Design of nanocapacitors and associated materials challenges', Current Applied Physics, vol. 4, no. 2-4, pp. 250-254.
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The International Technology Roadmap for Semiconductors (ITRS) projects that the spatial resolution of feature sizes in integrated circuits is rapidly approaching nanoscopic dimensions. Consequently, there is an active interest in the design of nanoscale circuit elements such as transistors, resistors, and capacitors. The properties of materials used to fabricate capacitors pose an important design factor, as with all circuit elements. We analyze the critical materials properties that would influence engineering nanocapacitors (nanoscopic capacitors), and show that at nanoscale, dielectric properties (dielectric constant, dielectric strength, and dielectric relaxation) determine the practicality of such capacitors.
Waclawik, E.R., Ford, M., Hale, P.S., Shapter, J. & Voelcker, N. 2004, 'Liquid-crystal displays: Fabrication and measurement of a twisted nematic liquid-crystal cell', Journal Of Chemical Education, vol. 81, no. 6, pp. 854-858.
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Examples of technologies that utilize the liquid crystalline phase of matter are not difficult to find. The liquid-crystal display is the most common application: twisted nematic liquid-crystal displays are found in digital wristwatches, microwave ovens, mobile phones, and video recorders. Worldwide, sales of flat-screen liquid-crystal displays have been projected to reach $47 billion in 2004 (1). With this in mind, intense efforts by researchers in industry and in academia continue to be made into the synthesis of new liquid-crystal compounds and the characterization of their properties (2). Applications of polymerizable liquid crystals have also been of great interest since the discovery of Kevlar and Nomex by Stephanie Kwolek at Du Pont. The casting of nanostructured and nanocomposite materials such as periodic mesoporous metals and metal alloys from lyotropic liquid crystals is another interesting materials science application of ordered mesophases (3, 4). Despite these advances, undergraduate chemistry students are still unlikely to encounter liquid crystals in the course of their experimental studies (5).
Mikajlo, E.A., Dorsett, H.E. & Ford, M. 2004, 'Trends in the band structures of the group-I and -II oxides', Journal Of Chemical Physics, vol. 120, no. 22, pp. 10799-10806.
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Measured and calculated band structures for the six lightest group-I and -II oxides are reported. Band structures have been measured using electron momentum spectroscopy, a technique that maps the ground-state occupied orbitals resolved both in energy and momentum. Measurements are compared with first-principles calculations carried out within the linear combination of atomic orbitals approximation using both HartreeFock (HF) and density functional (DFT) methods. Three DFT functionals are used representative of the local density approximation, the generalized gradient approximation, and a hybrid method incorporating exact exchange. The calculated O 2p bandwidths and O 2p2s band gaps generally scale linearly with the inverse of the oxygenoxygen separation squared, but consistently show an anomaly at Li2O. These trends, including the anomaly, are also observed in the experimental data. HF calculations consistently overestimate the oxygen 2p2s band gap by almost a factor of two. Measured band gaps lie within the range of the three DFT functionals employed, with evidence that the description of exchange becomes more important as the cation size increases. Both HF and DFT calculations overestimate the oxygen valence bandwidths, with DFT giving more accurate predictions. Both observed and calculated bandwidths converge as the cation size increases, indicating that exchange-correlation effects become less important as the metallic ion becomes larger
Soule, D.B.B.J., Ford, M. & Cortie, M.B. 2004, 'Low energy structured of gold nanoclusters in the size range 3-38 atoms', Journal of Molecular Structure, vol. 686, no. 1-3, pp. 193-205.
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Using a combination of first principles calculations and empirical potentials we have undertaken a systematic study of the low energy structures of gold nanoclusters containing from 3 to 38 atoms. A Lennard-Jones and many-body potential have been used in the empirical calculations, while the first principles calculations employ an atomic orbital, density functional technique. For the smaller clusters (n=35) the potential energy surface has been mapped at the ab initio level and for larger clusters an empirical potential was first used to identify low energy candidates which were then optimised with full ab initio calculations. At the DFT-LDA level, planar structures persist up to six atoms and are considerably more stable than the cage structures by more than 0.1 eV/atom. The difference in ab initio energy between the most stable planar and cage structures for seven atoms is only 0.04 eV/atom. For larger clusters there are generally a number of minima in the potential energy surface lying very close in energy. Furthermore our calculations do not predict ordered structures for the magic numbers n=13 and 38. They do predict the ordered tetrahedral structure for n=20. The results of the calculations show that gold nanoclusters in this size range are mainly disordered and will likely exist in a range of structures at room temperature.
Sashin, V.A., Bolorizadeh, M.A., Kheifets, A.S. & Ford, M. 2003, 'Electronic band structure of beryllium oxide', Journal of Physics: Condensed Matter, vol. 15, no. 21, pp. 3567-3581.
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The energymomentum resolved valence band structure of beryllium oxide has been measured by electron momentum spectroscopy (EMS). Band dispersions, bandwidths and intervalence bandgap, electron momentum density (EMD) and density of occupied states have been extracted from the EMS data. The experimental results are compared with band structure calculations performed within the full potential linear muffin-tin orbital approximation. Our experimental bandwidths of 2.1 ± 0.2 and 4.8 ± 0.3 eV for the oxygen s and p bands, respectively, are in accord with theoretical predictions, as is the s-band EMD after background subtraction. Contrary to the calculations, however, the measured p-band EMD shows large intensity at the ? point. The measured full valence bandwidth of 19.4 ± 0.3 eV is at least 1.4 eV larger than the theory. The experiment also finds a significantly higher value for the p-to-s-band EMD ratio in a broad momentum range compared to the theory.
Soule, D.B.B.J., Dorsett, H.E. & Ford, M. 2003, 'The electronic structure of Be and BeO: benchmark EMS measurements and LCAO calculations', Journal Of Physics And Chemistry Of Solids, vol. 64, no. 3, pp. 495-505.
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The electronic band structures of Be and BeO have been measured by transmission electron momentum spectroscopy (EMS). The low atomic number of beryllium and the use of ultrathin solid films in these experiments reduce the probability of electron multiple scattering within the sample, resulting in very clean `benchmark measurements for the EMS technique. Experimental data are compared to tight-binding (LCAO) electronic structure calculations using HartreeFock , and local density (LDA-VWN), gradient corrected (PBE) and hybrid (PBE0) density functional theory. Overall, DFT calculations reproduce the EMS data for metallic Be reasonably well. PBE predictions for the valence bandwidth of Be are in excellent agreement with EMS data, provided the calculations employ a large basis set augmented with diffuse functions. For BeO, PBE calculations using a moderately sized basis set are in reasonable agreement with experiment, slightly underestimating the valence bandgap and overestimating the O(2s) and O(2p) bandwidths. The calculations also underestimate the EMS intensity of the O(2p) band around the ?-point. Simulation of the effects of multiple scattering in the calculated oxide bandstructures do not explain these systematic differences.
Shapter, J., Hale, P.S., Maddox, L.M., Ford, M. & Waclawik, E.R. 2003, 'Teaching undergraduate nanotechnology', World Transactions on Engineering and Technology Education, vol. 2, no. 2, pp. 299-302.
Mikajlo, E.A., Nixon, K.L. & Ford, M. 2003, 'Electron momentum spectroscopy and linear combination of atomic orbitals calculation of bulk Na2O', Journal of Physics: Condensed Matter, vol. 15, no. 13, pp. 2155-2168.
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This paper presents an experimental measurement of the electronic structure of Na2O in the solid phase using electron momentum spectroscopy and compares the results with ab initio calculations performed within the linear combination of atomic orbitals (LCAO) approximation. While HartreeFock (HF) can reproduce elastic properties we find it overestimates splitting of the oxygen valence bands by around 30% and the width of the O 2p band by a factor of 2. Our experimental values are 15.85 ± 0.2 and 0.6 ± 0.2 eV for these two quantities, respectively. Density functional methods are significantly better, with the hybrid functional PBE0 predicting the oxygen bandgap to within the experimental error. PBE0 also gives the best estimate of the Na core level energies. In contrast, HF performs best for the splitting between the oxygen and sodium bands. Our experimental values of 32.85 ± 0.2 and 27.45 ± 0.2 eV for the Na 2pNa 2s and O 2pNa 2p splittings agree well with previous measurements. Distribution of electron density both within the bands and between the bands is not reproduced by any of the computational methods employed.
Mikajlo, E.A. & Ford, M. 2003, 'Energy and momentum resolved band structure of K2O: electron momentum spectroscopy and linear combination of atomic orbitals calculation', Journal of Physics: Condensed Matter, vol. 15, no. 41, pp. 6955-6968.
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This paper details an experimental and theoretical investigation into the electronic structure of the highly ionic, alkali oxide, potassium oxide (K2O). The experiments were carried out using the relatively new technique of electron momentum spectroscopy. This is an electron impact technique that is capable of measuring the electron intensity distribution as a function of energy and momentum. Calculations were performed within the linear combination of atomic orbitals approximation using both HartreeFock and density functional theory formalisms. We have been able to map the band dispersions and intensities in the oxygen valence bands and potassium 3p and 3s bands for the first time. Overlap of the O 2s and K 3p binding energy peaks makes it difficult to extract the band gaps involving either of these bands. The O 2p and K 3s peaks are resolved, however, and we observe a gap of 30.4 ± 0.2 eV. This value is reproduced by the PBE0 calculation. Intensities within the s bands are reproduced well by all our calculations, whereas the observed p bands show anomalous intensity at the ?-point, which is not present in any of the calculations.
Mikajlo, E.A., Nixon, K.L., Coleman, V. & Ford, M. 2002, 'The Electronic Band Structure of Li2O: Testing Theoretical Predictions using Electron Momentum Spectroscopy', Journal of Physics: Condensed Matter, vol. 14, no. 13, pp. 3587-3598.
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Using the technique of electron momentum spectroscopy (EMS) we have measured the oxygen 2p- and 2s-derived valence bands and lithium 1s-derived core level in lithium oxide. All three sets of bands have been measured in a single experiment allowing the energy gap between the bands to be determined. At the point the O(2p)-O(2s) band gap is measured to be 16.1?0.2 eV, and the O(2s)-Li(1s) band gap is 34.3?0.2 eV. We can also determine bandwidths since EMS measures the full band structure directly, resolved both in energy and momentum. As expected, the O(2s) and Li(1s) bands are essentially non-dispersing, while the O(2p) has an observed width of 1.6?0.2 eV. The experiment is compared with calculations using the linear combination of atomic orbitals approach. At the Hartree-Fock (HF) level these calculations overestimate the gap between the valence bands and the width of the O(2p) band. The three density functional methods used give a reduced intervalence band gap and bandwidth. The hybrid gradient corrected method, PBE0 (where PBE stands for `Perdew-Burke-Ernzerhof'), gives the closest agreement for the band gap at 16.7 eV, while the gradient corrected method, PBE, gives the best value for the bandwidth at 2.0 eV. At all levels the O(2s)-Li(1s) gap is underestimated; HF gives the closest agreement at 31.8 eV.
Shapter, J., Ford, M., Maddox, L.M. & Waclawik, E.R. 2002, 'Teaching Undergraduates Nanotechnology', International Journal of Engineering Education, vol. 18, no. 5, pp. 512-518.
The first nanotechnology undergraduate degree in Australia was established at Flinders University two years ago. In this paper we present our experience of developing and delivering this degree in a climate where `traditional' physical sciences are under considerable strain. We will discuss the motivation for this initiative, structure of the established course, and educational issues relating to its development.
Shapter, J.G., Ford, M.J., Maddox, L.M. & Waclawik, E.R. 2002, 'Teaching undergraduates nanotechnology', International Journal of Engineering Education, vol. 18, no. 5 SPEC., pp. 512-518.
The first nanotechnology undergraduate degree in Australia was established at Flinders University two years ago. In this paper we present our experience of developing and delivering this degree in a climate where 'traditional' physical sciences are under considerable strain. We will discuss the motivation for this initiative, structure of the established course, and educational issues relating to its development.
Sashin, V.A., Bolorizadeh, M.A., Kheifets, A.S. & Ford, M. 2001, 'Conduction band electronic structure of metallic beryllium', Journal of Physics: Condensed Matter, vol. 13, pp. 4203-4219.
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Ford, M., Dorsett, H.E. & Brunger, M.J. 2001, 'Applications of electron momentum spectroscopy in the study of matter', Trends in Applied Spectroscopy, vol. 3, pp. 145-180.
Sashin, V.A., Bolorizadeh, M.A. & Ford, M. 2001, 'Time-resolved study of beryllium surface reactions using electron momentum spectroscopy of the core-level', Surface Science, vol. 495, no. 1, pp. 35-43.
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We have measured the binding energy of the Be1s core-level in metallic beryllium using an electron-impact ionisation technique--electron momentum spectroscopy (EMS). The value we obtain, 111.7+/-0.1 eV, is in good agreement with previous results. We have also determined the chemical shift of the core level in an oxygen environment to be 2.68+/-0.06 eV. Using the same technique, we have followed the evolution of the core-level peak as Be undergoes surface reaction induced by background gases present in the vacuum (mainly water vapour and nitrogen). The core-level peak intensities as a function of time clearly show that reaction of the Be surface progresses in two distinct steps. The initial relatively rapid stage progresses up to a coverage of around 18 L of H2O and N2 after which the onset of a slower reaction process is observed. These results demonstrate the ability of EMS to provide time-resolved electronic structure measurements as a solid undergoes chemical modification.
Sashin, V.A., Canney, S., Ford, M., Bolorizadeh, M.A., Oliver, D. & Kheifets, A.S. 2000, 'Energy-resolved Momentum Densities For The Valence Band Of A Nanoscale Si Single Crystal', Journal of Physics: Condensed Matter, vol. 12, no. 2, pp. 125-136.
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We have measured the energy- and momentum-resolved band structure, and ground state of occupation of the bands, for a crystalline silicon sample along the ( 100) and ( 110) directions. Band structures were determined directly by the technique of electron momentum spectroscopy (EMS) for a self-supporting Si membrane with a thickness of approximately 7 nm. We compare our experimental results with nb initio calculations for bulk crystalline silicon performed within the linear muffin tin orbital approximation. Qualitative agreement is seen between experiment and theory for the main valence band peak. Additional intensity is observed in the measurement on either side of the main peak and is attributed mainly to multiple-scattering events. Satellite structure could also be present in these additional features, although there is no direct evidence for this.
Sashin, V.A., Dorsett, H.E., Bolorizadeh, M.A. & Ford, M. 2000, 'The Valence Band Structures Of Beo, Mgo, And Cao', Journal Of Chemical Physics, vol. 113, no. 18, pp. 8175-8182.
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We have performed direct measurements of the valence band structures of the light alkaline earth oxides BeO, MgO, and CaO using electron momentum spectroscopy (EMS). From these measurements, we have determined the band dispersions, valence bandwidths, and O(2s)-O(2p) intervalence bandgaps at the Gamma point. For comparison we have also performed Hartree-Fock (HF) and density-functional (DFT) calculations in the linear combination of atomic orbitals (LCAO) approximation. Intervalence bandgaps compare reasonably well with the DFT calculations and previous experimental and theoretical studies. Our measured bandwidths, however, are significantly smaller. In particular, we find that contrary to conventional wisdom, the local density approximation of DFT overestimates the valence bandwidths of these ionic solids. (C) 2000 American Institute of Physics. [S0021-9606(00)70642-8].
Utteridge, S., Sashin, V.A., Canney, S., Ford, M., Fang, Z., Oliver, D., Vos, M. & Weigold, E. 2000, 'Preparation Of A 10 Nm Thick Single-crystal Silicon Membrane Self-supporting Over A Diameter Of 1 Mm', Applied Surface Science, vol. 162, pp. 359-367.
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We report the fabrication of a 10 nm thick, self-supporting, single-crystal silicon membrane. The fabrication process can be broken up into four major stages. First, a buried SiO2 layer was formed by implantation of oxygen at a depth of 200 nm into a (100) silicon wafer. The size of the membrane was then established by removing the bulk of the silicon over a 1 mm area using a fast acid etch. After this the sample was etched in a hot EDP solution which stops at the buried SiO2 layer. The sample was then cleaned and the SiO2 layers removed, after which it was introduced into a plasma-etching chamber. The membrane was thinned down to a final thickness of 10 nm by RF plasma etching in a gas mixture of carbon tetrafluoride and oxygen. The thickness was monitored during plasma etching by measuring the intensity of He-Ne laser light transmitted through the membrane. The electron energy loss spectrum of the membrane has been measured and shows two features due to single and double plasmon excitation. The plasmon energy was 17.05 eV, in good agreement with previous measurements. Membrane thickness has also been estimated from the area of the plasmon energy loss peak. The final sample had good crystalline quality, was of even thickness over the membrane diameter and showed only a small amount of surface contamination due to the plasma etching stage. (C) 2000 Elsevier Science B.V. All rights reserved.
Sashin, V.A., Bolorizadeh, M.A., Kheifets, A.S. & Ford, M. 2000, 'Electronic Band Structure Of Metallic Calcium Measured By Electron Momentum Spectroscopy', Journal of Physics: Condensed Matter, vol. 12, no. 45, pp. 9407-9423.
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We have measured the bulk energy-momentum resolved conduction band structure of metallic calcium using electron momentum spectroscopy (EMS). From the EMS data we have extracted the band dispersion, occupied bandwidth and density of states. The experimental results are compared with band structure calculations performed within the linear muffin-tin orbital (LMTO) approximation. The free-electron parabola expected for the dispersion relation in a metallic solid is clearly reproduced in the experimental data and is in good agreement with our calculation A background produced by multiple-scattering events within the target is also evident in the EMS results. In order to make a quantitative comparison, we have included the effects of multiple scattering in the calculation using a Monte Carlo (MC) simulation. The results of this procedure reproduce the measured conduction band features and background intensity very well. The occupied bandwidth is measured to be 3.3+/-0.2 eV, and agrees with previous measurements and the value predicted by our LMTO calculation when the MC simulation is included. However, the experiment indicates that the band dispersion curve is narrower in momentum by as much as 0.1 au compared with the theory. We have also made measurements of the energies of the 3s and 3p core levels in metallic calcium, and obtained values of 45.0+/-0.4 eV and 25.6+/-0.2 eV respectively. These results are in good agreement with previous experiments.
Canney, S., Sashin, V.A., Ford, M. & Kheifets, A.S. 1999, 'Electronic Band Structure Of Magnesium And Magnesium Oxide: Experiment And Theory', Journal of Physics: Condensed Matter, vol. 11, no. 39, pp. 7507-7522.
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Electron momentum spectroscopy (EMS) has been used to measure the valence band electronic structure of thin magnesium and magnesium oxide films. The band structures have also been calculated within the linear muffin-tin orbital (LMTO) approximation. The free-electronlike parabola characteristic of metallic solids was observed for magnesium with a bandwidth of approximately 6 eV, in agreement with previous measurements. The inclusion of energy broadening due to finite hole-lifetime effects and a Monte Carlo simulation of multiple scattering events gives good agreement between calculated and measured band structures. However, we measure a much higher intensity due to plasmon excitation compared with the simulated intensity. Upon oxidation the valence structure splits into two distinct, less dispersive bands typical of an ionic solid. Intensity due to plasmon excitation was almost completely absent in the experimental spectra for magnesium oxide. The LMTO calculation reproduces the overall structure and dispersion range of the oxide. The measured and calculated energy gap between upper and lower valence bands and their relative intensities do not agree quantitatively. This discrepancy may be due to a contribution of magnesium s states to the predominantly oxygen p states in the upper band.
Fang, Z., Guo, X., Canney, S., Utteridge, S., Ford, M., Mccarthy, I., Kheifets, A.S., Vos, M. & Weigold, E. 1998, 'Valence-band Energy-momentum Densities Of Amorphous Sio2 By (e,2e) Spectroscopy', Physical Review B, vol. 57, no. 8, pp. 4349-4357.
We have measured the energy-momentum density of amorphous silicon dioxide using an (e,2e) spectrometer with 20.8 keV incident, 19.6 keV scattered, and 1.2-keV ejected electron energies. The amorphous SiO2 sample was prepared by oxidizing a thin silicon membrane. The experimental data show a valence electronic structure characteristic of upper p-like and lower s-like bands. The width of the upper valence band is 10 eV. This is separated by 9 eV from the lower valence band, which exhibits 2-eV dispersion. We have calculated the energy-momentum density of alpha-quartz using the ab initio linear muffin-tin orbital method and the result is spherically averaged over all crystal directions to enable comparison with the experiment. The calculated electron momentum densities show very good agreement with experiment for both the upper and lower valence bands. The theoretical prediction of the energy separation between the upper and lower valence bands is about 2 eV smaller than that measured and this discrepancy is discussed. The agreement between theory and experiment suggests that the short-range order in silicon dioxide plays an important role in determining the electronic structure of this material. [S0163-1829(98)04908-X].
Ford, M.J. 1998, 'Studies of the electron-impact double-ionisation process in magnesium using coincidence techniques', AUSTRALIAN JOURNAL OF PHYSICS, vol. 51, no. 4, pp. 665-678.
Ford, M.J., El-Marji, B., Doering, J.P., Moore, J.H., Coplan, M.A. & Cooper, J.W. 1998, 'Electron-impact double ionization of magnesium', PHYSICAL REVIEW A, vol. 57, no. 1, pp. 325-330.
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Ford, M.J., Moore, J.H., Coplan, M.A., Cooper, J.W. & Doering, J.P. 1996, 'Partitioning of momentum in electron-impact double ionization of magnesium', PHYSICAL REVIEW LETTERS, vol. 77, no. 13, pp. 2650-2653.
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FORD, M.J., DOERING, J.P., COPLAN, M.A., COOPER, J.W. & MOORE, J.H. 1995, '(E,3E) OBSERVATION OF THE ANGULAR-CORRELATION BETWEEN EJECTED AND AUGER ELECTRONS IN THE DOUBLE-IONIZATION OF MAGNESIUM', PHYSICAL REVIEW A, vol. 51, no. 1, pp. 418-423.
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FORD, M.J., DOERING, J.P., MOORE, J.H. & COPLAN, M.A. 1995, 'MULTIPLE DETECTOR TRIPLE COINCIDENCE SPECTROMETER FOR (E,3E) ELECTRON-IMPACT DOUBLE-IONIZATION MEASUREMENTS', REVIEW OF SCIENTIFIC INSTRUMENTS, vol. 66, no. 5, pp. 3137-3143.
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Ford, M.J., Doering, J.P., Cooper, J.W., Coplan, M.A. & Moore, J.H. 1993, 'Electron impact double ionization of neon', Journal De Physique. IV : JP, vol. 3, no. 6, pp. 117-123.
Electron-impact double ionization from the valence shell of neon has been measured at an incident electron energy of 3662.5 eV. Double-coincidence (e,(3-1)e) measurements have been made between the scattered electron and each of the ejected electrons in turn, ejected energies were 10 eV and 90 eV, respectively, at ejection angles of 45, 60, 90, 120 and 135 degrees with respect to the incident electron beam. Absolute four-fold-differential cross-sections have been derived from the measured data and can be interpreted in terms of a fast, single-step, shake-off process.
BENNETT, M.A., SMITH, P.A., WATERHOUSE, D.K., FORD, M.J., FLEXMAN, J. & WILLIAMS, J.F. 1992, 'HISTOGRAMMING DATA ACQUISITION-SYSTEM FOR AN (E,2E) COINCIDENCE EXPERIMENT', REVIEW OF SCIENTIFIC INSTRUMENTS, vol. 63, no. 3, pp. 1922-1926.
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FORD, M.J., PEJCEV, V., SMITH, D., ROSS, K.J. & WILSON, M. 1990, 'THE EJECTED-ELECTRON SPECTRA OF MANGANESE AND SAMARIUM VAPOR ATOMS ARISING FROM AUTOIONIZING AND AUGER TRANSITIONS FOLLOWING ELECTRON-IMPACT EXCITATION', JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, vol. 23, no. 23, pp. 4247-4262.
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Ford, M.J., Pejcev, V., Smith, D., Ross, K.J. & Wilson, M. 1990, 'Effect of the crystal field and electron self-consistency on radially dependent antishielding factors of an ion', Journal of Physics B: Atomic, Molecular and Optical Physics, vol. 23, no. 23, pp. 4247-4262.
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Autoionizing and Auger transitions in atomic manganese and samarium have been experimentally investigated by observation of the ejected electrons in the energy region 0 to 40 eV following electron impact excitation with incident beams in the energy range is 15-500 eV. Seventy-four spectral features are tabulated for manganese and a number of new assignments have been made based on pseudo-relativistic Hartree-Fock calculations and quantum defect analysis. A similar study of samarium reveals only a number of broad features in the ejected-electron energy range 8-10 eV. Three features have been observed consistently in the ejected-electron spectrum of samarium and assigned by comparison with previous work. © 1990 IOP publishing Ltd.
FORD, M.J., FORREST, L.F., PEJCEV, V., SMITH, D., SOKHI, R.S. & ROSS, K.J. 1987, 'AN EXPERIMENTAL INVESTIGATION OF THE EJECTED-ELECTRON SPECTRA ARISING FROM AUTOIONIZING AND AUGER TRANSITIONS IN EU-I AND EU-II EXCITED BY ELECTRON-IMPACT FOR THE RANGE OF INCIDENT-ELECTRON ENERGIES FROM 20 TO 500 EV', JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS, vol. 20, no. 16, pp. 4241-4253.
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Brady, S.E., Maher, J.P., Bromfield, J., Stewart, K. & Ford, M. 1976, 'An infrared sensitive stopped-flow apparatus (for studying fast chemical reactions)', Journal of Physics E: Scientific Instruments, vol. 9, no. 1, pp. 19-24.
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A Perkin-Elmer 237 infrared spectrophotometer has been modified to enable stopped-flow kinetic measurements to be made. The machine has a single-beam system, with the radiation chopped at 2 kHz; the detector is a liquid nitrogen cooled InSb photoconductive device; a new form of sampling circuit associated with this detector is described. A new form of 'diaphragm syringe' has been developed for the fluid handling system. The machine is sensitive from 4000 cm-1 to 1800 cm-1 with a signal to noise level less than 0.3%; kinetics of reactions may be studied with half lives ranging from ca. 10 ms to 10 s; it is purged of CO2 and H2O and may be thermostated between 10 degrees C and 40 degrees C. The apparatus is being applied to the study of the reactions of various organometallic and transition metal complexes containing ligands with infrared absorptions in the region of 2000 cm-1.
Blaber, M.G., Arnold, M.D. & Ford, M.J., 'Designing materials for plasmonic systems'.
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We use electronic structure calculations based upon density functional theory to search for ideal plasmonic materials among the alkali noble intermetallics. Importantly, we use density functional perturbation theory to calculate the electron-phonon interaction and from there use a first order solution to the Boltzmann equation to estimate the phenomenological damping frequency in the Drude dielectric function. We discuss the necessary electronic features of a plasmonic material and investigate the optical properties of the alkali-noble intermetallics in terms of some generic plasmonic system quality factors. We conclude that at low negative permittivities, KAu with a damping frequency of 0.0224 eV and a high optical gap to bare plasma frequency ratio, outperforms gold and to some extent silver as a plasmonic material. Unfortunately, a low plasma frequency (1.54 eV) reduces its utility in modern plasmonics applications. We also discuss, briefly, the effect of local fields on the optical properties of these materials.