T. J. Davis

The Commonwealth Scientific and Industrial Research Organisation, Canberra, Australian Capital Territory, Australia

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Publications (46)165.65 Total impact

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    ABSTRACT: In this paper we excite bound long range stripe plasmon modes with a highly focused laser beam. We demonstrate highly confined plasmons propagating along a 50 µm long silver stripe 750 nm wide and 30 nm thick. Two excitation techniques were studied: focusing the laser spot onto the waveguide end and focusing the laser spot onto a silver grating. By comparing the intensity of the out-coupling photons at the end of the stripe for both grating and end excitation we are able to show that gratings provide an increase of a factor of two in the output intensity and thus out-coupling of plasmons excited by this technique are easier to detect. Authors expect that the outcome of this paper will prove beneficial for the development of passive nano-optical devices based on stripe waveguides, by providing insight into the different excitation techniques available and the advantages of each technique.
    Full-text · Article · Apr 2015 · Optics Express
  • S K Earl · D E Gómez · T D James · T J Davis · A Roberts
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    ABSTRACT: There is great interest in aluminum based plasmonic devices due to the relatively high plasma frequency of this material as well as its low cost and self-passivating oxide layer. The passivation layer provides aluminum plasmonics with the long-term stability required for practical applications. While several studies have investigated the impact of this oxide layer on the plasmon resonances of aluminum nanostructures on glass substrates, little is known about the effect of high-refractive index substrates on these resonances. Here we present an investigation of aluminum V-shaped antennas resonant in the visible on a silicon substrate. Through comparison between numerical and experimental results, we show that the aluminium passivation layer has little effect on the antenna resonances by comparing numerical simulations both with and without. We show, however, that inclusion of the native oxide layer of the silicon substrate in numerical models is critical for achieving good agreement with experimental data. Furthermore, we computationally explore the influence of the 1.5 eV interband transition of aluminum on plasmon resonances, and find that its effect on the material properties of the resonant structures results in narrower resonances in the blue part of the spectrum than if it was not present.
    No preview · Article · Feb 2015 · Nanoscale
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    ABSTRACT: Metallic nano-antennas have been shown to be an excellent candidate for enhancing and directing optical emission from semiconductor based quantum dots (QD). QD photoluminescence (PL) enhancement is achieved by placing a suitably orientated QD in the near-field of a resonant metallic nano-antenna. Through the careful design of an optical Vee-antenna, two distinct visible resonances can be obtained, enabling the polarization dependant enhancement of two different QD sources, thus producing a polarization-to-colour transformation at the nano-scale. Possible future applications include an optical nano-scale demultiplexer device.
    No preview · Article · Feb 2015
  • T. J. Davis · D. E. Gómez
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    ABSTRACT: We analyze theoretically the interaction between chiral molecules and localized surface plasmons in subwavelength metallic structures of arbitrary shape. The chiral molecule is modeled using Condon's classical description of the molecular dipole moment that depends on the magnetic field [E. U. Condon, Rev. Mod. Phys. 9, 432 (1937)]. This model is included in an eigenmode theory of coupled plasmonic systems. In the limit of dipole-dipole interactions, the theory predicts there is no change in the resonance frequency of the surface plasmon in the presence of a chiral molecule and there is no change in the amplitude of the resonance in the presence of a uniform distribution of chiral molecules. This implies that to observe the effects of the chirality of molecules it may be necessary to form localized surface plasmons with more complex charge distributions. We also examine the absorption of light of the combined system of the metal structure and chiral molecule. The theory predicts that the chirality-dependent absorption in the metal structure averages to zero for a uniform distribution of molecules, with the observed absorption occurring entirely within the molecule due to excitation by the incident light and the fields from the surface plasmon. Apart from the expected circular dichroism, the theory also predicts a chirality-dependent absorption arising from a metal nanostructure illuminated with linearly polarized light and an absorption arising from those chiral properties of the molecule usually associated with optical activity.
    No preview · Article · Dec 2014 · Physical Review B
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    ABSTRACT: Manipulation of polarization states is an important feature of many applications including in telecommunication, remote sensing and photonic computing technologies. Here we present two plasmonic nanoaperture based devices for creating and filtering circularly polarized light. One acts as an ultra-compact quarter wave plate, the other, based upon a planar chiral design, leads to asymmetric transmission of left and right circularly polarized light.
    No preview · Article · Jan 2014 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: We discuss progress in the development of asymmetric cross-shaped plasmonic antennas based on resonant nanoscale apertures surrounded by surface corrugations. By tailoring the aperture and the surrounding surface, we show directionality and polarization control of transmitted light.
    No preview · Article · Nov 2013 · Proceedings of SPIE - The International Society for Optical Engineering
  • T. D. James · Z. Q. Teo · D. E. Gómez · T. J. Davis · A. Roberts
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    ABSTRACT: The plasmonic J-pole antenna is the nanoscale version of a radio frequency design, consisting of a half wavelength arm connected to a quarter wavelength feed pair. Here, we report on an optical J-pole antenna that displays both a dipole (1015 nm) and quadrupole resonance (653 nm). The excitation of the quadrupole resonance is optimum at an angle of incidence directly related to the geometry of the antenna, demonstrating the flexibility of the design. The J-pole antenna shows great promise for enhancing and shaping the angular emission pattern of quantum emitters.
    No preview · Article · Jan 2013 · Applied Physics Letters
  • T.D. James · T.J. Davis · A. Roberts
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    ABSTRACT: Optical antennas have garnered much interest from the optics community for their ability to manipulate light below the diffraction limit of conventional optics. This relatively new capability to transform light at a sub-wavelength scale has been applied to quantum source enhancement, infrared detection and solar cell design. This work aims to expand upon the range of optical antennas presented in literature by exploiting the rich array of well-known radio-frequency (RF) antenna designs and applying them to the optical spectral region, for the enhancement of quantum emitters.
    No preview · Conference Paper · Dec 2012
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    ABSTRACT: We show theoretically and with numerical simulations that the direction of the in-plane scattering from a subwavelength optical antenna system can be controlled by the frequency of the incident light. This optical steering effect does not rely on propagation phase shifts or diffraction but arises from phase shifts in the localized surface plasmon modes of the antenna. An analytical model is developed to optimize the parameters for the configuration, showing good agreement with a rigorous numerical simulation. The simulation predicts a 25° angular shift in the direction of the light scattered from two gold nanorods for a wavelength change of 12 nm.
    No preview · Article · Oct 2012 · Optics Letters
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    ABSTRACT: Electromagnetic coupling between localised plasmons on metal nanoparticles and the strong localised fields on a micro‐structured surface is demonstrated as a means to increase the enhancement factor in surface‐enhanced Raman scattering (SERS) spectroscopy. Au nanoparticles of diameter 20 nm were deposited on a micro‐structured Au surface consisting of a periodic array of square‐based pyramidal pits (Klarite). The spectra of 4‐aminothiophenol (4‐ATP) were compared before and after deposition of Au nanoparticles on the micro‐structured surface. The addition of Au nanoparticles is shown to provide significantly higher signal intensities, with improvements of the order of ∼103 per molecule compared with spectra obtained from the micro‐structured substrate alone. This hybrid approach offers promise for combining nanoparticles with micro‐ and nano‐structured surfaces in order to design SERS substrates with higher sensitivities. Copyright © 2011 John Wiley & Sons, Ltd.
    No preview · Article · Feb 2012 · Journal of Raman Spectroscopy
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    ABSTRACT: Here we report on the integration of metallic nanorods with the phase-change material Vanadium Dioxide (VO2). The change in its optical constants that accompanies the VO2 phase transition permits the modulation of the resonant frequencies of these dipoles. This technique will underpin the development of dynamically tunable optical antennas.
    No preview · Conference Paper · Jan 2012
  • J. Cadusch · T.D. James · T.J. Davis · A. Roberts
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    ABSTRACT: We report on a plasmonic metamaterial approach to controlling the polarisation state of visible and near infra-red (NIR) light.
    No preview · Conference Paper · Jan 2012
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    K. C. Vernon · D. E. Gomez · T. J. Davis · N. Tischler
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    ABSTRACT: Quantum dot–plasmon waveguide systems are of interest for the active control of plasmon propagation, and consequently, the development of active nanophotonic devices such as nano-sized optical transistors. This paper is concerned with how varying aspect ratio of the waveguide cross-section affects the quantum dot–plasmon coupling. We compare a stripe waveguide with an equivalent nanowire, illustrating that both waveguides have a similar coupling strength to a nearby quantum dot for small waveguide cross-section, thereby indicating that stripe lithographic waveguides have strong potential use in quantum dot–plasmon waveguide systems. We also demonstrate that changing the aspect ratio of both stripe and wire waveguides can increase the spontaneous emission rate of the quantum dot into the plasmon mode, by up to a factor of five. The results of this paper will contribute to the optimisation of quantum dot–plasmon waveguide systems and help pave the way for the development of active nanophotonics devices.
    Full-text · Article · Oct 2011 · Journal of Applied Physics
  • K.C. Vernon · D.E. Gomez · T.J. Davis
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    ABSTRACT: Quantum dot coupling to plasmon nanowires may enable the development of all-optical nano-scale transistors, revolutionizing integrated photonics and information processing. However positioning between the quantum dot and the nanowire is problematic. We investigate lithographic plasmon waveguides as an alternative to colloidal nanowires. In particular, we investigate the suitability of a stripe plasmon waveguide — quantum dot system. The investigation uses a numerical procedure implemented in COMSOL Multiphysics. We show that a stripe waveguide is a suitable candidate for quantum dot - plasmon coupling, with similar efficiency to the nanowire for small waveguide cross-section. We also show that by decreasing the thickness of wire and stripe waveguides it is possible to double the spontaneous emission factor.
    No preview · Conference Paper · Aug 2011
  • K.C. Vernon · D.E. Gomez · T.J. Davis
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    ABSTRACT: Quantum dot coupling to plasmon nanowires may enable the development of all-optical nano-scale transistors, revolutionizing integrated photonics and information processing. However positioning between the quantum dot and the nanowire is problematic. We investigate lithographic plasmon waveguides as an alternative to colloidal nanowires. In particular, we investigate the suitability of a stripe plasmon waveguide — quantum dot system. The investigation uses a numerical procedure implemented in COMSOL Multiphysics. We show that a stripe waveguide is a suitable candidate for quantum dot - plasmon coupling, with similar efficiency to the nanowire for small waveguide cross-section. We also show that by decreasing the thickness of wire and stripe waveguides it is possible to double the spontaneous emission factor.
    No preview · Conference Paper · Aug 2011
  • T. J. Davis · D. E. Gómez · K. C. Vernon
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    ABSTRACT: A theory of surface-enhanced Raman scattering (SERS) is developed based on the coupling between an ensemble of nanoparticles supporting localized surface-plasmon resonances (LSPRs) and a Raman-active molecule. The molecule is modeled by a dielectric particle supporting many different modes that represent its response to an applied electric field. It is shown that the modes can be modified to include the effects of the vibrational resonances of the molecule that lead to Raman scattering and the associated Stokes and anti-Stokes frequency shifts. The same theory can describe the LSPR in an ensemble of metallic nanoparticles of arbitrary shape which leads to a description of the coupling of the evanescent electric fields between the Raman-active molecule and the surface plasmons. The theory predicts the magnitudes of the SERS observed experimentally and can model many of the known Raman effects associated with the LSPR resonances in nanoparticles, including the dependence of the enhancement on the shape and geometry of the nanoparticles, and the effects of the polarization of the incident light. An analytical expression is derived for the enhancement associated with a nanoparticle ensemble that exhibits two degenerate modes and it includes an interference effect arising from the coupling between the modes and the Raman scattering from the molecule.
    No preview · Article · Nov 2010 · Physical review. B, Condensed matter
  • K. C. Vernon · T. J. Davis · F. H. Scholes · D. E. Gómez · D. Lau
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    ABSTRACT: In this paper we theoretically consider the physical mechanisms behind the surface-enhanced Raman scattering (SERS) enhancement produced by commercially available Klarite substrates, which consist of rectangular arrays of micrometre-sized pyramidal pits in silicon with a thin gold coating. Full three-dimensional numerical simulations of the pits are conducted for both a real gold metal coating and a perfect electrical conductor (PEC) to determine whether the SERS enhancement is due to diffraction or plasmon effects. The pit apex angle and metal coating thickness are also varied to determine whether it is possible to further enhance the SERS signal by optimising the structural parameters of these substrates. By decreasing the film thickness and adjusting the apex angle, it is possible to achieve an enhancement almost double that of a standard Klarite substrate. Copyright © 2010 John Wiley & Sons, Ltd.
    No preview · Article · Oct 2010 · Journal of Raman Spectroscopy
  • T J Davis · D E Gómez · K C Vernon
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    ABSTRACT: An "electrostatic" eigenmode method based on the coupling of evanescent electric fields is presented for modeling the hybridization of localized surface plasmon resonances in metallic nanoparticles of arbitrary shape. The method yields simple analytical expressions for the hybridized energies and excitation amplitudes of nanoparticle ensembles. Because of its ease of applicability and simple conceptual basis, we anticipate that the method will be of value in understanding and predicting the effects of interacting plasmonic nanoparticles.
    No preview · Article · Jul 2010 · Nano Letters
  • D. E. Gómez · K. C. Vernon · T. J. Davis
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    ABSTRACT: We present theoretical studies on the collective optical response of symmetric configurations of metallic nanoparticles. We show that within the electrostatic approximation, the surface plasmon resonance of these symmetric multiparticle systems can be expressed as symmetry-adapted linear combinations of the plasmon modes of each particle of the ensemble, closely resembling the situation encountered in molecular systems. By making use of group theoretical arguments, we show that such linear combinations can be written down by simple geometrical considerations through the use of point group character tables, without using extensive numerical computations. Furthermore, we apply this formalism to study the coupling of hierarchical arrays containing a large number of nanoparticles. This theory thus provides an intuitive and formal approach for the rational design of plasmonic nanostructures.
    No preview · Article · Feb 2010 · Physical review. B, Condensed matter
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    D. E. Gomez · K. C. Vernon · P. Mulvaney · T. J. Davis
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    ABSTRACT: We present an experimental demonstration of strong optical coupling between CdSe quantum dots of different sizes which is induced by a surface plasmon propagating on a planar silver thin film. Attenuated total reflection measurements demonstrate the hybridization of exciton states, characterized by the observation of two avoided crossings in the energy dispersion measured for the interacting system.
    Full-text · Article · Feb 2010 · Applied Physics Letters