School of Physics - Research Publications

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    Direct Assembly of Large Area Nanoparticle Arrays
    Zhang, H ; Cadusch, J ; Kinnear, C ; James, T ; Roberts, A ; Mulvaney, P (AMER CHEMICAL SOC, 2018-08)
    A major goal of nanotechnology is the assembly of nanoscale building blocks into functional optical, electrical, or chemical devices. Many of these applications depend on an ability to optically or electrically address single nanoparticles. However, positioning large numbers of single nanocrystals with nanometer precision on a substrate for integration into solid-state devices remains a fundamental roadblock. Here, we report fast, scalable assembly of thousands of single nanoparticles using electrophoretic deposition. We demonstrate that gold nanospheres down to 30 nm in size and gold nanorods <100 nm in length can be assembled into predefined patterns on transparent conductive substrates within a few seconds. We find that rod orientation can be preserved during deposition. As proof of high fidelity scale-up, we have created centimeter scale patterns comprising more than 1 million gold nanorods.
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    Directed Chemical Assembly of Single and Clustered Nanoparticles with Silanized Templates
    Kinnear, C ; Cadusch, J ; Zhang, H ; Lu, J ; James, TD ; Roberts, A ; Mulvaney, P (AMER CHEMICAL SOC, 2018-06-26)
    The assembly of nanoscale materials into arbitrary, organized structures remains a major challenge in nanotechnology. Herein, we report a general method for creating 2D structures by combining top-down lithography with bottom-up chemical assembly. Under optimal conditions, the assembly of gold nanoparticles was achieved in less than 30 min. Single gold nanoparticles, from 10 to 100 nm, can be placed in predetermined patterns with high fidelity, and higher-order structures can be generated consisting of dimers or trimers. It is shown that the nanoparticle arrays can be transferred to, and embedded within, polymer films. This provides a new method for the large-scale fabrication of nanoparticle arrays onto diverse substrates using wet chemistry.
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    Direct Assembly of Large Area Nanoparticle Arrays
    Mulvaney, P ; ZHANG, H ; KINNEAR, C ; Cadusch, J ; JAMES, T ; ROBERTS, ANN ( 2018-07-13)
    We describe the fabrication of large area arrays of single nanoparticles using electrophoretic deposition.
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    Plasmonics-enabled metal-semiconductor-metal photodiodes for high-speed interconnects and polarization sensitive detectors
    Panchenko, E ; Cadusch, JJ ; James, TD ; Roberts, A ; GarciaBlanco, SM ; Conti, GN (SPIE-INT SOC OPTICAL ENGINEERING, 2017-01-01)
    Metal-semiconductor-metal (MSM) photodiodes are commonly used in ultrafast photoelectronic devices. Re- cently it was shown that localized surface plasmons can su_ciently enhance photodetector capabilities at both infrared and visible wavelengths. Such structures are of great interest since they can be used for fast, broadband detection. By utilizing the properties of plasmonic structures it is possible to design photodetectors that are sensitive to the polarization state of the incident wave. The direct electrical readout of the polarization state of an incident optical beam has many important applications, especially in telecommunications, bio-imaging and photonic computing. Furthermore, the fact that surface plasmon polaritons can circumvent the di_raction limit, opens up signi_cant opportunities to use them to guide signals between logic gates in modern integrated circuits where small dimensions are highly desirable. Here we demonstrate two MSM photodetectors integrated with aluminum nanoantennas capable of distinguishing orthogonal states of either linearly or circularly polarized light with no additional _lters. The localized plasmon resonances of the antennas lead to selective screening of the un- derlying silicon from light with a particular polarization state. The non-null response of the devices to each of the basis states expands the potential utility of the photodetectors while improving precision. We also demonstrate a design of waveguide-coupled MSM photodetector suitable for planar detection of surface plasmons.
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    Switchable polarization rotation of visible light using a plasmonic metasurface
    Earl, SK ; James, TD ; Gomez, DE ; Marvel, RE ; Haglund, RF ; Roberts, A (AMER INST PHYSICS, 2017-01-01)
    A metasurface comprising an array of silver nanorods supported by a thin film of the phase change material vanadium dioxide is used to rotate the primary polarization axis of visible light at a pre-determined wavelength. The dimensions of the rods were selected such that, across the two phases of vanadium dioxide, the two lateral localized plasmon resonances (in the plane of the metasurface) occur at the same wavelength. Illumination with linearly polarized light at 45° to the principal axes of the rod metasurface enables excitation of both of these resonances. Modulating the phase of the underlying substrate, we show that it is possible to reversibly switch which axis of the metasurface is resonant at the operating wavelength. Analysis of the resulting Stokes parameters indicates that the orientation of the principal linear polarization axis of the reflected signal is rotated by 90° around these wavelengths. Dynamic metasurfaces such as these have the potential to form the basis of an ultra-compact, low-energy multiplexer or router for an optical signal.
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    Metasurfaces, dark modes, and high NA illumination
    Wesemann, L ; Achmari, P ; Singh, K ; Panchenko, E ; James, TD ; Gomez, DE ; Davis, TJ ; Roberts, A (OPTICAL SOC AMER, 2018-10-15)
    The interaction of a focused beam with a metasurface supporting dark modes is investigated. We show computationally and experimentally that the excitation of dark modes is accompanied by characteristic changes in the reflected Fourier spectrum. This spatial frequency filtering capability indicates an avenue for the all-optical, on-chip detection of phase gradients for biological and other imaging techniques.
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    Modified stripe waveguide design for plasmonic input port structures
    Panchenko, E ; James, TD ; Roberts, A (SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS, 2016-01)
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    Plasmonic Metasurface-Enabled Differential Photodetectors for Broadband Optical Polarization Characterization
    Panchenko, E ; Cadusch, JJ ; James, TD ; Roberts, A (AMER CHEMICAL SOC, 2016-10)
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    In-Plane Detection of Guided Surface Plasmons for High-Speed Optoelectronic Integrated Circuits
    Panchenko, E ; Cadusch, JJ ; Avayu, O ; Ellenbogen, T ; James, TD ; Gomez, D ; Roberts, A (WILEY, 2018-01)
    Abstract Constrains on the speed of modern digital integrated circuits are dominated by the metallic interconnects between logic gates. Surface plasmon polaritons have potential to overcome this limitation and greatly increase the operating speed of future digital devices. Nevertheless, an ongoing issue is the compatibility of modern planar microelectronic circuits with current methods for detecting surface plasmons. Here, a new approach to in‐plane surface plasmon polariton detection is proposed and experimentally demonstrated. The design is based on metal–semiconductor–metal photodetectors that are acknowledged as having one of the best speed characteristics among photodetectors. In the design, the photodetector structure also plays a dual role as the outcoupling grating for surface plasmons, significantly reducing the footprint of the resulting device. The technique has the potential to enable the integration of surface plasmons as signal carriers in future high‐speed optoelectronic integrated circuits.
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    Filling schemes at submicron scale: Development of submicron sized plasmonic colour filters
    Rajasekharan, R ; Balaur, E ; Minovich, A ; Collins, S ; James, TD ; Djalalian-Assl, A ; Ganesan, K ; Tomljenovic-Hanic, S ; Kandasamy, S ; Skafidas, E ; Neshev, DN ; Mulvaney, P ; Roberts, A ; Prawer, S (NATURE PUBLISHING GROUP, 2014-09-22)
    The pixel size imposes a fundamental limit on the amount of information that can be displayed or recorded on a sensor. Thus, there is strong motivation to reduce the pixel size down to the nanometre scale. Nanometre colour pixels cannot be fabricated by simply downscaling current pixels due to colour cross talk and diffraction caused by dyes or pigments used as colour filters. Colour filters based on plasmonic effects can overcome these difficulties. Although different plasmonic colour filters have been demonstrated at the micron scale, there have been no attempts so far to reduce the filter size to the submicron scale. Here, we present for the first time a submicron plasmonic colour filter design together with a new challenge - pixel boundary errors at the submicron scale. We present simple but powerful filling schemes to produce submicron colour filters, which are free from pixel boundary errors and colour cross- talk, are polarization independent and angle insensitive, and based on LCD compatible aluminium technology. These results lay the basis for the development of submicron pixels in displays, RGB-spatial light modulators, liquid crystal over silicon, Google glasses and pico-projectors.