School of Physics - Research Publications

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    A General Method for Direct Assembly of Single Nanocrystals
    Zhang, H ; Liu, Y ; Ashokan, A ; Gao, C ; Dong, Y ; Kinnear, C ; Kirkwood, N ; Zaman, S ; Maasoumi, F ; James, TD ; Widmer-Cooper, A ; Roberts, A ; Mulvaney, P (WILEY-V C H VERLAG GMBH, 2022-05-28)
    Controlled nanocrystal assembly is a pre-requisite for incorporation of these materials into solid state devices. Many assembly methods have been investigated which target precise nanocrystal positioning, high process controllability, scalability, and universality. However, most methods are unable to achieve all of these goals. Here, surface templated electrophoretic deposition (STED) is presented as a potential assembly method for a wide variety of nanocrystals. Controlled positioning and deposition of a wide range of nanocrystals into arbitrary spatial arrangements − including gold nanocrystals of different shapes and sizes, magnetic nanocrystals, fluorescent organic nanoparticles, and semiconductor quantum dots − is demonstrated. Nanoparticles with diameters <10 nm are unable to be deposited due to their low surface charge and strong Brownian motion (low Péclet number). It is shown that this limit can be circumvented by forming clusters of nanocrystals or by silica coating nanocrystals to increase their effective size.
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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, 2018-08-01)
    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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    Scalable and Consistent Fabrication of Plasmonic colors via Nanoimprint Lithography
    Shahidan, MFS ; Song, J ; James, TD ; Mulvaney, P ; Roberts, A ; Simpson, MC ; Juodkazis, S (SPIE-INT SOC OPTICAL ENGINEERING, 2019-01-01)
    We utilised thermal and UV-assisted Nanoimprint Lithography (NIL) i.e. thermal and UV-assisted to produce plasmonic coloration, and compare their ability for scalable fabrication. Several designs are presented and we show the generated colors are dependent on their geometry and the direction of polarisation of incident illumination. Finally, we demonstrated UV-NIL for consistent production of large-area (0.6×0.4 cm2) plasmonic color with extended color gamut.
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    Direct Assembly of Vertically Oriented, Gold Nanorod Arrays
    Zhang, H ; Liu, Y ; Shahidan, MFS ; Kinnear, C ; Maasoumi, F ; Cadusch, J ; Akinoglu, EM ; James, TD ; Widmer-Cooper, A ; Roberts, A ; Mulvaney, P (WILEY-V C H VERLAG GMBH, 2021-02-03)
    Although many nanoscale materials such as quantum dots and metallic nanocrystals exhibit size dependent optical properties, it has been difficult to incorporate them into optical or electronic devices because there are currently no methods for precise, large‐scale deposition of single nanocrystals. Of particular interest is the need to control the orientation of single nanocrystals since the optical properties are usually strongly anisotropic. Here a method based on electrophoretic deposition (EPD) is reported to precisely assemble vertically oriented, single gold nanorods. It is demonstrated that the orientation of gold nanorods during deposition is controlled by the electric dipole moment induced along the rod by the electric field. Dissipative particle dynamics simulations indicate that the magnitude of this dipole moment is dominated by the polarizability of the solution phase electric double layer around the nanorod. The resulting vertical gold nanorod arrays exhibit reflected colors due to selective excitation of the transverse surface plasmon mode. The EPD method allows assembly of arrays with a density of over one million, visually resolvable, vertical nanorods per square millimeter.
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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.