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Multilevel nanoimprint lithography with a binary mould for plasmonic colour printing.

Pigment-free colouration based on plasmonic resonances has recently attracted considerable attention for potential in manufacturing and other applications. For plasmonic colour utilizing the metal-insulator-metal (MIM) configuration, the generated colour is not only dependent on the geometry and transverse dimensions, but also to the size of the vertical gap between the metal nanoparticles and the continuous metal film. The complexity of conventional fabrication methods such as electron beam lithography (EBL), however, limits the capacity to control this critical parameter. Here we demonstrate the straightforward production of plasmonic colour via UV-assisted nanoimprint lithography (NIL) with a simple binary mould and demonstrate the ability to control this gap distance in a single print by harnessing the nanofluidic behaviour of the polymer resist through strategic mould design. We show that this provides a further avenue for controlling the colour reflected by the resulting plasmonic pixels as an adjunct to the conventional approach of tailoring the transverse dimensions of the nanostructures. Our experimental results exhibit wide colour coverage of the CIE 1931 XY colour space through careful control of both the length and periodicity and the resulting vertical gap size of the structure during the nanoimprinting process. Furthermore, to show full control over the vertical dimension, we show that a fixed gap size can be produced by introducing complementary microcavities in the vicinity of the nanostructures on the original mould. This demonstrates a simple method for obtaining an additional degree of freedom in NIL not only for structural colouration but also for other industrial applications such as high-density memory, biosensors and manufacturing.

Directed Chemical Assembly of Single and Clustered Nanoparticles with Silanized Templates.

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.

The Plasmonic Pixel: Large Area, Wide Gamut Color Reproduction Using Aluminum Nanostructures.

We demonstrate a new plasmonic pixel (PP) design that produces a full-color optical response over macroscopic dimensions. The pixel design employs arrays of aluminum nanorods "floating" above their Babinet complementary screen, Concepts from conventional cyan magenta yellow key (CMYK) printing techniques and red green blue (RGB) digital displays are integrated with nanophotonic design principles and adapted to the production of PP elements. The fundamental PP color blocks of CMYK are implemented via a composite plasmonic nanoantenna/slot design and then mixed in a digital display analog 3 × 3 array to produce a broad-gamut PP. The PP goes beyond current investigations into plasmonic color production by enabling a broad color gamut and physically large plasmonic color features/devices/images. The use of nanorods also leads to a color response that is polarization tunable. Furthermore, devices are fabricated using aluminum and the fabrication strategy is compatible with inexpensive, rapid-throughput, nanoimprint approaches. Here we quantify, both computationally and experimentally, the performance of the PP. Spectral data from a test palette is obtained and a large area (>1.5 cm lateral dimensions) reproduction of a photograph is generated exemplifying the technqiue.

Emission enhancement and polarization of semiconductor quantum dots with nanoimprinted plasmonic cavities: towards scalable fabrication of plasmon-exciton displays.

Here we present an application of a high throughput nanofabrication technique to the creation of a plasmonic metasurface and demonstrate its application to the enhancement and control of radiation by quantum dots (QDs). The metasurface consists of an array of cold-forged rectangular nanocavities in a thin silver film. High quantum efficiency graded alloy CdSe/CdS/ZnS quantum dots were spread over the metasurface and the effects of the plasmon-exciton interactions characterised. We found a four-fold increase in the QDs radiative decay rate and emission brightness, compared to QDs on glass, along with a degree of linear polarisation of 0.73 in the emitted field. Such a surface could be easily integrated with current QD display or organic solar cell designs.

Dynamics of glacier calving at the ungrounded margin of Helheim Glacier, southeast Greenland.

During summer 2013 we installed a network of 19 GPS nodes at the ungrounded margin of Helheim Glacier in southeast Greenland together with three cameras to study iceberg calving mechanisms. The network collected data at rates up to every 7 s and was designed to be robust to loss of nodes as the glacier calved. Data collection covered 55 days, and many nodes survived in locations right at the glacier front to the time of iceberg calving. The observations included a number of significant calving events, and as a consequence the glacier retreated ~1.5 km. The data provide real-time, high-frequency observations in unprecedented proximity to the calving front. The glacier calved by a process of buoyancy-force-induced crevassing in which the ice downglacier of flexion zones rotates upward because it is out of buoyant equilibrium. Calving then occurs back to the flexion zone. This calving process provides a compelling and complete explanation for the data. Tracking of oblique camera images allows identification and characterisation of the flexion zones and their propagation downglacier. Interpretation of the GPS data and camera data in combination allows us to place constraints on the height of the basal cavity that forms beneath the rotating ice downglacier of the flexion zone before calving. The flexion zones are probably formed by the exploitation of basal crevasses, and theoretical considerations suggest that their propagation is strongly enhanced when the glacier base is deeper than buoyant equilibrium. Thus, this calving mechanism is likely to dominate whenever such geometry occurs and is of increasing importance in Greenland.

Filling schemes at submicron scale: development of submicron sized plasmonic colour filters.

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.

Optical investigation of the J-pole and Vee antenna families.

The J-pole and Vee RF antenna design families are investigated for their suitability as optical antennas. The modal and spectral properties are experimentally examined to select the most suitable resonant optical plasmonic mode, which is used to inform the optimal positioning of a quantum emitter in relation to the antennas.

Tunable optical antennas enabled by the phase transition in vanadium dioxide.

Optical antennas, subwavelength metallic structures resonating at visible frequencies, are a relatively new branch of antenna technology being applied in science, technology and medicine. Dynamically tuning the resonances of these antennas would increase their range of application and offer potential increases in plasmonic device efficiencies. Silver nanoantenna arrays were fabricated on a thin film of the phase change material vanadium dioxide (VO(2)) and the resonant wavelength of these arrays was modulated by increasing the temperature of the substrate above the critical temperature (approximately 68 °C). Depending on the array, wavelength modulation of up to 110 nm was observed.

Experimental demonstration of a wave plate utilizing localized plasmonic resonances in nanoapertures.

Here we demonstrate the fabrication and characterization of a plasmonic wave plate. The device uses detuned, orthogonal nanometric apertures that support localized surface plasmon resonances on their interior walls. A device was fabricated in a thin silver film using focused ion beam milling and standard polarization tomography used to determine its Mueller matrix. We demonstrate a device that can convert linearly polarized light to light with an overall degree of polarization of 88% and a degree of circular polarization of 86% at a particular wavelength of 702 nm.