Imperial College London

Dr William Hart

Faculty of Natural SciencesDepartment of Physics

Casual - Academic Professional



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915Blackett LaboratorySouth Kensington Campus





Publication Type

4 results found

Hart WS, Panchal V, Melios C, StrupiƄski W, Kazakova O, Phillips CCet al., 2019, Highly resonant graphene plasmon hotspots in complex nanoresonator geometries, 2D Materials, ISSN: 2053-1583

Van der Waals surface polariton nanostructures are promising candidates for miniaturisation of electromagnetic devices through the nanoscale confinement of infrared light. To fully exploit these nanoresonators, a computationally efficient model is necessary to predict polariton behaviour in complex geometries. Here, we develop a general wave model of surface polaritons in 2D geometries smaller than the polariton wavelength. Using geometric approximation widely tuneable infrared nanoimaging and local work function microscopy, we test this model against complex mono-/bi-layer graphene plasmon nanoresonators. Direct imaging of highly resonant graphene plasmon hotspots confirms that the model provides quantitatively accurate, analytical predictions of nanoresonator behaviour. The insights built with such models are crucial to the development of practical plasmonic nanodevices.

Journal article

Hart WS, Bak AO, Phillips CC, 2018, Ultra low-loss super-resolution with extremely anisotropic semiconductor metamaterials, AIP Advances, Vol: 8, ISSN: 2158-3226

We investigate the mechanisms for the reduction of losses in doped semiconductormultilayers used for the construction of uniaxial metamaterials and show that maxi-mizing the mean scattering time of the doped layers is key to spectrally isolating lossesand maximizing anisotropy. By adjusting the layer thickness ratio of the multilayer,we show that the spectral regions of extreme anisotropy can be separated from thoseof high loss. Using these insights and coupled with realistic semiconductor growthparameters, we demonstrate an InAs-based superlens with an excellent loss factorα≈52mm-1and maximum perpendicular permittivity,ε⊥>250. By tuning the dopingconcentration, we show that such a system can be designed to operate anywhere in theregionλ0≈5 to 25μm. We find that such a structure is capable of deep sub-wavelengthimaging (< λ0/15) at superlens thicknesses up to∼85μm (∼8λ0).

Journal article

Amrania H, Drummond L, Coombes RC, Shousha S, Woodley-Barker L, Weir K, Hart W, Carter I, Phillips CCet al., 2016, New IR imaging modalities for cancer detection and for intra-cell chemical mapping with a sub-diffraction mid-IR s-SNOM, Faraday Discussions, Vol: 187, Pages: 539-553, ISSN: 1364-5498

We present two new modalities for generating chemical maps. Both are mid-IR based and aimed at the biomedical community, but they differ substantially in their technological readiness. The first, so-called "Digistain", is a technologically mature "locked down" way of acquiring diffraction-limited chemical images of human cancer biopsy tissue. Although it is less flexible than conventional methods of acquiring IR images, this is an intentional, and key, design feature. It allows it to be used, on a routine basis, by clinical personnel themselves. It is in the process of a full clinical evaluation and the philosophy behind the approach is discussed. The second modality is a very new, probe-based "s-SNOM", which we are developing in conjunction with a new family of tunable "Quantum Cascade Laser" (QCL) diode lasers. Although in its infancy, this instrument can already deliver ultra-detailed chemical images whose spatial resolutions beat the normal diffraction limit by a factor of ∼1000. This is easily enough to generate chemical maps of the insides of single cells for the first time, and a range of new possible scientific applications are explored.

Journal article

Hart WS, Amrania H, Beckley A, Brandt JR, Sundriyal S, Rueda-Zubiaurre A, Porter AE, Aboagye EO, Fuchter MJ, Phillips CCet al., Mid-infrared Chemical Nano-imaging for Intra-cellular Drug Localisation

In the past two decades a range of fluorescence cell microscopy techniqueshave been developed which can achieve ~10 nm spatial resolution, i.e.substantially beating the usual limits set by optical diffraction. However,these methods rely on specialised labelling. This limits the applicability,risks perturbing the biology, and it also makes them so-called "discoverytechniques" that can only be used when there is prior knowledge about thebiological problem. The alternative, electron microscopy (EM), requires complexand time-consuming sample preparation, that risks compromising the sample'sintegrity. Samples have to withstand vacuum, and staining with heavy metals tomake them conductive, and give usable electron-contrast. None of thesetechniques can directly map out drug distributions at a sub-cellular level.Recently infrared light-based scanning probe techniques have demonstrated acapability for ~1 nm spatial resolution. However, they need samples that areflat, dry and dimensionally stable and they only probe down to a depthcommensurate with the spatial resolution, so they yield essentially surfacechemical information. Thus far they have been applied only to artificiallyproduced test samples, e.g. gold particles, or isolated proteins on silicon.Here we show how these probe-based techniques can be adapted for use withroutinely prepared general biological specimens. This allows for "Mid-infraredChemical Nano-imaging" (MICHNI) that delivers chemical analysis at a ~10 nmspatial resolution, suitable for studying cellular ultrastructure. Wedemonstrate its utility by performing label-free mapping of the anti-cancerdrug Bortezomib (BTZ) within a single human myeloma cell. We believe that thisMICHNI technique has the potential to become a widely applicable adjunct to EMacross the bio-sciences.

Journal article

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