School of Chemistry - Research Publications

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Author: Akinoglu, Eser × Author: Kinnear, Calum × Author: Mulvaney, Paul × Start date: 2020 ×

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    Concealed Structural Colors Uncovered by Light Scattering
    Akinoglu, EM ; Song, J ; Kinnear, C ; Xue, Y ; Zhang, H ; Roberts, A ; Koehler, J ; Mulvaney, P (WILEY-V C H VERLAG GMBH, 2020-11)
    Abstract Unusual structural colors are demonstrated in thin‐film coatings due to a combination of optical interference and light scattering effects. These vivid colors are concealed under ambient illumination but can be observed when light is reflected from the film surface. The origin of the effect is explored computationally and it is shown that, in thin‐films of lossless dielectrics coated on near‐perfect conductors, incident electromagnetic waves form standing waves. Electric field intensities at the thin film interfaces are maximized for wavelengths that fulfil destructive interference conditions, while nanoscale roughness can enhance scattering at these boundaries. The interplay of these two factors yields vivid, thickness‐dependent colors. This approach increases the repertoire of optical effects and perceived colors in thin coatings. When combined with traditional thin‐film interference colours, dichromatic images with distinctly changing colors can be generated, which can function as a covert, optical security feature.
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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.