Riley Shurvinton, PhD

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Riley Shurvinton will defend her PhD thesis entitled "Design and optimization of multilayer coatings for the generation of colorimetric effects" on November 2 at 10:00 a.m. in Pierre Cotton Room.

Presentation and slides will be in English, and the thesis will also be broadcast over Zoom (link to follow).

Abstract : As a largely visual species, colour plays an important role in our lives. The ability to control the colour of an object has obvious applications for art, design and commercial products, but may also have more technical applications, such as display filters, security features on printed documents, and microscale image writing. One promising avenue for colour control is via thin film coatings. These can be used to precisely tailor the reflectance or transmittance of a surface to generate preciselycontrolled, high-chroma colours. They could also enable unique effects such as angle-dependent iridescence, or ‘active’ colour-shift coatings exploiting the refractive index change of phase-change materials. A four-layer stack using Ag, SiO2 and Ti is demonstrated for colour control and generation of high-chromacolours. Characterisation was performed for these three materials, with particular focus on the semi-transparent Ti layer. For this, we used an interference enhancement method and fit against a combined Forouhi-Bloomer and Modified Drude (FB-MD) refractive index model. We obtained the refractive index of thin Ti layers over a wavelength range of 370 – 835 nmfor layers between 6 nmand 100 nm. Red/green/blue and cyan/magenta/yellow colour coatings were designed using these materials. We explored the theoretical and experimental limits of simple fourlayer (metal/dielectric/metal/dielectric) coatings in terms of brightness and chroma, and obtained performances close to or exceeding the limits of known paint colours. In experiments, the deposited coatings (manufactured using electron-beam deposition) showed a very close agreement with the simulated results, demonstrating precise characterisation of the thin-film layers. Angle-metameric pairs were demonstrated at both normal and oblique incidence, showing a closely-controlled behaviour of the coating at different angles of incidence. Additionally, the possibility of using active materials with an exploitable index change was investigated. Two coating designs using the phase-change material Sb2S3 were deposited. It was shown that Sb2S3 has well-suited properties for design of colour-shift coatings, and can be used in different configurations to create different effects, enabling a large hue shift as the sample is heated. In addition, partial heating or annealing can be used to generate intermediate colours, increasing the versatility of these coatings. Potential applications include low-powered reflective display pixels, or microscale image writing/printmaking using a laser to selectively crystallise or amorphise the layer.

Keywords : thin films, colour coatings, active coatings, phase-change materials

Example of metameric pairs
These samples show the same color at normal incidence but the angular colorshift is different due to different multilayer structures between top and bottom of the glass plate