Tunable Plasmonic Colours by Atomic Layer Deposition of Alumina

We report the tuning of plasmonic colours on silver by controlling the thickness of alumina films deposited via atomic layer deposition. The colours are observed to shift with increasing alumina film thickness. Colour palettes produced with periodic topographical features are observed to recover their original vibrancy and Hue range after the deposition of a film thickness of ~ 60 nm while colours devoid of such topographical features are observed to gradually fade and their colour intensities are never recovered collapsing into a small visually unappealing region of the LCH color space. Analysis of the surfaces identifies the periodic topographical features as responsible for this behavior. Finite-difference time-domain simulations of flat and sine-modulated surfaces covered with nanoparticles and covered by a conformal alumina film were conducted to unravel the role played by the ALD thickness on the colour formation, where colour rotations and recovery were also observed. The coloured surfaces were evaluated for applications in colourimetric and radiometric sensing showing large sensitivities of up to 3.06/nm and 3.19 nm/nm, respectively. The colourimetric and radiometric sensitivities are ob-served to be colour dependent.