Papers by Graham Killaire
Journal of Materials Processing Technology, Sep 1, 2019
Polarization has been identified as an important parameter in the generation of micro-and nano-st... more Polarization has been identified as an important parameter in the generation of micro-and nano-structures during ultrafast laser machining. In this study, deep cavities (500 μm x 500 μm x 100 μm) were machined with a femtosecond laser. The influence of polarization on structure formation was investigated on a stainless steel, a commercially pure titanium, an aluminum alloy, and a silicon sample. Smooth surfaces relatively free of laser induced periodic surface structures (LIPSS or ripples) were achieved using a single set of laser parameters for all examined materials. We show that the influence of polarization on ripple formation in deep cavities is limited to metals with low thermal conductivity and a high electron-phonon coupling constant. A continuously rotating polarization was found to yield optically smooth cavities on both bottom and sidewalls. Obtaining smooth surfaces using ultrafast lasers is relevant in many applications where slower processes are currently used such as in sample preparation for electron microscopy, fabrication of microfluidic channels, 3D serial sectioning, microelectro-mechanical systems, and micro-optical elements.
We report the tuning of plasmonic colours on silver by controlling the thickness of alumina films... more 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. Finitedifference 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 observed to be colour dependent.
Langmuir, Mar 23, 2018
We report the passivation of angle-independent plasmonic colors on bulk silver by atomic layer de... more We report the passivation of angle-independent plasmonic colors on bulk silver by atomic layer deposition (ALD) of thin films of aluminium oxide. The colors are rendered by silver nanoparticles produced by laser ablation and re-deposition on silver. We then apply a two-step approach to aluminium oxide conformal film formation via ALD. In the first step, a low-density film is deposited at low temperature to preserve and pin the silver nanoparticles. In the second step, a second denser film is deposited at a higher temperature to provide tarnish protection. This approach successfully protects the silver and plasmonic colors against tarnishing, humidity and temperature, as demonstrated by aggressive exposure trials. The processing time associated with deposition of the conformal passivation layers meets industry requirements and the approach is compatible with mass manufacturing.
Optica, May 14, 2021
Silver gratings supporting surface plasmons at 532 nm catalyze the formation of light-emitting so... more Silver gratings supporting surface plasmons at 532 nm catalyze the formation of light-emitting solid carbon from C O 2 gas, revealing a low-energy C O 2 reduction pathway involving hot electrons. Reversibility and spatial control over the formation of carbon quantum emitters are achieved.
Nanophotonics, Mar 4, 2019
In this paper we discuss the optical response of laser-written plasmonic colours on silver coated... more In this paper we discuss the optical response of laser-written plasmonic colours on silver coated via the atomic layer deposition of alumina. These colours are due to nanoparticles distributed on a flat surface and on a surface with periodic topographical features (i.e. ripples). The colours are observed to shift with increasing alumina film thickness. The colours produced by surfaces with ripples recover their original vibrancy and hue after the deposition of film of thickness ~60 nm, while colours arising from flat surfaces gradually fade and never recover. Analysis of the surfaces identifies periodic topographical features to be responsible for this behaviour. Finitedifference time-domain simulations unravel the role played by the alumina thickness in colour formation and confirm the rotations and recovery of colours for increasing alumina thickness. 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 observed to be colour dependent.
Optics Express, Jan 6, 2023
Physical unclonable functions (PUFs) are receiving significant attention with the rise of cryptog... more Physical unclonable functions (PUFs) are receiving significant attention with the rise of cryptography and the drive towards creating unique structures for security applications and anti-counterfeiting. Specifically, nanoparticle based PUFs can produce a high degree of randomness through their size, shape, spatial distribution, chemistry, and optical properties, rendering them very difficult to replicate. However, nanoparticle PUFs typically rely on complex preparation procedures involving chemical synthesis in solution, therefore requiring dispersion, and embedding within a host medium for application. We propose laser machining of surfaces as a one-step process for the creation of complex nanoparticle based PUFs by machining 600 nm thick copper films on a silicon substrate to yield a complex spatial and chemical distribution of redeposited copper, silicon, and oxide species. The approaches and material system investigated have potential applications in silicon chip authentication.
Optics Express
Physical unclonable functions (PUFs) are receiving significant attention with the rise of cryptog... more Physical unclonable functions (PUFs) are receiving significant attention with the rise of cryptography and the drive towards creating unique structures for security applications and anti-counterfeiting. Specifically, nanoparticle based PUFs can produce a high degree of randomness through their size, shape, spatial distribution, chemistry, and optical properties, rendering them very difficult to replicate. However, nanoparticle PUFs typically rely on complex preparation procedures involving chemical synthesis in solution, therefore requiring dispersion, and embedding within a host medium for application. We propose laser machining of surfaces as a one-step process for the creation of complex nanoparticle based PUFs by machining 600 nm thick copper films on a silicon substrate to yield a complex spatial and chemical distribution of redeposited copper, silicon, and oxide species. The approaches and material system investigated have potential applications in silicon chip authentication.
Applied Surface Science, 2022
We report the tuning of plasmonic colours on silver by controlling the thickness of alumina films... more 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 col...
Applied Surface Science, 2020
Abstract Nanotexturing of silver substrates with silver (I) oxide, Ag2O, is demonstrated using a ... more Abstract Nanotexturing of silver substrates with silver (I) oxide, Ag2O, is demonstrated using a one-step laser micro-machining process. Where ablation of the silver substrate took place, a highly textured nanoscale topography is generated. In contrast, a film-like oxide is formed next to the machined areas. Interestingly, it was observed that Ag2O formed within the laser tool path was significantly more reactive towards atmospheric H2O and CO2 compared to the film-like oxide, leading to the formation of silver carbonate, Ag2CO3, only in this region. The ability to generate a periodic topography, in the form of a bulls-eye grating, combined with periodic surface chemistry, consisting of alternating regions of Ag2O and Ag2CO3 is also shown. Depending on the machining parameters and tool path used, the surfaces can become quite optically active. When combined with the propensity of a nanotextured Ag2O surface to react with carbon dioxide and water, an attractive system for applications involving photocatalytic CO2 reduction, CO2 capture and storage, and artificial photosynthesis is realized.
Journal of Materials Processing Technology, 2019
Abstract Polarization has been identified as an important parameter in the generation of micro- a... more Abstract Polarization has been identified as an important parameter in the generation of micro- and nano-structures during ultrafast laser machining. In this study, deep cavities (500 μm x 500 μm x 100 μm) were machined with a femtosecond laser. The influence of polarization on structure formation was investigated on a stainless steel, a commercially pure titanium, an aluminum alloy, and a silicon sample. Smooth surfaces relatively free of laser induced periodic surface structures (LIPSS or ripples) were achieved using a single set of laser parameters for all examined materials. We show that the influence of polarization on ripple formation in deep cavities is limited to metals with low thermal conductivity and a high electron-phonon coupling constant. A continuously rotating polarization was found to yield optically smooth cavities on both bottom and sidewalls. Obtaining smooth surfaces using ultrafast lasers is relevant in many applications where slower processes are currently used such as in sample preparation for electron microscopy, fabrication of microfluidic channels, 3D serial sectioning, micro-electro-mechanical systems, and micro-optical elements.
Nanophotonics, 2019
In this paper we discuss the optical response of laser-written plasmonic colours on silver coated... more In this paper we discuss the optical response of laser-written plasmonic colours on silver coated via the atomic layer deposition of alumina. These colours are due to nanoparticles distributed on a flat surface and on a surface with periodic topographical features (i.e. ripples). The colours are observed to shift with increasing alumina film thickness. The colours produced by surfaces with ripples recover their original vibrancy and hue after the deposition of film of thickness ~60 nm, while colours arising from flat surfaces gradually fade and never recover. Analysis of the surfaces identifies periodic topographical features to be responsible for this behaviour. Finite-difference time-domain simulations unravel the role played by the alumina thickness in colour formation and confirm the rotations and recovery of colours for increasing alumina thickness. The coloured surfaces were evaluated for applications in colourimetric and radiometric sensing showing large sensitivities of up t...
Langmuir : the ACS journal of surfaces and colloids, May 1, 2018
We report the passivation of angle-independent plasmonic colors on bulk silver by atomic layer de... more We report the passivation of angle-independent plasmonic colors on bulk silver by atomic layer deposition (ALD) of thin films of aluminum oxide. The colors are rendered by silver nanoparticles produced by laser ablation and redeposition on silver. We then apply a two-step approach to aluminum oxide conformal film formation via ALD. In the first step, a low-density film is deposited at low temperature to preserve and pin the silver nanoparticles. In the second step, a second denser film is deposited at a higher temperature to provide tarnish protection. This approach successfully protects the silver and plasmonic colors against tarnishing, humidity, and temperature, as demonstrated by aggressive exposure trials. The processing time associated with deposition of the conformal passivation layers meets industry requirements, and the approach is compatible with mass manufacturing.
Advanced Optical Materials, 2018
We report on the creation of angle-independent colors on silver using closely time-spaced laser b... more We report on the creation of angle-independent colors on silver using closely time-spaced laser bursts. The use of burst mode, compared to traditional non-burst is shown to increase the Chroma (color saturation) by ∼50% and to broaden the lightness range by up to ∼60%. Scanning electron microscope analysis of the surfaces created using burst mode, reveal the creation of 3 distinct sets of laser induced periodic surface structures (LIPSS): low spatial frequency LIPSS (LSFL), high spatial frequency LIPSS (HSFL) and large laser-induced periodic surface structures (LLIPSS) that are 10 times the laser wavelength and parallel to the laser polarization. Nanoparticles are responsible for each plasmonic color and their distributions are observed to be similar for both burst and non-burst modes, indicating that the underlying structures (i.e. LIPSSs) are responsible for the increased Chroma and Lightness. Two-temperature model simulations of silver irradiated by laser bursts show significant increase in the electron-phonon coupling coefficient which is crucial for the creation of well-defined ripple structures. Finite difference time domain (FDTD) simulations of the colored surfaces show the increase in Chroma to be attributable to the HSFL arising in burst mode.
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Papers by Graham Killaire