Color-shifting features for optically variable devices

Tompkin, Wayne R.; Schilling, Andreas; Staub, Rene

doi:10.1117/12.527571

Cited by 7 publications

(4 citation statements)

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“…Artificially designed organized structures that mimic nature are interesting for several applications [1,2], among which metal nanostructures have a prominent position [3,4]. Metal thin films are generally thermodynamically unstable and tend to dewet from the substrate to reduce the free energy of the system even at temperatures well below their melting temperature [5,6].…”

Section: Introductionmentioning

confidence: 99%

Period dependence of laser induced patterns in metal films

et al. 2014

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Periodic fringed patterns with four periods in the range 1.8-10.2 μm have been produced in continuous Ag films that have thicknesses of 14.6 nm and 19.5 nm by exposing a phase mask to single pulses of an excimer laser operating at 193 nm. The films were patterned either as-grown or after homogeneous exposure to the same laser beam. For fluences above the threshold, the films undergo liquid-state dewetting that, from low to high fluences, leads to their break into holes, fingers or elongated features and finally to isolated nanoparticles irrespective of the period, thickness or fluence. The period determines the range of fluences to achieve the different morphologies since the temperature profile across the pattern depends on the period due to the existence of significant lateral heat flow across the pattern. The maximum temperature achieved at the intensity maxima/minima sites thus decreases/increases as the period decreases, leading to solid-state dewetting at regions around the intensity minima; the shorter the period, the higher this type of dewetting. These regions eventually overcome the melting temperature for the shortest period and intermediate fluence, leading to the complete transformation of the films. Finally, the initial film morphology (discontinuities or holes) rather than thickness plays an essential role in the level of transformation at fluences around the threshold.

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Section: Introductionmentioning

confidence: 99%

Period dependence of laser induced patterns in metal films

et al. 2014

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“…Metal nano-objects organized in a two-dimensional array may exhibit grating induced plasmon modes [3] or surface plasmon-polaritons when the grating periodicity matches the SP excitation conditions [4]. In addition, there is a strong interest in producing artificially designed diffractive structures that mimic nature for decorative colouring, marking or even document security [5,6], and it has recently been reported that diffractive gratings offer advantages for integrated optical sensing [7].…”

Section: Introductionmentioning

confidence: 99%

2D plasmonic and diffractive structures with sharp features by UV laser patterning

Peláez¹,

Afonso²,

Bulı́ř³

et al. 2013

Nanotechnology

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The aim of this work is to produce 2D plasmonic and diffractive structures in Ag films with sharp features for which both a deeper understanding of laser induced transformation upon modulated laser intensity and a correlation between structural and optical properties are required. We compare results obtained by exposing silver films to an excimer laser operating at 193 nm whose intensity is either modulated or homogeneous. In all cases, one laser exposure is enough to break the film into nanoparticles (NPs). The use of the modulated beam intensity leads to diffractive 2D patterns that are formed by rectangular regions of untransformed material surrounded by transformed regions covered by NPs. The former have sharp edges that are consistent with the absence of significant mass transport that is discussed in terms of the thermal gradient induced. The latter contain NPs whose diameter increases as the initial film effective thickness increases. The surface plasmons associated with the NPs in the transformed regions dominate the reflectivity spectrum and the 2D array formed by the untransformed regions is responsible for the diffractive properties. Evidence for spinodal dewetting is only observed in our case for the steep gradient conditions achieved at the border of the homogeneously irradiated regions.

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“…green to red), opposite to that of Ref. [20], and the blue shift of single-peak in case 2 with less velocity for Â appears as color changing from res of Â = 0 • to shorter wavelength. The combination of them in color for Â / = 0 • can fabricate some unique effects of color conversion when the structure is inspected from case 1 to case 2 (and vice versa), with values of application especially in optical security.…”

Section: Resultsmentioning

confidence: 73%