Transient Structural Colors with Magnesium‐Based Reflective Filters

Abstract

can be induced on resonance, giving rise to the filtering of distinctive colors. Commonly used resonance structures include Fabry-Pérot (F-P) cavities, [6][7][8][9] plasmonic nanostructures, [10][11][12][13][14] and grating-coupled waveguides. [15][16][17] Compared with conventional approaches using organic dyes or chemical pigments, structural color filtering offers compelling advantages, including durability, environmental friendliness, high resolution, and compatible integration with monolithic fabrication. [2,[18][19][20] One fundamental constraint with those resonance structures is that the generated/ filtered colors are static post-fabrication, yet varieties of modern technologies such as cryptography, data storage, and dynamic color display entail on-demand alteration or vanishment of hue. Although mechanisms to dynamically tailor the optical properties in resonance nano structures have been well established via phasechanging materials, [21,22] electrical biasing/ gating, [23][24][25] mechanical actuation or strain, [3,26,27] methods with lower power consumption and better cost-effectiveness are still called for. From material's perspective, structural color filters consist prevalently of conventional metals (e.g., Au, Ag, and Al) owing to their low optical loss. However, they are either nonearth abundant and CMOS-incompatible (Au, Ag) or nonbiodegradable (Ag, Al), which often restricts their utilization in biosensing [28,29] and augmented reality. [30] Recently, magnesium (Mg) has drawn increasing research interest for nanophotonic and plasmonic applications as an earth-abundant, biodegradable, and CMOS-compatible alternative to conventional metals. [31][32][33][34] Besides, its optical property can be readily modified upon exposure to hydrogen or water, prompting its adoption in dynamic photonic devices. [9,35] Here, we experimentally implement an Mg-based colorfiltering multilayer structure based on two metal-insulatormetal (MIM) F-P cavities connected in tandem. Our devices visually exhibit multiple distinctive tints spanning the CMY reflective color gamut, verified by spectroscopic ellipsometry (SE)-measured reflection spectra featuring marked suppression at resonance wavelengths. We also find that the colors are insensitive to incident angles for most devices, which is a conducive characteristic for color display. In addition, we demonstrate that the colors can vanish within ≈40 s after immersion in water. The fast fading of hue is desirable for securing and protecting optical information as needed. Further, extending

Scalable Superabsorbers and Color Filters Based on Earth-Abundant Materials

“…Photonic and optoelectronic devices are omnipresent in technological applications spanning from sustainable energy utilization to advanced computing using photonic/plasmonic integrated circuits (PICs) as well as biosensing and imaging. − To date, they often employ conventional metals (e.g., Au, Ag, Cu, Al) and/or their alloys in the key components and building blocks such as in antennas, waveguides, modulators, and detectors. , Because the abundant free electrons and low optical loss in these metals can facilitate the excitation of surface plasmon or photonic resonances, these resonances lead to strong optical responses especially in the visible (VIS) and near-infrared (NIR) wavelength regimes. However, these metals are subject to certain limitations such as high-cost (e.g., Au, Ag), complementary metal-oxide semiconductor (CMOS) incompatibility (e.g., Au, Ag), bioincompatibility (e.g., Ag, Cu, Al), and the lack of adaptivity postfabrication, thrusting the continued search for alternative materials. − …”

“… 22 Over the years, various Mg-based optical devices with enticing dynamic or transient functionality, including color filtering, holography, and photocatalysis, have been successfully demonstrated. 4 , 11 , 23 − 27 However, hydrogen-loading typically involves cumbersome setups, while transient behaviors via water exposure have not exhibited superior photon absorption or generated all primary colors for printing and display purposes, impeding their use in many applications.…”

“…A characteristic that favorably distinguishes Mg from other mainstream metals is the actively tunable optical properties of Mg via hydrogenation (e.g., hydrogen loading or solid-state proton pumping) and dehydrogenation (e.g., exposure to oxygen), where the state of Mg switches between the metallic (original) and dielectric (hydride) state. − Concomitantly, Mg has also manifested transient behaviors when exposed to water or moisture due to irreversible chemical reactions . Over the years, various Mg-based optical devices with enticing dynamic or transient functionality, including color filtering, holography, and photocatalysis, have been successfully demonstrated. ,,− However, hydrogen-loading typically involves cumbersome setups, while transient behaviors via water exposure have not exhibited superior photon absorption or generated all primary colors for printing and display purposes, impeding their use in many applications.…”

Plasmonic Magnesium Nanoparticles Are Efficient Nanoheaters

“…Here, we aim to establish whether NPs of Mg, a newcomer in the plasmonics toolbox, ,− can produce enough heat at low NP concentrations and laser intensities to be a biodegradable alternative for PPTT. We present numerical results comparing the photothermal properties of identically shaped Mg and Au NPs of various sizes.…”