Tunable structural colors have diverse applications ranging from displays and photovoltaics to surface decoration and art. A metal−insulator−metal (MIM) cavity structure formed by thin continuous layers has drawn great interest as a lithography-free and scalable optical structure to control light transmission and reflection at the surface of a material. However, the production of distinct reflection colors from the structure is challenging because the typical MIM cavity absorbs a narrow wavelength range and reflects the rest of the spectrum. This study shows that the MIM structure can exhibit a reflection peak instead of a reflection dip if the metal layer has proper optical constants. Vivid reflection colors are generated by using thermally evaporated Au and Ag thin films whose refractive indices are much different from the standard handbook data. The strong thickness dependence of the refractive indices also enables color tuning by varying the thickness of the metal layer only. Consequently, color images can be printed by locally controlling the thickness of either the insulating spacer or the metal layer. The results of the study are attractive and useful for both practical and artistic purposes.

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Plasmonic color laser printing has several advantages over pigment-based technology, including the absence of ink and toner and the production of nonfading colors. However, the current printing method requires a template that should be prepared via nanofabrication processes, making it impractical for large-area color images. In this study, we show that laser-induced dewetting of metal thin films by a nanosecond pulsed laser can be effectively utilized for plasmonic color printing. Ag, Au, and their complex films deposited on a glass substrate were dewetted into different surface structures such as droplets, rods, and ripples, depending on the incident laser energy. The resulting morphological evolutions could be explained by Rayleigh and capillary instabilities. For a bimetallic film comprising Ag nanowires coated on a Au layer, a few different plasmonic colors were generated from a single sample simply by changing the laser fluence. This provides a possible method for implementing plasmonic color laser printing without using a prepatterned template.

Broadband light absorbers are highly desirable in various applications including solar-energy harvesting, thermo-photovoltaics, and photon detection. The Fabry−Perot (F−P) cavity comprising metal−insulator−metal (MIM) layers has attracted enormous interest as a lithography-free structure for realizing planar super absorbers. However, typical F−P cavity exhibits a narrow absorption band, and efforts have thus been made to increase the absorption bandwidth. This study demonstrates that near-perfect absorption over a broad spectral range can be obtained from the MIM structure by using thermally evaporated Ag and Au thin films whose dielectric and optical properties are much different from bulk-state properties because of their nanoscale features. A 55 nm thick SiO 2 spacer sandwiched between a 10 nm Ag top layer and a 100 nm Al back reflector exhibits absorption >95% in the visible range of 400−700 nm. The broad absorption band shifts to a near-infrared range of 650−1000 nm by replacing the top layer with a 10 nm thick Au film and increasing the SiO 2 spacer thickness to 115 nm. The experimental results are supported by finite-difference time-domain simulation. The large absorption bandwidth is attributed to the lossy nature of the nanostructured top metallic layer combined with the resonant absorption of the MIM cavity.

of metals rapidly extend into mobile electronics, home appliances, art/decoration, and building interiors, their aesthetic functions are becoming increasingly significant. Surface decoration with sensuous colors is essential for improving the aesthetic appearance of a material. Light control at the surface of metals endows them with additional functionality beyond their traditional roles as mechanical supporters and electrical conductors. Nature emanates brilliant structural colors. The beautiful colors of bird feathers and butterfly wings may be the brightest structural colors in nature. Over the past decades, numerous artificial structures have been investigated for reproducing the structural colors of living creatures, which include nanoparticle assemblies, multiscale structures, photonic crystals, diffraction gratings, plasmonic nanostructures, and selective mirrors. [7][8][9][11][12][13][14] However, these biomimetic structures have mostly been fabricated on glass, Si, and plastic substrates. Moreover, many are impractical to apply for bulk metals due to issues with fabrication complexity, scalability, and durability. A photonic crystal (PC) is a periodic optical structure that affects the motion of photons in much the same way that crystal lattices affect electrons in solids. PC films can be fabricated by various methods. [15][16][17] Metal surfaces finished in color images or patterns are useful in a range of applications, including reflective color filters, interiors, sculpture, art, and jewellery. While PC films can produce highly saturated structural colors, they are not suitable for printing color images on metal substrates. In order to tune the produced color, the periodicity or the refractive-index variation of the PC structure should be modified. A scheme for colorizing metals should be simple and scalable and, most importantly, allow for easy color tuning. Herein, we propose a simple surface structure for producing vivid colors on stainless steel (STS) and Al, which are two of the most widely used metals.The proposed structure comprises a dielectric film inserted between a bulk metal substrate and thin metallic layer (Figure 1a). Metal-insulator-metal (MIM) thin-film stacks, which are Fabry-Perot (FP)-type resonant cavities, have been extensively investigated to realize near-perfect absorbers on opaque substrates and transmissive color filters on transparent substrates. [18][19][20][21][22] Because this MIM cavity acts as a band-stop The aesthetic functions of metals have attracted increasing attention, and their colorization is of scientific and technological significance. This study demonstrates that vivid structural colors can be produced on stainless steel and Al, which are two of the most commonly used metals. It is well known that a transparent dielectric film coated onto a substrate exhibits a rippled spectrum consisting of alternating reflectance minima and maxima due to multibeam interference, making it appear colored. However, such a film does not produce strong colors on a highly reflect...