Research ArticleAPPLIED OPTICS

Resonant laser printing of structural colors on high-index dielectric metasurfaces

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Science Advances  05 May 2017:
Vol. 3, no. 5, e1602487
DOI: 10.1126/sciadv.1602487
  • Fig. 1 Structural colors based on high-index dielectrics.

    (A) Schematic demonstration of the structures. (B) A 45° side-angle SEM image of imprinted plastic structures after Ge deposition. Color information is shown to clarify the diameter and spacing of the nanopillar structure. (C) Full palette of colors is revealed in an array of squares. By varying the radius of the pillars and the deposited Ge film thickness, structures with the same periodicity display a wide range of colors (from bottom right to top left). The highlighted row was measured to produce the experimental reflection spectra in (E). (D) Experimental structural color gamut of measured reflectance spectra from color plates in (C) presented in a standard CIE-1931 color space. (E) Selected experimental and simulated spectra for Ge films with a thickness T = 35 nm. The dips shift to longer wavelengths with varying radius of the nanostructures from R = 30 to 90 nm. (F) Taken at (i) normal and (ii) 60° side angle, optical images of an imprinted 10 cm sample following deposition of thin Ge layers with a uniform thickness T = 40 nm, showing the color rendition of 5 mm–by–5 mm squares similar to the third row in (C). (G) Experimental and simulated reflection spectra for angles of incidence from 4° to 70° for a sample with T = 35 nm and R = 75 nm (reflectivity is indicated by color bars).

  • Fig. 2 Macroscopic RLP of structural colors.

    (A) Schematic setup of RLP. Synchronous motion solution with the laser pulses is provided by computer-controlled motor or piezo stages. (B) Reflection and transmission microimages of multicolored structures generated by gradually increasing laser powers. Microstructures (i to ix) are generated under gradually increasing laser power strengths from 0.2 to 1.8 μJ in steps of 0.2 μJ, controlled using a liquid crystal attenuator. Scale bars, 0.5 mm. (C) Corresponding SEM images of the microstructures (i, iii, v, vii, and ix) in (B), showing the change of the morphology of the unit cell from disk to sphere and eventually a hole. Scale bars, 200 nm. (D) Experimental reflection spectra of the corresponding laser-printed color squares in (B). Note that the dips (absorbed light) with varying printing laser powers blueshift, causing color changes from cyan to yellow. a.u., arbitrary units. (E) Corresponding simulated reflection spectra. (F) Gamut loop of laser-printed structural colors, which covers CMY colors. (G) Collection of laser-printed paintings with protective polymethyl methacrylate (PMMA) coating (sufficiently thick to suppress Fabry-Pérot interference) deposited before laser printing. Samples have R = 135 nm with deposited Ge film thicknesses T = 45 nm (i), 40 nm (ii), 35 nm (ii), and 30 nm (iv), respectively. Scale bars, 5 mm. (H) Image of a colorful portrait (i), CMY halftoning of the original image (ii), printing of halftoned magenta color onto the initial cyan background (iii), and laser-printed full-color CMY halftoned image (iv). Scale bars, 5 mm. (I) Structural color laser printing of a portrait image. CMY halftoning realizes red, brown, and especially a saturated black color.

  • Fig. 3 Mechanism and result of the super-resolution RLP.

    (A) Mechanism of the formation of a focal spot by overlapping the excitation beam and the periodical resonator array. A Gaussian excitation beam with low power (i) is enhanced and modified by the periodical resonators supporting highly confined localized resonances (ii), producing an effective photothermal heating area smaller than a diffraction-limited spot (iii). Scale bar, 200 nm. The original laser power for super-resolution printing should not exceed the threshold for melting an unstructured Ge thin film, whereas the locally enhanced energy density should overcome the threshold to initialize photothermal reshaping processes. (B) SEM image shows the RLP within a single unit cell, addressing the morphology change of the centered particle. Scale bar, 200 nm. (C) RLP images with a resolution of 127,000 DPI. The samples are with T = 35 nm and R = 70 nm (left), 80 nm (middle), and 90 nm (right), respectively. Scale bars, 10 μm. (D) SEM image of an RLP image in (C), which shows details of the structure and the corresponding electron scattering changes induced by laser printing. Scale bar, 10 μm. (E) SEM image of an enlarged region of the image in (D), showing the remarkable detail and morphology change on a single–unit cell level. These modified unit cells exhibit different colors in the optical image because of an RLP-induced variation in nanodisk sizes and the ablation of the disks. Scale bar, 200 nm.

  • Fig. 4 Polarization-sensitive RLP color generation.

    (A) SEM image of bar-hole structure shows the geometry parameters for polarization-sensitive RLP color generation. The dimensions of the long and short axes and the heights of the plastic pillars are 90, 55, and 50 nm, respectively. By varying the deposited Ge film thickness, we can still tune the color appearances and the strength of the polarization-dependent optical responses. Inset shows the polarization information, where the 0° polarized light field will excite the longitudinal mode along the long axis of the resonator, whereas the 90° polarized light field will excite the transverse mode along the short axis. Scale bar, 500 nm. (B) Optical images of color palettes printed by different laser power dosages illuminated under 0° to 90° polarized light. Note that switching in polarization-dependent colors is more feasible in low-power printed colors. Scale bar, 500 μm. (C) Corresponding SEM images of the laser-printed structures in (B), showing the gradual morphology change of the structures from bars to shortened bars and then to spheres and finally to holes. Scale bars, 200 nm. (D) Optical images of laser-printed pictures from a sample with Ge film thickness T = 45 nm illuminated under 0°, 45°, and 90° polarized light, respectively, showing polarization-sensitive colors. Scale bars, 10 μm. (E) Optical images of a laser-printed picture from a sample with Ge film thickness T = 30 nm illuminated under 0°, 45°, and 90° polarized light, respectively. Scale bars, 10 μm. The laser-printed pattern shows high color contrast under 0° polarized light but vanishes under 90° polarized light illumination.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/5/e1602487/DC1

    fig. S1. Permittivities of deposited amorphous Ge and Si and structural colors with silicon resonators.

    fig. S2. Ge resonator versus Al resonator.

    fig. S3. Radius-dependent resonances and colors for uncoated and coated samples.

    fig. S4. Simulations of the heat power generation and transferring within a resonant unit cell.

    fig. S5. Comparison of plasmonic laser printing with nonplasmonic RLP.

    fig. S6. Reflective and semitransparent colors that resulted from RLP on different samples.

    fig. S7. Flexible and robust samples.

    fig. S8. A collection of samples with a color printing resolution of 127,000 DPI.

    fig. S9. Measured and simulated reflectance spectra for laser-printed polarized samples.

    movies S1 to S3

    Reference (76)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Permittivities of deposited amorphous Ge and Si and structural colors with silicon resonators.
    • fig. S2. Ge resonator versus Al resonator.
    • fig. S3. Radius-dependent resonances and colors for uncoated and coated samples.
    • fig. S4. Simulations of the heat power generation and transferring within a resonant unit cell.
    • fig. S5. Comparison of plasmonic laser printing with nonplasmonic RLP.
    • fig. S6. Reflective and semitransparent colors that resulted from RLP on different samples.
    • fig. S7. Flexible and robust samples.
    • fig. S8. A collection of samples with a color printing resolution of 127,000 DPI.
    • fig. S9. Measured and simulated reflectance spectra for laser-printed polarized samples.
    • Reference (76)

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