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All-Dielectric Dual-Color Pixel with Subwavelength Resolution Yusuke Nagasaki, Masafumi Suzuki, and Junichi Takahara Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.7b03421 • Publication Date (Web): 15 Nov 2017 Downloaded from http://pubs.acs.org on November 15, 2017

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All-Dielectric Dual-Color Pixel with Subwavelength Resolution Yusuke Nagasaki†, Masafumi Suzuki†, and Junichi Takahara*,†,‡ †

Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871,

Japan ‡

Photonics Center, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita,

Osaka 565-0871, Japan KEYWORDS: all-dielectric, structural color, color printing, optical antenna, metamaterial, Si nanostructure

ACS Paragon Plus Environment

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ABSTRACT: An all-dielectric optical antenna supporting Mie resonances enables light confinement below the free-space diffraction limit. The Mie scattering wavelengths of the antenna depend on the structural geometry, which allows the antennas to be used for colored imprint images. However, there is still room for improving the spatial resolution, and new polarization-dependent color functionalities are highly desirable for realizing a wider color tuning range. Here, we show all-dielectric color printing by means of dual-color pixels with a subwavelength-scale resolution. The simple nanostructures fabricated with monocrystalline silicon exhibit various brilliant reflection color by tuning the physical dimensions of each antenna. The designed nanostructures possess polarization-dependent properties that make it possible to create overlaid color images. The pixels will generate individual color even if operating as a single element, resulting in the achievement of subwavelength-resolution encoding without color mixing. This printing strategy could be used to further extend the degree of freedom in structural color design.


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Structural color is produced by light scattering or interference in micro-nanostructures without any specific pigment, and this phenomenon is widely observed in nature; for example, Morpho butterfly wings exhibit a vivid blue color due to light interference in their combed scales.1,2 As nanofabrication technology has dramatically developed, structural colors have been able to be precisely controlled with artificially created nanostructures such as inversed opal films,3 dielectric multilayers,4 gratings,5 and photonic crystals.6,7 In the past several years, the color control variety has been extended by metallic (i.e., plasmonic) nanostructures as reflection color printing.8–17 Controlling the absorption peak wavelengths of plasmon resonances, which are standing waves of surface plasmon polaritons supported by a metallic nanostructure, the reflection color can be tuned in the visible wavelength region. Moreover, the capability of confining plasmon modes to smaller volumes beyond the optical diffraction limit of the operation wavelengths enables subwavelength color printing achieving ~100,000 dots per inch (dpi), which is the highest possible resolution. However, improving the color purity is a challenge because of the low Q-factor resonance property arising from the high inherent losses at visible wavelengths of the metallic material. Although color printing based on combining several absorption peaks for purity improvement has recently been reported,18 the existence of several low Q-factor resonances over a limited wavelength region leads to a decrease in the reflectance. Other potential candidates for structural color are Mie-resonance-based all-dielectric optical antennas.19–24 While plasmon resonances on a metallic antenna mainly respond to incident electric fields,25,26 both the electric and magnetic fields entering a high-index dielectric nanostructure are confined and Mie resonance occurs.27–31 The Mie resonance property of the color tunability dependent on the structural geometry32–34 has facilitated the realization of all-dielectric color printing.35-39 Owing to the resonance in a low-loss material, such antennas


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have a higher Q-factor compared with that of metal,35 providing the capability to create color printing with a higher reflectance and purity. The spatial resolution, described as the number of pixels where adjacent colors can be distinguished, is also important in printing applications, and all-dielectric printing with a resolution of ~16,000 dpi has been demonstrated;36 however, the resolution limit has not yet been reached, leaving room for further improvement. It should be noted that shrinking the gap between resonators leads to unexpected color generation owing to coupling with neighboring structures. Indeed, the individual high-index building blocks supporting resonant leaky modes can be perturbed by the presence of other closely spaced structures.40 This coupling effect causes non-negligible resonant peak shifts and peak splitting.41 Unless the structural position is carefully designed, unexpected color and color mixing could be generated at subwavelength resolution.

Therefore, the realization of color printing based on

high-resolution pixels independently producing an individual color without undesirable color mixing with closely spaced adjacent pixels is highly required. In addition, by extending the design guideline from a symmetric building block to a shape with different widths, the color property

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polarization-dependent feature is useful for high-density colored data printing with only a single layer, because more color information can be simultaneously encoded in one element.13 This also requires color independence and a high resolution to improve the density. Thus, this reinforces the importance of designing an independent color pixel that generates an individual color with a subwavelength resolution. Construction of antennas according to the new design guidelines would also facilitate intriguing polarization applications including circular polarization light control,42 polarized data storage,43 and color holography.44 Here, we show all-dielectric color printing by means of Si nanoblocks with a subwavelength


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resolution in the visible wavelength region. The simple nanoblock arrays consist of monocrystalline Si and exhibit Mie-type electric and magnetic resonances, which generate various brilliant reflection color by tuning the physical dimensions of each nanoblock. Since the designed nanoblocks have polarization-dependent properties, two-color information can be encoded in the same area. This allows us to create a switchable display image encoded with dual color states. Significantly, the fabricated nanoblock maintains the color phase even as an individual element. Thus, even though different sized nanoblocks are closely spaced, individual colors can be generated without color mixing. We start by designing all-dielectric nanostructures with a subwavelength resolution. A schematic of the proposed all-dielectric nanostructures, which are composed of arrays of Si nanoblocks of different widths wx and wy on a quartz substrate, is shown in Figure 1a. Nanoblocks with a thickness t of 150 nm are arranged in a square lattice with a periodicity p of 300 nm, which is below the free-space optical diffraction limit in the visible region. Si is used as a high-index, low-loss material at theses wavelengths to confine a sufficient amount of light to the nanoblock. The native surface oxide layer45 protects the Si nanoblocks from reactions with the environment and contributes to an enhancement in the color stability without the need for a polymer protective layer. Moreover, since Si has been used in the semiconductor industry in planar processes of mass-production complementary metal–oxide–semiconductor fabrication technology, one advantage is that substrates including monocrystalline Si can be obtained relatively easily. To experimentally obtain the desired optical properties, the Si nanoblock arrays were fabricated as follows. A chemical resist was coated on a “silicon-on-quartz” substrate (a thin monocrystalline Si layer on a quartz substrate; Shin-Etsu Chemical Co., Ltd.), and mask patterns


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were printed using electron beam lithography. A hard mask of Cr with a thickness of 30 nm was deposited using a heat resistive evaporator and lifted off to remove unnecessary metals. The Si layer was then selectively etched by plasma gases in a reactive ion etching chamber, and the top Cr mask was removed (see Supporting Information S1). Figure 1b shows a scanning ion microscope (SIM) image of the typical Si nanoblock arrays on the quartz substrate. Optical measurements were performed using a confocal reflection microscope with an objective lens connected to a charge-coupled device camera and a spectroscope (see Supporting Information S2)

. Figure 1. Structural geometry of the proposed all-dielectric nanostructures. (a) Schematic of the Si nanoblock array on a quartz substrate. Ex-polarized light is incident on the Si nanostructure normal to the substrate surface. (b) Oblique SIM image of the Si nanoblock array with widths of 200 nm (wx = wy = 200 nm), a thickness t of 150 nm, and a periodicity p of 300 nm.


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Figure 2 shows a bright-field optical image of the fabricated nanoblock arrays under linearly polarized white-light illumination through a ×20 objective (numerical aperture NA of 0.45). The widths wx and wy in the incident electric and magnetic field directions, respectively, are systematically varied from 60 to 200 nm in 10 nm increments. Distinct vivid color pixels exhibiting red, green, and blue can be obtained from each area. The color phase strongly depends on the physical geometry of the nanoblock. In addition, the color phase tends from blue to red with increasing width. Furthermore, rotating the incident polarization by 90° inverts the color pattern along the diagonal (see Supporting Figure S3). Switchable all-dielectric color pixels are thus achievable by changing the incident polarization.

Figure 2. Optical microscope image of the fabricated all-dielectric nanoblock arrays through a ×20 objective (NA: 0.45) irradiated with Ex-polarized white light. The widths wx and wy are changed from 60 to 200 nm in 10 nm increments. Each individual color area is 10 × 10 μm2. The black frame is provided by the unstructured regions. Scale bar = 20 µm.


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To further investigate the reflection properties of the fabricated nanoblock arrays, the experimental reflection spectrum for each nanoblock width was quantitatively compared with the corresponding spectrum simulated using commercially available three-dimensional rigorous coupled-wave analysis calculations (see Supporting information S4). Figure 3a,b shows the variation in the reflection spectrum for a fixed nanoblock width of 150 nm in one dimension as the width in the other dimension is changed from 60 to 200 nm. The electric and magnetic fields of the incident light propagating along the z-axis are oriented along the x- and y-axes, respectively. The relative permittivity of Si was determined from an ellipsometry measurement (see Supporting Information S5), and the refractive index of the quartz was fixed at 1.46. The experimental spectra can be tuned across all visible wavelengths and are in good agreement with the calculations. Strong reflection peaks are observed in the spectra, and there is a redshift in the peak positions as the width increases. These features are attributed to Mie resonances that both electric and magnetic dipoles resonate inside the high-index dielectric antenna. By tuning the physical dimensions of each antenna, the Mie resonance wavelengths are shifted, resulting in changes in the optical properties. Due to the presence of the electric and magnetic dipoles in the antenna, the reflection property is mainly determined by the resonant impedance matching.20,46 It is understood that when either the real part of the effective permittivity or permeability of the low-loss material nanostructure is negative, electric (or magnetic) polarization opposite to the incident electric (or magnetic) field occurs in the nanostructure, which can result in a reversal of the Poynting vector of electromagnetic waves, that is, reflection. The minor deviation between the numerical and experimental spectra may arise from the influence of the native oxide layer on the Si nanoblocks (see Supporting Information S6). Furthermore, oblique illumination through a


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microscope objective (see Supporting Information S7, and S8) can also cause undesired spectral shifts and reflection dips, because incident light includes various angles components with the vertical component due to the NA. To reduce simulation time, we assumed the nanoblocks were ideal rectangular parallelepipeds with sharp corners, and therefore, structural imperfections including rounded corners may affect the discrepancies as they are not accounted for in the numerical simulation. To improve the reflection intensity of the designed color, namely color saturation, it is important to increase the density of the nanoblock arrays. Since the resonant dipole of a high-index dielectric antenna is basically internally excited, the effect of the periodicity on the resonant mode is not as critical. Indeed, the color phase and reflection peak positions are maintained even when the periodicity is changed (see Supporting Information S9). Color saturation without a large color change can be controlled by varying the periodicity. Nanoblocks excite distinct resonant modes that depend on wx and wy. The electric and magnetic resonances generate sharp reflection peaks, leading to various polarization-dependent structural colors. To intuitively understand whether the reflection peaks originate from the excited resonances, we visualized both the electric and magnetic field distributions using vector plots over the unit cell for two typical reflection peaks of a (wx, wy) = (150 nm, 100 nm) nanoblock by employing finite-difference time-domain simulations (Figure 3c-f). For the peak at the longer wavelength (λ = 620 nm), the electric field rotates inside the antenna, while the magnetic field is concentrated near the center of the nanoblock (Figure 3c,d), as evidenced by the magnetic dipole resonance arising from the circular displacement current generated by the trapped incident electromagnetic waves.47,48 In contrast, for the peak at the shorter wavelength (λ = 545 nm), the magnetic field rotates inside the antenna and the electric field exhibits a dipole-like distribution (Figure 3e,f), which is generated from the linear displacement current


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inducing the magnetic field vortex. The peak at an even shorter wavelength (around λ = 470 nm) indicates the presence of higher multipole resonances. Analytical calculations by a multipole decomposition method also support these dipole contributions to the reflection peaks (see Supporting information S10). Owing to the presence of the substrate, which has a different index to the material surrounding the nanoblock, and retardation effects, the electric and magnetic fields are no longer symmetrical and are biased toward the interface between the nanoblock and substrate.49,50 Moreover, both dipole resonances are slightly rotated. This can be ascribed to the spatial superposition of the dipole and the rotated field distribution because the electric and magnetic resonance wavelengths are close and mutually influenced. Similar field distributions (not shown) for a (wx, wy) = (100 nm, 150 nm) nanoblock were also obtained. By tailoring the structural geometry to modulate the electric and magnetic resonances, a wider color range can be designed.


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Figure 3. Reflection properties of the Si nanoblock arrays. Reflection spectra for (a) wx and (b) wy fixed at 150 nm. The solid black and broken red lines show the experimental and simulated spectra, respectively. Insets show optical microscope images obtained from Figure 2 with an area of 5 × 5 µm2 corresponding to the nanoblock size. Vector plots of the magnetic and electric field distributions for a (wx, wy) = (150 nm, 100 nm) nanoblock at (c, d) λ = 620 nm and (e, f) λ = 545 nm.

The tunable range of the designed color printing is of importance for color printing applications physiologically perceived by the human eye. To quantitatively evaluate the obtained reflection spectra, the measured spectra were converted to the CIE1931 color space, which is commonly used for color evaluation (Figure 4a). Light reflection from an object stimulates three main types of photoreceptors in our retina that correspond to red, green, and blue (RGB), and we recognize colors from the ratio of the amount of stimulation. To describe perceived color, the spectral response properties of these photoreceptors are mathematically represented as the color-matching functions 𝑥̅ (𝜆), 𝑦̅(𝜆), and 𝑧̅(𝜆) in the CIE1931 color space. For a measured reflection spectra R(λ) from an object, the stimulation values on the photoreceptors can be written as X = ∫ 𝑅(𝜆)𝑥̅ (𝜆)𝑑𝜆, Y = ∫ 𝑅(𝜆)𝑦̅(𝜆)𝑑𝜆, and Z = ∫ 𝑅(𝜆)𝑧̅(𝜆)𝑑𝜆. These values are then normalized as x = X/(X + Y + Z) and y = Y/(X + Y + Z) for unambiguous identified color evaluation. The blue dots in Figure 4a show converted values of the reflection spectra of the fabricated nanoblock arrays in Figure 3a,b, and wide-range color printing can be achieved by using the designed antenna. Polarization-independent shapes (i.e., wx = wy) also exhibit good color variety capability as shown by the red triangles. Owing to the sharp reflection peaks based on the Mie resonances of the nanoblocks, various colors can be generated.


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For color management, white is also an essential color in the development of full-color printing. Although some nanoblocks have the potential to generate a white color, a pure white color, that is, a converted xy value close to the achromatic point (x, y) = (0.33, 0.33), is desired. We attempted to create a white pixel by arranging two nanoblocks of different sizes, (wx, wy) = (80 nm, 90 nm) and (120 nm, 100 nm), in a 300 × 300 nm2 unit cell as shown in Figure 4b. The obtained optical image (Figure 4c) exhibits a white color through a ×20 objective. To quantitatively analyze the optical properties, we performed reflection spectral measurements of the mixed nanoblock array under Ex-polarized white-light illumination. There are three reflection peaks in the experimental spectra (Figure 4d), and two of the reflection peaks reach a reflectance of 50%. The short- and long-wavelength peaks are in qualitative agreement with the numerical simulations shown in orange, but the central peak cannot be reproduced. This peak is thought to be generated by oblique incident light. Incident white light passing through the objective irradiates the substrate normally and obliquely to the surface because of the influence of the NA. A central reflection peak can be generated in the calculated spectra (broken blue line) by tilting the incident angle θ by 20° away from the surface normal while keeping the magnetic field parallel to the interface (p-polarized incidence). It is worth noting that for s-polarized incidence (electric field parallel to the interface), the original peak positions are preserved even when the incident angle is changed, and so the spectra for s-polarized incidence is not presented. The spectral discrepancy of the experimental and simulated spectra can result from fabrication errors as discussed above. The color space value of the experimental spectra is (x, y) = (0.34, 0.34) and is indicated by the black star in Figure 4a. This is close to the achromatic point, which indicates the successful creation of white. This approach has the potential to not only create white but also further extend the color variation.


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Figure 4. Wide color tunability of the designed nanoblock arrays. (a) CIE1931 color space under the CIE standard illumination light source (E). Blue dots represent the converted xy value from the spectra in Figure 3a,b; those from the spectra of the polarization-independent nanoblock arrays in Figure 2 are represented as red triangles. The converted xy value from the spectra of the 60 nm nanoblock array is not shown as the reflection peak lies outside the visible wavelength region. (b) SIM image of the array with two different sized nanoblocks created to produce white.


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Scale bar = 500 nm. (c) Optical microscope image through a ×20 objective (NA: 0.45) of the array in (b). Scale bar = 5 μm. (d) Experimental (solid black line) and simulated (broken orange and blue lines) reflection spectra of the created white color. Spectra were simulated for normal (θ = 0°) and oblique (θ = 20°) incidence. The obtained xy value is indicated by the black star in (a).

Since the designed nanoblocks have polarization-dependent properties, it is possible to switch the reflection peak positions and the color phase by changing the incident polarization. To apply this to printing, we demonstrate an overlaid optical image of which the letters can be tuned by the incident polarization direction. Figure 5a,b shows the exact same area of the same structure through a ×20 objective for two different polarization directions. This structure consists of four different types of pixels: (i) (wx, wy) = (120 nm, 120 nm) polarization-independent nanoblocks that constantly generate a green color for the background; (ii) (wx, wy) = (80 nm, 130 nm) nanoblocks that exhibit blue and green colors for Ex- and Ey-polarized incident light, respectively, to generate tunable pixels; (iii) (wx, wy) = (130 nm, 80 nm) nanoblocks that generate the tunable pixel in (ii) in reverse; and (iv) (wx, wy) = (90 nm, 90 nm) polarization-independent nanoblocks that constantly generate a blue color for the intersecting areas. Each color is specially chosen to be of roughly the same saturation. For Ex-polarized incident light, the letters “Si” emerge in blue from the green background, whereas Ey-polarized incident light produces the number “14” in blue on the green background (see Movie S1). There is no significant color deviation in any part of the letters or background in the fabricated color bitmap. This visual homogeneity due to the same degree of saturation allows the letters and background to be clearly distinguished. Our designed nanoblock array enables the encoding of two-color information in the same area.


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Figure 5. Dual color bitmap. Optical microscope image through a ×20 objective (NA: 0.45) for (a) Ex- and (b) Ey-polarized incident light. Grids are provided to clarify each 5 × 5 μm2 area as one pixel.

The amount of information encoded per unit area is an essential parameter for printing applications. To verify the achievement of subwavelength resolution, we demonstrate checkered patterns consisting of alternating nanoblocks of two different sizes with widths of 80 nm and 120 nm as shown in Figure 6a. The bright-field microscope image through a ×150 objective (NA: 0.9) in Figure 6b shows that individual blue and yellow pixels with a unit cell area of 300 × 300 nm2 can be distinguished and observed while maintaining the color phase corresponding to the selected size. This feature suggests that individual nanoblocks produce color without color mixing even at a subwavelength-scale resolution. Interestingly, this subwavelength nanoblock can dependently generate a specific color even though it is a single pixel without periodicity unlike photonic crystals. Figure 6c,d depicts an SIM and a bright-field (not dark-field) optical image of the characters “RGB” printed in the corresponding color. The nanoblocks widths of (wx, wy) = (160 nm, 170 nm), (120 nm, 90 nm), and (90 nm, 60 nm) for “R”, “G”, and “B”, respectively, were selected from the color map in Figure 2 for the character encoding. The characters are displayed using pixels with an area of 300 × 300 nm2 not in a periodic array and


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exhibit vivid RGB colors, which are sufficiently distinguishable through a ×150 objective (NA: 0.9). The slight color brightness difference (for example, the vertical and horizontal lines on the G) originates from the grating effect due to large NA. As shown in Supporting information S7, p-polarized oblique incidence with large angles excites grating modes only in the structures aligned in the direction of the electric fields (that is, the x axis), resulting in decrease in the brightness of the pixels aligned in the lateral direction. The pixels preserve the color phase selected by the corresponding area, and this suggests that the resonance property of the nanoblock is not dependent on adjacent nanoblocks. Indeed, as shown in Supporting information S11, the backscattering cross sections of a single element and the reflection spectra of the periodic arrays are strongly linked, supporting the assertion that the coupling between adjacent structures is very weak. Furthermore, experimentally measured reflection spectra for a single Si nanoblock are qualitatively in agreement with that of the arrayed nanoblock (see Supporting Information S12). These results make it possible to construct an intuitive design strategy with individual colors designed with a subwavelength element, applicable even to periodic systems. This feature is very useful for color printing applications. It is only necessary to design the color of a single pixel and then form the image because the pixel can be used in a periodic array without an unexpected color change. All-dielectric color printing with a subwavelength resolution can be realized by using the proposed simple nanostructure. The resonant behavior of the antenna can also be modified by the thickness of the Si nanoblock, the permittivity originating from the Si crystallinity, and the surroundings such as a polymer coating (see Supporting Information S13–S15). In this research, we focused on the simple geometry and the sample availability, but to further increase the reflectance, it would be important to use a material with negligible optical losses in the visible region such as GaN, AlAs,


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or diamond, or a substrate that has a reflective layer like a “silicon-on-insulator” substrate.

Figure 6. Demonstration of a subwavelength pixel. (a) SIM and (b) bright-field optical microscope images of a checkered pattern consisting of alternating nanoblocks of two different sizes. (c) SIM and (d) optical microscope images of the letters “RGB” by means of nanoblocks generating the corresponding color. Both scale bars = 1 µm. Optical images were obtained with a ×150 objective (NA: 0.9).

In conclusion, we have experimentally demonstrated all-dielectric dual color pixels with a subwavelength resolution. The fabricated Si nanoblock arrays exhibited distinct vivid colors, which were strongly dependent on the physical geometry of the antenna. Through numerical analysis, the origin of the size-dependent color change was shown to be Mie resonant electric and magnetic dipoles excited inside the antenna. Quantitative evaluation of the obtained reflection spectra indicated a wide tunable color range including white. These elements can also


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simultaneously possess two-color information, enabling switchable reflection images by changing the incident polarization. Furthermore, individual pixels in a checkered pattern could be distinguished, suggesting the realization of a subwavelength pixel without color mixing. Additionally, even an individual element with a pixel area of 300 × 300 nm2 not in a periodic array generated an individual color, which could lead to achieving a high resolution of ~85,000 dpi. Given the weak periodic dependence of the nanoblock, color printing with our designed nanostructure has sufficient potential to achieve a resolution of ~100,000 dpi. We believe that this printing approach can be used for further improvement in the degree of freedom of structural color design and has tremendous potential applications such as security certification, optical data storage, and three-dimensional displays. Generally, the refractive index of a semiconductor increases as the temperature increases, and thus the resonance properties would be also modified. The temperature dependence of the permittivity could also be utilized for tunable color printing, which remains a fascinating prospect.


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ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI:xxxxxx Fabrication details; optical setup; incident polarization dependence; calculation method; optical constants of Si; influence of structural oxidation on the spectra; incident angle dependence; influence of objectives on the spectra; periodic dependence; resonance mode analysis; backward scattering cross section of a single nanoblock; reflection spectra for a single Si nanoblock; thickness dependence; reflection spectra of amorphous Si nanoblock arrays; and optical image with a coating polymer (PDF) Movie showing switching of the overlaid image in Figure 5a,b (AVI) AUTHOR INFORMATION Corresponding Author *[email protected] Author Contributions Y.N. conceived the idea of the Si color printing and designed the structures. J.T. supervised the project. Y.N. and M.S. performed the numerical simulations. M.S. and Y.N. performed the experiments. Y.N. analyzed the experimental data and wrote the initial draft of the manuscript. All the authors discussed the results and contributed to the writing of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the Photonics Advanced Research Center (PARC), Osaka University. Y.N. is supported by a Research Fellowship from the Japan Society for the Promotion of Science (JSPS) for Young Scientists. Part of this work was supported by the “Nanotechnology Platform


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Project (Nanotechnology Open Facilities in Osaka University)” of the Ministry of Education, Culture, Sports, Science and Technology, Japan [No.: F-16-OS-0015, F-17-OS-0011, S-17-OS-0011]. We would like to thank Dr. Masashi Miyata for helpful discussions on this project. We also thank Shin-Etsu Chemical Co., Ltd. for the donation of high-quality silicon-on-quartz substrates.


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REFERENCES (1) Vukusic, P.; Sambles, J. R.; Lawrence, C. R.; Wootton, R. J. Proc. R. Soc. Lond. B 1999, 266, 1403−1411. (2)

Zhao, Y.; Xie, Z.; Gu, H.; Zhu, C.; Gu, Z. Chem. Soc. Rev. 2012, 41, 3297−3317.

(3)

Gu, Z.-Z.; Uetsuka, H.; Takahashi, K.; Nakajima, R.; Onishi, H.; Fujishima, A.; Sato, O.

Angew. Chem. Int. Ed. 2003, 42, 894−897. (4)

Wu, Z.; Lee, D.; Rubner, M. F.; Cohen, R. E. Small 2007, 3, 1445−1451.

(5)

Kanamori, Y.; Shimono, M.; Hane, K. IEEE Photonics Technol. Lett. 2006, 18,

2126−2128. (6)

Arsenault, A. C.; Puzzo, D. P.; Manners, I.; Ozin, G. A. Nat. Photonics 2007, 1,

468−472. (7)

Teyssier, J.; Saenko, S. V.; van der Marel, D; Milinkovitch, M. Nat Commun. 2015, 6,

6368. (8)

Kumar, K.; Duan, H.; Hegde, R. S.; Koh, S. C. W.; Wei, J. N.; Yang, J. K. W. Nat.

Nanotechnol. 2012, 7, 557−561. (9)

Wu, Y.-K. R.; Hollowell, A. E.; Zhang, C.; Guo, L. J. Sci. Rep. 2013, 3, 1194.

(10) Roberts, A. S.; Pors, A.; Albrektsen, O.; Bozhevolnyi, S. I. Nano Lett. 2014, 14, 783−787. (11) Tan, S. J.; Zhang, L.; Zhu, D.; Goh, X. M.; Wang, Y. M.; Kumar, K.; Qiu, C.-W.; Yang, J. K. W. Nano Lett. 2014, 14, 4023−4029. (12) Clausen, J. S.; Højlund-Nielsen, E.; Christiansen, A. B.; Yazdi, S.; Grajower, M.; Taha, H.; Levy, U.; Kristensen, A.; Mortensen, N. A. Nano Lett. 2014, 14, 4499−4504. (13) Goh, X. M.; Zheng, Y.; Tan, S. J.; Zhang, L.; Kumar, K.; Qiu, C.-W.; Yang, J. K. W. Nat. Commun. 2014, 5, 5361.


22

Page 23 of 26

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(14) Cheng, F.; Gao, J.; Luk, T. S.; Yang, X. Sci. Rep. 2015, 5, 11045. (15) Franklin, D.; Chen, Y.; Vazquez-Guardado, A.; Modak, S.; Boroumand, J.; Xu, D.; Wu, S.-T.; Chanda, D. Nat. Commun. 2015, 6, 7337. (16) Cheng, F.; Gao, J.; Stan, L.; Rosenmann, D.; Czaplewski, D.; Yang, X. Opt. Express 2015, 23, 14552–14560. (17) Miyata, M.; Hatada, H.; Takahara, J. Nano Lett. 2016, 16, 3166−3172. (18) Mudachathi, R.; Tanaka, T. Sci. Rep. 2017, 7, 1199. (19) Jahani, S.; Jacob, Z. Nat. Nanotech. 2016, 11, 23−36. (20) Moitra, P.; Yang, Y.; Anderson, Z.; Kravchenko, I. I.; Briggs, D. P.; Valentine J. Nat. Photonics 2013, 7, 791–795. (21) Zhang, J.; MacDonald, K. F.; Zheludev. N. I. Opt. Express 2013, 21, 26721−26728. (22) Vynck, K.; Felbacq, D.; Centeno, E.; Căbuz, A. I.; Cassagne, D.; Guizal, B. Phys. Rev. Lett. 2009, 102, 133901. (23) Yang, Y.; Kravchenko, I. I.; Briggs, D. P.; Valentine J. Nat. Commun. 2014, 5, 5753. (24) Ginn, J. C.; Brener, I.; Peters, D. W.; Wendt, J. R.; Stevens, J. O.; Hines, P. F.; Basilio, L. I.; Warne, L. K.; Ihlefeld, J. F.; Clem, P. G.; Sinclair, M. B. Phys. Rev. Lett. 2012, 108, 097402. (25) Zayats, A. V.; Smolyaninov, I. I.; Maradudin, A. A. Phys. Rep. 2005, 408, 131–314. (26) Schuller, J. A.; Barnard, E. S.; Cai, W.; Jun, Y. C.; White, J. S.; Brongersma, M. L. Nat. Mater. 2010, 9, 193–204. (27) Schuller, J. A.; Brongersma, M. L. Opt. Express 2009, 17, 24084−24095. (28) Krasnok, A. E.; Miroshnichenko, A. E.; Belov, P. A.; Kivshar, Y. S. Opt. Express 2012, 20, 20599−20604. (29) Person, S.; Jain, M.; Lapin, Z.; Sáenz, J. J.; Wicks, G.; Novotny, L. Nano Lett. 2013, 13,


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Page 24 of 26

1806–1809. (30) Landreman, P. E.; Chalabi, H.; Park, J.; Brongersma, M. L. Opt. Express 2016, 24, 29760−29772. (31) Kuznetsov, A. I.; Miroshnichenko, A. E.; Brongersma, M. L.; Kivshar, Y. S.; Luk’yanchuk, B. Science 2016, 354, aag2472. (32) Cao, L.; Fan, P.; Barnard, E. S.; Brown, A. M.; Brongersma, M. L. Nano Lett. 2010, 10, 2649–2654. (33) Proust, J.; Bedu, F.; Gallas, B.; Ozerov, I.; Bonod, N. ACS Nano 2016, 10, 7761−7767. (34) Wiecha, P. R.; Arbouet, A.; Girard, C.; Lecestre, A.; Larrieu, G.; Paillard, V. Nat. Nanotech. 2017, 12, 163−169. (35) Vashistha, V.; Vaidya, G.; Hegde, R. S.; Serebryannikov, A. E; Bonod, N.; Krawczyk, M. ACS Photonics 2017, 4, 1076−1082. (36) Sun, S.; Zhou, Z.; Zhang, C.; Gao, Y.; Duan, Z.; Xiao, S.; Song, Q. ACS Nano, 2017, 11, 4445–4452. (37) Zhu, X.; Yan, W.; Levy, U.; Mortensen, N. A.; Kristensen, A Science Advances 2017, 3, e1602487. (38) Wood, T.; Naffouti, M.; Berthelot, J.; David, T.; Claude, J. B.; Métayer, L.; Delobbe, A.; Favre, L.; Ronda, A.; Berbezier, I.; Bonod, N.; Abbarchi, M. ACS Photonics 2017, 4, 873-883. (39) Flauraud, V.; Reyes, M.; Paniagua-Domínguez, R.; Kuznetsov, A. I.; Brugger, J. ACS Photonics 2017, 4, 1913–1919. (40) Cao, L.; Fan, P.; Brongersma, M. L. Nano Lett. 2011, 11, 1463-1468. (41) Zywietz, U.; Schmidt, M. K.; Evlyukhin, A. B.; Reinhardt, C.; Aizpurua, J.; Chichkov, B. N. ACS Photon. 2015, 2, 913-920.


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Page 25 of 26

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(42) Kruk, S.; Hopkins, B.; Kravchenko, I. I.; Miroshnichenko, A.; Neshev, D. N.; Kivshar, Y. S. APL Photonics 2016, 1, 030801. (43) Mansuripur, M.; Zakharian, A. R.; Lesuffleur, A.; Oh, S.-H.; Jones, R. J.; Lindquist, N. C.; Im, H.; Kobyakov, A.; Moloney, J. V. Opt. Express 2009, 17, 14001−14014. (44) Wen, D.; Yue, F.; Li, G.; Zheng, G.; Chan, K.; Chen, S.; Chen, M.; Li, K. F.; Wong, P. W. H.; Cheah, K. W.; Pun, E. Y. B.; Zhang, S.; Chen, X. Nat. Commun. 2015, 6, 8241. (45) Morita, M.; Ohmi, T.; Hasegawa, E.; Kawakami, M.; Ohwada, M. J. Appl. Phys. 1990, 68, 1272−1281. (46) Slovick, B.; Yu, Z. G.; Berding, M.; Krishnamurthy, S. Phys. Rev. B 2013, 88, 165116. (47) Cao, L.; White, J. S.; Park, J.-S.; Schuller, J. A.; Clemens, B. M.; Brongersma, M. L. Nat. Mater. 2009, 8, 643–647. (48) Brongersma, M. L.; Cui, Y.; Fan, S. Nat. Mater. 2014, 13, 451−460. (49) Yi, N.; Sun, S.; Gao, Y.; Wang, K.; Gu, Z.; Sun, S.; Song, Q.; Xiao, S. Sci. Rep. 2016, 6, 25760. (50) Ee, H.-S.; Kang, J.-H.; Brongersma, M. L.; Seo, M.-K. Nano Lett. 2015, 15, 1759−1765.


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Table of Contents Graphic


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All-Dielectric Dual-Color Pixel with Subwavelength ... - ACS Publications

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