Research ArticleAPPLIED SCIENCES AND ENGINEERING

Nano-kirigami with giant optical chirality

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Science Advances  06 Jul 2018:
Vol. 4, no. 7, eaat4436
DOI: 10.1126/sciadv.aat4436
  • Fig. 1 Macro-kirigami and nano-kirigami.

    (A) Camera images of the paper kirigami process of an expandable dome (corresponding to a traditional Chinese kirigami named “pulling flower”). (B) SEM images of an 80-nm-thick gold film, a 2D concentric arc pattern and a 3D microdome. The high-dose FIB milling corresponds to the “cutting” process, and the global low-dose FIB irradiation of the sample area (enclosed by the dashed ellipse) corresponds to the “buckling” process in nano-kirigami. The buckling direction is downward along the FIB incident direction (fig. S1G). A 3D feature size of 50 nm is shown in the inset. (C to F) A 12-blade propeller and (G to J) a four-arm pinwheel formed in a macroscopic paper and a gold nanofilm, respectively. Top-view SEM images of the milled 2D patterns before (D and H) and after (E and I) global FIB irradiation from the top, respectively. (F) and (J) are the side views of (E) and (I), respectively, which are in good correspondence to the macro-kirigami in (C) and (G). The dashed lines in (H) and (I) indicate a connection between two corners of the central structure, revealing a rotation angle of ~41° by nano-kirigami. The in situ fabrication can be programmed into one step (movie S1). Scale bars in SEM images, 1 μm.

  • Fig. 2 Topography-guided nano-kirigami.

    (A) Schematic illustration of residual stress distribution of gold nanofilm under global ion beam irradiation. In this bilayer model (section S1), the constant tensile stress (σt) is dominant within the top amorphous layer, and the elastic stress (σb) is linearly distributed across the bottom polycrystalline layer. In such a case, when one edge is fixed (as noted by the red squares), the cantilever will bend upward. While both boundaries of the cantilever are fixed, the film could bend downward under the topography-guided stress equilibrium. (B and C) SEM images of (B) a tongue-like structure and (C) a flower-like structure before and after global ion beam irradiation. The calculated (Cal) structures well represent the upward bending process. (D and E) SEM images of (D) a spider web–like and (E) a concentric arc structure before and after global ion beam irradiation, showing distinctive downward buckling amplitudes under the same irradiation. (F to H) SEM images of (F) a twisted triple Fibonacci spiral, (G) window decoration–type nanobarriers, and (H) a deformable spiral. Calculated results in (B) to (E) are displayed with the same color bar as in (B). Scale bars, 1 μm.

  • Fig. 3 Functional designs for optical chirality.

    (A) Schematic of vertical helix array, horizontal cross-linked helices, and a 3D pinwheel array [the 3D pinwheel can also be treated as two cross-linked and twisted ohm-shaped circuits (28) standing onto a metallic hole array]. (B and C) Illustration of the responses to the (B) electric field (Ex) and (C) magnetic field (Hy) of incident light for the LH and RH twisted pinwheels, respectively. The direction of induced electric moments pi,j (i = x or y, j = L or R) and magnetic moments mi,j at the center parts is noted by the arrows for LH (j = L) and RH (j = R) pinwheels, respectively (generalized from the simulated results in fig. S7). (D) Numerical designs of three 2D spiral patterns (types I, II, and III), the top view, and side view of the numerically predicted 3D structures, respectively, under the same residual stress distribution. (E) SEM images of the fabricated 2D patterns and corresponding 3D pinwheels after global ion irradiation with the same doses, agreeing excellently with the numerical predictions. Scale bars, 1 μm.

  • Fig. 4 Giant optical chirality.

    (A and B) SEM images of (A) 2D and (B) 3D pinwheel array with periodicity of 1.45 μm. The height of the 3D pinwheels is about 380 nm. (C) Top-view SEM images of LH and RH 3D pinwheel arrays. Scale bars, 1 μm. (D) Measured CD in transmission [defined as CDT = (TLTR)/(TL + TR)] versus wavelength for 2D LH, 3D LH, and 3D RH pinwheels, respectively. a.u., arbitrary units. (E) Measured (circular points) and calculated (solid lines) linear polarization rotation angle (θ) versus wavelength for 3D and 2D LH pinwheels, respectively. The unrealistic abrupt peaks around 1.45 μm in calculation are not shown for clearance because of the inaccurate retrieval of polarization states at nearly zero transmission at Wood’s anomaly (see full calculated data in fig. S9). Inset: Schematic of the linear polarization rotation. (F) Polar plot of (top) experimental and (bottom) calculated transmission versus detection polarization angle at specific wavelengths under x-polarized incidence for the 3D LH pinwheels. Nearly linearly polarized states are observed. In comparison, for wavelengths in the strong CD region (around 1.45 μm), the measured transmission of light exhibits elliptical polarization states (fig. S9H). Spectra are measured from 1.1 to 2 μm because of the restriction of the quarter-wave plate (see Materials and Methods).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/7/eaat4436/DC1

    Section S1. Mechanical modeling

    Section S2. Optical modeling

    Section S3. Extension of nano-kirigami to other materials and geometries

    Fig. S1. Illustration of the overhead ion beam blocking and comparison between local and global ion beam irradiation.

    Fig. S2. Exotic 3D structures fabricated by nano-kirigami.

    Fig. S3. SRIM software simulation results.

    Fig. S4. Ion beam dosage test.

    Fig. S5. Schematic of the bottom layer under elastoplastic deformation.

    Fig. S6. Comparison between web-like structures of different topographies after nano-kirigami.

    Fig. S7. Origin of the chirality in 3D pinwheel structures.

    Fig. S8. Structural designs for optical chirality.

    Fig. S9. Numerical calculations and comparison with experiments.

    Fig. S10. Extension of nano-kirigami to other platforms.

    Movie S1. Nano-kirigami of different structures by programming ion beam irradiation in one step.

    Movie S2. Upward and downward buckling with nano-kirigami.

    Movie S3. Structural evolution of different web-like structures under nano-kirigami.

    Movie S4. Simultaneous upward buckling of an array of pinwheel structures.

  • Supplementary Materials

  • The PDF file includes:
    • Section S1. Mechanical modeling
    • Section S2. Optical modeling
    • Section S3. Extension of nano-kirigami to other materials and geometries
    • Fig. S1. Illustration of the overhead ion beam blocking and comparison between local and global ion beam irradiation.
    • Fig. S2. Exotic 3D structures fabricated by nano-kirigami.
    • Fig. S3. SRIM software simulation results.
    • Fig. S4. Ion beam dosage test.
    • Fig. S5. Schematic of the bottom layer under elastoplastic deformation.
    • Fig. S6. Comparison between web-like structures of different topographies after nano-kirigami.
    • Fig. S7. Origin of the chirality in 3D pinwheel structures.
    • Fig. S8. Structural designs for optical chirality.
    • Fig. S9. Numerical calculations and comparison with experiments.
    • Fig. S10. Extension of nano-kirigami to other platforms.

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  • Other Supplementary Material for this manuscript includes the following:
    • Movie S1 (.avi format). Nano-kirigami of different structures by programming ion beam irradiation in one step.
    • Movie S2 (.avi format). Upward and downward buckling with nano-kirigami.
    • Movie S3 (.avi format). Structural evolution of different web-like structures under nano-kirigami.
    • Movie S4 (.avi format). Simultaneous upward buckling of an array of pinwheel structures.

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