Research ArticleAPPLIED SCIENCES AND ENGINEERING

Plasmonic nanostructures through DNA-assisted lithography

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Science Advances  02 Feb 2018:
Vol. 4, no. 2, eaap8978
DOI: 10.1126/sciadv.aap8978
  • Fig. 1 DNA origami designs, a step-by-step fabrication procedure of the DALI method.

    (A) Top: Designed DNA origami shapes (from left to right): ST, BO, and CDL. Middle: AFM images of the folded structures on a mica substrate. Bottom: Scanning electron microscopy (SEM) images of gold nanostructures created by the fabrication method described in detail in (B). The AFM and SEM images are 150 nm × 150 nm in size. (B) Steps of the fabrication procedure. Step 1: A transparent sapphire (Al2O3)/silicon nitride (Si3N4) chip is freshly cleaned by acetone and isopropanol. Step 2: An amorphous silicon layer is grown on top of the substrate by PECVD. Step 3: The substrate is treated by oxygen plasma, after which the DNA origami nanostructures (BO shown here as an example) are drop-casted on the chip. Step 4: The silicon dioxide (SiO2) layer is selectively grown on the bare silicon by CVD, leaving DNA origami–shaped silhouettes in the layer. Step 5: Using the grown SiO2 layer as a mask, the silicon underneath is etched away by RIE. Step 6: The metal is deposited onto the chip using PVD in ultrahigh vacuum. Step 7: The SiO2 layer is removed in a liftoff process using hydrogen fluoride–based wet etching. Step 8: The remaining silicon is removed by RIE, thus leaving the DNA origami–shaped metal nanostructure on the substrate.

  • Fig. 2 Large-area SEM images of the structures created with DALI.

    (A) AuPd ST structures on Si3N4. (B) Au BO structures on Si3N4. (C) Au CDL structures on sapphire. All the inset images are 150 nm × 150 nm in size.

  • Fig. 3 Experimental and simulated linear polarization scattering spectra for single BO- and ST-shaped gold nanostructures.

    (A and B) Dark-field scattering spectra of the BO and ST shapes (SEM images shown in the left insets, 200 nm × 200 nm in size) measured at two different polarization angles (indicated by correspondingly colored arrows in the insets). Lines show the smoothed spectra, whereas the original data are shown faded in the background. Dashed lines show simulated scattering spectra for the BO and ST shapes in (A) and (B), respectively. The right-side insets show a field enhancement, that is, the local electric field (E) divided by the incoming electric field (E0) at the chosen polarization angles (shown by colored arrows) at the middle height of the structure, that is, 10 nm above the surface. The main LSPR modes are at 650 and 705 nm for the BO and at 670 and 700 nm for the slightly asymmetric ST. The maximum local field enhancement, Emax/E0, for each sample is also stated in each inset. a.u., arbitrary units.

  • Fig. 4 Metallic BO shapes for SERS and CDL shapes for creating chiral plasmonic response.

    (A) Raman spectra (baseline-corrected) measured from a sample containing nanosized gold BOs coated with either the rhodamine 6G (red) or 2,2-bipyridine molecules (black). Lighter dotted lines show the response of the same concentration of the molecules on a pure substrate without the BOs. (B) SEM of a sample containing 50:50 distribution of S- and Z-shaped metallic CDLs on a sapphire substrate. (C) SEM of a sample with ~99% of the CDLs in the S-configuration on a sapphire substrate. The SEM images (B and C) are 1.4 μm × 1 μm in size. (D) Orange and blue curves: Averaged and baseline-corrected CD spectra measured from the samples shown in (B) and (C). Black lines: Simulated CD response for a symmetric (dashed) and slightly asymmetric (dash-dotted) S-shaped CDL. Insets show the field enhancement (color scale) and power loss inside the metal (grayscale) for the symmetric CDL and for the right-handed (upper) and left-handed (lower) circularly polarized 640-nm excitation light.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/2/eaap8978/DC1

    note S1. DALI.

    note S2. Gap formation in a BO structure.

    note S3. Single-particle LSPR sample fabrication.

    note S4. Single-particle linear polarization LSPR measurement.

    note S5. Additional single-particle linear polarization LSPR spectra.

    note S6. UV-Vis measurement of CDL samples.

    note S7. Numerical simulations.

    fig. S1. Agarose gel electrophoresis of DNA origamis.

    fig. S2. DNA origami deposition on the Si surface.

    fig. S3. Schematic view of the reaction chamber setup for the SiO2 growth.

    fig. S4. Fabrication of trenches/silhouettes with different DNA origami shapes.

    fig. S5. Isotropic RIE etching of silicon.

    fig. S6. PVD of gold.

    fig. S7. HF liftoff (removal of the SiO2 mask).

    fig. S8. AFM images with the corresponding thickness profiles and a SEM image of Au bowtie antennas on a sapphire substrate.

    fig. S9. Schematic illustration of the oxide growth in the vicinity of the BO on a Si substrate.

    fig. S10. Schematics of the SPS setup.

    fig. S11. Single-structure spectra of different metallized origami shapes.

    fig. S12. Normalized UV-Vis spectra of CDL samples with S-configuration and random orientation.

    fig. S13. Simulation geometry for a CDL particle (S-shaped orientation) with a clockwise polarized incident light and used mesh.

    fig. S14. Geometries of the different types of particles for the Comsol simulations.

    fig. S15. Simulated LSPR spectra and field enhancements (E/E0 at resonance frequency) for the optimal bowtie structure and for the structures with geometries altered by the amount of the observed SDs.

    table S1. Parameters for a-Si CVD.

    table S2. Parameters for O2 plasma RIE.

    table S3. Parameters for RIE SiO2 etching.

    table S4. Parameters for RIE Si etching.

    Appendix

    Design and sequences of BO

    Design and sequences of CDL

    Additional SEM data set

    Fabrication yield analysis

    References (3941)

  • Supplementary Materials

    This PDF file includes:

    • note S1. DALI.
    • note S2. Gap formation in a BO structure.
    • note S3. Single-particle LSPR sample fabrication.
    • note S4. Single-particle linear polarization LSPR measurement.
    • note S5. Additional single-particle linear polarization LSPR spectra.
    • note S6. UV-Vis measurement of CDL samples.
    • note S7. Numerical simulations.
    • fig. S1. Agarose gel electrophoresis of DNA origamis.
    • fig. S2. DNA origami deposition on the Si surface.
    • fig. S3. Schematic view of the reaction chamber setup for the SiO2 growth.
    • fig. S4. Fabrication of trenches/silhouettes with different DNA origami shapes.
    • fig. S5. Isotropic RIE etching of silicon.
    • fig. S6. PVD of gold.
    • fig. S7. HF liftoff (removal of the SiO2 mask).
    • fig. S8. AFM images with the corresponding thickness profiles and a SEM image of Au bowtie antennas on a sapphire substrate.
    • fig. S9. Schematic illustration of the oxide growth in the vicinity of the BO on a Si substrate.
    • fig. S10. Schematics of the SPS setup.
    • fig. S11. Single-structure spectra of different metallized origami shapes.
    • fig. S12. Normalized UV-Vis spectra of CDL samples with S-configuration and random orientation.
    • fig. S13. Simulation geometry for a CDL particle (S-shaped orientation) with a clockwise polarized incident light and used mesh.
    • fig. S14. Geometries of the different types of particles for the Comsol simulations.
    • fig. S15. Simulated LSPR spectra and field enhancements (E/E0 at resonance frequency) for the optimal bowtie structure and for the structures with geometries altered by the amount of the observed SDs.
    • table S1. Parameters for a-Si CVD.
    • table S2. Parameters for O2 plasma RIE.
    • table S3. Parameters for RIE SiO2 etching.
    • table S4. Parameters for RIE Si etching.
    • Appendix
    • Design and sequences of BO
    • Design and sequences of CDL
    • Additional SEM data set
    • Fabrication yield analysis
    • References (39–41)

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