Research ArticleMATERIALS SCIENCE

Three-dimensional all-dielectric metamaterial solid immersion lens for subwavelength imaging at visible frequencies

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Science Advances  12 Aug 2016:
Vol. 2, no. 8, e1600901
DOI: 10.1126/sciadv.1600901
  • Fig. 1 Schematic illustration of the assembly of the all-dielectric TiO2 mSIL.

    (A) Anatase TiO2 nanoparticles (15 nm) were centrifuged into a tightly packed precipitate. (B) The supernatant was replaced by an organic solvent mixture consisting of hexane and tetrachloroethylene to form a TiO2 nano–solid-fluid. (C) To prepare a hemispherical mSIL, the nano–solid-fluid was directly sprayed onto the sample surface. (D) To prepare a super-hemispherical mSIL, the nano–solid-fluid was sprayed onto the sample surface covered by a thin layer of organic solvent mixture. (E and F) After evaporation of the solvents, the nanoparticles underwent a phase transition to form a more densely packed structure.

  • Fig. 2 Magnification factor and field of view of the TiO2 mSIL.

    (A to R) Optical microscopy images of a wafer pattern with a lattice spacing of 200 nm observed through the TiO2 mSIL with widths of about 10 μm (A to F), 15 μm (G to L), and 20 μm (M to R), corresponding to increasing magnification factors of 1.8 (A, G, and M), 2.5 (B, H, and N), 3.0 (C, I, and O), 3.6 (D, J, and P), 4.7 (E, K, and Q), and 5.3 (F, L, and R). Inset: Side-view SEM images of the corresponding mSIL located on the patterns.

  • Fig. 3 Super-resolution optical imaging through the TiO2 mSIL.

    (A to P) SEM images of a Blu-ray disk containing 100-nm-wide grooves (A) and the wafer patterns with 60-nm (E), 50-nm (I), and 45-nm pitches (M) after gold coating of sample (I). (B) and (C), (G), and (K) are the bottom surfaces of the mSIL detached from the surface of samples (A), (E), and (I), respectively. AFM images of the wafer pattern with 60-nm (F) and 50-nm pitches (J). Optical microscopy images of the TiO2 mSIL focused on the surface of a Blu-ray disk (D) and wafer patterns with 60-nm (H), 50-nm (L), and 45-nm pitches (N to P), with magnification factors of 1.8, 3.1, 3.0, and 3.1, respectively. The last mSIL was illuminated under white light (N), green light (λ ~ 540 nm) (O), or blue light (λ ~ 470 nm) (P). The mSIL had widths of about 20 μm.

  • Fig. 4 Propagating wave scattering by a dense all-dielectric medium.

    (A) Plane wave (λ = 550 nm) passing through the stacked TiO2 nanoparticles. Electric field hotspots are generated in the gaps between contacting particles, which guides light to the underlying sample. (B) Large-area nanoscale evanescent wave illumination can be focused onto the sample surface because of the excitation of nanogap mode. (C) The size of the illumination spots is equal to the particle size, having an FWHM resolution of ~8 nm.

  • Fig. 5 Comparisons between conventional TiO2 media and metamaterial TiO2 media to convert evanescent waves into propagating waves.

    (A) Conventional media composed of homogeneous anatase TiO2. (B) Metamaterial media derived from closely stacked 15-nm anatase TiO2 nanoparticles. (C) Mean electric field amplitude as a function of distance from point sources (transverse electric–polarized, incoherent). The amplitude decays exponentially in conventional media, and most of the evanescent wave energy is lost within a distance of 50 nm. (D) In metamaterial media, evanescent waves interact with TiO2 nanoparticles and turn into propagating waves that travel outward to the far field. A periodicity of 160 nm is observed. (E and F) Two point sources (45-nm separation) imaged with conventional (E) and metamaterial media (F), at positions z = 2 nm (near-source), z = 23 nm (near field, inside slab), and z = 650 nm (far field, outside slab). In the far field, the conventional media fails to resolve the two points, whereas the metamaterial media can successfully resolve them.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/8/e1600901/DC1

    fig. S1. Wafer pattern used for evaluating the magnification factor and field of view of a TiO2 mSIL.

    fig. S2. Estimation of the effective refractive index and particle volume fraction of a TiO2 mSIL.

    fig. S3. Field of view of a TiO2 mSIL.

    fig. S4. The limiting resolution obtained with a TiO2 hemispherical mSIL.

    fig. S5. The super-resolution images obtained with a TiO2 super-hemispherical mSIL.

    fig. S6. Direct imaging of wafer patterns by an optical microscope.

    fig. S7. Direct optical observation of 50-nm latex beads located on the surface of a Blu-ray disk.

    fig. S8. Comparisons of TiO2 hemispherical mSIL assembled from 15-or 45-nm anatase TiO2 nanoparticles.

    fig. S9. Nano–solid-fluid assembly for the TiO2 optical fiber.

    fig. S10. Characterizations of 15-nm anatase TiO2 nanoparticles.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Wafer pattern used for evaluating the magnification factor and field of view of a TiO2 mSIL.
    • fig. S2. Estimation of the effective refractive index and particle volume fraction of a TiO2 mSIL.
    • fig. S3. Field of view of a TiO2 mSIL.
    • fig. S4. The limiting resolution obtained with a TiO2 hemispherical mSIL.
    • fig. S5. The super-resolution images obtained with a TiO2 super-hemispherical mSIL.
    • fig. S6. Direct imaging of wafer patterns by an optical microscope.
    • fig. S7. Direct optical observation of 50-nm latex beads located on the surface of a Blu-ray disk.
    • fig. S8. Comparisons of TiO2 hemispherical mSIL assembled from 15- or 45-nm anatase TiO2 nanoparticles.
    • fig. S9. Nano–solid-fluid assembly for the TiO2 optical fiber.
    • fig. S10. Characterizations of 15-nm anatase TiO2 nanoparticles.

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