Research ArticleChemistry

Neat monolayer tiling of molecularly thin two-dimensional materials in 1 min

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Science Advances  30 Jun 2017:
Vol. 3, no. 6, e1700414
DOI: 10.1126/sciadv.1700414
  • Fig. 1 Precursor suspensions for spin coating and the obtained monolayer films.

    (A) Typical precursor DMSO nanosheet suspensions for spin coating: Bottles i to v contain the suspensions of Ti0.87O20.52− (large, 0.3 wt %), Ti0.87O20.52− (small, 0.36 wt %), Ca2Nb3O10 (1.38 wt %), GO (0.072 wt %), and rGO (0.045 wt %), respectively. (B) SEM image of the monolayer film obtained by spin coating the suspension of i. A single nanosheet is highlighted by a red polygon. (C to G) AFM images of the monolayer films via spin coating of the suspensions of i to v. The thickness of the nanosheets in (C) to (G) was ~1.4, 1.0, 2.3, 1.1, and 1.0 nm, respectively, which is consistent with the values reported for the unilamellar nanosheets. On the other hand, the average lateral size was ~10, 0.3, 2, 2, and 1 μm, respectively, which is compatible with the textural appearance of the suspensions.

  • Fig. 2 AFM images of the monolayer film of small-size Ti0.87O20.52− nanosheets along the radial direction.

    Images [(1) to (4)] on the left represent different positions (0 to 8, 10, 12, and 14 mm, respectively), away from the center of the substrate, and the corresponding AFM images are shown on the right. Scale bars, 1 μm. Within a radius of 8 mm from the center, the film was clean and uniform. Note that this central area nearly corresponds to the uniform blue area or the equal thickness region, which appeared in the final stage of the spin coating (left photograph). On the other hand, in the peripheral zone from 10 to 14 mm away from the center, an increasing number of overlaps was found.

  • Fig. 3 Relationships between the absorbance at 265 nm of spin-coated films of Ti0.87O20.52− nanosheets and the nanosheet concentration and rotation speed.

    (A and C) Small- size Ti0.87O20.52− nanosheets. (B and D) Large-size Ti0.87O20.52− nanosheets. The absorbance at 265 nm corresponds to the peak value of the absorption band of the nanosheets. The blue belts mark the absorbance range for monolayer films of Ti0.87O20.52− nanosheets (0.065 to 0.075). Determining the intersections between the fitted lines and the blue belts provides the proper parameters.

  • Fig. 4 Evolution of the spin-coating process and schematics of the edge-by-edge assembly of nanosheets.

    (A) Photographs of the spin-coating process with the suspension (40 μl, 0.40 wt %) of small-size Ti0.87O20.52− nanosheets at a rotation speed of 4500 rpm. The transition of the interference patterns indicates the gradual thinning of the suspension layer. (B) A plausible model for the formation of the monolayer film of neatly tiled nanosheets.

  • Fig. 5 Multilayer buildup process.

    (A) UV-visible absorption spectra of Ti0.87O20.52− nanosheet films fabricated by repeating the monolayer coverage on a quartz glass substrate. (B) XRD patterns of Ti0.87O20.52− nanosheet films with 1, 2, 3, 5, 7, and 10 layers (L) on a Si substrate. The profiles between 2° and 60° were magnified 85 times for clear observation. a.u., arbitrary units; cps, counts per second. (C and D) Cross-sectional HRTEM images of the 10-layer film of Ti0.87O20.52− nanosheet on a Si substrate. (E) UV-visible absorption spectra from GO nanosheet films fabricated by repeating the monolayer coverage. (F) XRD patterns of GO nanosheet films with 1, 3, 5, 7, and 10 layers on a Si substrate.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/6/e1700414/DC1

    section S1. Synthesis of Ti0.87O20.52−, Ca2Nb3O10, GO, and rGO nanosheets

    section S2. Characterizations of nanosheet films

    section S3. Derivation of the dependence of the absorbance on the concentration and rotation speed

    fig. S1. Schematic representation for 2D materials used in this study.

    fig. S2. Photograph and SEM images of the Si substrate (30 mmφ) after spin coating the DMSO suspension of large-size Ti0.87O20.52−.

    fig. S3. SEM images of monolayer films of large-size Ti0.87O20.52− nanosheets on various substrates.

    fig. S4. AFM images of monolayer films.

    fig. S5. Photographs of the spin-coating process.

    fig. S6. The schematic of the optical path to calculate the nanosheet suspension thickness.

    fig. S7. Contact angle of a water droplet on the monolayer film of large-size Ti0.87O20.52− nanosheets upon exposure to UV light.

    fig. S8. XRD data of SrTiO3 film grown on the monolayer film of large-size Ti0.87O20.52− nanosheets.

    fig. S9. XRD patterns of dried samples of GO and rGO.

    References (33, 34)

  • Supplementary Materials

    This PDF file includes:

    • section S1. Synthesis of Ti0.87O20.52−, Ca2Nb3O10, GO, and rGO nanosheets
    • section S2. Characterizations of nanosheet films
    • section S3. Derivation of the dependence of the absorbance on the concentration and rotation speed
    • fig. S1. Schematic representation for 2D materials used in this study.
    • fig. S2. Photograph and SEM images of the Si substrate (30 mmφ) after spin coating the DMSO suspension of large-size Ti0.87O20.52−.
    • fig. S3. SEM images of monolayer films of large-size Ti0.87O20.52− nanosheets on various substrates.
    • fig. S4. AFM images of monolayer films.
    • fig. S5. Photographs of the spin-coating process.
    • fig. S6. The schematic of the optical path to calculate the nanosheet suspension thickness.
    • fig. S7. Contact angle of a water droplet on the monolayer film of large-size Ti0.87O20.52− nanosheets upon exposure to UV light.
    • fig. S8. XRD data of SrTiO3 film grown on the monolayer film of large-size Ti0.87O20.52− nanosheets.
    • fig. S9. XRD patterns of dried samples of GO and rGO.
    • References (33, 34)

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