Research ArticleMATERIALS SCIENCE

Electron microscopy of nanoparticle superlattice formation at a solid-liquid interface in nonpolar liquids

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Science Advances  13 May 2020:
Vol. 6, no. 20, eaba1404
DOI: 10.1126/sciadv.aba1404
  • Fig. 1 Schematic of representation of LP-EM of oleylamine-capped AuNPs in nonpolar liquids.

    From left to right: Schematic of the assembled liquid cell. A droplet of AuNPs is placed on a microchip with a thin SiN membrane window and containing a spacer of 150-nm thickness, after which a liquid cell is assembled using a second microchip. Images are obtained by scanning the electron beam over the sample and recording transmitted electrons, whereby the liquid is protected from evaporation by the SiN membrane window. Data of self-assembled nanoparticles are then analyzed.

  • Fig. 2 AuNPs films formed in liquid at the interface with a SiN membrane.

    Exemplary STEM images observed in different nonpolar liquids: (A) hexadecane (liquid thickness lsolv = 3.9 μm, electron flux D = 1.3 e/sÅ2), (B) octane (lsolv = 6.9 μm, D = 0.3 e/sÅ2), (C) cyclohexane (lsolv = 2.3 μm, D = 0.3 e/sÅ2), and (D) toluene (lsolv = 1.0 μm, D = 0.3 e/sÅ2).

  • Fig. 3 Single layers of AuNP at the solid-liquid interface in hexadecane.

    (A) STEM image of a single layer of AuNPs. The inset corresponds to the FFT: lsolv = 3.9 μm, D = 5.0 e/sÅ2. (B) Plot of the gray value versus position acquired for the red line shown in (A).

  • Fig. 4 Self-assembled multi-layer structures in hexadecane.

    (A) Double layer of AuNPs at the interface between the SiN membrane with the corresponding FFT in the inset: lsolv = 2.1 μm, D = 30.4 e/sÅ2. (B) Plot of the gray value versus position acquired for the red line in (A) showing the presence of two layers of nanoparticles. (C) Digital zoom of the region shown in (A) and its corresponding body-centered cubic model.

  • Fig. 5 Crystal and quasi-crystal AuNP structures self-assembled at a solid-liquid interface.

    (A) Hexagonal lattice observed for AuNPs in cyclohexane: lsolv = 0.5 μm, D = 30.4 e/sÅ2. (B) AuNPs in toluene arranged in a rhombitrihexagonal pattern (colored area): lsolv = 0.8 μm, D = 30.4 e/sÅ2. (C) Schematic of rhombitrihexagonal tiles. The dimensions found for the triangles, parallelograms, and hexagons (each side) were 8.3 nm, 8.3 nm by 10 nm, and 10 nm, respectively. (D) AuNPs in toluene arranged in a non–self-similar modification of the BMQC (colored area) (lsolv = 0.8 μm, D = 30.4 e/sÅ2), (E) dimensions of the non–self-similar BMHC, and (F) its tiles and fundamental dodecagon symmetry.

  • Table 1 Geometries observed for different solvents.

    Information about regular structures of nanoparticle films that spontaneously formed on polar Si3N4 in different solvents as derived from liquid-phase electron micrographs. Values are indicated for the solvent’s dielectric constant εr.

    SolventεrSymmetry in
    single layers
    Symmetry in
    double layers
    Toluene2.38HexagonalQuasi-crystal,
    dodecagonal
    Hexadecane2.09HexagonalCubic
    (body-centered
    cubic)
    Cyclohexane2.02HexagonalHexagonal
    Octane2.00HexagonalCubic

Supplementary Materials

  • Supplementary Materials

    Electron microscopy of nanoparticle superlattice formation at a solid-liquid interface in nonpolar liquids

    E. Cepeda-Perez, D. Doblas, T. Kraus, N. de Jonge

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    The PDF file includes:

    • Table S1
    • Legends for movies S1 and S2
    • Figs. S1 to S4
    • Supplementary Methods
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