Research ArticleChemistry

Self-assembly of electronically abrupt borophene/organic lateral heterostructures

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Science Advances  22 Feb 2017:
Vol. 3, no. 2, e1602356
DOI: 10.1126/sciadv.1602356
  • Fig. 1 Homogeneous-phase borophene.

    (A) Schematic of borophene growth on Ag(111) thin film on mica. Inset: Atomic-resolution STM image of the Ag(111) surface (Vs = 0.01 V, It = 100 pA). (B) STM image of triangular borophene islands on Ag(111). Under these imaging conditions (Vs = 1.2 V, It = 160 pA), the borophene islands appear as depressions. (C) In situ XPS spectra of the B 1s core level on pristine borophene (top) and Ag 3d core levels (vertically offset) before and after borophene growth (bottom). (D) Ex situ AFM image of borophene/Ag(111) with borophene islands appearing as protrusions.

  • Fig. 2 Structural and electronic properties of homogeneous-phase borophene.

    (A) Atomic-resolution STM image of homogeneous-phase borophene showing the brick wall structure (Vs = −1.2 V, It = 2.4 nA). Inset: Fast Fourier transform of the image. Scale bar, 2 nm−1. (B) STM image showing a borophene 60° grain boundary (Vs = −0.15 V, It = 3.0 nA). (C) STM images showing line defects in borophene. Brick wall patterns and the line defects are highlighted with green ovals and arrowheads, respectively, in the bottom image (Vs = −1.1 V, It = 500 pA). (D) STM image showing aligned point defects along a line defect, as indicated by the yellow and green arrowheads, respectively (Vs = −60 mV, It = 4.3 nA). (E) Current-voltage and (F) differential tunneling conductance spectra of Ag(111) and borophene. (G) STS maps of borophene on Ag(111) at sample biases of −0.2 and 0.1 V.

  • Fig. 3 Borophene/PTCDA lateral heterostructure.

    (A) Large-scale STM image of a borophene/PTCDA lateral heterostructure and the cross-sectional profile along the white dashed line (Vs = −1.7 V, It = 90 pA). Borophene-to-PTCDA step edges, Ag-to-PTCDA step edges, and Ag atomic step edges under PTCDA and borophene are indicated by the yellow, gray, green, and blue arrowheads, respectively. Inset: PTCDA molecule structure. (B) Schematic of a borophene/PTCDA lateral heterostructure. (C) Unit cell of the PTCDA herringbone structure. (D) STM image of a borophene/PTCDA lateral heterostructure with the green, yellow, and blue boxes indicating regions of PTCDA, borophene, and Ag, respectively (Vs = −1.1 V, It = 90 pA). (E to G) STM images of the square regions indicated in (D). The pairs of yellow and blue arrows indicate the lattice orientations of borophene and Ag(111) [(E) Vs = −0.45 V, It = 140 pA; (F) Vs = −1.1 V, It = 500 pA; (G) Vs = −70 mV, It = 6.1 nA].

  • Fig. 4 MD simulation results.

    (A) ΔG(z), ΔH(z), and TΔS(z) as a function of center-of-mass distance z to the homogeneous substrate of a single PTCDA molecule with ΔHads = 10kBT. (B) ΔGads and the probability ratio of finding a molecule beyond and within a threshold z0 = 5.635 Å from the substrate, as a function of ΔHads. (C) Surface coverage as a function of ΔHads. Inset: Simulation snapshots of PTCDA adsorption and self-assembly on homogeneous Ag(111) substrates at different ΔHads. (D) Self-assembled structure of PTCDA on heterogeneous borophene/Ag(111) substrates with ΔHads,B = 10kBT, 16kBT, 18kBT, and 22kBT.

  • Fig. 5 Spectroscopic properties of the borophene/PTCDA lateral heterostructure.

    (A) In situ XPS spectra of the B 1s core level and (B) C 1s core level before and after the formation of the borophene/PTCDA lateral heterostructure. (C) Differential tunneling conductance spectra of Ag(111), borophene, and PTCDA. HOMO, highest occupied molecular orbital. (D) STS map of a borophene/PTCDA lateral heterostructure overlaid on a three-dimensionally rendered STM topography image (Vs = −1 V, It = 90 pA). Spatially resolved STS spectra across the interfaces of (E) borophene/Ag and (F) borophene/PTCDA. The vertical black lines in (E) and (F) indicate the positions of the Ag surface state feature and the LUMO+1 orbital of PTCDA far from the borophene/Ag and borophene/PTCDA interfaces, respectively. a.u., arbitrary units.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/2/e1602356/DC1

    fig. S1. Carpet-mode growth of homogeneous-phase borophene.

    fig. S2. XPS spectra of Ag 3d and O 1s core levels.

    fig. S3. Bias-dependent atomic-resolution images of homogeneous-phase borophene.

    fig. S4. Additional atomic-resolution image of borophene.

    fig. S5. Growth of PTCDA across various interfaces.

    fig. S6. Additional images of PTCDA/borophene lateral heterostructures.

    fig. S7. Design of a coarse-grained model for PTCDA.

    fig. S8. Entropy variation ΔS(z) of a single PTCDA molecule as a function of logarithmic distance ln(zzmin) to a homogeneous substrate.

    fig. S9. Probability ratio from thermodynamic integration and single-molecule simulation as a function of threshold z0 at ΔHads = 10kBT.

    fig. S10. Additional simulated adsorption of PTCDA on borophene/Ag(111).

    fig. S11. C 1s core-level XPS spectrum of a clean Ag(111) surface.

    fig. S12. Self-assembled PTCDA on Ag(111).

    movie S1. STS maps of homogeneous-phase borophene on Ag(111).

    movie S2. Self-assembly process of PTCDA on heterogeneous borophene/Ag(111) with ΔHads,Ag = 38kBT and ΔHads,B = 10kBT.

    movie S3. Self-assembly process of PTCDA on heterogeneous borophene/Ag(111) with ΔHads,Ag = 38kBT and ΔHads,B = 22kBT.

    References (4951)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Carpet-mode growth of homogeneous-phase borophene.
    • fig. S2. XPS spectra of Ag 3d and O 1s core levels.
    • fig. S3. Bias-dependent atomic-resolution images of homogeneous-phase borophene.
    • fig. S4. Additional atomic-resolution image of borophene.
    • fig. S5. Growth of PTCDA across various interfaces.
    • fig. S6. Additional images of PTCDA/borophene lateral heterostructures.
    • fig. S7. Design of a coarse-grained model for PTCDA.
    • fig. S8. Entropy variation ΔS(z) of a single PTCDA molecule as a function of logarithmic distance ln(z − zmin) to a homogeneous substrate.
    • fig. S9. Probability ratio from thermodynamic integration and single-molecule simulation as a function of threshold z0 at ΔHads = 10kBT.
    • fig. S10. Additional simulated adsorption of PTCDA on borophene/Ag(111).
    • fig. S11. C 1s core-level XPS spectrum of a clean Ag(111) surface.
    • fig. S12. Self-assembled PTCDA on Ag(111).
    • Legend for movies S1 to S3
    • References (49–51)

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.avi format). STS maps of homogeneous-phase borophene on Ag(111).
    • movie S2 (.avi format). Self-assembly process of PTCDA on heterogeneous borophene/Ag(111) with ΔHads,Ag = 38kBT and ΔHads,B = 10kBT.
    • movie S3 (.avi format). Self-assembly process of PTCDA on heterogeneous borophene/Ag(111) with ΔHads,Ag = 38kBT and ΔHads,B = 22kBT.

    Files in this Data Supplement:

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