Research ArticleChemistry

Near-equilibrium growth from borophene edges on silver

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Science Advances  27 Sep 2019:
Vol. 5, no. 9, eaax0246
DOI: 10.1126/sciadv.aax0246
  • Fig. 1 Borophene edges on silver.

    (A) The v1/6 sheet has two armchair edges, denoted as A1 and A2, and two zigzag edges, denoted as Z1 and Z2. (B) Preferred edges of the v1/6 sheet on Ag(111) along with calculated edge energies. (C) Equilibrium shapes of the v1/6 and triangular sheets. Black and blue lines stand for the A1 and Z1 edges, while black and blue dotted lines stand for the A2 and Z2 edges, respectively.

  • Fig. 2 Growth kinetics of borophene on silver.

    Energetically optimal atomic configurations during the step-by-step addition of boron dimers to (A) A1 and (B) Z1 edges. (C) EPs for the kinetic growth along the (left) A1 and (right) Z1 edges, with ΔμB = 0 eV. At each step, we scanned a number of candidate structures whose energies are shown by gray bars. The red solid lines present the optimal EP, while the black solid lines show another EP with a slightly higher maximum. The blue dotted lines show the case of a mixture of monomers and dimers as feeding species.

  • Fig. 3 Kinetic equilibrium shapes of borophene on silver.

    (A) Growth barriers at different edges with μB = 0.01 eV. The hatched bars denote energy barriers of the optimal EPs for the growth of different edges, while the shaded bars denote barriers of the EPs shown by the black lines in Fig. 2C. The K12, K22, and K21 label the data for the screwed edges illustrated in figs. S7 to S9, respectively. (B) Borophene shapes resulting from combinations of growth barriers at different edges shown in (A). The four shapes result from barrier combinations 2.07 eV (Z1) versus 1.78 eV (Z2), 2.21 eV (Z1) versus 1.93 eV (Z2), 2.07 eV (Z1) versus 1.93 eV (Z2), and 2.21 eV (Z1) versus 1.78 eV, respectively. (C) Large-scale scanning tunneling microscopy (STM) topography image of borophene islands (Vsample = 2.0 V and It = 100 pA). Typical islands are marked by the numbers 1 to 6. (D) Statistics of orientations of borophene islands with respect to Ag(111). (E) Statistical distribution of aspect ratios of islands.

  • Fig. 4 Edges and lattices of borophene islands.

    (A) STM topography image of a borophene island (Vsample = 0.1 V and It = 1.0 nA). Inset: Zoomed-in image of the area marked by the black rectangle. (B) Simulated STM image of the v1/6 sheet on silver, overlaid with an atomic model (Vsample = 1.0 V). The blue arrow indicates the Z1 direction. (C) Top: STM topography image of the Z1 and Z2 edges of a typical borophene island (Vsample = 2.0 V and It = 100 pA). The lattice periodicities of the two edges are measured by x (middle) and y (bottom) derivatives of the STM topography. (D) Schematic model of a v1/6 sheet island on Ag(111) along with calculated edge periodicities.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/9/eaax0246/DC1

    Fig. S1. Considered candidate structures for the Z1 edge on Ag(111) and their edge energies (eV/Å).

    Fig. S2. Considered candidate structures for the Z2 edge on Ag(111) and their edge energies (eV/Å).

    Fig. S3. Preferred edges of the triangular sheet on Ag(111), along with calculated edge energies.

    Fig. S4. Energetically preferred atomic configurations for a boron (left) monomer, (middle) dimer, and (left) trimer on Ag(111).

    Fig. S5. Growth kinetics at the A2 edge.

    Fig. S6. Growth kinetics at the Z2 edge.

    Fig. S7. Growth kinetics at the K12 edge.

    Fig. S8. Growth kinetics at the K22 edge.

    Fig. S9. Growth kinetics at the K21 edge.

    Fig. S10. Borophene shapes of kinetic equilibrium under other growth conditions.

    Fig. S11. Borophene shape of kinetic equilibrium when feeding boron species are provided in the form of mixed monomers and dimers, with Δμ = 0.01 eV and kBT = 0.08.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Considered candidate structures for the Z1 edge on Ag(111) and their edge energies (eV/Å).
    • Fig. S2. Considered candidate structures for the Z2 edge on Ag(111) and their edge energies (eV/Å).
    • Fig. S3. Preferred edges of the triangular sheet on Ag(111), along with calculated edge energies.
    • Fig. S4. Energetically preferred atomic configurations for a boron (left) monomer, (middle) dimer, and (left) trimer on Ag(111).
    • Fig. S5. Growth kinetics at the A2 edge.
    • Fig. S6. Growth kinetics at the Z2 edge.
    • Fig. S7. Growth kinetics at the K12 edge.
    • Fig. S8. Growth kinetics at the K22 edge.
    • Fig. S9. Growth kinetics at the K21 edge.
    • Fig. S10. Borophene shapes of kinetic equilibrium under other growth conditions.
    • Fig. S11. Borophene shape of kinetic equilibrium when feeding boron species are provided in the form of mixed monomers and dimers, with Δμ = 0.01 eV and kBT = 0.08.

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