Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs

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Science  18 Dec 2015:
Vol. 350, Issue 6267, pp. 1513-1516
DOI: 10.1126/science.aad1080
  1. Fig. 1 Growth and atomic-scale characterization of borophene sheets.

    Schematics of (A) distorted B7 cluster and (B) growth setup with atomic structure model and STM topography rendering. (C) AES spectra of clean Ag(111) before and after boron deposition. (D to I) Series of large-scale STM topography (left) and closed-loop dI/dV (right) images of borophene sheets, showing (D and E) low coverage (Vsample = 2.0 V, It = 100 pA), (F and G) medium coverage (Vsample = 3.5 V, It = 100 pA), and (H and I) high coverage (Vsample = 3.5 V, It = 100 pA). Regions of homogeneous-phase, striped-phase island, and striped-phase nanoribbon are indicated with red, white, and blue arrows, respectively. (J to L) STM topography images showing (J) striped-phase atomic-scale structure (Vsample = 0.1 V, It = 1.0 nA). Inset shows rectangular lattice with overlaid lattice vectors. (K) Striped phase with rhombohedral (indicated by white rhombus) and honeycomb (indicated by purple arrow) Moiré patterns (Vsample = 3.5 V, It = 100 pA). (L) Striped-phase island, demonstrating carpet-mode growth (Vsample = 3.5 V, It = 100 pA). Inset shows atomic continuity across the Ag(111) step (Vsample = –0.5 V, It = 700 pA).

  2. Fig. 2 Computational prediction of borophene structure and electronic properties.

    Top (A) and side (B) views of the low-energy monolayer structure (unit cell indicated by green box). (C) Simulated empty states STM image (Vsample = 1.0 V), with overlaid atomic structure and unit cell of 0.500 nm by 0.289 nm and (D) experimental STM images (Vsample = 0.1 V, It = 1.0 nA), with overlaid unit cell of 0.51 nm by 0.29 nm. Density functional theory–calculated electronic (E) band structure (inset: 2D Brillouin zone) and (F) DOS for freestanding borophene.

  3. Fig. 3 Borophene structural and chemical characterization.

    Cross-sectional AC-STEM images from (A) HAADF and (B) ABF detectors. (C) Juxtaposition (left to right) of Si-capped borophene structure model, simulated ABF image, and magnified ABF image. (D) XPS B 1s core–level spectra and fitted components for samples with and without Si capping layers. (E) Angle-resolved XPS data acquired on Si-capped samples. Inset: schematic showing measurement angle and sample structure determined by angle-resolved XPS.

  4. Fig. 4 Scanning tunneling spectroscopy of borophene.

    (A) STS I-V curves and (B) STS dI/dV spectra [inset: clean Ag(111) dI/dV spectrum] from the borophene sheets, which demonstrate metallic characteristics (feedback loop opened at Vsample = 1.0 V, It = 1.0 nA).

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