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Quasi-freestanding epitaxial silicene on Ag(111) by oxygen intercalation

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Science Advances  22 Jul 2016:
Vol. 2, no. 7, e1600067
DOI: 10.1126/sciadv.1600067
  • Fig. 1 Topographic images of pristine and oxygen-intercalated epitaxial silicene grown on Ag(111).

    (A) STM topographic image of pristine √3 × √3 silicene that was formed on a √13 × √13/4 × 4 buffer layer. Inset is a high-resolution image of √3 × √3 silicene, which demonstrates a honeycomb structure with a lattice constant of 0.64 nm (Vbias= −0.8 V, I = 0.2 nA). (B) Oxygen-intercalated √3 × √3 silicene after an oxygen dose of 600 L (Vbias = 0.6 V, I = 2 nA). (C) Line profile for the straight line in (B). (D and E) Enlarged STM images of intercalated region [red frame in (B)] and nonintercalated √3 × √3 silicene [black frame in (B)], respectively. The red rhombus and black rhombus stand for the unit cells of 1 × 1 silicene and √3 × √3 silicene, respectively (Vbias = 3 mV, I = 4 nA). (F) Oxygen-intercalated silicene layers after an oxygen dose of 1200 L, in which the buffer layer is fully oxidized, whereas the √3 × √3 silicene shows robust structural stability against oxygen intercalation (Vbias = −1.2 V, I = 0.1 nA).

  • Fig. 2 XPS and Raman spectra of pristine and oxygen-intercalated silicene.

    (A) Si 2p core-level XPS spectra of pristine (top) and oxygen-intercalated (middle, lower dose; bottom, higher dose) silicene layers grown on Ag(111). The Si1 and Si2 peaks are attributed to Si–Si bonds in √3 × √3 silicene, whereas Si3 and Si4 are attributed to the √13 × √13/4 × 4 silicene buffer layer. a.u., arbitrary units. (B) Raman spectra of √13 × √13/4 × 4 silicene buffer layer (black), √3 × √3 silicene with 0.3 monolayer coverage on √13 × √13/4 × 4 buffer layer (pristine sample; red), and oxygen-intercalated sample (blue). The oxidized buffer layer features a broad Raman peak at 494 cm−1 in the spectrum of the oxygen-intercalated sample.

  • Fig. 3 Simulations for atomic structures of oxygen adsorbed on both buffer layer and top layer silicene.

    (A to C) Atomic structures of an O2 molecule adsorbed on 4 × 4 silicene buffer layer (A), top layer silicene (B), and 4 × 4 buffer layer underneath √3 × √3 silicene (C). (D and E) Atomic structure of silicene/SiOx/Ag(111) from ab initio molecular dynamics (AIMD) simulation: side view (D) and top view (E) of the top layer silicene only. (F) Simulated (top) and experimental (bottom) high-resolution STM images of silicene/SiOx/Ag(111), showing the 1 × 1 silicene honeycomb lattice.

  • Fig. 4 ARPES results of pristine and oxygen-intercalated silicene.

    (A to D) Energy versus k dispersion measured by ARPES for clean Ag(111) surface (A), as-grown √3 × √3 silicene formed on buffer layer (B), oxygen-intercalated silicene with an oxygen dose of 600 L (C), and intercalated silicene with an oxygen dose of 1200 L (D). The SSS and the sp band in (A) are attributed to the Ag(111) substrate. The DP in (B) to (D) is lifted up with increased oxygen dose from 0 to 1200 L, indicating less electron doping from the Ag(111) substrate due to oxygen intercalation. (E) ARPES energy cuts reveal a Dirac cone structure in pristine silicene. (F) Schematic view of shifting of Dirac cone due to oxygen intercalation in ARPES measurement.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/7/e1600067/DC1

    fig. S1. Observation of 1 × 1 lattice induced by oxygen intercalation.

    fig. S2. XPS spectra of oxygen-intercalated silicene.

    fig. S3. In situ temperature-dependent Raman spectra of silicene samples in different structures.

    fig. S4. Ex situ Raman spectra of oxygen-intercalated samples exposed to ambient air.

    fig. S5. STM results on intercalated silicene layers.

    fig. S6. STM images of samples after oxygen intercalation under different doses and STS dI/dV measurements.

    fig. S7. Additional ARPES results on intercalated silicene under an oxygen dose of 600 L.

    fig. S8. ARPES results on silicene buffer layer grown on Ag(111).

    fig. S9. STS in intercalated and pristine areas of silicene.

    fig. S10. DFT results on the electronic band structure of oxygen-intercalated bilayer silicene.

    fig. S11. DFT results on the partial density of states of bilayer silicene before and after oxygen intercalation.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Observation of 1 × 1 lattice induced by oxygen intercalation.
    • fig. S2. XPS spectra of oxygen-intercalated silicene.
    • fig. S3. In situ temperature-dependent Raman spectra of silicene samples in different structures.
    • fig. S4. Ex situ Raman spectra of oxygen-intercalated samples exposed to ambient air.
    • fig. S5. STM results on intercalated silicene layers.
    • fig. S6. STM images of samples after oxygen intercalation under different doses and STS dI/dV measurements.
    • fig. S7. Additional ARPES results on intercalated silicene under an oxygen dose of 600 L.
    • fig. S8. ARPES results on silicene buffer layer grown on Ag(111).
    • fig. S9. STS in intercalated and pristine areas of silicene.
    • fig. S10. DFT results on the electronic band structure of oxygen-intercalated bilayer silicene.
    • fig. S11. DFT results on the partial density of states of bilayer silicene before and after oxygen intercalation.

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