Research ArticleSURFACE CHEMISTRY

Defect passivation of transition metal dichalcogenides via a charge transfer van der Waals interface

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Science Advances  20 Oct 2017:
Vol. 3, no. 10, e1701661
DOI: 10.1126/sciadv.1701661
  • Fig. 1 Investigation of a bare ML MoS2 surface deposited on HOPG.

    (A) Large-area STM image showing the ML MoS2 terrace (Vs = 2 V, It = 40 pA). (B) Line trace analysis of the white line in (A) and the schematic model of defects in MoS2. (C and D) Zoomed-in STM images of a single defect located on the ML MoS2 in the empty (Vs = 1 V) and filled (Vs = −1 V) states, respectively (It = 230 pA). Scale bar, 1 nm; (D) at same magnification as (C). (E) STS measured on the terrace of a ML MoS2; the black spectra are measured far away from the defects, whereas the red spectra are measured near a defect. (F) Spatial STS near the CB edge as a function of the distance from the defect.

  • Fig. 2 Effects of the formation of the interface at TiOPc/MoS2.

    (A) Few TiOPc molecules deposited on a MoS2 ML at 300 K (Vs = 2 V, It = 30 pA). Inset shows the molecular structure of TiOPc. (B) Cross-sectional line trace of an adsorbed TiOPc molecule. (C) Single TiOPc adsorption with a black background. (D) Subset of dI/dV/I/V spectra taken along the dashed arrow in (C). (E) Formation of a full-coverage ML TiOPc on a ML MoS2 and corresponding Fourier transform (Vs = 2 V, It = 50 pA). (F) STS of ML TiOPc on a ML MoS2.

  • Fig. 3 DFT of TiOPc molecules adsorbed on ML MoS2.

    (A) PDOS of MoS2 with no defects and a sulfur vacancy. (B) Absorption of two TiOPc molecules on MoS2 with a sulfur vacancy. (C) PDOS of TiOPc and MoS2 in TiOPc/MoS2. HOMO, highest occupied molecular orbital.

  • Fig. 4 Electrical and PL characteristics of MoS2 ML, with and without ML TiOPc.

    (A) Back-gated transfer characteristics of a ML MoS2 FET in log (solid curves) and linear (dashed curves) scales, before and after deposition of ML TiOPc. (B) Room temperature PL of exfoliated ML MoS2 before and after deposition of ML TiOPc. CPS, counts per second.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/10/e1701661/DC1

    Supplementary Materials and Methods

    fig. S1. The SEM of as-grown MoS2 on HOPG via CVD showing two different areas.

    fig. S2. STS of MoS2 ML taken far away from defects with fitting in a linear scale.

    fig. S3. The large-area STM image of bare MoS2 grown by CVD on HOPG.

    fig. S4. Raman spectra of a MoS2 ML before and after deposition of TiOPc under a 488-nm laser excitation.

    fig. S5. The deposition of TiOPc molecules on MoS2 ML via molecular beam epitaxy at 300 K.

    fig. S6. Reproduced subset of dI/dV/I/V near the TiOPc molecule on MoS2 ML.

    fig. S7. Tip-induced diffusion of TiOPc molecule on MoS2.

    fig. S8. STM image and STS recorded in bulk MoS2–deposited TiOPc molecules.

    fig. S9. Full ML of TiOPc on bulk MoS2 and corresponding STS of a TiOPc ML.

    fig. S10. Thermal stability of a TiOPc ML on an MoS2 ML.

    fig. S11. DFT calculations of net charge in a TiOPc/MoS2 ML; three different locations in MoS2 ML are selected, as shown in the circles.

    fig. S12. Back-gated leakage current of a single-layer MoS2 FET, with VD = 1 V before and after deposition of a TiOPc ML.

    fig. S13. Back-gated transfer characteristics of a single-layer MoS2 FET, with VD = 0.1 V before and after deposition of a TiOPc ML.

    table S1. Summary of relative net charge of TiOPc and MoS2 (neutral) from three different locations.

    table S2. Net charge of TiOPc and MoS2 (−2e).

    References (33, 4260)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Materials and Methods
    • fig. S1. The SEM of as-grown MoS2 on HOPG via CVD showing two different areas.
    • fig. S2. STS of MoS2 ML taken far away from defects with fitting in a linear scale.
    • fig. S3. The large-area STM image of bare MoS2 grown by CVD on HOPG.
    • fig. S4. Raman spectra of a MoS2 ML before and after deposition of TiOPc under a 488-nm laser excitation.
    • fig. S5. The deposition of TiOPc molecules on MoS2 ML via molecular beam epitaxy at 300 K.
    • fig. S6. Reproduced subset of dI/dV/I/V near the TiOPc molecule on MoS2 ML.
    • fig. S7. Tip-induced diffusion of TiOPc molecule on MoS2.
    • fig. S8. STM image and STS recorded in bulk MoS2–deposited TiOPc molecules.
    • fig. S9. Full ML of TiOPc on bulk MoS2 and corresponding STS of a TiOPc ML.
    • fig. S10. Thermal stability of a TiOPc ML on an MoS2 ML.
    • fig. S11. DFT calculations of net charge in a TiOPc/MoS2 ML; three different locations in MoS2 ML are selected, as shown in the circles.
    • fig. S12. Back-gated leakage current of a single-layer MoS2 FET, with VD = 1 V before and after deposition of a TiOPc ML.
    • fig. S13. Back-gated transfer characteristics of a single-layer MoS2 FET, with VD = 0.1 V before and after deposition of a TiOPc ML.
    • table S1. Summary of relative net charge of TiOPc and MoS2 (neutral) from three different locations.
    • table S2. Net charge of TiOPc and MoS2 (−2e).
    • References (33, 42–60)

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