Research ArticleMATERIALS SCIENCE

Atomically thin three-dimensional membranes of van der Waals semiconductors by wafer-scale growth

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Science Advances  26 Jul 2019:
Vol. 5, no. 7, eaaw3180
DOI: 10.1126/sciadv.aaw3180
  • Fig. 1 Conformal deposition of 3D TMDC ML films on a quartz needle array.

    (A and B) Schematic of the growth of TMDC ML films on a 4-inch wafer-scale quartz needle array, with photographs of (A) pristine and (B) as-grown MoS2 on a quartz wafer. (C) Raman and PL spectra measured from marked spots of as-grown MoS2 ML on a quartz wafer. (D to F) scanning electron microscopy (SEM) images of (D) pristine arrays of pyramids and needles and (E) partially and (F) fully covered MoS2 ML film on pyramids and needles. Inset: A partially covered MoS2 ML on the pyramidal podia. (G) Low-magnification and (H) high-magnification TEM images of multiple arrays of needles covered with a MoS2 ML. (I) HRTEM image of a conformal MoS2 ML on a needle. (J) HAADF-STEM image at the side region. Inset: Magnified HAADF-STEM image with an atomic model of the MoS2 ML. (K) HAADF-STEM image at the tip region with corresponding STEM-EDS elemental maps obtained by characteristic S-Kα and Mo-Lα x-ray signals. a.u., arbitrary units; e-beam, electron beam.

  • Fig. 2 Growth of 3D TMDCs on microscale trenches with reliable formation of semiconducting channels.

    (A) Photograph of wafer-scale SiO2/p+-Si trench-patterned substrate. (B) Schematic for conformal growth of MoS2 ML film using MOCVD. (C) Cross-sectional HAADF-STEM images of a MoS2 ML on microscale SiO2 trench. (D to E) SEM images of (D) partially and (E) fully covered MoS2 ML films on SiO2 trenches. (F) OM image of conformally deposited MoS2 ML on trenches. Inset: Magnified SEM image of the substrate. (G) PL images focused on the top (left) and bottom surface (right) at MoS2 A exciton peak (hν = 1.88 eV). (H) False-color SEM image of FET devices for transfer length method along 3D MoS2 ML channels (light blue, MoS2; yellow, metal contact). (I) Lch-dependent resistance at Vg = 0 V. (J) Transfer (I-Vg) curves at Vd = 0.1 V along 3D MoS2 ML channels on the trench (light blue) and flat region (black).

  • Fig. 3 Optical properties of 3D TMDC ML films on a needle array and their membranes by delamination from 3D textured substrates.

    (A) OM image of a conformally coated WS2 ML on a SiO2/p+-Si needle array. Inset: Magnified SEM image of the substrate. (B) Large-area PL image at the WS2 exciton peak ( = 1.99 eV) obtained from the region corresponding to (A). (C) Magnified PL image. (D) PL and (E) Raman spectra obtained from the needle region (red and blue) and flat region (black). Inset: PL intensity line profile indicated in (C). (F) Photographs of the peel-off process and illustration of a delaminated vdW WS2 membrane separated from the 3D substrate. Photo credit: Gangtae Jin, Pohang University of Science and Technology. (G) Low-magnification TEM image of a few-layer 3D WS2 membrane at a −36.2° tilt angle. (H) SAED pattern of the 3D WS2 membrane. (I) Diffracted beam path for planar and tilted TMDC crystals on the pyramidal array. (J) Low-magnification TEM image of the suspended WS2 needle array at the 36.2° tilt angle. (K) Low-magnification TEM image of sharp 13-L WS2 needle at a tilt angle of approximately 90°. (L and M) High-magnification TEM images of the (L) tip region (red) and (M) side region (yellow) of the WS2 needle.

  • Fig. 4 Kinetic origin of conformal ML deposition via MOCVD process.

    (A) TEM images of MOCVD-grown MoS2 crystals for different growth time. (B) False-color dark-field (DF) TEM image of suspended MOCVD-grown MoS2 ML film on holey carbon grid. (C) Grain size distribution of MOCVD MoS2 crystals. (D) Schematic of 3D ML texturing by MOCVD. (E) OM images of powder CVD-grown MoS2 crystals for different growth time. (F) DF-TEM image of powder CVD-grown MoS2 MLs. Inset: SAED pattern from MoS2 ML film. (G) Grain size distribution of powder CVD-grown MoS2. (H) Schematic of CVD-grown MLs from solid powder precursors.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/7/eaaw3180/DC1

    Fig. S1. Layer-number–dependent PL spectra (ML and bilayer) of MoS2 and WS2 films.

    Fig. S2. OM images as different pitch sizes in patterned SiO2/p+-Si trenches.

    Fig. S3. False-color SEM image of the FET devices on flat regions.

    Fig. S4. Length-dependent resistance of 3D MoS2 ML films on microtrench substrates up to l mm.

    Fig. S5. Length-dependent FET characteristics of 3D MoS2 ML films on microtrench substrates.

    Fig. S6. PL intensity maps and the corresponding PL spectra of TMDC ML films on planar SiO2/p+-Si substrates.

    Fig. S7. Raman mapping of 3D WS2 ML films on SiO2/p+-Si needle arrays.

    Fig. S8. Raman and PL mapping of 3D MoS2 ML films on SiO2/p+-Si needle arrays.

    Fig. S9. Second harmonic generation in MoS2.

    Fig. S10. Schematic illustration of the DI water–assisted transfer of 3D TMDC membranes.

    Fig. S11. TEM images of delaminated WS2 ML films on a TEM grid.

    Fig. S12. Local diffraction patterns generated on the 3D WS2 membranes.

    Fig. S13. PL and Raman spectra of MoS2 ML and WS2 ML films before and after delamination.

    Fig. S14. Nonconformal MoS2 film growth on microtrench substrates by a powder CVD method.

    Fig. S15. MOCVD growth of MoS2 films on 3D trench substrates at a faster growth rate.

    Section S1. Pyramid structure analysis using the diffraction patterns

    Section S2. Determination of sticking coefficients

    Section S3. Powder CVD growth of MoS2 ML crystals

    Movie S1. Peeling off the WS2 ML films from the quartz substrates by immersing in DI water.

    Movie S2. TEM tilting of suspended 3D WS2 membranes.

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. Layer-number–dependent PL spectra (ML and bilayer) of MoS2 and WS2 films.
    • Fig. S2. OM images as different pitch sizes in patterned SiO2/p+-Si trenches.
    • Fig. S3. False-color SEM image of the FET devices on flat regions.
    • Fig. S4. Length-dependent resistance of 3D MoS2 ML films on microtrench substrates up to l mm.
    • Fig. S5. Length-dependent FET characteristics of 3D MoS2 ML films on microtrench substrates.
    • Fig. S6. PL intensity maps and the corresponding PL spectra of TMDC ML films on planar SiO2/p+-Si substrates.
    • Fig. S7. Raman mapping of 3D WS2 ML films on SiO2/p+-Si needle arrays.
    • Fig. S8. Raman and PL mapping of 3D MoS2 ML films on SiO2/p+-Si needle arrays.
    • Fig. S9. Second harmonic generation in MoS2.
    • Fig. S10. Schematic illustration of the DI water–assisted transfer of 3D TMDC membranes.
    • Fig. S11. TEM images of delaminated WS2 ML films on a TEM grid.
    • Fig. S12. Local diffraction patterns generated on the 3D WS2 membranes.
    • Fig. S13. PL and Raman spectra of MoS2 ML and WS2 ML films before and after delamination.
    • Fig. S14. Nonconformal MoS2 film growth on microtrench substrates by a powder CVD method.
    • Fig. S15. MOCVD growth of MoS2 films on 3D trench substrates at a faster growth rate.
    • Section S1. Pyramid structure analysis using the diffraction patterns
    • Section S2. Determination of sticking coefficients
    • Section S3. Powder CVD growth of MoS2 ML crystals
    • Legends for movies S1 and S2

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.avi format). Peeling off the WS2 ML films from the quartz substrates by immersing in DI water.
    • Movie S2 (.avi format). TEM tilting of suspended 3D WS2 membranes.

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