K-Λ crossover transition in the conduction band of monolayer MoS2 under hydrostatic pressure

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Science Advances  03 Nov 2017:
Vol. 3, no. 11, e1700162
DOI: 10.1126/sciadv.1700162
  • Fig. 1 Sample and technical information.

    (A) Schematic diagram of the lattice structure and band structure of monolayer MoS2, where a represents the in-plane lattice constants. (B) The left image is the surface morphology of the as-grown sample under optical microscope. The green area is monolayer MoS2, and pink area is the Si/SiO2 substrate without MoS2. The right image is the AFM image of the as-grown sample, showing that the MoS2 is monolayer. (C) Raman spectra of the as-grown sample. (D) Schematic diagram of the diamond anvil cell (DAC) used for applying hydrostatic pressure to the sample.

  • Fig. 2 Pressure-dependent PL spectra of monolayer MoS2.

    (A) PL spectra of monolayer MoS2 for various pressures, with background signal subtracted. (B) The evolution of energy of the predominant PL peak versus pressure. Black dots represent peak energies of monolayer MoS2 under various pressures, taken as the lower branch; red solid line represents the fitting result of the lower branch; and black and red dotted lines represent the direct and indirect transition under various pressures extracted from the fitting, respectively. (C) Integrated intensities of PL peak under various pressures.

  • Fig. 3 First-principles calculations for the relationship of bandgap versus pressure.

    (A to C) are calculated band structures at 0, 2.1, and 2.5 GPa, respectively. The VBM of K point is set to be zero. (D) Functional relationships of bandgap versus pressure. Black, red, and blue dots represent the Λ-K, K-K, and K-Γ transitions, respectively.

Supplementary Materials

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Raman spectra of monolayer MoS2 under various pressures.
    • References (45, 46)

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