Figure 1.

1T phase quantum dot superlattice created on 2H phase monolayer MoS₂ at room temperature. (a) Schematic of electron beam irradiation on 2H (semiconducting) phase MoS₂ to trigger the transition of 1T (metallic) phase triangular MoS₂ quantum dots, where $L$ is the lattice spacing (or pitch) and $a$ is the side length of the 1T phase triangle. (b) Raman spectra before and after electron beam irradiation. The inset shows the partially enlarged view of the E¹ _2g peaks and A_1g peaks. As the electron beam irradiation dose increases, the intensities of E¹ _2g peak at 381.56 cm⁻¹ and A_1g peak at 404.82 cm⁻¹ decrease, and E¹ _2g peak moves to lower wavenumbers and A_1g peak moves to higher wavenumbers, which is different from the Raman peaks of MoS₂′s defects^{24, 25}. The intensities of the three peaks at 151.58 cm⁻¹, 227.99 cm⁻¹, and 305.02 cm⁻¹ increase, which is the signature of the 1T phase MoS₂ ^26–28. (c) Cross-sectional view of the periodic quantum well, where E _C is the conduction band minima, E _V is the valance band maxima, E _g is the bandgap. (d) Two-dimensional periodic finite potential well model for calculating the emerging bandgap from quantum dot superlattice. The bottom of the triangular well is 1T phase MoS₂. The top of the triangular potential barrier is the conduction band of 2H phase MoS₂. $U_e$ is the height of the potential well. (e) Calculated band diagram of the first electron band for $a=2$nm and $L=4$nm.