Fig. 1. Transition and electrical control of neutral exciton and trions in 2D materials. (a) PL spectrum of monolayer WS₂ at 4.5-275 K, where the blue and red parts are fitted to the neutral exciton and trion components, respectively^[57]; (b)-(d) MoS₂ PL intensity distribution variance as function of time at different back-gate voltage (V_g=-20, 0, 20 V)^[60]; (e) trion formation and schematic diagram of the monolayer WS₂^[61]; (f) drift distances of the trions as function of the dacay time at different applied bias (V_ext=20, 40, 60 V)^[61]; (g) the peak position of the PL emission as function of decay time at applied bias V_ext=-60 V and 60 V^[61]

Fig. 2. Control of exciton flux by SAWs at room temperature. (a),(b) Real-space PL mapping of bilayer WSe₂ when SAW is off (a) and when SAW is on with 6 mW power (b); (c) schematic illustration of hBN encapsulated bilayer WSe₂ stacked on SAW devices^[73]. (d) Schematic of strain induced diffusion of excitons in monolayer WS₂; (e) large diffusion length due to exciton-exciton annihilation by one exciton providing additional kinetic energy to another; (f) diffusion length of neutral excitons as function of generation rates in monolayer WS₂ at different strains (ε=0, 0.5%)^[75]

Fig. 3. Interlayer exciton transport modulated by moiré potentials. (a),(b) Schematic plot of the moiré potential in MoSe₂/WSe₂ heterostructures, with twist angles near 0° (H-type) and 60° (R-type); (c) interlayer exciton diffusivity as function of temperature with twist angles of 0.15° (purple), 2.49° (green), 5.12° (yellow), and 53.9° (blue)^[89]. (d) Illustration of different stackings from hBN/graphene moiré superlattice; (e) MSD of exciton density distribution in bare WSe₂ on SiO₂/Si substrate (blue dots), PDMS-WSe₂ on SiO₂/Si substrate (black diamonds) and hBN encapsulated WSe₂ (red squares), where inset plots diffusivities as function of time for three samples; (f) comparison of exciton diffusivities with and without graphene layer^[91]