Ultrafast Charge Dynamics in Dispersions of Monolayer MoS₂ Nanosheets

Abstract

Ultrafast charge dynamics in dispersions of MoS2 nanosheets in N-methyl-2-pyrrolidone are reported. Samples were prepared by the ultrasonication-assisted exfoliation of MoS2 powder, resulting in nanosheets that were predominantly monolayer and had an average sheet size of 32.4 ± 0.1 nm. These dispersions were characterized using absorption and photoluminescence spectroscopy, transient photoluminescence measurements, and atomic force microscopy before the ultrafast charge dynamics were studied via transient absorption spectroscopy. The transient absorption spectra exhibited bleach peaks and photoinduced absorption peaks in spectral regions corresponding to both the A and B excitons of MoS2. The growth and decay of the features in the B exciton region were determined largely by the dynamics of the exciton population, while the features in the A exciton region depend on the dynamics of both excitons and trions.

Ultrafast dynamics of defect-assisted carrier capture in MoS2 nanodots investigated by transient absorption spectroscopy

“…These carriers in the excited state absorb the probe pulse, thus new excited state absorption signals are produced. In addition, we observed the gradual shift of A, B peaks with the increase of delay time, a phenomenon consistent with previous reports [19,24], suggesting that the bandgap renormalization occurs in the process.…”

“…For the A (670 nm) and B (620 nm), both are corresponding to the K, deriving from the excitonic transitions of the spin-orbit split top valence band, around K and K ′ [15][16][17]. For the conspicuous C peak (470 nm), it is ascribed to a weakly bound exciton, with a complex composition mainly resulting from interband transitions around Γ [13,16,18,19]. The spectra show at least five apparent features, including two positive peak signals and three negative peak signals.…”

Controlled Production of MoS2 Full‐Scale Nanosheets and Their Strong Size Effects

“…Obviously, the saturation thresholds were decreased with reducing NS sizes. Notably, dramatic decrease of the saturation thresholds was observed with the NS sizes down to 41 nm, indicating the sharp rise of quantum confinement [ 43,44 ] and edge effects. [ 45 ] The size‐dependent NSA performances of the MoS 2 NSs would facilitate their potential applications in mode‐locked lasers and related fields.…”

Enhanced Trion Emission and Carrier Dynamics in Monolayer WS2 Coupled with Plasmonic Nanocavity

“…[56,57] For the photoinduced absorption peak at the 1.89 eV (positive signal), according to related researches from Kime et al and Goswami et al, it can be assigned to the A − trion. [53,54] Its rising dynamics can be fitted with a mono-exponential function, and the recovery dynamic can be fitted with a triple-exponential function. The rising component (τ rise ) can be assigned to the trion formation process (indicated by the pink arrow labeled by trion formation (τ rise ) in Figure 3G).…”