Trap State Dynamics in MoS₂ Nanoclusters

Abstract

The trap-to-trap relaxation and recombination dynamics of photogenerated electron/hole pairs in MoS 2 nanoclusters have been studied. Static and time-resolved emission experiments have been performed on 3.0 and 4.5 nm diameter nanoclusters in ternary inverse micelles, acetonitrile, and octane at room temperature and at 20 K. The results indicate that, following synthesis in ternary inverse micelles, the nanoclusters have both shallow and deep traps. The deep traps are retained upon extraction into acetonitrile and passivated upon charge neutralization and reextraction into octane. The emission kinetics show that trap-to-trap relaxation is fast (<40 ps) at room temperature and slows (∼200 ps) at 20 K. A distributed kinetics model is presented that quantitatively describes electron/hole recombination. The trapped electron Bohr radius is found to be 2.0-2.5 nm in all cases. Charge neutralization and reextraction into octane passivates both the deep and the shallow traps on some nanoclusters, resulting in indirect band edge emission at 20 K.

Exciton Dynamics in Suspended Monolayer and Few-Layer MoS2 2D Crystals

“…37 The exact nature and the depth of the traps require a further temperature-dependent study, which is currently underway. The intermediate decay time constant (τ 2 ) is similar to the interband carrier-phonon scattering time observed in recent photoluminescence lifetime measurements, which was found to be strongly dependent on temperature.…”

Valley Trion Dynamics in Monolayer MoSe2

“…The corresponding exciton or trion is trapped in the defect state. The defect trapping has been experimentally studied in MoS 2 monolayers 41 and nanoclusters 54 . Two defect states have been observed to provide both fast and slow traps, which can explain the bi-exponential decay.…”

Quantum Size Effects in the Photonics of Semiconductor Nanoparticles

“…As follows from Eq. [142,143], Sb 2 S 3 [142], HgS [83,144,145], ZnS [37,76,83,129,[146][147][148][149][150][151][152][153][154][155][156][157], Zn 1-x Mn x S [157], In 2 S 3 [158,159], MoS 2 [160,161], PbS [33,37,58,59,76,77,110, [75,123,[189][190][191][192][193][194], PbO 2 [195], CeO 2 [134,196,197], Cu 2 O [198,199], VO 2 [200], selenides and composites based on themCdSe [20, 22, 24, 27, 30, 44-48, 91, 94, 96, 128, 141, 165, 201-232]...…”

“…4) [261]. The relations between the positions of the exciton and "defect" emission maxima and the particle size were obtained for nanoparticles of CdS [21, 42, 46, 77-79, 82, 83, 90, 92, 98, 99, 114, 116, 118, 119, 123, 126, 130, 131, 133, 138, 139, 305-307], HgS [83,144], MoS 2 [160], ZnS [83,[152][153][154][155][156]308], PbS [163,167,168], In 2 S 3 [158], Cu x S [174], CdSe [24, 46, 48, 71, 205, 212-223, 226, 228, 229, 253, 309], CdSe/ZnS [234,235], CdSe/CdS [223,236], ZnSe [244,245,247], PbSe [73,241,242], HgSe [310], CdTe [51, 253-259, 265, 269, 271, 272, 304, 310, 311], CdSe x Te 1-x [239,240,294], CuInSe 2x Te 2(1-x) [252], AgI [276], AgBr [273], CuBr [279], CuCl [4], PbI 2 [282], ZnO [77, 178-180, 184, 188, 295, 312-315], TiO 2 [190,194], In 2 O 3 [316], CeO 2 [134], Al 2 O 3 …”

“…is realized very quickly and is complete in 50-100 fs after the formation of the electron-hole pair [1,97,160,297,300], whereas holes are captured by the surface traps after times in the order of 1 ps[1,97].…”