Synthesis and optical properties of MoS2 and isomorphous nanoclusters in the quantum confinement regime

Abstract

Highly crystalline nanoclusters of hexagonal (2H polytype) MoS2 and several of its isomorphous Mo and W chalcogenides have been synthesized with excellent control over cluster size down to ∼2 nm. These clusters exhibit highly structured, bandlike optical absorption and photoluminescence spectra which can be understood in terms of the band-structures for the bulk crystals. Key results of this work include: (1) strong quantum confinement effects with blue shifts in some of the absorption features relative to bulk crystals as large as 4 eV for clusters ∼2.5 nm in size, thereby allowing great tailorability of the optical properties; (2) the quasiparticle (or excitonic) nature of the optical response is preserved down to clusters ≲2.5 nm in size which are only two unit cells thick; (3) the demonstration of the strong influence of dimensionality on the magnitude of the quantum confinement. Specifically, three-dimensional confinement of the carriers produces energy shifts which are over an order of magnitude larger than those due to one-dimensional (perpendicular to the layer planes) confinement emphasizing the two-dimensional nature of the structure and bonding; (4) the observation of large increases in the spin-orbit splittings at the top of the valence band at the K and M points of the Brillouin zone with decreasing cluster size, a feature that reflects quantum confinement as well as possible changes in the degree of hybridization of the electronic orbitals which make up the states at these points; and (5) the observation of photoluminescence due to both direct and surface recombination. Several of these features bode well for the potential of these materials for solar photocatalysis.

Effect of edge plasmons on the optical properties of MoS2 monolayer flakes

“…This edge configuration is particularly interesting because the metallic edge state on the S 2 dimers supports a strong 1D edge plasmon [19]. Depending on the growth conditions, the flakes favor different edge terminations or shapes [16,[25][26][27]. However, for alternative S-terminated edges, the 1D plasmons are expected to couple weaker to light [19] and they have not been reported in previous computational studies of Sterminated triangular flakes [28,29].…”

Highly fluorescent C-dots obtained by pyrolysis of quaternary ammonium ions trapped in all-silica ITQ-29 zeolite

“…There are precedents in the literature showing that homogeneous particle size in MoS 2 of a few nm leads to defined absorption bands in contrast to the continuous absorption of mixtures of quantum dots of a broad size distribution. 40,41 As expected, the material extracted with ethyl acetate was strongly photoluminescent and the position of emission maximum ( em ) increases along the excitation wavelength in the range from 350 to 500 nm (Figure 4). Excitation wavelength also determines the Stokes shift and the broadness of the emission.…”

Dissulfeto de molibdênio, um material multifuncional e surpreendente

“…As aplicações do dissulfeto de molibdênio vão desde baterias no estado sólido que utilizam meio não aquoso e íons lítio intercaláveis [9][10][11] , células solares 12 , como lubrificantes sólidos 13 , catalisadores [14][15][16][17][18] , onde desempenha um papel de importância fundamental, além de outras.…”