Size-Dependent Spectroscopy of MoS₂ Nanoclusters

Abstract

The synthesis and characterization of 3.5, 4.5, and 8 nm diameter MoS 2 nanoclusters are described. Each size is characterized by TEM images, electron diffraction, and optical spectroscopy. These nanoclusters can be synthesized directly or may be synthesized from samples of polydisperse nanoclusters. Obtaining larger or smaller discrete sizes from polydisperse samples indicates that these nanocluster sizes are thermodynamically favored, that is, these sizes correspond to free-energy minima. Electron diffraction and static spectroscopic results indicate that the particles are three atoms thick, specifically, single S-Mo-S trilayer disks. Static and time-resolved absorption and emission spectroscopy were used to determine the polarizations of the lowest energy allowed transitions in each case. We find that the 8 nm particles have a lowest energy absorption maximum at 473 nm that has mixed xy and z polarizations, 4.5 nm particles have absorption maxima at 400 and 440 nm that are xy and z polarized, respectively, and 3.5 nm particles have an absorption maximum at 362 nm that is z polarized. These results indicate that the polarization of the lowest observed transition is size-dependent and that the ordering of the lowest excited states changes as the particle size decreases.

Synthesis of chain-like MoS2 nanoparticles in W/O reverse microemulsion and application in photocatalysis

“…The as-synthesized chain-like MoS 2 nanoparticles exhibit strong absorption in UV region with a maximum at 276 nm and a weaker broad absorption in the visible region of 400 nm, which is very similar to that of MoS 2 nanoparticles reported by Zong et al [6], Chikan et al [15] and Zhang et al [22]. The photocatalytic H 2 -production activity was determined by dispersing the freshly-prepared …”

“…For example, Wilcoxon et al [13,14] synthesized the nanosized MoS 2 crystals as small as 2.5 and 4 nm in EHAB/hexanol/octane and TDAB/hexanol/octane micelle solutions. Chikan et al [15] obtained MoS 2 nanocrystals with the size of 3.5, 4.5 and 8 nm in DDAB/hexanol/ octane and TDAI/hexanol/octane ternary micelles, respectively. Osseo-Asare and co-workers [11] got MoS 2 nanoparticles ranging 10-80 nm in NP-5/cyclohexane/water microemulsion system.…”

CdS/MoS 2 heterojunction-based photoelectrochemical DNA biosensor via enhanced chemiluminescence excitation

“…1C). The weaker threshold at 390 nm could be assigned to the direct transition from the deep valence band to the conduction band (Gopalakrishnan et al, 2014), while the absorption peaks below 300 nm was assigned to the excitonic feature of MoS 2 QDs (Chikan and Kelley, 2002). In addition, the FL spectrum of MoS 2 QDs was measured under 290 nm excitation wavelength (Fig.…”

Discrete quantum dot like emitters in monolayer MoSe2: Spatial mapping, magneto-optics, and charge tuning

“…[4][5][6] The 2D host materials have the advantage of being cost efficient, with highly tunable properties 3,7 and optical access to the electron valley index in momentum space, 8,9 an additional degree of freedom compared to other solid state qubits in III-V quantum dots (QDs) or NV centres in diamond, for example. There are several approaches to achieve 3D quantum confinement, such as patterning TMD MLs, 10 chemically synthesized TMD nano-crystals, [11][12][13][14][15][16] and defect engineering. [17][18][19][20] In photoluminescence (PL) experiments at T ¼ 4 K, we observe QD-like, discrete emission lines (full width at half maximum (FWHM) typ.…”