Effects of ultrasonic cavitation intensity on the efficient liquid-exfoliation of MoS₂nanosheets

Abstract

An optimal power to exfoliate MoS2nanoflakes for high yield and small lateral size with narrow size distribution was obtained.

Quantum confinement effects across two-dimensional planes in MoS2 quantum dots

“…6,22 These excitonic transitions should also blue-shift or exhibit other changes in the quantum size regime. 22 The unaltered absorption features reported so far 16,17,20 suggest that the QCE is negligible but it is contradictory to the PL results. Herein, we report PL from MoS 2 with obvious indication of the quantum confinement effects across twodimensional planes.…”

“…[15][16][17][18][19][20][21] Although monitoring the PL has applications in the detection of glucose, 15 DNA, 21 and 2,4,6-trinitrophenol, 18 previously reported PL signals have been ambiguous and unreliable. The PL peak position should blue-shift compared to big MoS 2 sheets due to the quantum confinement effects (QCE) across 2D planes.…”

“…22,23 However, the observed PL peak always appears in the visible range although the size distributions vary from several nanometers 16 to tens of and even a hundred nanometers. 15,17,19,20 The excitonic Bohr radius of MoS 2 is about 2.0 nm (Refs. 24 and 25) and it is thus unreasonable to consider the QCE for a planar size as large as tens of nanometers.…”

“…This has been verified by absorption spectra. 16,17,20 The bulk MoS 2 shows well-defined features having two excitonic transitions, one (band A) at $670 and the other (band B) at $620 nm with an energy separation of $0.20 eV, due to the spin-orbit splitting of the top of the valence band at the K point. 6,22 These excitonic transitions should also blue-shift or exhibit other changes in the quantum size regime.…”

“…The PLE maximum peak position, absorption band edge, and size distribution are consistent with each other thus furnishing clear evidence of the size effect and complementing previous results. [15][16][17][18][19][20][21] The PL and PLE spectra acquired from the colorless QDs also vary with excitation or monitoring emission wavelengths. The maximum emission wavelength is about 460 nm and corresponding excitation wavelength is 380 nm being consistent with the absorption spectrum ( Fig.…”