Raman and resonance Raman investigation of MoS2 nanoparticles

Raman and resonance Raman spectra of MoS2 nanoparticles, in the form of inorganic fullerenelike nanoparticles with diameters ranging from 200 to 2000 Angstrom in size, and platelets ranging from 50 to 5000 Angstrom in size, are presented. Off resonance, the first-order Raman bands are broadened, but not significantly shifted, and no additional bands are observed, indicating that the atomic structure is preserved, at least locally, in the nanoparticles. The broadening effect is assigned to phonon confinement by facet boundaries. In the resonance Raman spectra of the nanoparticles, several additional first-order peaks are observed. The electron-phonon coupling responsible for the strong-resonance conditions is identified through dynamic band calculations. Using temperature-dependent resonance Raman measurements, we assign these peaks to zone-boundary phonons activated by disorder and finite-size effects. By analyzing the position of the dispersive peak at 429 (-1) under resonance conditions, it was possible to probe the softening of modes propagating in the c-axis cm direction. [S0163-1829(99)08827-X].