Molybdenum disulfide (MoS2) of single and few-layer thickness was exfoliated on SiO2/Si substrate and characterized by Raman spectroscopy. The number of S-Mo-S layers of the samples was independently determined by contact-mode atomic-force microscopy. Two Raman modes, E12g and A1g, exhibited sensitive thickness dependence, with the frequency of the former decreasing and that of the latter increasing with thickness. The results provide a convenient and reliable means for determining layer thickness with atomic-level precision. The opposite direction of the frequency shifts, which cannot be explained solely by van der Waals interlayer coupling, is attributed to Coulombic interactions and possible stacking-induced changes of the intralayer bonding. This work exemplifies the evolution of structural parameters in layered materials in changing from the 3-dimensional to the 2-dimensional regime.
@article{arxiv.1005.2509,
title = {Anomalous Lattice Vibrations of Single and Few-Layer MoS2},
author = {Changgu Lee and Hugen Yan and Louis E. Brus and Tony F. Heinz and James Hone and Sunmin Ryu},
journal= {arXiv preprint arXiv:1005.2509},
year = {2010}
}