MoS2 is a highly interesting material system, which exhibits a crossover from an indirect band gap in the bulk crystal to a direct gap for single layers. Here, we perform a direct comparison between large-area MoS2 films grown by chemical vapor deposition (CVD) and MoS2 flakes prepared by mechanical exfoliation from natural bulk crystal. Raman spectroscopy measurements show differences between the in-plane and out-of-plane phonon mode positions in CVD-grown and exfoliated MoS2. Photoluminescence (PL) mapping reveals large regions in the CVD-grown films that emit strong PL at room temperature, and low-temperature PL scans demonstrate a large spectral shift of the A exciton emission as a function of position. Polarization-resolved PL measurements under near-resonant excitation conditions show a strong circular polarization of the PL, corresponding to a valley polarization.
@article{arxiv.1310.8470,
title = {A direct comparison of CVD-grown and exfoliated MoS2 using optical spectroscopy},
author = {G. Plechinger and J. Mann and E. Preciado and D. Barroso and A. Nguyen and J. Eroms and C. Schüller and L. Bartels and T. Korn},
journal= {arXiv preprint arXiv:1310.8470},
year = {2014}
}