2012/12/20 by Weijie Zhao, Zohreh Ghorannevis, Leiqiang Chua +6 · 11 citations
Chemistry · Engineering · Materials Science · Physics and Astronomy · #2D Materials and Applications #Band gap #Chemistry #Condensed matter physics #Direct and indirect band gaps #Exciton #MXene and MAX Phase Materials #Materials science #Molecular physics #Monolayer #Nanotechnology #Optics #Optoelectronics #Perovskite Materials and Applications #Photoluminescence #Physics #Quantum yield #cond-mat.mtrl-sci
paper · pdf · doi:10.1021/nn305275h
published as ACS Nano, 2013, 7 (1), pp 791 · to be published in ACS Nano
openalex publication_date 2012/12/20 · arxiv created 2012/12/21 · arxiv updated 2014/03/13 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
Geometrical confinement effect in exfoliated sheets of layered materials leads to significant evolution of energy dispersion in mono- to few-layer thickness regime. Molybdenum disulfide (MoS(2)) was recently found to exhibit indirect-to-direct gap transition when the thickness is reduced to a single monolayer. Emerging photoluminescence (PL) from monolayer MoS(2) opens up opportunities for a range of novel optoelectronic applications of the material. Here we report differential reflectance and PL spectra of mono- to few-layer WS(2) and WSe(2) that indicate that the band structure of these materials undergoes similar indirect-to-direct gap transition when thinned to a single monolayer. The transition is evidenced by distinctly enhanced PL peak centered at 630 and 750 nm in monolayer WS(2) and WSe(2), respectively. Few-layer flakes are found to exhibit comparatively strong indirect gap emission along with direct gap hot electron emission, suggesting high quality of synthetic crystals prepared by a chemical vapor transport method. Fine absorption and emission features and their thickness dependence suggest a strong effect of Se p-orbitals on the d electron band structure as well as interlayer coupling in WSe(2).