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Multivalency-Induced Band Gap Opening at MoS<sub>2</sub> Edges
Lucking, Michael C.,Bang, Junhyeok,Terrones, Humberto,Sun, Yi-Yang,Zhang, Shengbai American Chemical Society 2015 Chemistry of materials Vol.27 No.9
<P>Zigzag edges of monolayer MoS<SUB>2</SUB> and other transition-metal (TM) dichalcogenides are experimentally shown to exhibit strong photoluminescence. Atomic models that have been proposed for these edges, however, are all metallic. Here, we address this puzzle by using first-principles calculations. We found that a more generic electron counting model (ECM) can be developed, which, when coupled with the ability of TM atoms at edges to change their valency from 4+ to 5+, can quantitatively account for the band gap opening at the zigzag edges. Due to the ECM, a 3× periodicity along the zigzag edge is necessary to open the band gap. Moreover, consistent with experiment, oxygen adsorption is shown to open even larger band gaps than intrinsic edges.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2015/cmatex.2015.27.issue-9/acs.chemmater.5b00398/production/images/medium/cm-2015-003989_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm5b00398'>ACS Electronic Supporting Info</A></P>
Chen, Nian-Ke,Li, Xian-Bin,Bang, Junhyeok,Wang, Xue-Peng,Han, Dong,West, Damien,Zhang, Shangbai,Sun, Hong-Bo American Physical Society 2018 Physical review letters Vol.120 No.18
<P>Time-dependent density-functional theory molecular dynamics reveals an unexpected effect of optical excitation in the experimentally observed rhombohedral-to-cubic transition of GeTe. The excitation induces coherent forces along [001], which may be attributed to the unique energy landscape of Peierls-distorted solids. The forces drive the A(lg) optical phonon mode in which Ge and Te move out of phase. Upon damping of the A(1)g mode, phase transition takes place, which involves no atomic diffusion, defect formation, or the nucleation and growth of the cubic phase.</P>