Writing in Nano Letters a team led by Professor Chih-Kang Shih from the University of Texas at Austin studied the electronic structures of single layer transition metal dichalcogenides WSe2 and WS2, by scanning tunneling spectroscopy.
It is generally well understood within academia that monolayer semiconductor transition metals dichalcogenides, such as WS2, WSe2, MoS2 and others, have an indirect-to-direct band gap transition as they make the transition from bulk to single layer. This is typically manifested as a strong photoluminescence in monolayer flakes. Although this is true for MoSe2, the team found that the band gap minimum for WS2 is in fact located at the Q-point of the Brillouin zone, instead of the K, although the two states are nearly degenerate.
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