Internal photoemission spectroscopy was used to determine the valence band top energy position in few-monolayer WS 2 and WSe 2 films directly synthesized on top of the SiO 2 insulator. It is found that in WS 2 the valence band top edge lies systematically higher (by 0.4–0.7 eV) in energy than that in WSe 2 . This unexpected trend is seen for several synthesis methods suggesting it to be the intrinsic property of these W-based layered dichalcogenides. At the same time, a change in the WS 2 synthesis method from metal sulfurization to chemical vapor deposition leads to a ≈0.3 eV barrier change indicating a non-negligible impact of interface charges or dipoles. The influence of synthesis chemistry on the WSe 2 /SiO 2 interface barrier appears to be marginal at least for the selenization and molecular-beam epitaxy growth methods.

中文翻译：

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利用内部光发射光谱法研究SiO 2的单分子层WS 2和WSe 2的能带取向

内部光发射光谱法用于确定直接在SiO 2绝缘体上合成的几层单层WS 2和WSe 2膜的价带顶部能量位置。发现在WS 2中，价带上边缘的能量系统地比WSe 2中高（0.4-0.7 eV）。对于几种合成方法而言，这种意想不到的趋势表明，这是这些基于W的层状二硫代双氰化物的固有特性。同时，WS 2合成方法从金属硫化到化学气相沉积的变化导致≈0.3eV的势垒变化，表明界面电荷或偶极子的影响不可忽略。至少对于硒化和分子束外延生长方法而言，合成化学对WSe 2 / SiO 2界面势垒的影响似乎微不足道。