School of Engineering, Brown University, Providence, Rhode Island 02906, USA.
ACS Nano. 2011 Jul 26;5(7):5903-8. doi: 10.1021/nn201698t. Epub 2011 Jul 1.
Since discovery of graphene, layered materials have drawn considerable attention because of their possible exfoliation into single and multilayer 2D sheets. Because of strong surface effects, the properties of these materials vary drastically with the number of layers in a sheet. We have performed first-principles density functional based calculations to evaluate the electron energy loss spectrum (EELS) of bulk, monolayer, and bilayer configurations of several transition metal dichalcogenides, which include semiconducting as well as metallic compounds. Our investigation shows that the peaks in the EELS spectra move toward larger wavelengths (red shift) with the decrease in number of layers. The π plasmon peak shifts slightly by 0.5-1.0 eV, while a significant shift of around 5.5-13.0 eV is obtained for π + σ plasmon, when exfoliated from bulk to single-layer. This underscores the importance of the interlayer coupling on the loss spectra and the dielectric properties. Our results are found to be in very good agreement with the recent measurements performed by Coleman et al. (Science2011, 331, 568).
自从石墨烯被发现以来，由于它们有可能剥落成单层和多层 2D 薄片，层状材料引起了相当大的关注。由于强烈的表面效应，这些材料的性质随薄片中的层数而急剧变化。我们已经进行了基于第一性原理密度泛函的计算，以评估几种过渡金属二卤化物的体相、单层和双层结构的电子能量损失谱 (EELS)，其中包括半导体和金属化合物。我们的研究表明，随着层数的减少，EELS 谱中的峰向较大的波长（红移）移动。当从体相剥离到单层时，π 等离子体峰仅略有 0.5-1.0 eV 的位移，而 π + σ 等离子体的位移约为 5.5-13.0 eV。这强调了层间耦合对损耗谱和介电性质的重要性。我们的结果与科尔曼等人最近进行的测量非常吻合（Science2011, 331, 568）。
