Transition metal dichalcogenide (TMD) materials have received enormous attention due to their extraordinary optical and electrical properties, among which MoS2 is the most typical one. As the thickness increases from monolayer to multilayer, the photoluminescence (PL) of MoS2 is gradually quenched due to the direct-to-indirect band gap transition. How to enhance PL response and decrease the layer dependence in multilayer MoS2 is still a challenging task. In this work, we report, for the first time, simultaneous generation of three PL peaks at around 1.3, 1.4 and 1.8 eV on multilayer MoS2 bubbles. The temperature dependent PL measurements indicate that the two peaks at 1.3 and 1.4 eV are phonon-assisted indirect-gap transitions while the peak at 1.8 eV is the direct-gap transition. Using first-principles calculations, the band structure evolution of multilayer MoS2 under strain is studied, from which the origin of the three PL peaks of MoS2 bubbles is further confirmed. Moreover, PL standing waves are observed in MoS2 bubbles that creates Newton-Ring-like patterns. This work demonstrates that the bubble structure may provide new opportunities for engineering the electronic structure and optical properties of layered materials.

中文翻译：

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在多层MoS2气泡中同时产生直接和间接间隙的光致发光

过渡金属二硫化碳（TMD）材料因其非凡的光学和电学性能而受到了广泛的关注，其中MoS2是最典型的材料。随着厚度从单层增加到多层，由于直接到间接的带隙跃迁，MoS2的光致发光（PL）逐渐被淬灭。如何增强PL响应并降低多层MoS2中的层依存性仍然是一项艰巨的任务。在这项工作中，我们首次报告了在多层MoS2气泡上同时产生约1.3、1.4和1.8 eV的三个PL峰。与温度相关的PL测量表明，在1.3和1.4 eV处的两个峰是声子辅助的间接间隙跃迁，而在1.8 eV处的峰是直接间隙跃迁。使用第一性原理计算，研究了多层MoS2在应变下的能带结构演化，从中进一步证实了MoS2气泡的三个PL峰的起源。此外，在MoS2气泡中观察到PL驻波，从而产生类似牛顿环的图案。这项工作表明气泡结构可能为工程化层状材料的电子结构和光学性质提供新的机会。