School of Physics, State Key Laboratory of Crystal Materials, Shandong University , Shandong, Jinan 250100, P. R. China.
Center for Phononics and Thermal Energy Science, School of Physics Science and Engineering, Tongji University , 200092 Shanghai, P. R. China.
Nano Lett. 2017 Apr 12;17(4):2621-2626. doi: 10.1021/acs.nanolett.7b00412. Epub 2017 Mar 30.
Raman enhancement on a flat nonmetallic surface has attracted increasing attention, ever since the discovery of graphene enhanced Raman scattering. Recently, diverse two-dimensional layered materials have been applied as a flat surface for the Raman enhancement, attributed to different mechanisms. Looking beyond these isolated materials, atomic layers can be reassembled to design a heterostructure stacked layer by layer with an arbitrary chosen sequence, which allows the flow of charge carriers between neighboring layers and offers novel functionalities. Here, we demonstrate the heterostructure as a novel Raman enhancement platform. The WSe (W) monolayer and graphene (G) were stacked together to form a heterostructure with an area of 10 mm × 10 mm. Heterostructures with different stacked structuress are used as platforms for the enhanced Raman scattering, including G/W, W/G, G/W/G/W, and W/G/G/W. On the surface of the heterostructure, the intensity of the Raman scattering is much stronger compared with isolated layers, using the copper phthalocyanine (CuPc) molecule as a probe. It is found that the Raman enhancement effect on heterostructures depends on stacked methods. Phonon modes of CuPc have the strongest enhancement on G/W. W/G and W/G/G/W have a stronger enhancement than that on the isolated WSe monolayer, while lower than the graphene monolayer. The G/W/G/W/substrate demonstrated a comparable Raman enhancement effect than the G/W/substrate. These differences are due to the different interlayer couplings in heterostructures related to electron transition probability rates, which are further proved by first-principle calculations and probe-pump measurements.
在非金属平面上的拉曼增强引起了越来越多的关注，自从发现石墨烯增强拉曼散射以来。最近，各种二维层状材料已被用作拉曼增强的平面，归因于不同的机制。超越这些孤立的材料，原子层可以重新组装成一个具有任意选择顺序的异质结构堆叠层，这允许载流子在相邻层之间流动，并提供新的功能。在这里，我们展示了异质结构作为一种新的拉曼增强平台。WSe（W）单层和石墨烯（G）堆叠在一起，形成一个 10mm×10mm 的异质结构。具有不同堆叠结构的异质结构被用作增强拉曼散射的平台，包括 G/W、W/G、G/W/G/W 和 W/G/G/W。在异质结构的表面上，使用铜酞菁（CuPc）分子作为探针，与孤立层相比，拉曼散射的强度要强得多。结果发现，异质结构的拉曼增强效果取决于堆叠方法。CuPc 的声子模式在 G/W 上具有最强的增强效果。W/G 和 W/G/G/W 的增强效果强于孤立的 WSe 单层，但低于石墨烯单层。G/W/G/W/衬底的拉曼增强效果与 G/W/衬底相当。这些差异是由于与电子跃迁概率率相关的异质结构中的不同层间耦合引起的，这通过第一性原理计算和探针泵浦测量进一步得到证实。
