由h-BN包封激活的少层MoTe $_2$中的呼吸模式
Breathing modes in few-layer MoTe$_2$ activated by h-BN encapsulation
摘要：
在六方氮化硼（h-BN）中封装少量过渡金属二硫属化物（TMD）可以显著改善其光学和电学性能。然而，可以预期的是，由于h-BN层的原子级平坦表面，h-BN封装也可能影响TMD的振动性质。为了研究其对少层TMD中层间相互作用的影响，我们研究了双层和三层MoTe $_2$的低能拉曼散射光谱。令人惊讶的是，与沉积在SiO $_2$ /Si衬底上的薄片的单一呼吸模式相比，在沉积在h-BN上或包封在h-BN中的结构的拉曼光谱中观察到三种呼吸模式。切变模式不受MoTe $_2$环境变化的影响。出现的呼吸模式的结构归因于MoTe $_2$层和底部的h-BN薄片之间的明显的相互作用。由于前片的高质量表面，结构变得可见。因此，所观察到的呼吸模式的三重结构起源于由于层间和层-基底相互作用的组合模式。我们的研究结果证实，h-BN封装影响层状材料的振动性能。
英文摘要：
The encapsulation of few-layer transition metal dichalcogenides (TMDs) in hexagonal boron nitride (h-BN) is known to improve significantly their optical and electronic properties. However, it may be expected that the h-BN encapsulation may affect also vibration properties of TMDs due to an atomically flat surface of h-BN layers. In order to study its effect on interlayer interactions in few-layer TMDs, we investigate low-energy Raman scattering spectra of bi- and trilayer MoTe$_2$. Surprisingly, three breathing modes are observed in the Raman spectra of the structures deposited on or encapsulated in h-BN as compared to a single breathing mode for the flakes deposited on a SiO$_2$/Si substrate. The shear mode is not affected by changing the MoTe$_2$ environment. The emerged structure of breathing modes is ascribed to the apparent interaction between the MoTe$_2$ layer and the bottom h-BN flake. The structure becomes visible due to a high-quality surface of the former flake. Consequently, the observed triple structure of breathing modes originates from the combination modes due to interlayer and layer-substrate interactions. Our results confirm that the h-BN encapsulation affects substantially vibration properties of layered materials.
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