Coherent acoustic phonons in van der Waals nanolayers and heterostructures
Coherent acoustic phonons in van der Waals nanolayers and heterostructures
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DOI：
10.1103/physrevb.98.075408
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发表时间：
2018-08-09
影响因子：
3.7
通讯作者：
Patane, A.
中科院分区：
文献类型：
--
作者：
Greener, J. D. G.;Akimov, A., V;Patane, A.
太赫兹（THz）和亚太赫兹相干声学声子已被成功地用作各种量子系统的探针。由于它们的波长在纳米范围内，因此它们可以以纳米分辨率探测埋在表面下的纳米结构，并能够在皮秒时间尺度上控制电学和光学特性。然而，相干声学声子尚未被广泛用于研究货车德瓦耳斯（vdW）二维（2D）材料和异质结构。这类二维系统的特点是层平面中原子的共价键很强，层与层之间的货车范德华吸引力很弱。层之间或层与其支撑衬底之间的界面的动力学性质通常被忽略，因为它们难以探测。另一方面，这些在解释实验和/或设计新的器件结构中起着至关重要的作用。在这里，我们使用皮秒超声波技术来研究声子输运在VDW InSe纳米层和InSe/hBN异质结。在这些二维系统中产生和检测相干声学声子，并允许我们探测不同层及其界面的弹性参数。特别是，我们对vdW层之间界面的弹性特性的研究揭示了在高达0.1 THz的宽频率范围内的强耦合，为需要控制界面上的电荷和声子传输的高频电子和技术提供了前景。相比之下，我们揭示了InSe纳米层和蓝宝石衬底之间的弱耦合，相关的热电和传感应用，这可能需要准悬浮层。
Terahertz (THz) and sub-THz coherent acoustic phonons have been successfully used as probes of various quantum systems. Since their wavelength is in the nanometer range, they can probe nanostructures buried below a surface with nanometer resolution and enable control of electrical and optical properties on a picosecond time scale. However, coherent acoustic phonons have not yet been widely used to study van der Waals (vdW) two-dimensional (2D) materials and heterostructures. This class of 2D systems features strong covalent bonding of atoms in the layer planes and weak van der Waals attraction between the layers. The dynamical properties of the interface between the layers or between a layer and its supporting substrate are often omitted as they are difficult to probe. On the other hand, these play a crucial role in interpreting experiments and/or designing new device structures. Here, we use picosecond ultrasonic techniques to investigate phonon transport in vdW InSe nanolayers and InSe/hBN heterostructures. Coherent acoustic phonons are generated and detected in these 2D systems and allow us to probe elastic parameters of different layers and their interfaces. In particular, our study of the elastic properties of the interface between vdW layers reveals a strong coupling over a wide range of frequencies up to 0.1 THz, offering prospects for high-frequency electronics and technologies that require control over the charge and phonon transport across an interface. In contrast, we reveal a weak coupling between the InSe nanolayers and sapphire substrates, relevant in thermoelectrics and sensing applications, which can require quasi-suspended layers.