Department of Physics, University of California at Berkeley, Berkeley, California 94720, USA.
Nat Commun. 2013;4:1375. doi: 10.1038/ncomms2367.
Van der Waals-coupled materials, ranging from multilayers of graphene and MoS(2) to superlattices of nanoparticles, exhibit rich emerging behaviour owing to quantum coupling between individual nanoscale constituents. Double-walled carbon nanotubes provide a model system for studying such quantum coupling mediated by van der Waals interactions, because each constituent single-walled nanotube can have distinctly different physical structures and electronic properties. Here we systematically investigate quantum-coupled radial-breathing mode oscillations in chirality-defined double-walled nanotubes by combining simultaneous structural, electronic and vibrational characterizations on the same individual nanotubes. We show that these radial-breathing oscillations are collective modes characterized by concerted inner- and outer-wall motions, and determine quantitatively the tube-dependent van der Waals potential governing their vibration frequencies. We also observe strong quantum interference between Raman scattering from the inner- and outer-wall excitation pathways, the relative phase of which reveals chirality-dependent excited-state potential energy surface displacement in different nanotubes.
范德华耦合材料，从多层石墨烯和 MoS(2)到纳米粒子超晶格，由于单个纳米尺度成分之间的量子耦合，表现出丰富的新兴行为。双壁碳纳米管为研究这种由范德华相互作用介导的量子耦合提供了一个模型系统，因为每个组成的单壁纳米管可以具有明显不同的物理结构和电子特性。在这里，我们通过在同一单个纳米管上同时进行结构、电子和振动特性的综合研究，系统地研究了手性定义的双壁纳米管中量子耦合的径向呼吸模式振荡。我们表明，这些径向呼吸振荡是由同心内外壁运动协调的集体模式，并定量确定了控制其振动频率的管依赖性范德华势能。我们还观察到来自内外壁激发途径的拉曼散射之间的强烈量子干涉，其相对相位揭示了不同纳米管中手性相关激发态势能面位移。
