Confined Acoustic Phonons in Colloidal Nanorod Heterostructures Investigated by Nonresonant Raman Spectroscopy and Finite Elements Simulations
Confined Acoustic Phonons in Colloidal Nanorod Heterostructures Investigated by Nonresonant Raman Spectroscopy and Finite Elements Simulations
复制标题
通过非共振拉曼光谱和有限元模拟研究胶体纳米棒异质结构中的受限声子
DOI：
10.1021/acs.nanolett.6b03706
复制
发表时间：
2016
期刊：
影响因子：
10.8
通讯作者：
Krahne Roman
中科院分区：
文献类型：
--
作者：
Miscuglio Mario;Lin Miao-Ling;Di Stasio Francesco;Tan Ping-Heng;Krahne Roman
镉镉纳米晶体的晶格振动模式对激子的载流子动力学和这些纳米材料的光学性质有很大的影响。发光应用的突出材料是CdSe/CdS芯壳点插棒。本文用非共振拉曼光谱法详细研究了激光激发能低于其带隙的点状棒中的声子模式。在5-50 cm-1的频率范围内具有高信噪比，我们揭示了与受限伸展和径向呼吸模式（RBM）相关的不同拉曼波段。将实验结果与有限元模拟和解析分析进行比较，可以详细了解声振动模式及其共振频率的局域性。特别是，点状棒的RBM不能通过嵌入在CdS棒矩阵中的CdSe球的振荡来理解。相反，棒中点结构导致棒核心区域的声速降低，从而导致棒RBM频率的红移以及发生光学跃迁的核心附近声子诱导应变的局部化。这种局域效应有可能被用作调节纳米晶体异质结构中激子-声子耦合的工具。
Lattice vibrational modes in cadmium chalcogenide nanocrystals (NCs) have a strong impact on the carrier dynamics of excitons in such confined systems and on the optical properties of these nanomaterials. A prominent material for light emitting applications are CdSe/CdS core–shell dot-in-rods. Here we present a detailed investigation of the acoustic phonon modes in such dot-in-rods by nonresonant Raman spectroscopy with laser excitation energy lower than their bandgap. With high signal-to-noise ratio in the frequency range from 5–50 cm–1, we reveal distinct Raman bands that can be related to confined extensional and radial-breathing modes (RBM). Comparison of the experimental results with finite elements simulation and analytical analysis gives detailed insight into the localized nature of the acoustic vibration modes and their resonant frequencies. In particular, the RBM of dot-in-rods cannot be understood by an oscillation of a CdSe sphere embedded in a CdS rod matrix. Instead, the dot-in-rod architecture leads to a reduction of the sound velocity in the core region of the rod, which results in a redshift of the rod RBM frequency and localization of the phonon induced strain in vicinity of the core where optical transitions occur. Such localized effects potentially can be exploited as a tool to tune exciton–phonon coupling in nanocrystal heterostructures.