Semiconductor Physics, Technische Universität Chemnitz, D-09107 Chemnitz, Germany.
A.V. Rzhanov Institute of Semiconductor Physics, 630090 Novosibirsk, Russia and Novosibirsk State University, Pirogova street 2, 630090 Novosibirsk, Russia.
Nanoscale. 2016 Oct 6;8(39):17204-17212. doi: 10.1039/c6nr06949e.
Recently developed two-dimensional colloidal semiconductor nanocrystals, or nanoplatelets (NPLs), extend the palette of solution-processable free-standing 2D nanomaterials of high performance. Growing CdSe and CdS parts subsequently in either side-by-side or stacked manner results in core-crown or core/shell structures, respectively. Both kinds of heterogeneous NPLs find efficient applications and represent interesting materials to study the electronic and lattice excitations and interaction between them under strong one-directional confinement. Here, we investigated by Raman and infrared spectroscopy the phonon spectra and electron-phonon coupling in CdSe/CdS core/shell and core-crown NPLs. A number of distinct spectral features of the two NPL morphologies are observed, which are further modified by tuning the laser excitation energy E between in- and off-resonant conditions. The general difference is the larger number of phonon modes in core/shell NPLs and their spectral shifts with increasing shell thickness, as well as with E. This behaviour is explained by strong mutual influence of the core and shell and formation of combined phonon modes. In the core-crown structure, the CdSe and CdS modes preserve more independent behaviour with only interface modes forming the phonon overtones with phonons of the core.
最近开发的二维胶体半导体纳米晶体或纳米薄片（NPL）扩展了高性能可溶液处理的独立二维纳米材料的调色板。以并排或堆叠的方式分别在两侧生长 CdSe 和 CdS 部分，分别得到核-冠或核/壳结构。这两种异质 NPL 都找到了有效的应用，并代表了有趣的材料，可以在强单向限制下研究电子和晶格激发以及它们之间的相互作用。在这里，我们通过拉曼和红外光谱研究了 CdSe/CdS 核/壳和核-冠 NPL 的声子谱和电子-声子耦合。观察到两种 NPL 形态的许多不同的光谱特征，进一步通过调整激光激发能量 E 在共振和非共振条件之间进行了修饰。一般的区别是核/壳 NPL 中声子模式的数量更多，并且随着壳层厚度的增加以及随着 E 的增加而发生光谱位移。这种行为是通过核心和外壳的强烈相互影响以及组合声子模式的形成来解释的。在核-冠结构中，CdSe 和 CdS 模式保持更独立的行为，只有界面模式与核心的声子形成声子泛音。
