Surface and Nanoscience Division , Indira Gandhi Centre for Atomic Research, HBNI , Kalpakkam 603102 , India.
Nano Lett. 2018 Nov 14;18(11):7181-7187. doi: 10.1021/acs.nanolett.8b03300. Epub 2018 Oct 26.
The optical phonons in semiconductor nanostructures play an indispensable role in fundamental phenomenon and device applications based on these nanostructures. We study the Raman spectroscopy of optical phonons in Si nanowires (NWs) whose sizes are beyond the phonon confinement regime. The peak shift and unusual asymmetric broadening by one-phonon mode in Si NWs is observed during far-field Raman studies. Using an appropriate thermal anchoring and localized Raman measurements on single NWs by near-field tip-enhanced Raman spectroscopy (TERS), we demonstrate the decoupling of multiple origins responsible for the peak shift accompanied by asymmetric broadening of the one-phonon mode and the appearance of multiple phonon peaks from a single measurement area. A model based on the localized phonon population induced by NW size-dependent charge depletion is proposed to explain the observed dependence of phonon characteristics on NW size. The scanning Kelvin probe force microscopy measurements confirm the size-dependent intrinsic semiconductor surface and interface states-induced charge depletions in single Si NWs. The study clearly suggests the size-dependent phonon characteristics of Si NWs which are crucial for several NW-based photovoltaic and thermoelectric devices.
半导体纳米结构中的光学声子在基于这些纳米结构的基础现象和器件应用中起着不可或缺的作用。我们研究了尺寸超出声子限制范围的硅纳米线（NWs）中的光学声子的喇曼光谱。在远场喇曼研究中观察到 Si NWs 中一个声子模式的峰位移和异常不对称展宽。通过近场尖端增强喇曼光谱学（TERS）对单个 NW 进行适当的热锚定和局域喇曼测量，我们证明了多个起源的解耦，这些起源导致了伴随单一声子模式不对称展宽的峰位移以及来自单个测量区域的多个声子峰的出现。提出了一个基于由 NW 尺寸相关的电荷耗尽引起的局域声子分布的模型，以解释所观察到的声子特性对 NW 尺寸的依赖性。扫描 Kelvin 探针力显微镜测量证实了单根 Si NW 中尺寸相关的本征半导体表面和界面态诱导的电荷耗尽。这项研究清楚地表明了 Si NWs 的尺寸相关声子特性，这对于基于 NW 的光伏和热电器件至关重要。
