Visualization of localized strain of a crystalline thin layer at the nanoscale by tip-enhanced Raman spectroscopy and microscopy
Visualization of localized strain of a crystalline thin layer at the nanoscale by tip-enhanced Raman spectroscopy and microscopy
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DOI：
10.1002/jrs.1728
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发表时间：
2007-06-01
影响因子：
2.5
通讯作者：
Kawata, Satoshi
中科院分区：
文献类型：
--
作者：
Hayazawa, Norihiko;Motohashi, Masashi;Kawata, Satoshi
由于应变硅薄层中的载流子迁移率与未应变层相比得到增强，应变硅作为组装在一个衬底上的超大型集成电子电路的有前途的材料受到极大的关注。然而，这些应变基板，遭受纳米尺度的应变分布的波动，这可以强烈地影响器件的性能。由于拉曼光谱中的光学声子受应变的强烈影响，因此拉曼光谱是一种强有力的工具。然而，薄层的拉曼效率非常小，并且经常在下面的缓冲衬底的拉曼散射下黯然失色。此外，空间分辨率受到探测光的衍射极限的限制。在这里，在这篇文章中，我们演示了使用表面增强的拉曼散射，以克服这两个问题。在第一步中，应变硅薄层覆盖有银层以引起表面增强拉曼光谱（Sers），并且发现Sers可以有效地增强源自应变硅层的拉曼信号，使得其明显地远离源自缓冲层的背景信号。在接下来的步骤中，我们演示了利用相同的机制来增强点表面，而不是大表面增强。这是通过利用银涂层的尖锐尖端来完成的，就像Sers一样，但是仅从非常接近尖端顶点的样品区域进行。这种技术，被称为尖端增强拉曼光谱（TERS），在我们的测量提供纳米分辨率。我们利用TERS观察了定位菌株。TERS光谱揭示了拉曼波数的明显纳米级变化。然而，由于光的衍射极限的平均效应，显微拉曼测量仅显示出均匀的特征。为了进一步提高硅材料的TERS，我们讨论了利用更短的波长，专门的尖端，尖端压力效应，和去极化配置。版权所有（c）2007约翰威利父子有限公司。
Since the carrier mobility in a strained silicon thin layer is enhanced compared to unstrained layers, strained silicon is finding tremendous attention as a promising material for ultralarge integrated electronic circuits assembled on one substrate. These strained substrates, however, suffer from nanoscale fluctuation of strain distribution, which can strongly affect the performance of devices. Raman spectroscopy is a powerful tool because the optical phonons in the Raman spectra are strongly influenced by strain. However, Raman efficiency of a thin layer is extremely small and is often eclipsed under the Raman scattering of the underlying buffer substrates. Also, the spatial resolution is restricted by the diffraction limits of the probing light. Here, in this article we demonstrate the use of surface enhancement in Raman scattering to overcome both these problems. In the first step, a strained silicon thin layer was covered with a silver layer to invoke surface-enhanced Raman spectroscopy (SERS), and it was found that SERS can effectively enhance the Raman signal originating from the strained silicon layer, so that it stands distinctly apart from the background signal originating from the buffer layer. In the next step, we demonstrate the utilization of the same mechanism for a point surface enhancement, rather than a large surface enhancement. This is done by utilizing a silver-coated sharp tip, just like SERS, but only from the sample region very close to the tip apex. This technique, known as tip-enhanced Raman spectroscopy (TERS), provides nanometric resolution in our measurement. We observed localized strains by utilizing TERS. The TERS spectra revealed clear nanoscale variation in the Raman wavenumber. Micro-Raman measurements, however, show only uniform features because of the averaging effect due to the diffraction limit of light. For further improvement of TERS on silicon materials, we discuss the utilization of shorter wavelength, specialized tip, tip-pressure effect, and depolarization configurations. Copyright (c) 2007 John Wiley & Sons, Ltd.