Si-SiO2纳米复合材料中Si颗粒尺寸与界面氧键关系的Raman研究
Correlation of size and oxygen bonding at the interface of Si nanocrystal in Si-SiO2 nanocomposite: A Raman mapping study
摘要：
Si-SiO2多层纳米复合材料（NCp）薄膜，使用不同的Si沉积时间的脉冲激光沉积生长的影响，使用拉曼光谱/映射研究的Si声子频率的变化观察到这些NCp。在所有研究的样品中，在拉曼映射数据（图1A）中观察到的低频（LF）声子（~ 495 - 510 cm-1）和高频（HF）声子（~ 515 - 519 cm-1）分别来自Si纳米晶体的表面（Si-SiO2界面）和核。这种理解的一致的图片开发使用拉曼光谱监测的激光加热/退火和冷却（LHC）实验在所需的频率的位置选择的帮助下的拉曼映射，这带来了明确的区别核心和表面（界面）声子的Si纳米晶体。为了进一步支持LF是表面（界面）声子的观点，我们对Si 41团簇进行了Raman光谱计算，结果表明，在512 cm-1处有较强的Si声子频率，对应于表面Si原子。这可以被认为类似于在Si-SiO2界面（扩展）处起源的495 - 510 cm-1范围内观察到的声子频率。这些结果与XPS数据一起表明，界面的性质（氧键合）反过来取决于纳米晶体的尺寸，因此LF声子起源于较小的Si纳米晶体的表面。开发的理解可以扩展到解释在文献中报道的Si-SiO2纳米复合材料中观察到的Si声子频率的大的变化，特别是较低的频率。
英文摘要：
Si-SiO2 multilayer nanocomposite (NCp) films, grown using pulsed laser deposition with varying Si deposition time are investigated using Raman spectroscopy/mapping for studying the variation of Si phonon frequency observed in these NCps. The lower frequency (LF) phonons (~ 495 - 510 cm-1) and higher frequency (HF) phonons (~ 515 - 519 cm-1) observed in Raman mapping data (Fig. 1A) in all samples studied are attributed to have originated from surface (Si-SiO2 interface) and core of Si nanocrystals, respectively. The consistent picture of this understanding is developed using Raman spectroscopy monitored laser heating/annealing and cooling (LHC) experiment at the site of a desired frequency chosen with the help of Raman mapping, which brings out clear difference between core and surface (interface) phonons of Si nanocrystals. In order to further support our attribution of LF being surface (interface) phonons, Raman spectra calculations for Si41 cluster with oxygen termination are performed which shows strong Si phonon frequency at 512 cm-1 corresponding to the surface Si atoms. This can be considered analogous to the observed phonon frequencies in the range 495 - 510 cm-1 originating at the Si-SiO2 interface (extended). These results along with XPS data show that nature of interface (oxygen bonding) in turn depends on the size of nanocrystals and thus LF phonons originate at the surface of smaller Si nanocrystals. The understanding developed can be extended to explain large variation observed in Si phonon frequencies of Si-SiO2 nanocomposites reported in the literature, especially lower frequencies.
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