Nonlinear Spectroscopy of Silicon Nano-Interfaces

技术：本项目主要利用非线性光学方法，特别是二次谐波产生（SHG）和和频产生（SFG）光谱，研究嵌入非晶氧化物材料和相邻Si（001）和Si（111）表面阶边的硅纳米晶体（nc）。非线性光谱学用于探测这些材料的电子结构、化学修饰和飞秒动力学。实验将扩展到多电子伏特光谱范围，利用光学参量放大器获得界面态光谱。嵌入式Si纳米晶体的研究包括全面研究由Si=O双键、Si悬空键、非晶Si过渡区、应变Si-Si和Si-O键等引起的纳米晶体界面态之间的辐射和非辐射光学跃迁，这对理解纳米晶体的发光至关重要。由于球形硅纳米晶体的复合材料具有反转对称性，因此它们缺乏传统的电偶极子SHG响应，但具有对界面化学钝化高度敏感的光学四极SHG响应。在硅台阶边缘的研究中，SHG将与反射-各向异性光谱（RAS）相结合，并使用简化的键超极化模型进行分析，以获得键特异性光谱。非技术：该项目涉及材料科学主题领域的基础研究问题，具有高技术相关性。该研究有望使人们对硅纳米晶体界面的结构和性质以及晶体硅表面的步骤有更基本的了解。该项目的成功将有助于纳米晶体发光和闪存器件以及纳米技术的未来发展。通过这个项目，研究生和本科生将在对美国工业和技术至关重要的领域接受培训。该项目还包括与德克萨斯大学圣安东尼奥校区合作开展教育和推广活动，该校区的拉美裔学生入学率很高。

Technical: This project is to study silicon nanocrystals (NCs) embedded in amorphous oxide materials and step edges at vicinal Si(001) and Si(111) surfaces mainly using nonlinear optical methods, particularly second harmonic generation (SHG) and sum-frequency generation (SFG) spectroscopy. The nonlinear optical spectroscopy is used to probe electronic structures, chemical modifications, and femtosecond dynamics of these materials. The experiments will be extended to a multi-electron-volt spectral range using an optical parametric amplifier to obtain interface state spectra. The research on embedded Si nanocrystals includes a comprehensive study of both radiative and nonradiative optical transitions between nanocrystals' interface states arising from, e.g., Si=O double bonds, Si dangling bonds, the amorphous Si transition region, and strained Si-Si and Si-O bonds, which are crucial for understanding luminescence of nanocrystals. Because composites of spherical silicon nanocrystals possess inversion symmetry, they lack a conventional electric-dipole SHG response, but possess an allowed, optically quadrupolar SHG response that is highly sensitive to interface chemical passivation. In studies of silicon step edges, SHG will be combined with reflectance-anisotropy spectroscopy (RAS), and analyzed with a simplified bond hyperpolarizability model to achieve bond-specific spectra.Non-technical: The project addresses basic research issues in a topical area of materials science with high technological relevance. The research is expected to yield much needed basic understanding on structures and properties of silicon nanocrystal interfaces and steps at crystalline silicon surfaces. The success of the project would help in the future progress of nanocrystal-based light-emitting and flash-memory devices and nanotechnology in general. Through this project, graduate and undergraduate students will receive training in a field of critical importance to U.S. industry and technology. The project also includes education and outreach activities in collaboration with the University of Texas - San Antonio campus, which has very high Hispanics student enrollment.