Probing the Vibrational States of Surface Sites on Catalytic Nanoparticles with Atomic Resolution Electron Energy-Loss Spectroscopy

在化学系化学测量和成像（CMI）项目的支持下，以及化学系催化项目和物理系原子、分子和光学物理项目的部分共同资助下，亚利桑那州立大学的Peter Crozier教授正在研究开发一种新的成像工具，用于测量小颗粒表面原子的振动。后者被定位为重要化学转化过程的催化剂。材料表面的原子以各种不同的方式不断振动，这些不同类型的振动对应于不同的振动路径，称为模态。材料表面原子的这些振动模式有助于将能量传递给与材料表面结合的分子，这可能会导致表面结合分子的分子结构发生催化化学变化。然而，获得小颗粒表面振动模式信息的方法有限。Crozier教授将开发和应用新的显微镜技术，利用电子进行成像过程，以检测和研究非常小的颗粒表面振动模式的特征。从这项研究中预期的基本原理不仅在催化方面，而且在材料和生命科学的其他领域都有可能产生长期影响。为了让学生、教师和公众参与到这项研究中来，一个名为“良好振动”的教育模块将被开发出来，它将把原子级振动的领域与音乐中的振动声波联系起来。将开发一个基于网络的应用程序，允许学生和公众将音乐段落分解为基本振动（谐波）模式。通过结合当代艺术家的音乐，该团队希望能让高中生对振动科学产生兴趣，并激发他们对科学、技术、工程和数学职业的热情。这个项目的目标是用原子分辨率探测和发展对催化纳米颗粒不同表面位置的振动状态的基本理解。为了提高我们对振动能量交换过程的理解，有必要了解存在于表面位置的局部振动模式。纳米颗粒表面的振动动力学还没有得到很好的理解，部分原因是没有方法对表面振动模式进行原子分辨率探测。Krozier团队将利用非弹性电子散射的冲击分量，在扫描透射电子显微镜（STEM）中开发振动电子能量损失谱（EELS）的新方法，以解决这一缺陷。STEM中的电子散射以类似于非弹性中子散射的方式携带有关振动状态的信息，但它可以提供原子分辨率。此外，信号可能与对原子缺陷最敏感的短波长模式相关联。总的来说，这项研究有可能为催化剂表面提供一种有用的新的振动描述。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With the support of the Chemical Measurement and Imaging (CMI) Program in the Division of Chemistry, and partial co-funding from the Catalysis Program in the Division of Chemistry and the Atomic, Molecular, and Optical Physics Program in the Division of Physics, Professor Peter Crozier of Arizona State University is studying development of a new imaging tool to measure the vibrations of atoms on the surface of small particles, with the latter being targeted as catalysts for important chemical conversion processes. The atoms on the surface of a material are constantly vibrating in a variety of different ways, with those different types of vibrations corresponding to different vibrational pathways, referred to as modes. These vibrational modes of the atoms on the surface of a material can help transfer energy to molecules bound to the surface of the material, which may drive catalytic chemical changes in the molecular structure of the surface-bound molecules. However, there are limited methods for gaining information about vibrational modes across the surface of small particles. Professor Crozier will develop and apply novel microscopy techniques that use electrons for the imaging process so as to detect and study the characteristics of surface vibrational modes on very small particles. The fundamental principles anticipated from this study have the potential for long-term impact not only in catalysis but also in other areas of materials and life science. To engage students, teachers, and the public in this research, an educational module entitled “Good Vibrations” will be developed, which will link the area of atomic-level vibrations to vibrational sound waves found in music. A web-based application will be developed that allows students and the public to decompose music passages into fundamental vibrational (harmonic) modes. By incorporating music from contemporary artists, the team hopes to engage high school students in the excitement of vibrational science and generate enthusiasm for careers in science, technology, engineering, and mathematics. The goal of this project is to probe and develop a fundamental understanding of vibrational states at distinct surface sites on catalytic nanoparticles with atomic resolution. To improve our understanding of the vibrational energy exchange process, it is necessary to have information on the local vibrational modes that exist at surface sites. Vibrational dynamics on nanoparticle surfaces are not well understood, in part because there have been no methods to perform atomic resolution probing of surface vibrational modes. The Krozier team will address this deficiency by developing novel approaches to vibrational electron energy-loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM) using the impact component of inelastic electron scattering. Electron scattering in STEM carries information about vibrational states in a manner similar to inelastic neutron scattering, but it can provide atomic resolution. Moreover, the signal may be associated with short wavelength modes that are most sensitive to atomic defects. Overall, this research has the potential to provide a useful new vibrational description of the surfaces of catalysts.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.