Chemically Tunable Acoustic Phonons in 2D Materials

声学声子是在材料中移动的声波，它控制着诸如刚度、热传导以及材料在电子设备中的工作方式等重要特性。这个项目得到了材料研究部固态和材料化学项目的支持，加州大学戴维斯分校的克里斯蒂·科斯基教授将在新的二维（2D）材料中研究声子，这种材料只有几个原子厚，声子的行为非常不寻常，而且还没有被很好地理解。从电子到能源再到传感器，二维材料的广泛应用令人兴奋。要充分实现这些应用，需要了解和控制材料的性能。该项目使用精确的激光光谱学测量来详细绘制声子行为，并探索如何使用化学来修改和定制声子行为，以生产以前从未存在过的二维材料。这是为未来设备、能源系统和服务于国家利益的行业设计优化二维材料所需的知识。教育和更广泛的推广目标包括为科学和更广泛的公共社区建立在线布里渊光谱数据库。美国退伍军人被招募参与这项研究工作。本科生有针对性地招收女性和少数民族学生，接受科学和工程方面的职业培训。随着二维材料融入新技术，材料尺寸达到量子极限，声子效应改变材料的力学性能，影响热输运，并影响电子输运。在该项目中，由材料研究部固态与材料化学项目支持，旨在了解二维材料中的声子，填补基础知识的主要空白，同时解决悬而未决的问题：在二维材料中，从体到量子声子行为的交叉在哪里？这项工作开发了一套变革性的固态化学技术，用于合成和化学控制二维氧化物和硫族化合物（S, Se， te基）材料的基本声子行为。这些材料是通过新的异质结构合成途径和新的零价插层化学反应生成的。布里渊激光散射光谱用于测量和理解二维层状材料中的声子。测量给出了完整的声子色散关系、声速、折射率、机械性能和二维材料从体到单层的刚度系数。这为今后二维材料中声子的基本认识和化学控制奠定了重要的基础。这项工作开发、增强和扩展了在线布里渊光谱数据库，补充了类似的拉曼和x射线衍射数据库。这项工作训练大学生的研究能力，重点是招募妇女和少数民族。退伍军人通过加州大学戴维斯分校退伍军人成功中心招募参与研究。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。

NON-TECHNICAL SUMMARYAcoustic phonons are sound waves that move in materials and control important properties like stiffness, heat conduction, and how materials work in electronic devices. With this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, Professor Kristie Koski at the University of California, Davis, will study acoustic phonons in new two-dimensional (2D) materials that are only a few atoms thick, where the behavior of phonons is very unusual and not well understood. 2D materials are exciting for a wide range of applications from electronics to energy to sensors. To fully realize these applications requires understanding and controlling material properties. This project uses precise laser-light spectroscopy measurements to map out the phonon behavior in detail, and it also explores how to modify and customize the phonon behavior using chemistry to produce 2D materials that have never before existed. This is the kind of knowledge needed to design 2D materials optimized for future devices, energy systems, and industries serving the national interest. Educational and broader outreach goals include an online Brillouin spectroscopy database for the scientific and broader public communities. US Military Veterans are recruited for participation in this research effort. Undergraduate students, with targeted recruitment of women and minorities, are trained for careers in science and engineering.TECHNICAL SUMMARYAs 2D materials become integrated into new technologies, and material dimensions reach quantum limits, acoustic phonon effects alter material mechanical properties, affect heat transport, and impact electronic transport. In this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, aims to understand acoustic phonons in 2D materials, filling a major gap in fundamental knowledge while addressing the outstanding question: Where is the cross-over from bulk to quantum acoustic phonon behavior in a 2D material? This effort develops a transformative set of solid-state chemistry techniques to synthesize and chemically control the fundamental acoustic phonon behavior of 2D oxide and chalcogenide (S, Se, Te-based) materials. These materials are generated using new synthetic routes to heterostructures and new zero-valent intercalation chemistries. Brillouin laser light scattering spectroscopy is used to measure and understand acoustic phonons in 2D layered materials. Measurements give complete acoustic phonon dispersion relations, sound velocities, refractive indices, mechanical properties, and stiffness coefficients of 2D materials from the bulk to a monolayer. This effort lays critical foundation for the fundamental understanding and chemical control of phonons in 2D materials for future application. This work develops, enhances, and expands upon an online Brillouin spectroscopy database complementing similarly available databases in Raman and X-ray Diffraction. This work trains undergraduates in research with emphasis on recruitment of women and minorities. Military Veterans are recruited for participation in research through the UC Davis Veteran Success Center.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.