Materials World Network: Mapping Oxide Surface Reactivity Through Spacially-Resolved Atomic Interaction Forces

这是耶鲁大学和西班牙马德里自治大学的合作研究项目。该项目的目标是使用带功能化尖端的非接触原子力显微镜来表征过渡金属氧化物表面上单个表面原子的化学反应性。为此，一种能够在原子尺度上绘制化学相互作用强度的新技术将通过实验（由耶鲁大学的Udo Schwarz和Eric Altman小组进行）和理论指导（由马德里自治大学的Ruben Perez小组进行）来开发。这项工作建立在最近的实验证明的基础上，在原子分辨率的短程化学力制度下，实验获得了作用于探针尖端和表面之间的整个三维力场。使用这种方法，用功能化的尖端暴露亲电和亲核的头基，可以在特定的位置几何形状上，对控制表面单个阳离子和阴离子氧化催化的关键性质进行表征和量化。新方法最初应用于金红石（110）和锐钛矿（001）表面Ti阳离子和O阴离子的局部化学性质的比较，尽管化学和结构相似，但化学行为明显不同。为了对测量的尖端-样品相互作用有一个基本的理解，实验程序与协同的多尺度理论努力相结合，包括短程化学力的量子力学描述，长距离色散力的经典描述，以及力对探测几何形状影响的分子动力学模拟。耶鲁大学和马德里自治大学的国际合作是该项目的核心，为参与该项目的研究生和本科生提供了独特的教育体验。通过每年的学生交流，学生们既能接触到最先进的实验和理论成果，又能接触到真正的国际研究环境。此外，作为一种强大的技术，该方法的进一步发展有望影响其他由局部表面相互作用控制的领域，包括摩擦学、薄膜生长、电子设备设计和许多生物学中心的特定化学相互作用。

This is a collaborative research project between Yale University and the Universidad Autonoma de Madrid in Spain. The goal of the project is to characterize the chemical reactivity of individual surface atoms on transition metal oxide surfaces using non-contact atomic force microscopy with functionalized tips. For this purpose, a new technique capable of mapping the strengths of chemical interactions on the atomic scale will be developed through experimentation (carried out in Udo Schwarz' and Eric Altman's groups at Yale University) guided by theory (performed by Ruben Perez' group at the Universidad Autonoma de Madrid). The work builds upon recent demonstration of the ability to experimentally obtain the entire three-dimensional force field acting between a probe tip and surface in the short-range chemical forces regime with atomic resolution. Using this method with tips functionalized to expose electrophilic and nucleophilic head groups allows for the characterization and quantification of the key properties that govern oxide catalysis for individual cations and anions on the surface, in specific site geometries. The new method is initially applied to a comparison of the local chemical properties of Ti cations and O anions on the rutile (110) and anatase (001) surfaces, which, despite chemical and structural similarities, behave markedly differently chemically. For a fundamental understanding of the measured tip-sample interaction, the experimental program couples with a synergistic multi-scale theoretical effort that includes a quantum mechanical description of the short-range chemical forces, a classical description of the longer range dispersion forces, and molecular dynamics simulations of the influence of the forces on the probing geometry.The international collaboration of Yale University and the Universidad Autonoma de Madrid that is at the heart of this project provides a unique educational experience for the graduate and undergraduate students involved in the project. Through extended student exchanges during each year of the project, students are immersed in state-of-the-art experimental and theoretical efforts while being exposed to a truly international research environment. Also, further development of the method as a robust technique promises to impact other fields that are governed by local surface interactions including tribology, thin film growth, electronic device design, and the specific chemical interactions at the center of much of biology.