Probing the structure and electronics of self-assembled carbene monolayers

哥伦比亚大学的Xavier Roy和Latha Venkataraman教授得到化学系大分子、超分子和纳米化学（MSN）计划的支持，在金属表面上产生卡宾分子的自组装单分子层，并研究所得自组装单分子层的结构、电子性质和稳定性。 用具有可调性质的分子涂覆金属表面赋予表面适合于各种实际应用的特殊功能，包括传感、纳米电子学、纳米纤维和电化学。 由于金属表面涂层的化学、电化学和热稳定性差，在金表面上用硫醇化学基团制成的传统自组装单层的有用性受到限制。 这项对卡宾单分子膜的研究有可能显着提高表面分子单分子膜的稳定性，可调性和金属相容性，从而积极影响其潜在的实际应用。 该项目将研究与教育和推广活动结合起来。 来自不同背景的研究生和本科生都参与了研究;研究课题整合在化学和应用物理课程中;来自纽约中央哈莱姆的中学少数民族学生接触到纳米科学概念。 此外，参与研究的学生通过与意大利和捷克共和国的国际团体合作，提供了一个国际研究机会。在这个研究项目中，研究小组通过化学合成，x射线光谱，电化学表征，电子传输测量和理论。 卡宾是制备热稳定性和化学稳定性超好的自组装单分子膜的理想材料。 作为具有不寻常电子结构的异常强的σ-供体，卡宾比传统硫醇更强地结合到金属表面，从而打开了作为（生物）传感、芯片实验室、电化学、电催化和纳米机电系统的可调平台的新应用的大门。 卡宾还可以潜在地钝化纳米电极和修改金属功函数，同时作为新的配体。 尽管有这些承诺和大量的科学文献对金属-卡宾配合物，组装和表面上的卡宾构象知之甚少，和电子结构和所得的单分子膜的性质在很大程度上是未知的。 为了解决这一知识差距，本研究项目侧重于三个研究目标：（1）设计和合成具有不同电子和空间特性的卡宾单分子膜，（2）使用X射线光谱和扫描隧道显微镜探测卡宾单分子膜与金属表面的结构和电子耦合，以及（3）开发室温和基于溶液的方法以在金属表面制备卡宾单分子膜，该奖项反映了NSF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。

Professors Xavier Roy and Latha Venkataraman of Columbia University are supported by the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program of the Division of Chemistry to generate self-assembled monolayers of carbene molecules on metallic surfaces, and to investigate the structure electronic properties and stability of the resulting self-assembled monolayers. Coating metallic surfaces with molecules having tunable properties imparts the surface with special functionalities suitable for a variety of practical applications, including sensing, nanoelectronics, nanofabrication and electrochemistry. The usefulness of traditional self-assembled monolayers made with thiol chemical groups on gold surfaces is limited due to the poor chemical, electrochemical and thermal stability of the metal surface coating. This research on carbene monolayers has the potential to significantly improve the stability, tunability and metal compatibility of molecular monolayers on surfaces, thus positively impacting their potential practical applications. The project integrates research with educational and outreach activities. Graduate and undergraduate students from diverse backgrounds are involved in the research; research topics are integrated in Chemistry and Applied Physics curricula; and middle-school minority students from Central Harlem in New York are exposed to nanoscience concepts. In addition, the students involved in the research are provided with an international research opportunity through collaboration with international groups in Italy and the Czech Republic.In this research project the research team study the formation, stability, structure and electronic properties of self-assembled carbene monolayers on metallic surfaces through an interdisciplinary effort that includes chemical synthesis, x-ray spectroscopy, electrochemical characterization, electron transport measurements and theory. Carbenes are promising candidates for creating thermally and chemically ultra-stable self-assembled monolayers. Being exceptionally strong sigma-donors with unusual electronic structures, carbenes bind much more strongly to metal surfaces than traditional thiols, thus opening the door to novel applications as tunable platforms for (bio)sensing, lab-on-a-chip, electrochemistry, electrocatalysis and nanoelectromechanical systems. Carbenes could also potentially passivate nanoelectrodes and modify metal work functions while serving as novel ligands. Despite these promises and the vast scientific literature on metal-carbene complexes, the assembly and conformation of carbenes on surfaces is poorly understood, and the electronic structure and properties of the resulting monolayers are largely unknown. To address this knowledge gap, this research project focuses on three research objectives: (1) Designing and synthesizing carbene monolayers with varying electronic and steric characteristics, (2) Probing the structure and electronic coupling of carbene monolayers to metal surfaces using x-ray spectroscopy and scanning tunneling microscopy, and (3) Developing room temperature and solution-based methods to prepare carbene monolayers on metal surfaces, and characterizing the structure and electronic coupling using electrochemical and scanning probe techniques.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.