Terahertz Spectroelectrochemical Methods to Study Semiconductors, 2D Materials, and Metal Organic Frameworks (MOFs)

该项目由化学结构，动力学和机制-A（CSDM-A）计划和化学测量和成像（CMI）计划资助。在该奖项下，耶鲁大学Charles Schmuttenmaer教授的实验室利用一种称为太赫兹光谱电化学的激光技术，研究在催化和电子学中具有潜在应用的材料表面的化学结构和反应。 太赫兹光的频率大约从每秒三千亿到三十万亿次。 它的频率范围高于微波辐射（用于无线通信和微波炉），但频率低于红外光（用于夜视镜和我们感觉到的热量）。 太赫兹光可以用来测量半导体等材料的电导率。 Schmuttenmaer教授和他的研究小组对半导体材料施加不同的电压，并使用太赫兹光来探索材料的导电性如何影响半导体表面发生的化学反应。 太赫兹光和电驱动化学反应的结合使用使新技术“太赫兹光谱电化学”得名。本科生，研究生和博士后助理正在接受最先进的实验和计算技术的培训，为理解和改进分子和半导体材料的基础科学提供关键信息。这为在工业相关设备中有效利用新半导体材料提供了见解。该项目开发和应用太赫兹（THz）光谱电化学到几类与电极相关的材料，包括半导体，2D材料和金属有机框架（MOFs）。太赫兹范围内的光谱电化学是具有挑战性的，因为太赫兹辐射被诸如电极的导电材料吸收和反射。Schmuttenmaer小组表明，线栅结构中的光学透明电极的电子照相图案允许太赫兹光的强透射。然后，图案化的电极可以用于三电极薄层电化学电池中，以在施加的电压下进行THz测量。该技术用于进行稳态太赫兹实验，以研究半导体材料中移动的态的密度等。该方法还用于与超快激光激发结合进行时间分辨测量，以获得亚皮秒的动态响应的材料下施加的电位，从而调查光电极材料在工作条件下。这种时间分辨技术被用来研究分子-半导体给体-受体二元体中的异质电子转移，但也适用于本项目中讨论的材料范围。这些属性使太赫兹光谱电化学在研究新兴材料中的操作电荷传输方面处于独特的地位，例如过渡金属二硫属化物（TMD），这是一种二维材料，以及导电MOFs。该奖项反映了NSF的法定使命，并被认为值得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来支持。

This project is funded by the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program and the Chemical Measurement and Imaging (CMI) Program. Under this award, Professor Charles Schmuttenmaer’s laboratory at Yale University utilizes a laser technique known as Terahertz Spectroelectrochemistry, to study chemical structure and reactions at the surfaces of materials that have potential applications in catalysis and electronics. Terahertz light has frequencies roughly from three hundred billion to thirty trillion cycles per second. Its frequency range is higher than microwave radiation (used in wireless communications and microwave ovens), but lower in frequency than infrared light (used in night vision goggles and what we feel as heat). Terahertz light can be used measure the electrical conductivity of materials like semiconductors. Professor Schmuttenmaer and his research group apply different voltages to semiconductor materials and use terahertz light to explore how the conductivity of the material affects the chemical reactions that occur on the semiconductor surfaces. The combined use of terahertz light and electrically-driven chemical reactions gives the new technique, “Terahertz Spectroelectrochemistry” its name. Undergraduate students, graduate students, and postdoctoral associates are being trained in state-of-the-art experimental and computational techniques to provide critical information toward understanding and improving the fundamental science of molecular and semiconductor materials. This provides insight into effectively utilizing the new semiconductor materials in industrially-relevant devices. This project develops and applies Terahertz (THz) Spectroelectrochemistry to several classes of materials relevant to electrodes, including semiconductors, 2D materials, and metal-organic frameworks (MOFs). Spectroelectrochemistry in the THz range is challenging because THz radiation is absorbed and reflected by conductive materials such as electrodes. The Schmuttenmaer group showed that photolithographically patterning optically transparent electrodes in a wire-grid configuration allows strong transmission of THz light. The patterned electrodes can then be used in three-electrode thin layer electrochemical cells to perform THz measurements under applied voltage. The technique is utilized to perform steady-state THz experiments to investigate the density of mobile states in semiconducting materials, among other things. The method is also used in conjunction with ultrafast laser excitation to perform time-resolved measurements to obtain the sub-picosecond dynamic response of materials under applied potential, thereby investigating photoelectrode materials under operating conditions. This time-resolved technique is utilized to investigate heterogeneous electron transfer in molecule-semiconductor donor-acceptor dyads, but is also applicable across the scope of materials discussed in this project. These attributes uniquely position THz spectroelectrochemistry to study operando charge transport in emerging classes of materials, such as transition metal dichalcogenides (TMDs), which are 2D materials, and conductive MOFs.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.