Photoelectron Emission at Semiconductor-Liquid Interfaces

第1部分：非技术概述这项研究项目由美国国家科学基金会的固体和材料化学计划支持，重点是利用固体材料实现光诱导电子发射到水和其他非真空环境中的新方法。水和其他液体中的电子具有许多不寻常和重要的性质，包括能够引发非常困难的化学反应。虽然几乎所有其他电子发射材料在水中都不稳定，但金刚石薄膜在化学上是稳定的，能够向水、空气和其他非真空环境中发射电子，但只有在紫外线照射下才能发射电子。在这个项目中，研究人员正在对金刚石薄膜和其他固态材料进行基础研究，目的是提高光致电子发射的效率和稳定性。研究包括研究光致电子发射的基本机制，探索通过操纵实验室生长的金刚石薄膜的光学特性来提高这一过程效率的新方法。这项工作可能导致新一代高度稳定、多功能和高效的电子发射器，可以用来启动高能化学反应，并在光学探测器等其他技术中有更广泛的用途。该项目包括为学生和博士后学者提供高级培训和专业发展机会，并努力通过为代表性不足群体的学生提供暑期研究机会来增加科学劳动力的多样性。第2部分：技术概述这项研究由美国国家科学基金会的固态和材料化学项目支持，旨在了解控制钻石和相关宽带隙半导体向水和其他非真空环境发射电子的能力的原子尺度因素。金刚石的氢端表面化学稳定，并表现出负电子亲和力，从而使导带电子无障碍地发射到水和其他非真空环境中。然而，要激发穿过钻石带隙的电子，需要波长小于220 nm的深紫外光。这项研究探索了金刚石与光学活性材料耦合的异质结构的形成、光学性质和光电化学性质，这种材料可以利用更长波长的光更有效地将电子注入到其导带中。一种方法是将具有低功函数或等离子体共振的纳米颗粒引入钻石薄膜。对光电化学响应和电子发射特性随波长和其他参数的函数的详细测量正在被用来提取对电子激发和发射机制的基本见解。正在使用其他具有高位导带的宽带隙材料进行探索性工作。该项目资助的研究生和博士后学者将获得广泛的指导和职业发展机会。该项目还支持来自代表性不足群体的学生的暑期研究，并支持更广泛的努力，以加强科学工作队伍的多样性。最终，这项研究为内部光电发射过程的本质提供了全新的见解，并可能导致新的材料和结构，这些材料和结构可以作为稳定、节能的电子发射器进入水和其他非真空环境。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARY This research project, supported by the Solid State and Materials Chemistry program at NSF, focuses on new approaches to achieving light-induced electron emission into water and other non-vacuum environments using solid-state materials. Electrons in water and other liquids have many unusual and important properties, including the ability to initiate very difficult chemical reactions. While nearly all other electron-emitting materials are unstable in water, diamond thin films are chemically stable and able to emit electrons into water, air, and other non-vacuum environments, but only when illuminated with ultraviolet light. In this project, researchers are conducting fundamental research on diamond films and other solid-state materials with the goal of enhancing efficiency and stability of light-induced electron emission. Research includes investigating the fundamental mechanisms involved in light-induced electron emission and exploring new approaches to enhancing the efficiency of this process by manipulating the optical properties of laboratory-grown diamond films. This work could lead to a new generation of highly stable, versatile and efficient electron emitters that could be used to initiate high-energy chemical reactions and would have broader use in other technologies such as optical detectors. This project incorporates advanced training and professional development opportunities for students and postdoctoral scholars and includes efforts to increase the diversity of the scientific workforce by providing summer research opportunities for students from under-represented groups. PART 2: TECHNICAL SUMMARY This research, supported by the Solid State and Materials Chemistry program at NSF, is aimed at understanding the atomic-scale factors that control the ability of diamond and related wide-bandgap semiconductors to emit electrons into water and other non-vacuum environments. Hydrogen-terminated surfaces of diamond are chemically stable and exhibit negative electron affinity, thereby yielding barrier-free emission of conduction-band electrons into water and other non-vacuum environments. However, excitation of electrons across the diamond bandgap requires deep ultraviolet light with wavelengths less than 220 nm. This research explores the formation, optical properties, and photoelectrochemical properties of heterostructures coupling diamond with optically active materials that can inject electrons into its conduction band more efficiently using longer-wavelength light. One approach involves incorporating nanoparticles that have low workfunctions or plasmonic resonances into diamond films. Detailed measurements of photoelectrochemical response and electron emission properties as a function of wavelength and other parameters are being used to extract fundamental insights into the mechanisms of electron excitation and emission. Exploratory work is being performed using other wide-bandgap materials with high-lying conduction bands. Graduate students and postdoctoral scholars supported on this project receive extensive mentoring and professional development opportunities. This project also supports summer research for students from under-represented groups and broader efforts to enhance diversity of the scientific work force. Ultimately this research provides fundamental new insights into the nature of internal photoemission processes and may lead to new materials and structures that can act as stable, energy-efficient electron emitters into water and other non-vacuum environments.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.