Photoelectron Emission at Semiconductor-Liquid Interfaces

该研究项目由美国国家科学基金会固态和材料化学项目支持，重点研究使用固态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同寻常的重要性质，包括引发非常困难的化学反应的能力。几乎所有其他的电子发射材料在水中都是不稳定的，而金刚石薄膜在化学上是稳定的，并且能够在水、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，目标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，并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。这项工作可能会导致新一代高度稳定、多功能和高效的电子发射器，可用于引发高能化学反应，并将在光学探测器等其他技术中有更广泛的应用。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，并通过为来自代表性不足群体的学生提供暑期研究机会，努力增加科学劳动力的多样性。这项研究由美国国家科学基金会固态和材料化学项目支持，旨在了解控制金刚石和相关宽带隙半导体向水和其他非真空环境中发射电子能力的原子尺度因素。金刚石的端氢表面具有化学稳定性，并表现出负电子亲和性，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，通过金刚石带隙激发电子需要波长小于220纳米的深紫外光。本研究探讨了金刚石与光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，这些材料可以利用更长的波长光更有效地将电子注入其导带。一种方法是将具有低功函数或等离子共振的纳米颗粒掺入金刚石薄膜中。作为波长和其他参数的函数的光电化学响应和电子发射特性的详细测量被用于提取对电子激发和发射机制的基本见解。目前正在使用其他具有高导带的宽带隙材料进行探索性工作。该项目支持的研究生和博士后学者将获得广泛的指导和专业发展机会。该项目还支持来自代表性不足群体的学生的暑期研究，以及加强科学工作人员多样性的更广泛努力。最终，这项研究为内部光电过程的本质提供了基本的新见解，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。

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.