Harnessing Electrochemically-Injected Interstitial Atoms in Oxide Semiconductors for Doping and Purification

非技术元素和氧形成固体陶瓷化合物，如二氧化钛，不仅可用于防晒霜等商业产品，还可用于尖端电子产品、传感器以及能源生产和储存材料。陶瓷在这种高级用途中的用途通常取决于构成固体的规则原子阵列中原子尺度不规则性的微小浓度。某些类型的这种不规则性，例如嵌在结构中的额外原子(“间隙原子”)，可以有意地引入到固体中，以改善其性质。这项由这笔赠款支持的工作调查了如何使用经过特殊准备的表面暴露在带有电压的水溶液中，以可控的方式产生间隙金属原子。成功将允许金属原子以接近室温的精确方式引入，而不是典型方法在数百度的高温条件下引入。因此，先进陶瓷的制造应该变得更便宜、更快，并产生性能更优越的固体。这笔赠款下的工作还在为高中生开发在伊利诺伊大学世界青年科学与工程计划中实施的真实世界学习模块，以帮助提高他们对科学和工程的兴趣，特别是可持续能源应用的新材料。正在开展若干活动，以宣传科学和工程中伦理道德的重要性。特别是针对高中女生和第一代学生的其他外联活动包括为期一周的夏令营，以鼓励人们对科学和工程感兴趣。研究人员还邀请了几名本科生研究人员参与这项工作。技术总结半导体中的间隙原子是嵌在晶体结构中的额外原子，代表原子尺度的不规则性，或称“缺陷”。特殊制备的表面暴露在水溶液中，在室温附近有效且可控地将间隙原子注入底层，特别是在受到电化学偏压的情况下。将曲面用于此目的代表了一种新的、多功能的工具，用于在初始合成后调整材料属性。该方法实现了直接和廉价的处理方法，并进入了一种由动力学而不是热力学效应主导缺陷行为的区域。因此，有可能制造出具有迄今无法达到的特性的材料和结构，从而绕过热力学限制。例如，对超出自然丰度限制的同位素进行提纯成为可能。预计将应用于缺陷工程、化学和同位素提纯以及电子产品、传感器和可再生能源生产和储存的掺杂--所有这些都是在合成后进行的。这种方法最适合于高表面体积比的应用，如纳米结构、薄膜或多孔性材料。这项工作旨在了解在电化学偏压下注入金属间隙在陶瓷氧化物中的扩散和陷阱。这项工作使用单晶金红石二氧化钛作为具有重要技术应用的示范氧化物。实验方法主要依赖于钛和氧示踪同位素的扩散测量，以及实例掺杂锰的扩散测量。对介观尺度(2-500 nm)的缺陷扩散和反应的模拟将实验扩散分布与原子计算联系起来，以揭示预计将伴随掺杂和固态净化的复杂的时间现象。密度泛函理论的原子计算提供了与中尺度模型的输出相比较的激活势垒，并确定了可能抑制金属间隙组织移动到固体中的间隙聚集的可能性。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。

NON-TECHNICAL SUMMARYMetallic elements and oxygen form solid ceramic compounds such as titanium dioxide that can be used, not only in commercial products like sunscreens, but also in sophisticated electronics, sensors, and materials for energy production and storage. The usefulness of ceramics for such advanced purposes often depends upon tiny concentrations of atomic scale irregularities in the regular array of atoms that make up the solid. Certain kinds of these irregularities, such as extra atoms wedged into the structure ("interstitial atoms") can be introduced into the solid intentionally to benefit its properties. The work supported by this grant investigates how to use specially prepared surfaces exposed to water solutions with an electrical voltage to controllably create interstitial metal atoms. Success will permit metal atoms to be introduced in precise ways near room temperature, in contrast to the hot conditions at hundreds of degrees used by typical methods. As a result, manufacturing advanced ceramics should become cheaper, faster, and lead to solids with far superior performance. Work under this grant is also developing real-world learning modules implemented within the Worldwide Youth in Science and Engineering program at the University of Illinois for high-school students to help raise interest in science and engineering, and especially in new materials for sustainable energy applications. Several activities to promote the importance of ethics in science and engineering are being pursued. Additional outreach aimed especially at high school girls and first-generation students involve weeklong summer residential camps to encourage interest in science and engineering. The investigators are also hosting several undergraduate researchers to participate in the work.TECHNICAL SUMMARYInterstitial atoms in semiconductors are extra atoms wedged into the crystalline structure that represent atomic-scale irregularities, or "defects." Specifically prepared surfaces that are exposed to aqueous liquids act efficiently and controllably to inject interstitial atoms into the underlying bulk near room temperature, especially when subjected to electrochemical bias. Using surfaces for this purpose represents a new and versatile tool for tuning material properties after initial synthesis. The approach enables straightforward and inexpensive processing methods, and accesses a regime wherein kinetic, rather than thermodynamic, effects dominate defect behavior. It therefore becomes possible to create materials and structures with heretofore unattainable properties that circumvent thermodynamic constraints. For example, purification of isotopes beyond natural-abundance limits becomes possible. Applications are expected to span defect engineering, chemical and isotopic purification, and doping for electronics, sensors, and renewable energy production and storage – all performed post-synthesis. The approach is most suited for applications involving high surface-to-volume ratios, such as nanostructures, thin films, or porous materials. This work aims to understand the diffusion and trapping of injected metal interstitials in ceramic oxides under electrochemical bias. The work employs single-crystal rutile titanium dioxide as an exemplary oxide with important technological applications. The experimental approach relies mainly upon diffusion measurements of titanium and oxygen tracer isotopes, and of the example dopant manganese. Modeling of defect diffusion and reaction at the mesoscale (2-500 nm) links experimental diffusion profiles to atomistic calculations to unravel the complicated temporal phenomena that are expected to accompany both doping and solid-state purification. Atomistic calculations by density functional theory provide activation barriers for comparison with the outputs of mesoscale modeling, and identify possibilities for interstitial clustering that might inhibit movement of metal interstitials into the solid.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.