Diffusion of Guests, Dopants, and Impurity Atoms Through Open Cage Allotropes of Si and Related Structures

非技术描述：非常需要开发来自地球丰富元素的下一代材料，这些材料将为包括计算机芯片、激光和探测器在内的未来几代设备的电子工业带来革命性的变化。硅是地壳中第二丰富的元素，也是最具技术意义的元素。许多奇异的硅形式，表现出笼状或隧道状的晶体结构，具有高效率和低成本的破坏性电子和光子特性，将把硅推向一个新的水平。然而，这些奇异的硅结构往往是围绕离子客体原子形成的。只有完全去除离子客体，才能实现它们的潜力。这项研究项目通过阐明客体离子在硅笼/隧道结构中的基本扩散和迁移路径，以及揭开客体扩散机制的复杂性来满足这一重要要求。这项研究将从根本上理解开放硅结构中的离子运动，这是迄今为止尚未实现的。与研究紧密结合的是强有力的教育和外展计划，为材料科学领域的本科生、研究生和代表性不足的群体提供重要的培训和指导机会，包括为本科生和高中生举办暑期研讨会和实习计划，以及社区外展。该团队还与落基山阅读障碍儿童夏令营合作，为对科学、技术、工程和数学(STEM)感兴趣和有天赋的阅读障碍学生提供夏令营。技术描述：理论上预测，许多奇异的地球富含硅的形式具有直接带隙等特性，将给电子和光电子行业带来革命性的变化。这一潜力还没有实现，关键的限制是完全去除这些开放晶体结构形成周围的客体原子的关键要求。这个项目的最终目标是阐明硅笼和隧道结构中碱和碱土离子、惰性客体原子和掺杂物的离子和原子扩散路径和迁移率。虽然已经有许多奇异的硅形式通过理论、模拟和小规模合成进行了研究，但对客体扩散/迁移率机制的基础知识严重缺乏。阻碍客体扩散/迁移率研究的主要障碍是无法生产足够数量的薄膜、粉末和块体形式的相纯材料。这一障碍可以通过研究团队采用的合成方法来克服，使研究能够探索：哪种客体扩散路径更可取，即通过小笼子或大笼子、五重或六重环笼；非理想性的作用，如空位或杂质，以及部分占据和离子相互作用如何创建不寻常的扩散/溶解动力学；带电物种与中性物种和电子给予对扩散的影响。研究工作包括：合成和开发具有良好扩散特性的相纯硅同素异形体的薄膜和粉末(克尺度)；研究通过硅同素异形体薄膜晶格的宏观扩散；探索客体位置/环境和动力学、薄膜和粉末中的缺陷杂质和本征缺陷。关键技术包括：飞行时间二次离子质谱仪、电子自旋共振和固态核磁共振波谱。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 Description: There is a great need for development of next generation materials, derived from earth abundant elements, that would revolutionize the electronics industry for future generations of devices including computer chips, lasers, and detectors. Silicon is the second most abundant element on the Earth's crust and the most technologically significant. Many exotic forms of silicon, which exhibit caged or tunnel crystalline structures, hold the promise of high efficiency and low cost disruptive electronic and photonic properties that would push silicon to a new level. These exotic silicon structures, however, tend to form around ionic guest atoms. Their potential can be only realized with complete ionic guest removal. This research project addresses this vital requirement by elucidating the fundamental diffusion and mobility pathways for guest ions in silicon caged/tunnel structures and unraveling the complexities of the mechanistic pathways to guest diffusion. The research will create a fundamental understanding of ionic motion in open silicon structures that has not been achieved to-date. Closely integrated with the research are strong education and outreach programs to provide significant training and mentoring opportunities for undergraduate, graduate and underrepresented groups in materials science, including summer workshops and internship programs for undergraduate and high school students, and community outreach. The team also collaborates with the Rocky Mountain Camp for Dyslexic Kids to provide summer camps developed for students with dyslexia who have interest in and aptitude for science, technology, engineering, and mathematics (STEM).Technical Description: Many exotic forms of earth abundant silicon are theoretically predicted to have properties, such as a direct bandgap, that would revolutionize electronics and photonics industries. This potential has not been realized and the key limitation is the critical requirement of complete removal of the guest atoms around which these open crystal structures form. The ultimate goal of this project is to elucidate the ionic and atomic diffusional pathways and mobility of alkali and alkaline earth ions, inert guest atoms, and dopants in silicon caged and tunnel structures. Although there have been a number of exotic forms of silicon investigated via theory, simulation, and small-scale synthesis, a fundamental knowledge of the guest diffusion/mobility mechanisms is severely lacking. The major barrier that prohibits guest diffusion/mobility studies is the inability to produce sufficient quantities of phase pure material in thin-film, powder and bulk form. This barrier can be overcome by synthesis approach undertaken by the research team, allowing the research to explore: which guest diffusion pathways are preferable, i.e., via small or large cages, five-fold or six-fold rings of cages; the role of non-idealities, like vacancies, or impurities, and how partial occupancy and ion-ion interaction create unusual diffusion/solubility kinetics; the effect of charged versus neutral species and electron donation on diffusion. The research efforts include: synthesis and development of thin films and powders (on the grams-scale) of phase pure silicon allotropes with well-defined diffusive properties; investigation of macroscopic diffusion through the crystalline lattice of thin films of silicon allotropes; exploring the guest location/environment and dynamics, the defect impurities, and intrinsic defects in both films and powders. Key techniques include: time-of-flight secondary ion mass spectroscopy, electron spin resonance, and solid-state nuclear magnetic resonance spectroscopy.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.