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

非技术描述：我们非常需要开发从地球上丰富的元素中提取的下一代材料，这将彻底改变电子工业的未来几代设备，包括计算机芯片、激光器和探测器。硅是地壳中第二丰富的元素，也是技术上最重要的元素。许多奇特形式的硅，表现出笼状或隧道状晶体结构，具有高效率和低成本的破坏性电子和光子特性，将硅推向一个新的水平。然而，这些奇异的硅结构倾向于在离子客体原子周围形成。它们的潜力只有在离子客体完全去除的情况下才能实现。本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途径，并揭示客体扩散机制途径的复杂性，解决了这一重要要求。这项研究将对开放硅结构中的离子运动产生迄今尚未实现的基本理解。与研究紧密结合的是强大的教育和外展项目，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提供的暑期讲习班和实习项目，以及社区外展。该团队还与Rocky Mountain夏令营合作，为对科学、技术、工程和数学（STEM）有兴趣和天赋的阅读障碍学生提供夏令营。技术描述：理论上，许多奇异形式的地球丰富硅被预测具有属性，例如直接带隙，这将彻底改变电子和光电子工业。这种潜力尚未实现，关键的限制是完全去除这些开放晶体结构周围的客体原子的关键要求。这个项目的最终目标是阐明离子和原子的扩散途径和迁移的碱和碱土离子，惰性客体原子，和掺杂剂在硅笼和隧道结构。尽管已经通过理论、模拟和小规模合成研究了许多奇异形式的硅，但对客体扩散/迁移机制的基本知识严重缺乏。阻碍客体扩散/迁移率研究的主要障碍是无法以薄膜、粉末和块状形式生产足够数量的相纯材料。这一障碍可以通过研究团队采用的综合方法来克服，从而允许研究探索：哪种客体扩散途径是优选的，即通过小型或大型笼子，五倍或六倍笼子环；非理想的作用，如空位或杂质，以及部分占有和离子-离子相互作用如何产生不寻常的扩散/溶解度动力学；带电与中性物质及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性能的纯硅同素异形体薄膜和粉末（克级）；同素异形体硅薄膜晶格宏观扩散研究探索客体的位置/环境和动态，缺陷杂质，以及薄膜和粉末的内在缺陷。关键技术包括：飞行时间二次离子质谱、电子自旋共振和固态核磁共振谱。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。

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.