CAREER: Synthesis and Properties of Group IV Colloidal Quantum Wells

在过去的五十年中，计算机处理器的性能每年都在提高，从而改善了教育、医疗保健、科学研究和国家安全。然而，使用传统的硅基计算机处理器，计算性能的进一步提高不可能无限期地持续下去。这个由材料研究部固态和材料化学项目支持的NSF CAREER奖项目，使用了爱荷华州立大学Matthew Panthani教授的研究小组开发的新技术，并将其扩展到制备独特的极薄（不到人类头发的千分之一）硅片或硅和锗的组合。通过精确控制薄片的厚度、组成和附着在表面的分子，这些薄片具有不同的特性，最终可以使计算机更有效地运行。理论计算机模拟补充了实验方法，以更好地了解控制这些超薄片性能的因素。这项研究有助于开发一种新型材料，例如，可以提高计算机的能力并降低计算成本。计算性能的最终进步将对社会产生广泛的积极影响，加速药物发现和材料研究，改善国家安全，减少全球能源消耗。与这项研究相结合的是一项教育计划，通过以下两项活动扩大下一代STEM劳动力的参与：(1)与高中科学教师合作开发课程，这些教师在夏季在Panthani研究小组中进行研究，目的是通过强调科学与他们生活的相关性来增强代表性不足群体的学生对STEM研究职业的兴趣，以接触社会经济上处于不利地位的学生，例如Panthani博士与来自监狱学校的老师合作；(2)旨在增加来自不同背景的高中生、本科生和社区大学生从事科学和工程职业的可能性的暑期研讨会活动。本NSF职业奖项目由材料研究部固态和材料化学项目支持，建立了第四组半导体（Si， Ge及其合金）胶体量子阱（c- qw）的合成策略。爱荷华州立大学的Matthew Panthani教授的研究小组沿着两条研究方向进行研究(1)合成具有可控成分、结构和表面化学的Si-Ge合金c-QWs；(2)利用实验表征和密度泛函数理论确定结构和化学如何影响所得到的光电性能。合成IV族c-QWs的起点是含有由碱金属原子或盐分离的原子薄的IV族元素片的Zintl化合物。这些Zintl化合物被脱嵌以释放出独立的纳米片，这些纳米片随后被有机或无机表面配体功能化，以提供电子钝化并稳定胶体悬浮液中的c-QWs。研究的c-QWs的相关光电特性包括带隙和导价带极值。此外，该研究提供了一个以设计活动为中心的教育推广平台，帮助学生形成科学身份。科学身份是一个被认为对一个人至关重要的因素。她选择从事科学或工程方面的职业。该教育计划包括与在Matthew Panthani教授的实验室工作的高中教师合作开发课程，以及开发一个研讨会，旨在提高参加暑期研究的有才华的高中生、本科生和社区大学生在科学和工程领域追求职业道路的可能性。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 The performance of computer processors has improved each year for the past five decades, leading to improvements in education, healthcare, scientific research, and national security. However, further improvements in computational performance cannot continue indefinitely using conventional Si-based computer processors. This NSF CAREER award project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, uses novel techniques developed in Prof. Matthew Panthani's research group at Iowa State University and extends them to prepare unique very thin (less than one thousandth of that of a human hair) sheets of silicon or a combination of silicon and germanium. By precisely controlling the sheet thickness, composition, and the molecules bound to the surface, the sheets have different properties that could eventually make computers perform much more effectively. The experimental methods are complemented by theoretical computer simulations to better understand which factors control the properties of these ultrathin sheets. This research contributes towards developing a new type of material that could, for example, improve the capabilities of computers and reduce the cost of computing. This eventual advancement in computational performance would have a broad positive impact on society by accelerating drug discovery and materials research, improving national security, and reducing energy consumption worldwide. Integrated with this research is an educational plan that broadens participation in the next-generation STEM workforce through two activities: (1) collaborative curriculum development with high school science teachers that conduct research in the Panthani research group during summers, with the aim of strengthening the interest of students from underrepresented groups in STEM research careers by highlighting the relevance of science to their lives, to reach socioeconomically disadvantaged students, Dr. Panthani for example partners with a teacher from a prison school; and (2) summer workshop activities that are designed to increase the likelihood that high school, undergraduate and community college students from diverse backgrounds pursue careers in science and engineering. PART 2: TECHNICAL SUMMARYThis NSF CAREER award project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, establishes synthetic strategies for Group IV semiconductor (Si, Ge, and their alloys) colloidal quantum wells (c-QWs). Prof. Matthew Panthani's research group at Iowa State University pursues research along two lines of studies (1) synthesizing Si-Ge alloy c-QWs with controlled composition, structure, and surface chemistry and (2) determining how structure and chemistry influence the resulting optoelectronic properties using experimental characterization and density functional theory. The starting point for synthesizing the Group IV c-QWs are Zintl compounds that contain atomically-thin Group IV element sheets that are separated by alkali metal atoms or salts. These Zintl compounds are deintercalated to liberate freestanding nanosheets, which are subsequently functionalized with organic or inorganic surface ligands to provide electronic passivation and stabilize the c-QWs in colloidal suspensions. Relevant optoelectronic properties of the c-QWs that are studied include band gaps and conduction/valence band extrema. Additionally, the research provides a platform for educational outreach centered around designing activities that help form a science identity in students. Science identity is a factor that is thought to be critical to one?s choice to pursue a career in science or engineering. The educational plan involves collaborative curriculum development with high school teachers who work in Prof. Matthew Panthani's lab and the development of a workshop session that aims to improve the likelihood that talented high school, undergraduate, and community college students, who participate in summer research, pursue a career paths in science and engineering.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.