CAREER: From Emergence of Collective Electronic States to Materials by Design in Layered Chalcogenides

技术综述紧密相关的电子材料在能源生产和存储、传感器以及许多高技术需求方面有着广泛的应用。该提案得到了固态和材料化学计划的支持，其目的是探索层状二维材料的结构与相关的电子和磁性之间的关系。这将通过系统的、综合的电子计数变化以及详细的物理性质表征来实现。将解决的广泛问题是：(A)在层状金属硫化物中，金属-金属键在磁性、电荷密度波和金属行为之间的切换中起什么作用？以及(B)多层拓扑绝缘体和普通绝缘体/金属是否会产生新的、在拓扑上截然不同的电子态(正如最近预测的那样)？前者将通过将新的软化学技术应用于高度还原的碱金属硫化物(KCo2(S/Se)2和KCu2(S/Se)2)来实现。后者将通过合成和物理表征--包括通过合作进行角度分辨光电子能谱--来解决众所周知的错配层状化合物。失配对于这一目的很有吸引力，因为它们“自然”包含两个化学(和电子)不同的层，它们交替堆叠形成所需的多层结构，并且每种层类型都可以调整到所需的化学和电子计数。预计这项研究将有助于开发设计和控制固态反应的改进技术，特别是创造具有新的和奇异的物质电子态的材料，并可能在未来开发制备亚稳态材料的大块晶体的方法(一项具有挑战性的壮举)。非技术总结创新材料几乎在所有研究领域都具有突破，从医学上的生物兼容材料到用于太空探索的超灵敏探测器和轻质合金。这些材料进步的广泛采用依赖于合理的设计方法。这项提议试图合成和表征新的层状材料，这种材料含有电子活性的二维片，表现出一种被称为浮现的惊人现象：行为似乎超过了各部分的总和。这种“强相关”的电子材料在能源生产、储存和传感器方面有许多应用，但却是最难建模和预测的；这一提议旨在阐明这种电子出现的起源，以使我们能够驾驭和控制这种行为。此外，该提案还将研究、教育和社区推广紧密联系在一起。研究生和本科生研究人员都将在开展拟议的研究中发挥重要作用，每个研究人员都会给出自己的项目，以鼓励独立、探索和批判性分析。此外，有效的科学教育不能局限于事实和“书本工作”，而必须包括动手实验(一种主动学习的形式)，这一想法构成了从小学到研究生的材料化学教育综合计划的基础。以社区为导向的努力侧重于将动手实验带给巴尔的摩市中心学校的高中生和地区社区的中小学生。这些努力尤其侧重于向弱势儿童灌输对科学和工程的兴奋和兴趣，这对于鼓励他们追求科学、技术、工程和数学(STEM)职业至关重要。

TECHNICAL SUMMARYStrongly correlated electronic materials have numerous applications in energy production and storage, sensors, and a multitude of high technology needs. the purpose of the proposal, supported by the Solid State and Materials Chemistry program is to explore the relationships between structure and correlated electronic and magnetic properties in layered, two-dimensional materials. This will be accomplished through systematic, synthetic variation of electron counts coupled with detailed physical property characterization. The broad questions that will be addressed are: (a) what is the role of metal-metal bonding in switching between magnetic, charge-density-wave, and metallic behavior in layered metal chalcogenides? and (b) do multilayers of topological insulators and normal insulators/metals produce new, topologically distinct electronic states (as has recently been predicted)? The former will be accomplished by applying new soft chemistry techniques to highly reduced alkali metal chalcogenides (KCo2(S/Se)2 and KCu2(S/Se)2). The latter will be addressed through the synthesis and physical characterization - including angle-resolved photoemission spectroscopy through collaboration - of well-known misfit layered compounds. Misfits are attractive for this purpose because they 'naturally' contain two chemically (and electronically) distinct layers that alternately stack to form the desired multilayer structures, and each layer type can be tuned to the desired chemistry and electron count. It is anticipated that this research will allow for the development of improved techniques for the design and control of solid state reactions, especially for the creation of materials with new and exotic electronic states of matter, and possibly the future development of methods to prepare bulk crystals of metastable materials (a challenging feat).NON TECHNICAL SUMMARYInnovative materials underlie breakthroughs in virtually all fields of study, from biocompatible materials in medicine to supersensitive detectors and lightweight alloys for space exploration. Widespread adoption of these material advances relies on rational design methods. This proposal seeks to synthesize and characterize new layered materials which contain electronically active two-dimensional sheets that exhibit the striking phenomenon known as emergence: behaviors that appear to be more than the sum of the parts. Such 'strongly correlated' electronic materials have numerous applications in energy production and storage and sensors, but are among the most difficult to model and predict; this proposal seeks to elucidate the origins of such electronic emergence to allow us to harness and control such behavior. Additionally, the proposal closely links research, education, and community outreach. Both graduate and undergraduate researchers will play an essential role in carrying out the proposed research, with each researcher given his or her own project to encourage independence, exploration, and critical analysis. Further, the idea that effective scientific education cannot be limited to facts and 'bookwork', but must involve hands-on experimentation (a form of active learning), forms the basis for a comprehensive program in materials chemistry education from grade school to graduate levels. Community-oriented efforts focus on bringing hands-on experimentation to high school students in inner-city Baltimore schools and to elementary and middle school students in area communities. These efforts are particularly focused on instilling excitement and interest in science and engineering in disadvantaged children, which are essential for encouraging the pursuit of science, technology, engineering, and mathematics (STEM) careers.