Hybrid Materials by Integration of Semiconductor Nanowires and Layered Crystals: Chemical Transformations and Functional Properties

非技术摘要在固态和材料化学计划的支持下，该项目探索通过固态反应部分将半导体纳米线转化为层状晶体来创造新型杂化材料。这种转变迫使结构不同的纳米材料整合，这有望产生与组成成分截然不同的新颖和独特的性质。为了研究这种固态化学，正在开发微型反应堆单元，当将组件材料装载到电子显微镜中时，可以启动并直接观察到原子级别的复杂材料的转变和集成过程。这一新方法有可能成为开发高科技材料合成和加工策略的变革性工具。除了有针对性的技术进步外，该项目还为相关的研究生和本科生提供了影响深远的教育和培训机会。它包括对来自农村地区和美洲原住民人口的高中生的专门外联努力，使学生-教师团队有机会参与与研究相关的动手活动。在研究小组的指导下，学生们准备新的科学学习材料，他们带回学校与同龄人分享他们的经验，并帮助在STEM学科的职业生涯中建立兴奋。技术摘要该项目致力于研究通过固态化学转化将晶体半导体纳米线与层状金属硫化物晶体相结合来创造新型杂化纳米材料。纳米线部分转化为层状结构迫使结晶学和拓扑学上不同的材料进行集成，这是一个兼容性挑战，该系统需要通过找到能量上首选或动力学上最容易获得的混合结构来克服这一挑战。新型膜反应器单元-在研究和工业中广泛用于材料合成和加工的管式炉的微型类似物-被开发为单纳米线水平的原位透射电子显微镜实验的平台，提供了对目标固态转变的原子反应路径、质量传输、相成核和生长动力学的前所未有的洞察。主要的模拟体系是均匀的Ge，Si1-xGex合金和轴向分段的Ge-AuGe纳米线的硫族元素(S，Se，Te)诱导的反应及其转变为层状Ge-硫族化合物。这种方法的推广被用于研究其他杂化系统，例如那些将GaN或GaN纳米线与GAS/Se层状晶体集成的系统。通过低于激子半径分辨率的阴极发光，结合电荷输运和电化学测量，确定界面和缺陷对杂化材料的带隙、激子结合以及载流子、电荷和能量转移的作用，从而将所获得的杂化材料的结构和形貌与其光电性能相关联。总体而言，这项研究工作有望促进对通过固态反应将不同材料集成到杂化纳米结构中的基本理解，以及对这些复杂系统新兴的光学和电子功能的理解。

Non-Technical AbstractWith the support of the Solid State and Materials Chemistry program, this project explores the creation of new classes of hybrid materials by solid-state reactions that partially transform semiconductor nanowires into layered crystals. Such transformations force the integration of structurally dissimilar nanomaterials, which is expected to give rise to novel and unique properties that are distinctly different from those of the constituents. To study this solid-state chemistry, miniature reactor cells are being developed that, when loaded with the component materials and introduced into an electron microscope, provide the possibility to initiate and directly observe complex materials transformation and integration processes down to the atomic level. This novel approach has the potential to become a transformative tool for developing synthesis and processing strategies for high-technology materials. In addition to the targeted technical advances, the project provides far-reaching educational and training opportunities for the involved graduate and undergraduate students. It includes dedicated outreach efforts to high-school students from rural areas and Native American populations that give student-teacher teams the opportunity to participate in hands-on activities related to the research. Under the guidance of the research team the students prepare new science learning materials, which they bring back to their school to share their experience with their peers and to help build excitement for careers in STEM disciplines.Technical AbstractThis project is dedicated to studying the creation of novel classes of hybrid nanomaterials by integrating crystalline semiconductor nanowires with layered metal chalcogenide crystals via solid-state chemical transformations. Partial conversion of nanowires into a layered structure forces the integration of crystallographically and topologically dissimilar materials, which presents a compatibility challenge that the system needs to overcome by finding the energetically preferred or kinetically most accessible hybrid configuration. Novel membrane reactor cells - miniature analogues of tube furnaces that are widely used for materials synthesis and processing in research and in industry - are developed as platforms for in-situ transmission electron microscopy experiments at the single nanowire level that provide unprecedented insight into the atomistic reaction pathways, mass transport, and phase nucleation and growth kinetics of the targeted solid-state transformations. The primary model systems are chalcogen (S, Se, Te) induced reactions of homogeneous Ge, Si1-xGex alloy, and axially segmented Ge-AuGe nanowires and their transformations into layered Ge-chalcogenides. Generalization of the approach is used to study other hybrid systems, such as those integrating GaAs or GaN nanowires with GaS/Se layered crystals. The structure and morphology of the obtained hybrid materials is correlated with their optoelectronic properties via cathodoluminescence at resolution below the exciton radius, complemented by charge transport and electrochemical measurements, to determine the role of interfaces and defects on bandgaps, exciton binding, as well as carrier, charge and energy transfer between the different components of the hybrids. Overall, the research effort is expected to advance the fundamental understanding of the integration of dissimilar materials into hybrid nanostructures via solid-state reactions, and of the emerging optical and electronic functionalities of these complex systems.