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项目的支持下，该项目探索了通过固态反应将半导体纳米线部分转化为层状晶体的新型混合材料的创造。这种转变迫使结构不同的纳米材料的整合，这有望产生与组分明显不同的新颖和独特的性质。为了研究这种固态化学，正在开发微型反应器单元，当装载组分材料并引入电子显微镜时，可以启动并直接观察复杂的材料转化和整合过程，直至原子水平。这种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，该项目还为参与的研究生和本科生提供了意义深远的教育和培训机会。它包括专门针对农村地区高中生和美洲原住民的外联工作，使学生-教师团队有机会参加与研究有关的实践活动。在研究团队的指导下，学生们准备了新的科学学习材料，他们带回学校与同龄人分享他们的经验，并帮助建立对STEM学科职业生涯的兴奋。技术摘要本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族化物晶体相结合来创造新型混合纳米材料。纳米线到层状结构的部分转换迫使晶体学和拓扑学上不同的材料的集成，这提出了系统需要通过找到能量上优选的或动力学上最容易获得的混合配置来克服的兼容性挑战。新型膜反应器单元-广泛用于研究和工业中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，该实验提供了对原子反应途径，质量传输以及相成核和目标固态转化的生长动力学的前所未有的洞察。主要的模型系统是硫族元素（S，Se，Te）诱导的反应的均匀Ge，Si 1-xGex合金，和轴向分段Ge-AuGe纳米线和它们的转换成层状Ge硫族化物。推广的方法是用来研究其他混合系统，如集成GaAs或GaN纳米线与GaAs/Se层状晶体。所获得的混合材料的结构和形态与它们的光电性能相关，通过阴极发光在激子半径以下的分辨率，补充电荷传输和电化学测量，以确定带隙，激子结合，以及载流子，电荷和能量转移的界面和缺陷的作用之间的混合物的不同组件。总体而言，研究工作预计将推进通过固态反应将不同材料整合到混合纳米结构中的基本理解，以及这些复杂系统的新兴光学和电子功能。

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.