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

在固态和材料化学项目的支持下，本项目探索通过固态反应将半导体纳米线部分转化为层状晶体来创造新型混合材料。这种转变迫使结构不同的纳米材料整合在一起，这有望产生与成分截然不同的新颖和独特的性能。为了研究这种固态化学，正在开发微型反应堆电池，当装载组件材料并引入电子显微镜时，提供了启动和直接观察复杂材料转化和整合过程的可能性，直至原子水平。这种新颖的方法有可能成为一种革命性的工具，用于开发高科技材料的合成和加工策略。除了有针对性的技术进步外，该项目还为参与的研究生和本科生提供了深远的教育和培训机会。它包括专门向来自农村地区和美洲原住民的高中生伸出援手，让学生-教师团队有机会参与与研究相关的实践活动。在研究团队的指导下，学生们准备了新的科学学习材料，并将这些材料带回学校，与同学们分享他们的经验，并为STEM学科的职业生涯建立激情。技术摘要：本项目致力于通过固态化学转化，将晶体半导体纳米线与层状金属硫族化物晶体相结合，研究新型杂化纳米材料的制备。纳米线部分转换成层状结构迫使晶体学和拓扑结构不同的材料集成，这提出了一个兼容性挑战，系统需要通过寻找能量上优先或动力学上最容易接近的混合结构来克服。新型膜反应器细胞-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平台，提供前所未有的洞察原子反应途径，质量传递，相成核和目标固态转化的生长动力学。主要的模型体系是由（S, Se, Te）诱导的均相Ge， Si1-xGex合金和轴向分割的Ge- auge纳米线的反应及其向层状Ge-硫族化物的转变。该方法的推广用于研究其他混合系统，例如将GaAs或GaN纳米线与GaS/Se层状晶体集成的混合系统。通过在激子半径以下的分辨率下进行阴极发光，并辅以电荷输运和电化学测量，确定界面和缺陷对带隙、激子结合以及载流子、电荷和能量在杂化材料不同组分之间的传递的作用，得到了杂化材料的结构和形貌与其光电性能的相关性。总的来说，这项研究工作有望推进对通过固态反应将不同材料集成到混合纳米结构中的基本理解，以及对这些复杂系统的新兴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.