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

University Of Nebraska-Lincoln, Lincoln NE

Investigators

Abstract

Non-Technical Abstract With 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 Abstract This 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.