SGER: Spin Injection from Ferromagnetic Nanodot Electrode to Organic Semiconducting Conjugated Polymers

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Objective: This SGER project seeks to understand the mechanism of recently observed spin injection across the Co/polymer nanoscale heterojunction. Specifically, we will use Xenon buffer layer assisted MBE (molecular beam epitaxy) growth to prepare Co/ nanodots with precisely tunable size and density on conjugated polymer thin films. Then, the spin-dependent transport across Co/polymer nano-heterojunction will be studied as a function of temperature by using four-tip STM (scanning tunneling microscope). In addition, polymer light-emitting diodes (LEDs) will be used as a tool to study how spin injection affects the singlet and triplet exciton formation and singlettriplet intersystem crossing in conjugated polymers based on steady and transient electroluminescence and photoluminescence. The goal is to increase the critical understanding of spin injection mechanism and to develop a new methodology of controlling exciton formation by using ferromagnetic nanoscale spin injector.Intellectual merit: The proposed studies of spin transport across the Co/polymer nano-heterojunction expects to elucidate the spin transport processes at the interface between ferromagnetic nanosize electrode and organic semiconductor polymer thin film. The understanding of the spin injection mechanism is critically important for the fabrication of efficient spin injectors in organic semiconductor devices. Especially, efficient spin injection will create a new pathway to magnetically control the singlet and triplet exciton formation and relevant optoelectronic properties in conjugated polymers. Therefore, the project will impact the light-emitting, lasing, and photovoltaic properties in easy-processing and property-tunable polymer semiconductor devices. Broad impact: The research consists of cross-field investigations and thus will provide multi-disciplinary training in optics, electronics, and magnetism to the involved graduate and undergraduate students. To further enhance its educational impact, new course work of spin transport will be developed for Polymer Physics (MSE 543) and Optoelectronic Processes in Polymeric Materials and Devices (MSE 674) at the University of Tennessee (UT). The project will also continue to demonstrate the concepts and principles of polymer optoelectronic devices to high school students through the Materials Camp co-sponsored by UT Department of Materials Science and Engineering.