This project aims to discover new ways of controlling how electrons move across arrays of quantum dots by using light as a switch. Quantum dots are nanoparticles of semiconductors with optical and electrical properties that can be tuned through changing the size of the particles. This research is focused on studying how flow of electrons between neighboring quantum dots can be turned ?on? and ?off? by switching the shape of molecules connecting the quantum dots using light with different colors. Such phenomena can be exploited to make materials for optically switchable components for optical computing and memory devices that are faster and more efficient compared to traditional electronics. Broadly, this research has a potential to advance the fundamental understanding of nanoscale charge transfer which is crucial for understanding optical and electrical processes in macromolecular, nanoscale, and biological systems. The research activities are integrated with educational efforts aimed at enhancing the recruitment, training, and retention of students in the science and engineering fields, especially among underrepresented groups at the University of Virginia and Old Dominion University. With an emphasis on middle and high school students, hands-on activities on 'Switching Molecules with Light' are provided. Undergraduate researchers are recruited through the Virginia-North Carolina Alliance for Minority Participation and other programs.
The proposed research aims to test a hypothesis that the rates of charge transfer and exciton dissociation in colloidal quantum dot assemblies can be modulated by changing conformation of the 'bridge' photochromic molecules that inter-connect the quantum dots. To this end, a combination of nanoparticle synthesis, organic synthesis, surface chemistry characterization, optical spectroscopy, electrical measurements and X-ray scattering is employed. In the context of Marcus theory, the impact of potential barrier height on nanoscale charge transfer is systematically studied while keeping exactly the same charge donor-acceptor pair and the surface chemistry at contacts. This research has a potential to result in the discovery of a novel class of quantum dot assemblies with optically switchable light emission and non-volatile ?read? and ?write? operations. The dense, fast and reliable on-chip compatible non-volatile optical memory materials potentially obtained through this research can lead to new research directions and capabilities for optical computing, data storage, processing and transmission. The research team from the two universities will (1) determine the relationship between the potential barrier height and the rates of charge transfer and exciton dissociation in quantum dot assemblies in the context of Marcus theory, (2) investigate the relationship between bridge molecule structure and functional groups on charge transfer and exciton dissociation in quantum dot assemblies, and (3) demonstrate quantum dot assemblies with optically switchable photoluminescence intensity.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
