Crystal orientation and defect control in active and passive plasmonic systems

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Nontechnical description: Noble metals are important materials in electronic and optical systems because they can conduct electrical currents with exceptional ease. Material defects strongly dictate the electronic, optical, thermal, and structural properties of these metals. To date, the precise role of defects in device performance is not well understood, in part because there do not exist robust and scalable ways to define defects in metallic structures. This research project aims to investigate the role of individual defects in the electronic and optical properties of gold devices. This work leverages a new technique for metal growth that specifies single defects in a simple and scalable way. An experimental understanding of how to control and characterize defects in noble metals provides new insights into how noble metal devices can be made to be more energy efficient, optically responsive, and mechanically robust. Experimental quantification of defect properties also enables theoretical researchers to more accurately model devices. The education component of this project targets engineering education at the high school level, by working with teachers in the lab to provide them with a research perspective in nanotechnology education, and by engaging with high school students through seminars and discussion.Technical description: In this research project, the principle investigator explores methods to control the crystal orientation, grain boundary orientation, and grain boundary position in single- and bi-crystal gold metal microstructures. These material systems serve as model systems to explore the role of defects in active and passive plasmonic devices. A crystal growth technique called rapid melt growth specifies crystal orientation and defects in the metal. In this technique, a silica microcrucible encapsulates polycrystalline gold and a platinum seed, where the gold is first heated to its melting point and is then cooled. Liquid phase epitaxy initiates from the seed region, is directional, and specifies the crystal orientations of the metal microstructures based on the seed crystal. As such, this method serves as a versatile and scalable platform for defining the crystallographic properties of metals through lithographic patterning. For example, two seed structures at each end of a gold stripe produce bi-crystals with a range of tilt-boundary angles. The principle investigator aims to correlate parameters, such as tilt-boundary angle, with plasmon transport, using optical and electronic microscopy techniques. The education component of this project focuses on high school engineering education, by providing teachers with nanotechnology experience and students with summer laboratory programs and seminars.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.