In addition to its annual lectures, ChBE hosts a weekly seminar throughout the year with invited lecturers who are prominent in their fields. Unless otherwise noted, all seminars are held on Wednesdays in the Molecular Science and Engineering Building ("M" Building) in G011 (Cherry Logan Emerson Lecture Theater) at 4 p.m. Refreshments are served at 3:30 p.m. in the Emerson-Lewis Reception Salon.

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"Developing New Inorganic Nanostructures for Ferroelectrics and Nanophotonics"

Mark J. Polking, Harvard University

Abstract:
The synthesis of inorganic nanostructures provides a versatile avenue to the engineering of functionalities such as ferroelectricity and nanoscale optical phenomena. In the first portion of my talk, I will discuss the synthesis and properties of nanoscale ferroelectrics, which have been widely explored for nonvolatile memories, energy storage and conversion devices, and new types of biosensors. The synthesis of size-controlled nanocrystals of the simplest ferroelectric, germanium telluride (GeTe), is first demonstrated using colloidal chemistry. Local ferroelectric order is probed in individual nanocrystals of both GeTe and BaTiO3 down to atomic-scale dimensions using aberration-corrected transmission electron microscopy, off-axis electron holography, and direct electrical measurements. These experiments demonstrate the persistence of coherent ferroelectric order and phase transitions at sub-5 nm dimensions and shed light on the origins of size-dependent changes in ferroelectricity. In the second portion of my talk, I will discuss the development of thin-film heterostructures for inorganic passivation of defect-based single-photon emitters, which have emerged as leading candidates for quantum optics, biological imaging probes, and magnetic and electric field sensors. Inorganic heterostructures composed of cubic BN on diamond and AlN on 4H-SiC are developed to stabilize emission from nitrogen vacancy centers in diamond and carbon antisite-vacancy pairs in 4H-SiC, respectively. Substantial improvements in defect photostability and brightness are observed. In addition, by harnessing polarization effects in polar 4H-SiC/AlN heterostructures, selective stabilization of a desired defect charge state is demonstrated. These results point the way towards bright, highly photostable, and environmentally robust single-photon emitters with permanently fixed charge states.