Nanostructured flash memory devices based on radical polymers and carbon-based nanomaterials
Professor, Department of Physics and Astronomy and Department of Chemistry
Western University, London, Ontario
Monday, January 21, 2019
C2-361 (Reading Room)
In this talk, we will review the use of thin films of organic polyradicals – organic polymers with one unpaired electron per monomer  – for memory devices and other applications. Although memory devices based on radical polymers have been often proposed, their stability was frequently limited to a few writing cycles, despite the excellent quality of the active layer. To date, the most common nonvolatile memory components used data storage technology are devices that are writable once and readable multiple times (WORM). Memory components that are writable, readable and erasable multiple times (FLASH) are more attractive, but their costs are still high.  Here, design criteria for flash memory devices are given using a combination of Kelvin-probe force microscopy (KPFM), electrical transport and optical measurements.  As a case study, ultrathin devices in which the active layer is formed by a 10-nm homogeneous film of poly-[1,5-diisopropyl-3-(cis-5-norbornene-exo-2,3-dicarboxiimide) 6-oxoverdazyl] (P6OV) are presented.  We will show that high performance of these devices must be associated to the presence three tunable charge states in each monomer: positive, neutral, and negative. In the last part of our talk, as a complement of polyradical memory devices, we will present a very similar class of organic flash memory devices, based on “curved” carbon quantum dots containing fivefold and sevenfold aromatic carbon rings, in addition to sixfold rings typically featured by commonly synthesized sp2 carbon-based nanomaterials, including graphene, carbon nanotubes, and flat and luminescent graphene quantum dots. Paramagnetic centers associated to fivefold and sevenfold rings are anticipated to be essential to memory effects and memory device operation from these systems.  We will demonstrate that careful engineering of the anode and cathode work functions, specifically aligning them with the negative and positive energy levels of polyradicals and carbon quantum dots, is vital to maximize the on/off current ratio and ensure flash operation in these devices based on organic neutral radicals in a nanostructured environment.
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