Browsing by Author "Ji, Yongsung"

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    Porous SiOx materials for improvement in SiOx switching device performances
    (2018-06-12) Tour, James M.; Wang, Gunuk; Yang, Yang; Ji, Yongsung; Rice University; United States Patent and Trademark Office
    A porous memory device, such as a memory or a switch, may provide a top and bottom electrodes with a memory material layer (e.g. SiOx) positioned between the electrodes. The memory material layer may provide a nanoporous structure. In some embodiments, the nanoporous structure may be formed electrochemically, such as from anodic etching. Electroformation of a filament through the memory material layer may occur internally through the layer rather than at an edge at extremely low electro-forming voltages. The porous memory device may also provide multi-bit storage, high on-off ratios, long high-temperature lifetime, excellent cycling endurance, fast switching, and lower power consumption.
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    Rivet Graphene
    (American Chemical Society, 2016) Li, Xinlu; Sha, Junwei; Lee, Seoung-Ki; Li, Yilun; Ji, Yongsung; Zhao, Yujie; Tour, James M.; NanoCarbon Center
    Large-area graphene has emerged as a promising material for use in flexible and transparent electronics due to its flexibility and optical and electronic properties. The anchoring of transition metal nanoparticles on large-area single-layer graphene is still a challenge. Here, we report an in situ preparation of carbon nano-onion-encapsulated Fe nanoparticles on rebar graphene, which we term rivet graphene. The hybrid film, which allows for polymer-free transfer and is strong enough to float on water with no added supports, exhibits high optical transparency, excellent electric conductivity, and good hole/electron mobility under certain tensile/compressive strains. The results of contact resistance and transfer length indicate that the current in the rivet graphene transistor does not just flow at the contact edge. Carbon nano-onions encapsulating Fe nanoparticles on the surface enhance the injection of charge between rivet graphene and the metal electrode. The anchoring of Fe nanoparticles encapsulated by carbon nano-onions on rebar graphene will provide additional avenues for applications of nanocarbon-based films in transparent and flexible electronics.
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    Three-Dimensional Networked Nanoporous Ta2O5–x Memory System for Ultrahigh Density Storage
    (American Chemical Society, 2015) Wang, Gunuk; Lee, Jae-Hwang; Yang, Yang; Ruan, Gedeng; Kim, Nam Dong; Ji, Yongsung; Tour, James M.; Richard E. Smalley Institute of Nanoscale Science and Technology
    Oxide-based resistive memory systems have high near-term promise for use in nonvolatile memory. Here we introduce a memory system employing a three-dimensional (3D) networked nanoporous (NP) Ta2O5-x structure and graphene for ultrahigh density storage. The devices exhibit a self-embedded highly nonlinear I-V switching behavior with an extremely low leakage current (on the order of pA) and good endurance. Calculations indicated that this memory architecture could be scaled up to a ∼162 Gbit crossbar array without the need for selectors or diodes normally used in crossbar arrays. In addition, we demonstrate that the voltage point for a minimum current is systematically controlled by the applied set voltage, thereby offering a broad range of switching characteristics. The potential switching mechanism is suggested based upon the transformation from Schottky to Ohmic-like contacts, and vice versa, depending on the movement of oxygen vacancies at the interfaces induced by the voltage polarity, and the formation of oxygen ions in the pores by the electric field.