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Daejeon, South Korea

Hwang S.K.,KAIST | Lee J.M.,KAIST | Kim S.,KAIST | Park J.S.,KAIST | And 5 more authors.
Nano Letters | Year: 2012

B- and N-doped carbon nanotubes (CNTs) with controlled workfunctions were successfully employed as charge trap materials for solution processable, mechanically flexible, multilevel switching resistive memory. B- and N-doping systematically controlled the charge trap level and dispersibility of CNTs in polystyrene matrix. Consequently, doped CNT device demonstrated greatly enhanced nonvolatile memory performance (ON-OFF ratio >10 2, endurance cycle >10 2, retention time >10 5) compared to undoped CNT device. More significantly, the device employing both B- and N-doped CNTs with different charge trap levels exhibited multilevel resistive switching with a discrete and stable intermediate state. Charge trapping materials with different energy levels offer a novel design scheme for solution processable multilevel memory. © 2012 American Chemical Society. Source

Romankov S.,Chonbuk National University | Park Y.C.,National NanoFab Center | Shchetinin I.V.,National University of Science and Technology "MISIS" | Yoon J.M.,Chonbuk National University
Acta Materialia | Year: 2013

Al, Zr, Ni, Co, Fe and Cr were introduced into a Cu plate using ball collisions to fabricate a multicomponent composite layer. The application of severe plastic deformation induced by repeated ball collisions with the as-fabricated composite layer led to intermixing of the components and the formation of a surface alloyed layer on the Cu plate. The microstructural development of the surface alloyed layer was a function of the treatment time. After 1 h of treatment, an alternating laminated amorphous/crystalline composite structure with a mean lamellar thickness of ∼10 nm was formed as a result of the combined effects of the deformation-induced plastic flow, interdiffusion and intermixing of the elements. The crystalline lamellae were related to the multicomponent non-equilibrium solid solution based on the Cu crystal structure. Increase in treatment time to 4 h led to structural changes. The crystalline lamellae underwent refinement that was attributed to dislocation activity and were subdivided into interlamellar blocks. The amorphous lamellae tended to disappear. A body-centered cubic (bcc) Fe solid solution was formed in the layer. Nucleation and growth of bcc Fe precipices in amorphous and crystalline phases were related to increase in Fe content in the layer, which increased with treatment time. The hardness of the as-fabricated layer was almost ten times that of the initial Cu plate. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Source

Kim J.E.,Korea Advanced Institute of Science and Technology | Han T.H.,Korea Advanced Institute of Science and Technology | Lee S.H.,Korea Advanced Institute of Science and Technology | Kim J.Y.,Korea Advanced Institute of Science and Technology | And 3 more authors.
Angewandte Chemie - International Edition | Year: 2011

(Figure Presented) Crystal clear: The liquid crystallinity of graphene oxide platelets in aqueous dispersion is demonstrated. Graphene oxide sheets are arranged around liquid-crystal disclinations (see picture). The orientation of the liquid crystals can be manipulated by a magnetic field or mechanical deformation. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA. Source

Romankov S.,Chonbuk National University | Park Y.C.,National NanoFab Center
Journal of Alloys and Compounds | Year: 2015

We observed the moment of material escape from a surface of CoFeNi/Cu/Zr(Al)O2 composite into the amorphous carbon layer when we studied the phase transformation of the structure using in situ transmission electron microscopy (TEM) technique at 800 °C. To protect the top surface of the TEM specimen against focused-ion beam process damage, the specimen had been coated with an amorphous carbon layer, a thin Pt film and a W protective layer. During our high-temperature experiments at 800 °C, we detected that the CoFeNi nanoparticles moved from the surface of the TEM specimen into the amorphous carbon layer. A porous amorphous carbon layer had a large impact on the visualization of this phenomenon. Liquid-like behavior of the CoFeNi phase, which possessed some crystalline order, was detected before the material escaped from the surface. After heating, the carbon layer became tightly packed with small particles and single atoms. The majority of the particles in the carbon layer were in the size range of 1-4 nm. The particles were assigned to the CoFeNi, FePt, and W phases. The CoFeNi particles escaped directly from the specimen surface, while the FePt and W particles were formed in the carbon layer during heating as a result of atomic reactions. The single atoms observed in the carbon layer were attributed to the heavy elements Pt and W. © 2015 Elsevier B.V. Source

Freedman K.J.,Drexel University | Ahn C.W.,National NanoFab Center | Kim M.J.,Drexel University
ACS Nano | Year: 2013

Graphene is a unique material with a thickness as low as a single atom, high in-plane conductivity and a robust lattice that is self-supporting over large length scales. Schematically, graphene is an ideal solid-state material for tuning the properties of a nanopore because self-supported sheets, ranging from single to multiple atomic layers, can create pores with near-arbitrary dimensions which can provide exquisite control of the electric field drop within the pore. In this study, we characterize the drilling kinetics of nanopores using a thermionic electron source and various electron beam fluxes to minimize secondary hole formation. Once established, we investigated the use of multilayer graphene to create highly tailored nanostructures including nanopores with graphite polyhedral crystals formed around the nanopore edge. Finally, we report on the translocation of double stranded and single stranded DNA through such graphene pores and show that the single stranded DNA translocates much slower allowing detection of extremely short fragments (25 nucleotides in length). Our findings suggest that the kinetic and controllable properties of graphene nanopores under sculpting conditions can be used to further enhance the detection of DNA analytes. © 2013 American Chemical Society. Source

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