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Choi J.,Pukyong National University | Kim B.-J.,Mobrik Co. | Seo G.,KAIST | Kim H.-T.,Metal Insulator Transition Creative Research Center | And 2 more authors.
Current Applied Physics | Year: 2016

We investigated the magnetic field-dependent Hall effect and the thermopower in VO2 thin films at various temperatures by using physical property measurement systems. From the ordinary Hall effect measured at 300-370 K, it was found that the Hall voltage decreased with increasing magnetic field, attributed to the weakening of strong electron correlation, and dominant charge carriers were changed implying the existence of mixed phases near the critical temperature of VO2. A gradual thermopower increase and its sign inversion with increasing temperature gradient were observed at 320-350 K, which seems to stem from percolation processes during the phase transition in VO2. © 2015 Elsevier B.V. All rights reserved.


Rathi S.,Sungkyunkwan Advanced Institute of Nanotechnology | Lee I.-Y.,Sungkyunkwan Advanced Institute of Nanotechnology | Park J.-H.,Sungkyunkwan Advanced Institute of Nanotechnology | Kim B.-J.,Metal Insulator Transition Creative Research Center | And 3 more authors.
ACS Applied Materials and Interfaces | Year: 2014

(Figure Presented) In order to investigate the metal-insulator transition characteristics of VO2 devices annealed in reducing atmosphere after device fabrication at various temperature, electrical, chemical, and thermal characteristics are measured and analyzed. It is found that the sheet resistance and the insulator-metal transition point, induced by both voltage and thermal, decrease when the devices are annealed from 200 to 500 °C. The V 2p3/2 peak variation in X-ray photoelectron spectroscopy (XPS) characterization verifies the reduction of thin-films. A decrease of the transition temperature from voltage hysteresis measurements further endorse the reducing effects of the annealing on VO2 thin-film. © 2014 American Chemical Society.


Maaroof A.I.,Seoul National University | Cho D.-G.,Seoul National University | Kim B.-J.,Metal Insulator Transition Creative Research Center | Kim H.-T.,Metal Insulator Transition Creative Research Center | And 2 more authors.
Journal of Physical Chemistry C | Year: 2013

Hybrid nanostructure-based VO2 semishells (SSs) and Au nanohemispheres (NHs) were developed as a tunable plasmonic nanostructrue. The hybrid structures exhibited an enhanced optical absorbance due to a strong plasmonic coupling between VO2 SSs and Au NHs compared to that of the VO2 SSs alone. Furthermore, its absorption peak can be controlled by the phase transition of VO2 SS under different temperature conditions. The simulation results showed the enhanced plasmonic coupling near the edges of Au NHs, indicating the hemispherical shape of our Au nanostructures can be advantageous in achieving the enhanced plasmonic coupling in our hybrid structures. These "smart" functions of the hybrid nanostructures should provide great opportunities in the development of various optical devices, such as photothermal nanoregulators and ultrafast optical switches. © 2013 American Chemical Society.


Liu M.,University of California at San Diego | Liu M.,State University of New York at Stony Brook | Sternbach A.J.,University of California at San Diego | Wagner M.,University of California at San Diego | And 24 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2015

We have systematically studied a variety of vanadium dioxide (VO2) crystalline forms, including bulk single crystals and oriented thin films, using infrared (IR) near-field spectroscopic imaging techniques. By measuring the IR spectroscopic responses of electrons and phonons in VO2 with sub-grain-size spatial resolution (∼20nm), we show that epitaxial strain in VO2 thin films not only triggers spontaneous local phase separations, but also leads to intermediate electronic and lattice states that are intrinsically different from those found in bulk. Generalized rules of strain- and symmetry-dependent mesoscopic phase inhomogeneity are also discussed. These results set the stage for a comprehensive understanding of complex energy landscapes that may not be readily determined by macroscopic approaches. © 2015 American Physical Society.


Goldflam M.D.,University of California at San Diego | Liu M.K.,University of California at San Diego | Chapler B.C.,University of California at San Diego | Stinson H.T.,University of California at San Diego | And 13 more authors.
Applied Physics Letters | Year: 2014

We demonstrate an electrolyte-based voltage tunable vanadium dioxide (VO2) memory metasurface. Large spatial scale, low voltage, non-volatile switching of terahertz (THz) metasurface resonances is achieved through voltage application using an ionic gel to drive the insulator-to-metal transition in an underlying VO2 layer. Positive and negative voltage application can selectively tune the metasurface resonance into the "off" or "on" state by pushing the VO2 into a more conductive or insulating regime respectively. Compared to graphene based control devices, the relatively long saturation time of resonance modification in VO2 based devices suggests that this voltage-induced switching originates primarily from electrochemical effects related to oxygen migration across the electrolyte-VO2 interface. © 2014 AIP Publishing LLC.

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