Browsing by Author "Kravchenko, Ivan I."

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Probing Local Ionic Dynamics in Functional Oxides at the Nanoscale
(2013-08-01)
Strelcov, Evgheni
;
Kim, Yunseok
;
Jesse, Stephen
;
Cao, Ye
;
Ivanov, Ilia N.
A scanning probe microscopy technique for probing local ionic dynamics in electrochemically active materials based on the first-order reversal curve current-voltage (FORC-IV) method is presented. FORC-IV imaging mode is applied to a Ca-substituted bismuth ferrite (Ca-BFO) system to separate the electronic and ionic phenomena in this material and visualize the spatial variability of these behaviors. The variable-temperature measurements further demonstrate the interplay between the thermally and electric-field-driven resistance changes in Ca-BFO. The FORC-IV is shown to be a simple, powerful, and flexible method for studying electrochemical activity of materials at the nanoscale and, in conjunction with the electrochemical strain microscopy, it can be used for differentiating ferroelectric and ionic behaviors.
Space- and Time-Resolved Mapping of Ionic Dynamic and Electroresistive Phenomena in Lateral Devices
(2013-08-01)
Strelcov, Evgheni
;
Jesse, Stephen
;
Huang, Yen-Lin
;
Teng, Yung-Chun
;
Kravchenko, Ivan I.
A scanning probe microscopy-based technique for probing local ionic and electronic transport and their dynamic behavior on the 10 ms to 10 s scale is presented. The time-resolved Kelvin probe force microscopy (tr-KPFM) allows mapping of surface potential in both space and time domains, visualizing electronic and ionic charge dynamics and separating underlying processes based on their time responses. Here, tr-KPFM is employed to explore the interplay of the adsorbed surface ions and bulk oxygen vacancies and their role in the resistive switching in a Ca-substituted bismuth ferrite thin film.
UV ozone treatment for improving contact resistance on graphene
(2012-11-01)
Chen, Chung Wei
;
Ren, Fan
;
Chi, Gou-Chung
;
Hung, Sheng-Chun
;
Huang, Y. P.
Optimized UV ozone cleaning of graphene layers on SiO2/Si substrates is shown to improve contact resistance of e-beam evaporated Ti/Au contacts by three orders of magnitude (3 x 10(-6) Omega-cm(2)) compared to untreated surfaces (4 x 10(-3) Omega-cm(2)). Subsequent annealing at 300 degrees C lowers the minimum value achieved to 7 x 10(-7) Omega-cm(2). Ozone exposure beyond an optimum time (6 min in these experiments) led to a sharp increase in sheet resistance of the graphene, producing degraded contact resistance. The UV ozone treatment is a simple and effective method for producing high quality contacts to graphene. (C) 2012 American Vacuum Society. [http://dx.doi.org/10.1116/1.4754566]