Nonequilibrium Ionic Response of Biased Mechanically Controllable Break Junction (MCBJ) Electrodes

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• 作者：Kentaro Doi ; Makusu Tsutsui ; Takahito Ohshiro ; Chih-Chun Chien ; Michael Zwolak ; Masateru Taniguchi ; Tomoji Kawai ; Satoyuki Kawano ; Massimiliano Di Ventra
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：February 20, 2014
• 年：2014
• 卷：118
• 期：7
• 页码：3758-3765
• 全文大小：576K
• ISSN：1932-7455

文摘

Novel experimental techniques allow for the manipulation and interrogation of biomolecules between metallic probes immersed in micro/nanofluidic channels. The behavior of ions in response to applied fields is a major issue in the use of these techniques in sensing applications. Here, we experimentally and theoretically elucidate the behavior of background currents in these systems. These large currents have a slowly decaying transient response, as well as noise that increases with ionic concentration. Using mechanically controllable break junctions (MCBJ), we study the ionic response in nanogaps with widths ranging from a few nanometers to millimeters. Moreover, we obtain an expression for the ionic current by solving time-dependent Nernst鈥揚lanck and Poisson equations. This expression shows that after turning on an applied voltage, ions rapidly respond to the strong fields near the electrode surface, screening the field in the process. Ions subsequently translocate in the weak electric field and slowly relax within the diffusion layer. Our theoretical results help to explain the short- and long-time behavior of the ionic response found in experiments, as well as the various length scales involved.