Redox-Driven Conductance Switching via Filament Formation and Dissolution in Carbon/Molecule/TiO₂/Ag Molecular Electronic Junctions

Abstract

Carbon/molecule/TiO2/Au molecular electronic junctions show robust conductance switching, in which a metastable high conductance state may be induced by a voltage pulse which results in redox reactions in the molecular and TiO2 layers. When Ag is substituted for Au as the "top contact", dramatically different current/voltage curves and switching behavior result. When the carbon substrate is biased negative, an apparent breakdown occurs, leading to a high conductance state which is stable for at least several hours. Upon scanning to positive bias, the conductance returns to a low state, and the cycle may be repeated hundreds of times. Similar effects are observed when Cu is substituted for Au and for three different molecular layers as well as "control" junctions of the type carbon/TiO2/Ag/Au. The polarity of the "switching" is reversed when the Ag layer is between the carbon and molecular layers, and the conductance change is suppressed at low temperature. Pulse experiments show very erratic transitions between high and low conductivity states, particularly near the switching threshold. The results are consistent with a switching mechanism based on Ag or Cu oxidation, transport of their ions through the TiO2, and reduction at the carbon to form a metal filament.

Reversible switching characteristics of polyfluorene-derivative single layer film for nonvolatile memory devices

“…10,14 For example, by investigating the currentvoltage relationships of I-V curves on the log-log scale, space charge limited current 15-17 ͑SCLC͒ or filamentary conductions [18][19][20] has been suggested as a potential mechanism for charge transport in organic devices. Figure 3͑a͒ shows a log-log plot of the I-V curve in the positive bias region for a WPF-oxy-F memory device.…”

Electron Transport and Redox Reactions in Molecular Electronic Junctions

“…Redox exchange is activated and temperature dependent, incoherent, and can transport electrons (or holes) over much greater distances than coherent tunneling. Reported cases of redox reactions occurring in molecular junctions a few tens of nm thick include metal filament formation, [9,10] conformational changes in rotaxanes [8,11] , and dynamic doping of conducting polymers. [12] We consider here several cases between the limits of a tunnel junction and a~100 nm "thick" junction in which coherent tunneling cannot occur.…”

Enhancement of electrical bistability through semiconducting nanoparticles for organic memory applications

“…This leads to two I -V characteristics with an associated memory phenomenon. Conformation change and/or electroreduction of organic molecules plays a key role in changing the conductivity of the devices (Donhauser et al 2001;Solak et al 2002;Bandhopadhyay & Pal 2003;Ssenyange et al 2006). In devices with soft metals as electrodes, filament formation may occur to yield conductance switching.…”