The electrical behavior of nitro oligo(phenylene ethynylene)’s in pure and mixed monolayers

Abstract

In order to realize molecular electronic devices, molecules with electrically interesting behavior must be identified. One molecule that has potential for use in devices is an oligo(phenylene ethynylene) (OPE) molecule with nitro sidegroup(s). These "nitro" molecules have been reported to show electrical switching with memory behavior, as well as negative differential resistance (NDR). However, different research groups testing the nitro molecules in different test beds have observed different electrical behaviors. In this work, we assembled two different nitro monolayers: one completely composed of nitro molecules and the second a mixed matrix where nitro molecules were separated by dodecanethiol molecules. We used scanning tunneling microscopy to image each of the monolayers and observed that the nitro molecules were effectively inserted into the ordered dodecanethiol monolayer. We tested the electrical behavior of the pure monolayer, as well as the mixed monolayer, in our nanowell test device. The nanowell devices were fabricated on micron-size gold lines patterned on oxide-coated silicon wafers. The gold lines were covered with a silicon dioxide layer, through which a nanometer size well was milled. This nanowell device was filled with a self-assembling monolayer of organic molecules, and capped with titanium and gold. The nanowell electrical results showed switching with memory for the pure nitro monolayer, but not for the mixed monolayer. This switching behavior consisted of a molecule starting in a high conductivity state and switching to a low conductivity state upon application of a threshold voltage. The high conductivity state could only be returned by application of an opposite threshold voltage.

Interaction-induced negative differential resistance in asymmetric molecular junctions

“…The situation is, however, complicated by inconsistencies in the experimental findings, and while some experiments observe NDR in individual OPE-type molecules, 16 others seem to indicate that NDR is only observed when large assemblies of such molecules are measured. 17 In the above works the tunnel coupling between the molecule and electrodes was rather strong. In gated (threeterminal) single-molecule junctions, [3][4][5] the tunnel coupling is often much smaller, on the same scale as the thermal energy, k B T .…”

Effects of Molecular Environments on the Electrical Switching with Memory of Nitro-Containing OPEs

“…The specifics of this behavior have been reported in more detail elsewhere. 5 Out of the 208 devices tested, 86% were electrical opens or shorts. The rest of the devices showed one of four different behaviors.…”

“…The parameter values from fitting to Simmons equation for these curves also matched the values found for the homogeneous monolayers of dodecanethiol. 5 Thus, these devices may have had few to nitro-OPE molecules participating in the conduction. The third observed behavior was an early electrical device breakdown that occurred before any reversible results could be observed ͑35% of working devices͒.…”

“…2,4 In our previous work, we used our nanowell test device to address a possible correlation between contacting a large area of nitro molecules and observing memory behavior. 5 However, that previous work only considered the type of molecules and not the ordering of the nitro-OPE monolayer's environment. A recent report indicates that this environment may correlate strongly with the rate of electrical switching for the nitro-OPEs.…”

A Programmable Majority Logic Array Using Molecular Scale Electronics

“…With this, the major contribution of this . Models for the molecular switches considered here are primarily based on devices fabricated by researchers at the University of Virginia [17]- [19].…”