A three terminal molecular memory device was monitored with in situ Raman spectroscopy during bias-induced switching between two metastable states having different conductivity. The device structure is similar to that of a polythiophene field effect transistor, but ethylviologen perchlorate was added to provide a redox counter-reaction to accompany polythiophene redox reactions. The conductivity of the polythiophene layer was reversibly switched between high and low conductance states with a "write/erase" (W/E) bias, while a separate readout circuit monitored the polymer conductance. Raman spectroscopy revealed reversible polythiophene oxidation to its polaron form accompanied by a one-electron viologen reduction. "Write", "read", and "erase" operations were repeatable, with only minor degradation of response after 200 W/E cycles. The devices exhibited switching immediately after fabrication and did not require an "electroforming" step required in many types of memory devices. Spatially resolved Raman spectroscopy revealed polaron formation throughout the polymer layer, even away from the electrodes in the channel and drain regions, indicating that thiophene oxidation "propagates" by growth of the conducting polaron form away from the source electrode. The results definitively demonstrate concurrent redox reactions of both polythiophene and viologen in solid-state devices and correlate such reactions with device conductivity. The mechanism deduced from spectroscopic and electronic monitoring should guide significant improvements in memory performance.
The performance of redox-gated organic nonvolatile memory (NVM) based on conducting polymers was investigated by altering the polymer structure, composition, and local environment of three-terminal devices with a field-effect transistor (FET) geometry. The memory function was dependent on the presence of a redox active polymer with high conducting and low conducting states, the presence of a redox counter-reaction, and the ability to transport ions between the polymer and electrolyte phases. Simultaneous monitoring of both the "write" current and "readout" current revealed the switching dynamics of the devices and their dependence on the local atmosphere. Much faster and more durable response was observed in acetonitrile vapor than in a vacuum, indicating the importance of polar molecules for both ion motion and promotion of electrochemical reactions. The major factor determining "write" and "erase" speeds of redox-gated polymer memory devices was determined to be the rate of ion transport through the electrolyte layer to provide charge compensation for the conducting polarons in the active polymer layer. The results both confirm the mechanism of redox-gated memory action and identify the requirements of the conducting polymer, redox counter reaction, and electrolyte for practical applications as alternative solid-state nonvolatile memory devices.
Steam-assisted
gravity drainage (SAGD) process water contains high
concentrations of dissolved organic and inorganic matter. A wide range
of analytical techniques including electrospray ionization mass spectrometry,
gas chromatography–mass spectrometry, Fourier transform infrared
spectrometry, and fluorescence spectrophotometry have been utilized
for the identification and measurement of dissolved organic matter
(DOM) in oil sands process-affected water. The composition of DOM
in the SAGD water is relatively complex, and thus one plausible method
for its analysis is the fractionation of DOM into hydrophilic and
hydrophobic portions using suitable resin columns and the characterization
of these fractions using standard analytical methods. Comparing the
fractionation and characterization of the SAGD produced water from
different plant sites can provide considerable insight into better
management, recycle, and reuse of this process water. Also, a detailed
knowledge of the chemical composition of the SAGD produced water provides
guidelines for identifying the constituents that are responsible for
scaling and fouling at various stages of the SAGD process. This study
aims at developing a systematic approach for the fractionation and
characterization methods of SAGD process water samples.
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