Portland State University. Department of Physics
Date of Award
Master of Science (M.S.) in Physics
1 online resource, (p108.)
Bilayer lipid membranes, Titanium dioxide, Solar cells, Impedance spectroscopy
It has been proposed in the literature that a novel class of biosensors can be based on a bimolecular layer of lipids supported on one side by a metallic surface. In order to estimate the potential of this system for the design of membrane sensors, we have studied properties of a two-electrode system consisting of a tefion insulated metallic wire and a Ag/ AgCl electrode, both immersed in KCl solution. The lipid bimolecular layer was formed on the metal surface of the cut tefion insulated wire. The electrical conductivity properties of such a device were studied in the frequency range 20 Hz - 1 MHz using the methods of impedance spectroscopy.
The admittance spectra were analyzed in terms of equivalent circuits. We have searched for the simplest equivalent circuit that can reproduce, with one set of parameters simultaneously, the frequency dependence of the conductance and the susceptance. It was shown that it is possible to assign the individual R and C elements and the Warburg-type impedance of the equivalent circuit to physical units present in the device and the measuring circuit. The presence of the Warburgtype impedance was assigned to the roughness of the interface at which the charge transfer is taking place. The major finding is that the use of equivalent RC circuits to represent electrical properties of devices based on self-assembled lipid bilayers formed on cut insulated wires is inadequate.
Another system that was studied by means of impedance spectroscopy was a solar cell based on porphyrin-sensitized porous Ti02 layer in contact with 12/13 redox pair. To construct an equivalent circuit of the solar cell we have measured admittance spectra of the cell with an increasing number of components comprising the solar cell. In this manner it was possible to arrive at an equivalent circuit that can reproduce the experimental admittance spectra of the cell and to associate the circuit elements with the major structures or regions of the solar cell. We have discovered changes of the admittance spectra on illumination of this cell and identified the elements of the equivalent circuit that change in the presence of light.
Hermes, Uwe, "Impedance spectroscopy of bilayer lipid membranes and TiO₂ based solar cells" (1997). Dissertations and Theses. Paper 5402.