Mott-Schottky Experimental Sequence
Run the Mott-Schottky Plot technique by selecting Experiment>Electrochemical Impedance>Mott-Schottky Plot from the Framework™ menu bar. This initiates the following sequence of events:
- The Framework creates a Runner window, and the Mott Schottky.exp script is run in this window.
- The script creates the Setup dialog box and accepts changes in the parameters.
- The script now obtains the use of the potentiostat specified during Setup and opens the data file specified in the Output name. The Runner window's Title reflects the Output filename. If the potentiostat is in use or the file cannot be opened, the script returns you to the Setup dialog box. The AC frequency is checked to see if it is valid for the Potentiostat being used. If it is not valid, the script displays a warning message and sets the frequency to the limit allowed by the potentiostat. The script determines the sign and magnitude of the voltage step and the total number of points that will be required in the plot.
- The file header information is written to the data file. This header information includes; a) Tags identifying possible analyses, b) the current time and date, and c) a list of the Setup parameters. This information is written to the file prior to data-acquisition. If the experiment is aborted prior to acquisition of the first data point, the output file contains only this information. The output file is configured such that each data point is written to disk as soon as it is acquired. This prevents any loss of data if the computer suffers a loss of power or other failure. The script conditions the electrode if Conditioning was specified in the Setup. Conditioning is done by applying a fixed potential for a defined time. It establishes a known surface state on the working electrode. A plot of current versus time is displayed during the Conditioning.
- The cell is turned off and the specimen's Eoc is measured. If an Initial Delay is turned on in the Setup, this step lasts for the time specified as the Delay Time, or until the potential stabilizes . If no Initial Delay is specified, this step only lasts long enough for Eoc to be measured. A plot of potential versus time is always displayed. The last measured potential is recorded as Eoc.
- The script then sets up data-acquisition. The Initial Voltage requested in setup is applied to the cell which is turned on. The measurement parameters are set to measure an impedance equal to the Estimated Z parameter. An AC signal at the requested frequency and with the requested AC voltage amplitude is then applied to the cell. The cell's response to this frequency is measured using the selected FRA. If the readings of both the E and I signals are acceptable, the script proceeds to the voltage sweep. If the values are not acceptable, the script generates new estimate for the cell's impedance, resets the measurement parameters for this impedance, and reruns the measurement. If an acceptable reading cannot be reached after a set number of attempts, the script reports an error, asks if you want to quit or continue, and waits for your answer.
- The script then begins the voltage sweep. The sweep is actually a staircase ramp. The voltage for the Nth step in the ramp calculated as follows: Voltage = Initial Voltage + (N × Voltage Step) This voltage is applied. The script sets the measurement parameters to measure an impedance equal to the last recorded impedance, and then takes an FRA reading. If the readings of both the E and I signals are acceptable, the script converts the readings to an impedance, records the impedance point on disk, updates the displayed curve, and then proceeds to the next point in the voltage sweep. If the values are not acceptable, the script generates new estimate for the cell's impedance, resets the measurement parameters for this impedance, and reruns the measurement. If an acceptable reading cannot be reached after a set number of attempts, the script reports an error, asks if you to quit or continue, and waits for your answer. As each point is measured, a real-time Lissajous plot is displayed. When done, two plots of 1/C2 vs. E are displayed. The top graph labeled (RC) calculates the capacitance assuming a model of a series resistor to a capacitor and the bottom graph labeled (R//C) calculates the capacitance assuming a parallel resistor to a capacitor.
- When the calculated voltage exceeds the Final Voltage, the script halts, and waits for you to select F2-SKIP. When you do, the script closes everything that's open, including the Runner window.