DISSERTATION

_____________________________________________________________ Results and Discussion
Figure 3.31. Schematic representation of the setup used for real-time impedance
measurements during potential-pulse assisted acceleration of SAM formation: A – signal
in, R – AC current magnitude, θ – AC current phase, AD/DA – analog-digital/digitalanalog
conversion for potential application and data acquisition, RE – reference electrode,
CE – counter electrode, WE – working electrode. The potentiostat receives the DC
potential signal as potential pulses from the function generator and superimposes an AC
signal with a single high frequency generated by the oscillator in the lock-in amplifier.
The recorded current is fed back to the lock-in amplifier and the AC current at the
excitation frequency is amplified providing the magnitude and the phase of the resulting
AC response. Figure adapted from ref. 89 .
The real-time impedance measuring setup consists of several components: a potentiostat, a
function generator, a lock-in amplifier, an AD/DA card and an electrochemical cell (Figure
3.31). The function generator is used to create a pulse-type DC potential modulation and to
apply it to the external potential input of the potentiostat. In order to be able to apply potential
pulses for accelerated SAM formation while simultaneously applying an AC frequency for
impedance measurements, a summing amplifier is used to superimpose the square wave DC
signal with a high-frequency AC signal. It should be noted that the AC signal needs to be of a
significantly higher frequency with respect to the pulse time of the DC signal to prevent any
influence of the small AC perturbation on the behavior of the investigated system. The current
3.3 Importance of controlling the surface 69