DISSERTATION

_____________________________________________________________ Results and Discussion
high frequency. The fact that the OCP does not significantly change over the course of the SAM
formation by simple incubation (data not shown) justifies this approach.
As in the previous section, the influence of different parameters on the potential-pulse assisted
SAM formation is investigated: potential intensities in the potential-pulse cycle and duration of
the potential pulse (Figure 3.33). Emphasis in this chapter is on the dependence of these
parameters on the length of a alkyl chain of the thiol derivative.
Figure 3.33. Scheme of investigated potential pulse profiles (ΔE = 400 mV, 0.3/-0.1 V; ΔE
= 700 mV, 0.5/-0.2 V; ΔE = 900 mV, 0.5/-0.4 V, all vs. Ag/AgCl/3 M KCl) and pulse
durations (1 ms, 10 ms, 100 ms and 10 s). Figure adapted from ref. 89 .
It was previously shown that the pzc shifts from 0.5 V vs. Ag/AgCl/3 M KCl (pzc of the bare
electrode) towards more negative values due to surface modification with DNA strands. The
same behavior is expected in the case of thiol SAM formation, since it was reported that the
pzc of a thiol-modified electrode is around 0.1 V 93 (vs. Ag/AgCl/3 M KCl). Therefore, this shift
in the pzc value was taken into account during the selection of the potential pulse intensities.
Using the ΔE = 400 mV pulse profile (0.3/-0.1 V vs. Ag/AgCl/3 M KCl) potentials of +200 mV
and -200 mV relative to the pzc value of the thiol-modified surface are applied, while for ΔE =
700 mV (0.5/-0.2 V vs. Ag/AgCl/3 M KCl) +400 mV and -300 mV are applied and for ΔE =
900 mV (0.5/-0.4 V vs. Ag/AgCl/3 M KCl) +400 mV and -500 mV are applied.
Figure 3.34 shows capacitance curves obtained during the formation of a MCU SAM using
different potential-pulse profiles. It presents the influence of potential intensities on the kinetics
3.3 Importance of controlling the surface 71