Figure 6

Longterm surface stress measurement of gold coated cantilever in buffer. Longterm surface stress of a gold coated cantilever in TN buffer recorded for 14 hrs. A square wave potential between +/− 200 mV with a period of 10 min was applied to the cantilever. A zoom of three sections are shown and labeled as 1, 2 and 3. At (1) a large surface stress change is measured. After around 9.5 hours (2), the pattern starts to change resulting in a negative slope for +200 mV and a positive slope for −200 mV, clearly visible after 13 hrs (3). Furthermore, the overall surface stress change amplitude decreases indicating that that ions chemisorb onto the surface over time covering part of the gold surface.