Figure 6.

AFM images of Au-tethered PEG-layers obtained at different forces in good solvent (PBS; upper row) and in poor solvent (20% 2-propanol in PBS; lower row) conditions. Images in PBS show an improved resolution of the underlying Au surface (on the same area) as the force set point is increased from 30 → 60 → 80 pN indicating penetration/splaying of the PEG layer by the tip. The Au surface is covered again after the force set point is reduced back to 30 pN. The lower series of images were acquired in 20% 2-propanol and do not show any dependence on the force applied. This effect was similar over different areas on the sample (the 30 pN area is different from the 60 and 120 pN area), and implies that the tethered chains have collapsed under poor solvent conditions. All images were obtained on the same microcantilever array chip. The scale bar is 100 nm.