Adhesion force imaging in air and liquid by adhesion mode atomic force microscopy

A new imaging mode for the atomic force microscope (AFM), yielding images mapping the adhesion force between tip and sample, is introduced. The adhesion mode AFM takes a force curve at each pixel by ramping a piezoactuator, moving the silicon-nitride tip up and down towards the sample. During the retrace the tip leaves the sample with an adhesion dip showing up in the force curve. Adhesion force images mapping parameters describing this adhesion dip, such as peak value, width, and area, are acquired on-line together with the sample topography. Imaging in air gives information on the differences in hydrophobicity of sample features. While imaging a mercaptopentadecane-gold layer on glass in demineralized water, the adhesion force could be modulated by adding phosphate buffered saline.