Mapping the tip–sample interactions on DPPC and DNA by dynamic force spectroscopy under ambient conditions

Self-assembled monolayers of DPPC and DNA adsorbed on mica are examined by dynamic force spectroscopy under ambient conditions. By a systematic recording of the frequency shift caused by the tip–sample interaction we determine the corresponding tip–sample potential and force curves. In difference to the conventional measurement of force-vs.-distance curves this technique allows the continuous measurement of tip–sample forces without instabilities caused by a jump-to-contact. Due to the systematic mapping of the tip–sample interaction we are able to compute contour maps of the tip-surface potential of the DPPC films and to extract local properties like contact stiffness and adhesion force. The lateral resolution capabilities of the introduced spectroscopy method are examined by the example of lambda phage DNA.