Comment on "Damping mechanism in dynamic force microscopy"

Bimodal atomic force microscopy driving the higher eigenmode in frequency-modulation mode: Implementation, advantages, disadvantages and comparison to the open-loop case

We present an overview of the bimodal amplitude-frequency-modulation (AM-FM) imaging mode of atomic force microscopy (AFM), whereby the fundamental eigenmode is driven by using the amplitude-modulation technique (AM-AFM) while a higher eigenmode is driven by using either the constant-excitation or the constant-amplitude variant of the frequency-modulation (FM-AFM) technique. We also offer a comparison to the original bimodal AFM method, in which the higher eigenmode is driven with constant frequency and constant excitation amplitude. General as well as particular characteristics of the different driving schemes are highlighted from theoretical and experimental points of view, revealing the advantages and disadvantages of each. This study provides information and guidelines that can be useful in selecting the most appropriate operation mode to characterize different samples in the most efficient and reliable way.

Ab initio simulation of atomic-scale imaging in noncontact atomic force microscopy

In this paper, we summarize some results of our ab initio simulations aimed at investigating the mechanism of the NC-AFM image contrast on semiconductor and metallic surfaces. We start with an introduction into the basic ideas behind the ab initio simulation process of the NC-AFM experimental results. Our simulations reveal that the interaction of a clean silicon tip with a semiconductor surface like InAs(110) might lead to bond-formation and bond-breaking processes during the approach and retraction of the tip. This imaging mechanism is very similar to that observed on a metallic surface like Ag(110). Interestingly, a clean silicon tip can become contaminated with Ag surface atoms. On both types of surface we observe a significant energy dissipation which is caused by a hysteresis in the tip-sample force curves calculated on the approach and retraction path.

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.