Theoretical and experimental study of phase optimization of tapping mode atomic force microscope

Abstract

Phase image in tapping mode atomic force microscope (TM-AFM) results from various dissipation in microcantilever system. The phases mainly reflected the tip-sample contact dissipations which allowed the nanoscale characteristics to be distinguished. In this research investigation, two factors affecting the phase and phase contrast were analyzed. It was concluded from the theoretical and experimental results that the phases and phase contrasts in the TM-AFM were related to the excitation frequencies and energy dissipation of the system. For a two-component blend, it was theoretically and experimentally proven that there was an optimal excitation frequency for maximizing the phase contrast. Therefore, selecting the optimal excitation frequency could potentially improve the phase contrast results. In addition, only the key dissipation between the tip and sample was found to accurately reflect the sample properties. Meanwhile, the background dissipation could potentially reduce the contrasts of the phase images and even mask or distort the effective information in the phase images. In order to address the aforementioned issues, a self-excited method was adopted in this study in order to eliminate the influencing effects of the background dissipation on the phases. Subsequently, the real phase information of the samples was successfully obtained. It was considered in this study that eliminating the background dissipation had effectively improved the phase contrast results and the real phase information of the samples was accurately reflected. These results are of great significance to optimize the phase of two-component samples and multi-component samples in atomic force microscope.

Effect of excitation frequencies on phase contrast in tapping mode atomic force microscope

“…where 𝑚 represents the equivalent mass of the microcantilever beam; 𝑐 represents the equivalent external damping that describes background dissipation; 𝑘 is the spring constant of the microcantilever beam; 𝑧 represents the absolute displacement of the tip; and 𝑧 represents the support excitation. A number of studies have now shown that the tip-sample contact stiffness is small and has little effect on the intrinsic frequency of the probe [5,16,17]. Therefore, the effect of 𝑘 can be neglected and Eq.…”