Abstract
In this work, amplitude modulation atomic force microscopy (AM-AFM) based on the higher flexural modes of the microcantilever is investigated by a numerical approach. The amplitude-distance and phase-distance curves for the first four flexural modes are obtained and compared. The dependence of phase on elastic modulus and viscosity of the sample is analyzed. Results show that a higher flexural mode yields a larger amplitude and phase in the repulsive regime and reduces the bistability, but causes a larger sample deformation and peak repulsive force. Compared to that of a lower flexural mode, the phase of a higher flexural mode provides higher sensitivity to viscosity variation for relatively large moduli.
Highlights
Amplitude modulation atomic force microscopy (AM-AFM) method has been widely used in nanoscale surface characterization.[1,2]
In amplitude modulation atomic force microscopy (AM-AFM) imaging, the excitation frequency is usually set at the first free resonance frequency (FRF) of the microcantilever and the response amplitude is adjusted to be constant by a feedback circuit
The change in phase for the fourth mode from η = 0 Pa·s to η = 200 Pa·s is about five times as that of the fundamental mode. These results reveal that the phase of a higher flexural mode in phase imaging is much more sensitive to viscosity variation
Summary
Amplitude modulation atomic force microscopy (AM-AFM) method has been widely used in nanoscale surface characterization.[1,2] In AM-AFM imaging, the excitation frequency is usually set at the first free resonance frequency (FRF) of the microcantilever and the response amplitude is adjusted to be constant by a feedback circuit. Similar to the quasi-static force-distance curves in contact mode, the amplitude-distance as well as the phase-distance curve can be measured in AM-AFM, which is usually called dynamic force-distance curves (or dynamic force spectroscopy). The relationship between the energy dissipation and the phase shift has been established based on the principle of energy balance.[8,9] Virial and energy dissipation method has been used to investigate the contributions from the conservative and non-conservative forces.[10,11] Besides, the tip-sample interaction force reconstruction or force inversion in AM-AFM, an inverse problem in cantilevertip dynamics, has been studied.[12,13,14,15,16] in recent years, multifrequency atomic force microscopy (MF-AFM) has attracted more and more attentions from researchers in this field.[17,18]
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