Abstract
For simultaneously measuring specimen’s surface morphology and material properties, multifrequency atomic force microscopy is often employed. In this kind of atomic force microscopy, if the probe’s higher-order resonance frequencies match the integer multiples of its fundamental frequency, the probe’s responses at such harmonic frequencies will be enhanced. Meanwhile, an enlarged effective slope during vibration at the probe’s tip results in an improved probe sensitivity. Moreover, increasing the probe’s natural frequency leads to a fast scanning speed. In this study, we propose to design cantilever probes that satisfy the aforementioned requirements via a structural optimization technique. A cantilever probe is represented by a three-layer symmetrical geometric model, and its width profile is continuously varied through the optimization procedure. Thereafter, an optimized design of probe considering the fifth harmonic is prepared by focused ion beam milling. Both simulation and experiment results show that the prepared probe agrees well with design requirements.
Highlights
Given its increasing applications in biology, physics, and material science, tapping-mode atomic force microscopy (TM-AFM)[1] is receiving increasing attention
The results prove that our method is effective in designing a harmonic probe with a large tip slope at its fundamental resonant mode
The fundamental resonant frequency is maximized during optimization to ensure scanning speed
Summary
Given its increasing applications in biology, physics, and material science, tapping-mode atomic force microscopy (TM-AFM)[1] is receiving increasing attention. In contrast to traditional contact-mode AFM, TM-AFM avoids lateral friction in measurement, and it results in minimal damage to the specimen. In a TM-AFM measurement, a vibration signal excites the probe at its fundamental resonant frequency, so that the tip of probe touches the specimen surface periodically. The topography of the specimen is attained by scanning the desired area. Apart from traditional topography measurement, TM-AFM has been used for material property characterization. Periodic tapping results in a periodic pulse-like nonlinear interaction force. Higher harmonic components extracted from the response of the probe contain rich information of the material properties of samples.[4,5,6,7]
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