Abstract
Background: Encased cantilevers are novel force sensors that overcome major limitations of liquid scanning probe microscopy. By trapping air inside an encasement around the cantilever, they provide low damping and maintain high resonance frequencies for exquisitely low tip–sample interaction forces even when immersed in a viscous fluid. Quantitative measurements of stiffness, energy dissipation and tip–sample interactions using dynamic force sensors remain challenging due to spurious resonances of the system.Results: We demonstrate for the first time electrostatic actuation with a built-in electrode. Solely actuating the cantilever results in a frequency response free of spurious peaks. We analyze static, harmonic, and sub-harmonic actuation modes. Sub-harmonic mode results in stable amplitudes unaffected by potential offsets or fluctuations of the electrical surface potential. We present a simple plate capacitor model to describe the electrostatic actuation. The predicted deflection and amplitudes match experimental results within a few percent. Consequently, target amplitudes can be set by the drive voltage without requiring calibration of optical lever sensitivity. Furthermore, the excitation bandwidth outperforms most other excitation methods.Conclusion: Compatible with any instrument using optical beam deflection detection electrostatic actuation in encased cantilevers combines ultra-low force noise with clean and stable excitation well-suited for quantitative measurements in liquid, compatible with air, or vacuum environments.
Highlights
Dynamic atomic force microscopy requires excitation of the cantilever oscillation
Frequently applied in microelectromechanical systems, electrostatic actuation is rarely used in scanning probe force microscopy
Built into the encasement and located between cantilever and sample, the actuation electrode does not need alignment and the device remains compatible with any scanning probe force microscope using optical beam deflection detection
Summary
Dynamic atomic force microscopy requires excitation of the cantilever oscillation Most commonly, this is achieved using a dither piezo built into the cantilever holder of the microscope. This is achieved using a dither piezo built into the cantilever holder of the microscope This technique is simple and effective, but it typically results in spurious peaks in the frequency response spectrum that are not directly related to the cantilever resonance. Built into the encasement and located between cantilever and sample, the actuation electrode does not need alignment and the device remains compatible with any scanning probe force microscope using optical beam deflection detection. By trapping air inside an encasement around the cantilever, they provide low damping and maintain high resonance frequencies for exquisitely low tip–sample interaction forces even when immersed in a viscous fluid. Quantitative measurements of stiffness, energy dissipation and tip–sample interactions using dynamic force sensors remain challenging due to spurious resonances of the system
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