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(Color online) (a) Schematic of a cantilever with a thin-film capacitor on its bottom face. (b) The application of a voltage across the capacitor causes a deflection that changes the dimensions and dielectric properties of the capacitor.
(Color online) Comparison of mechanical and capacitive driving of the first mechanical resonance mode for a conventional tapping-mode (left column) and a high-frequency (right column) cantilever. Points are experimental data and lines are fits of the data to theory. (a) and (e) Optical images of the tapping mode and high-frequency AFM probes after fabrication. (b) and (f) Thermal amplitude spectra nA vs. frequency f showing the first mechanical resonance peak. (c) and (g) Cantilever vibration amplitude A vs. f when the probe is driven by mechanically shaking it with the piezoelectric element. (c) The frequency dependant transfer function between the actuator and the cantilever creates only a small deviation from the theoretical fit for the tapping mode cantilever but (g) mixing with unwanted mechanical modes makes the resonance unintelligible for the high-frequency cantilever. (d) and (h) When driven capacitively, the measured response A vs. f is in excellent agreement with theory, demonstrating the advantage of high-fidelity capacitive drive.
(Color online) Cantilever vibration amplitude A for (a) tapping-mode and (b) high-frequency AFM cantilevers driven capacitively using an ac-voltage VAC at half the resonant frequency f = f 0/2. The experimental data points are fit very well by A = αexp , shown by the line. The insets show optical images of each cantilever with a 100 μm scale bar.
Properties of the conventional (1) and high-frequency (2) cantilevers used in this study. f 0 and k are found through fitting of nA from Figs. 2(b) and 2(f), typical cantilever geometries are measured in a SEM, and D is estimated from ellipsometry of a test wafer.
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