Abstract
The shear force position system has been widely used in scanning near-field optical microscopy (SNOM) and recently extended into the force sensing area. The dynamic properties of a tuning fork (TF), the core component of this system, directly determine the sensing performance of the shear positioning system. Here, we combine experimental results and finite element method (FEM) analysis to investigate the dynamic behavior of the TF probe assembled structure (TF-probe). Results from experiments under varying atmospheric pressures illustrate that the oscillation amplitude of the TF-probe is linearly related to the quality factor, suggesting that decreasing the pressure will dramatically increase the quality factor. The results from FEM analysis reveal the influences of various parameters on the resonant performance of the TF-probe. We compared numerical results of the frequency spectrum with the experimental data collected by our recently developed laser Doppler vibrometer system. Then, we investigated the parameters affecting spatial resolution of the SNOM and the dynamic response of the TF-probe under longitudinal and transverse interactions. It is found that the interactions in transverse direction is much more sensitive than that in the longitudinal direction. Finally, the TF-probe was used to measure the friction coefficient of a silica–silica interface.
Highlights
IntroductionBecause of its capacity to break through the boundaries of conventional diffraction-limited optical microscopy and no-contact sensing property, the applications of Scanning near-field optical microscopy (SNOM) have been extended to near-field spectroscopy [3,4,5,6,7], topographic detecting [8], residual stress measurement [9], and soft matter testing [10,11,12]
Scanning near-field optical microscopy (SNOM) was developed more than three decades ago [1,2].Because of its capacity to break through the boundaries of conventional diffraction-limited optical microscopy and no-contact sensing property, the applications of SNOM have been extended to near-field spectroscopy [3,4,5,6,7], topographic detecting [8], residual stress measurement [9], and soft matter testing [10,11,12]
The shear-force detection technique uses a tuning fork (TF) to produce probe oscillation parallel to the sample surface and measure its oscillation amplitude [18,19,20,21], where a tapered optical fiber is attached to one prong of the TF, and the whole structure works at its resonance under a harmonic voltage excitation
Summary
Because of its capacity to break through the boundaries of conventional diffraction-limited optical microscopy and no-contact sensing property, the applications of SNOM have been extended to near-field spectroscopy [3,4,5,6,7], topographic detecting [8], residual stress measurement [9], and soft matter testing [10,11,12]. The shear-force detection technique uses a tuning fork (TF) to produce probe oscillation parallel to the sample surface and measure its oscillation amplitude [18,19,20,21], where a tapered optical fiber is attached to one prong of the TF, and the whole structure works at its resonance under a harmonic voltage excitation. Investigating the dynamic property and understanding the capability of controlling the probe–sample distance of this TF-probe are critical issues to improve the image quality of SNOM or the sensitivity of the TF-probe sensor when applied to the measurement of displacement or of interactions between the probe tip and the sample surfaces
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