Dynamic force microscopy with quartz tuning forks at high oscillation amplitudes

Abstract

Dynamic force microscopy (DFM) with the self-oscillator (SO) method allows reasonably high scanning rates even with high Q-factors of the resonant force sensor, typical of cantilevers in ultra-high vacuum and of quartz tuning forks. However, due to simpler interpretation of force spectroscopy measurements, small oscillation amplitudes (sub-nm level) are generally preferred. In applications like ‘apertureless’ scanning near-field optical microscopy (SNOM), oscillation amplitudes of the order of 5–10 nm are needed to increase optical sensitivity and to apply standard optical artefact suppression methods. This motivates the study of the behaviour of tuning forks driven at such high amplitudes, as compared to usual air-operated cantilevers. Both constant-excitation-amplitude (CE) and constant-oscillation-amplitude (CA) modes of SO-DFM are analysed, since the CA mode is more convenient for SNOM applications, denoting remarkable differences. In particular, possible instability effects, previously found in CE mode, are not anticipated for CA mode. It is shown how resonance and approach (‘isophase’) curves in both modes can be conveniently described in terms of the usual ‘normalized frequency shift’ γ and of a ‘normalized gain’ η, defined as a measurement of surface dissipation.

Plasma Polymerized Films for Mass Sensitive Biosensors

“…These forks have replaced the mechanical pendulum and spring used in watches since the late 1960s, allowing the production of more stable watches. The key component of these high-stability watches, QTF, is manufactured by mass production at low cost, making QTF use even more attractive [42][43][44][45][46][47][48][49][50][51].…”

“…Basically, the QTF consists of two forks which is coated with metal films. These forks vibrate under vacuum at a frequency of 32758 Hz, moving lateral when stimulated by alternating current excitation voltage [14,[42][43][44][45][46][47][48][49][50][51]. When hermetic casing of the QTFs were removed, resonance frequency of QTFs decreased due to air damping.…”

Dynamics of probes attached to quartz tuning forks for the detection of surface forces

“…High spring constants allow us to use low-amplitude oscillations, avoiding the jumpin-contact phenomenon, well known in DFM since it prevents the full exploration of the force curve. Sensitivity loss due to the higher spring constant of TFs can be counterbalanced by their high quality factor [15]. Since measurement bandwidth of AFM is limited by the oscillation recovery time τ r = Q/π f [16], to increase scanning speed with high-Q probes one can resort to self-oscillator constant-phase modes [16] or to appropriate resonance frequency tuning [17].…”

High-resolution quantitative determination of dielectric function by using scattering scanning near-field optical microscopy

“…Scattering scanning near-field optical microscopy (s-SNOM)12345 has attracted massive interest in the past couple of decades because of its capabilities for probing the optical properties of unlabeled samples at sub-diffraction resolutions. To date, s-SNOM has been successfully employed for multiple applications such as nano-imaging367, characterization of plasmonic structures891011, near-field spectroscopy45121314, nano-chemical characterization1516, or for the measurement of the dielectric function in the infrared domain1718.…”