Amplitude calibration of quartz tuning fork (QTF) force sensor with an atomic force microscope

• Main Authors: Hussain, Danish, Hao Zhang, Jianmin Song, Wen Yongbing, Xianghe Meng, Fan Xinjian, Hui Xie
• Format: Conference Proceeding
• Language: English
• Subjects: Atomic Force Microscopy (AFM); Calibration; force sensor; Probes; Quartz tuning fork (QTF); Resonant frequency; Sensitivity; sensitivity factor; Servomotors; Vibrations; Voltage measurement
• ISSN: 1944-9380
• DOI: 10.1109/NANO.2017.8117406

Amplitude calibration of the quartz tuning fork (QTF) sensor includes the measurement of the sensitivity factor (α TF ). We propose, AFM based methods (cantilever tracking and z-servo tracking of the QTF's amplitude of vibration) to determine the sensitivity factor of the QTF. The QTF is mounted on a xyz-scanner of the AFM and a soft AFM probe is approached on the apex of a tine of the QTF by driving the z-servo and using the normal deflection voltage (V tb ) of position sensitive detector (PSD) as feedback signal. Once the tip contacts the tine, servo is switched off. QTF is electrically excited with a sinusoidal signal from OC4 (Nanonis) and amplitude of the QTF's output at transimpedance amplifier (V tf ) and amplitude of V TB (Vp) is measured by individual lock-in amplifiers which are internally synchronized to the phase of the excitation signal of the QTF. Before, the measurements optical lever is calibrated. By relating the both voltages (Vp & V tf ), sensitivity factor of the QTF (α TF ) is determined. In the second approach, after the tip contacts the tine, the z-servo is switched off firstly, then the feedback signal is switched to Vp and frequency sweep for the QTF, V tb as well as z-servo are started, instantaneously. To keep the V p at set-point the feedback control moves the z-servo to track the vibration amplitude of the QTF and thus the distance traveled by the z-servo (Δζ) during sweep is equal to the fork's amplitude of vibration (Δx TF ). α tf is determined by relating Δz and V TF . Both approaches can be non-destructively applied for QTF sensor calibration. AFM imaging of the AFM calibration grating TGZ1 (from NT-MDT Russia) has been performed with a calibrated QTF sensor.