Improving the performance of rebalanced quartz tuning fork force sensors with tungsten tips for atomic force microscopy under ambient conditions

An experimental and simulation study of the balanced quartz tuning fork (QTF) force sensor in an atmospheric environment is presented. The experimental results demonstrate that a QTF force sensor with a balanced structure shows a significant improvement in the Q-factor in an atmospheric environment. With a rational configuration of the QTF probe structure, the Q-factor can be increased by 2–3 times compared to that of the unbalanced ones, even when the length of the attached probe tip (tungsten wire) is longer than 2.5 mm. More precisely, the Q-factor can reach 3000 when the tip length is around 1.0 mm. For a probe length of about 3.5 mm, the Q-factor is ∼1800, which also suits the working of the atomic force microscope (AFM) and shows more stability than the length near 1.0 mm. Nevertheless, the highest Q-factor of the QTF probe does not occur under the most symmetric condition. To explain these results, simplified models associated with the basic QTF probe working situation were simulated using the commercial software COMSOL Multiphysics®. By analyzing these results, we elucidated the mechanism of the QTF probe working in an atmospheric environment and some of its vibration modes connected with its Q-factor. According to the experimental and simulation study results, the balanced QTF probe exhibits a significantly higher Q-factor than conventional ones. The probe tip, with its length near 1.0 mm or 3.5 mm, can achieve an opportune Q-factor for AFM, demonstrating its potential for further improving the performance of QTF probes for atomic force microscopes under ambient conditions.