用于原子力显微镜的qPlus探针的扫描电镜表征

Characterization of qPlus probe for atomic force microscopy using scanning electron microscopy

基于q Plus探针的原子力显微镜有更高的空间分辨率,但其工作原理有别于传统的悬臂梁探针,结构也更加复杂,其探针尖端机械振动的振幅和方向是影响实验结果的核心问题。通常通过锁相放大器直接测量到的是来自音叉的压电电流,而不是针尖的机械振动本身。本文提出了一种借助扫描电子显微镜在实空间实时观测q Plus探针振动状态的方法,在实验上得到了在压电陶瓷激励下,探针尖端振动的方向和振幅等要素,针尖振幅与激励电压呈线性关系,针尖机械振动的共振频率与压电电流的共振频率一致,符合理论预期;然而实验观察到的振动方向却接近于水平方向。本文的研究结果对优化q Plus探针结构,提升性能提供了参考。

Atomic force microscopes equipped with q Plus probes exhibit higher spatial resolution,but the working mechanism is different from that of the traditional cantilever probes. Their structures are more complicated. The amplitude and direction of mechanical vibration of probe tips are of great importance to the experimental results. In experiments,the vibration modes are usually characterized by measuring the piezoelectric current from the tuning fork with a lock-in amplifier,but not the mechanical vibration of the tip itself. In this paper,we present a real-time method to observe the vibration state of q Plus probe in real space by scanning electron microscope. The vibration amplitude and direction of tip apex can be directly measured from SEM images. The amplitude and excitation voltage show a good linear relationship,which is in line with the theoretical expectation. The mechanical resonance frequency of the tip vibration is consistent with the resonance frequency of the piezoelectric current. However,the vibration direction in our experiments is almost parallel to the prong of the tuning fork. These results will benefit the structure design of q Plus probe and the improvement of their performance.