SNOM光学探针高度控制技术研究

The study of the height regulation technique of SNOM optical probe tip

本文介绍采用非光学方法实现剪切力（ｓｈｅａｒｆｏｒｃｅ）检测和轻敲（ｔａｐｐｉｎｇ）模式微振动检测。通过检测压电片上的电压输出，用作探针与样品间距控制信号，实现扫描近场光学显微镜（ＳＮＯＭ）光学探针与样品间距控制。文中给出了探针－压电片检测系统的的频率特性，并比较了剪切力探测和轻敲模式探测特性的区别。在剪切力作用下探针在正负半周振动时受到的作用力是对称施加的，谐振状态受剪切影响，随作用力增大振幅连续减小。而在轻敲模式工作时探针受到非对称力作用，因而在探针的谐振状态与作用力关系（力曲线）上表现出不同特征。采用轻敲方式时存在最佳工作频率，只有在该频率下才能得到合适的力曲线，并获得较好的图像。

An non optical detection of shear force and probe tip resonance was developed. By detecting the output from a tiny piezo chip attached to the fiber tip, the distance between the optical probe tip and the sample was successfully controlled. The frequency responses of the system combing probe tip and piezo chip were detected, the difference between the shear force detection and the tapping mode detection was discussed. We found that the shear force exerts on the tip reduce the vibration amplitude. In tapping mode for the force exerts on the fiber tipasymmetrically, the resonance frequency varies with the force, so special care should be taken to adjust excitation frequency in order to get the proper force curve and the fine image.