基於雷射共焦方法之微懸臂探針偵測系統

Abstract

原子力顯微鏡具奈米級解析度，並可在真空、大氣、甚至液體環境中量測樣品之表面輪廓，並已被廣泛應用於各領域。透過使用高共振頻率超小型微懸臂探針，高速原子力顯微鏡進一步提升原子力顯微鏡之成像速度，可應用於許多動態現象之量測。然而，為量測超小型之微懸臂探針，微懸臂雷射感測系統需要有更小之聚焦光點。此外，由於需高量測頻寬，亦無法使用一般的低通濾波器降低雜訊，因此較難以達到高解析度之要求。為提升微懸臂感測系統靈敏度，本研究提出一共軛焦式光路設計，透過更換不同聚焦透鏡、針孔孔徑，以及不同感測器進行靈敏度比較。其中使用氦氖雷射作為光源，並使用微懸臂探針FMAuD、聚焦透鏡49-665、50 μm針孔孔徑、位置感測器SPOT-9DMI於Gain值為30時可組合出最佳靈敏度為0.6789 mV/nm，且雜訊峰對峰值為4.2 mV，雜訊對應位移量為6.19 nm。

Atomic force microscope(AFM) has nanoscale resolution and can measure the surface profile in vacuum, air, and even liquid environments, which has been widely used in various fields. By using an ultra-small cantilever tip with a high resonance frequency, the high-speed AFM further improves the imaging speed, which can be applied to measure many dynamic phenomena. However, in order to measure the ultra-small cantilever tip, the laser beam deflection system needs a smaller focused light spot. In addition, due to the requirement of high measurement bandwidth, common low-pass filter cannot be adopted to reduce noise, thus increasing the difficulties to achieve high resolution imaging. To improve the sensitivity of the cantilever detection system, this study proposed a confocal optical system design, and attempted to optimize the sensitivity by replacing different focusing lenses, pinhole apertures, and photodetectors. The experimental results show that the combination of a He-Ne laser, a cantilever tip FMAuD, a focusing lens 49-665, a 50 μm pinhole aperture, and a position sensitive detector SPOT-9DMI achieves a highest sensitivity of 0.6789 mV/nm with a gain value of 30. The cantilever deflection signal peak-to-peak noise is 4.2 mV, and corresponds to a displacement of 6.19 nm.