音叉的工作原理與在探針顯微鏡上之應用

Abstract

本文探討掃描式探針顯微鏡的探針與試片間非接觸作用力對於剪力回饋裝置共振頻率的影響，應用作用力與感測器振幅變化之特性，調控探針高度。剪力回饋感測器採用市售石英音叉振盪器，黏貼光纖探針完成，以尤拉梁振動模型分析軸向作用力與共振頻率改變的關係，並結合Argento和French計算公式，由實驗及共振分析獲得探針與試片間非接觸作用力與剪力回饋感測器共振頻率的關係曲線，得到一致性趨勢的結果。本研究撰寫Labview圖控式軟體，透過GPIB介面連結鎖相放大器及函數產生器，並以運動控制卡之數位訊號處理功能，成功研製成一部閉迴路剪力回饋掃描式探針顯微鏡。

This thesis presents a study on the working principle of tuning-fork-based shear force feedback devices frequently used in a scanning probe microscope. Resonant frequency of the tuning fork varies since non-contact interaction force acts on the probe as its tip becomes very close to a sample. Variation of the vibrating amplitude at the inherent resonant frequency is often used as an index to adjust the tip-sample distance within optical near-field range. The shear force feedback device is made of a commercial quartz tuning fork glued together with an optic probe of 50 nm aperture along one of the fork arms. The fork arm is modeled as an Euler beam that vibrates laterally and subjects to an axial force. The resonant frequency shifts due to geometric stiffness change caused by the axial interaction force. Combined with the tip force-distance formula presented by Argento and French, this study establishes a useful relation between the resonant frequency shift and the tip force. It is also successfully used to measure the interaction force between an optic probe and a silicon wafer. A shear force feedback scanning probe microscope was further developed during this research by a LabVIEW program integrating a lock-in amplifier, function generator, DSP-based PI controller through a GPIB interface.