新型原子力顯微鏡使用DVD讀取頭在水裡之應用

Abstract

本文提出的原子力顯微鏡（atomic force microscope），是可以在液體裡利用光碟讀取頭(DVD pick-up-head)，來量測探針懸臂撓曲的掃樣品型原子力顯微鏡系統。為了實現上述的系統，我們設計了一個適應性Q控制器來控制樣品與探針之間的接觸力，藉著增加Q因子來增加探針在水裡的振幅，可以解決探針在水裡由於阻尼過大使得探針難以震盪的問題。此外，這個方法也可以減低樣品與探針之間的接觸力，這樣在掃描柔軟的生物細胞時，也不會造成破壞，所以可以得到細胞更真實的表面形貌。 另外我們還設計了一個新的原子力顯微鏡機構並且使用適應性滑動模式控制器（adaptive sliding-mode controller），用以取代傳統上人工手動調整參數的正比積分控制器（proportion-integration controller）。使用這種控制器，任何使用者都可以輕鬆得到高品質的原子力顯微鏡影像。 藉著調整光路對焦系統以及合適的控制器，我們可以得到不同的液體環境裡，準確探針的垂直振幅值。而使用光學讀取頭來量測懸臂的撓曲，更可以大大的減少整個原子力顯微鏡機台的體積以及量測的誤差。

The system proposed here is a tapping mode scanning sample type Atomic Force Microscope (AFM) equipped with a CD/DVD pick-up-head (PUH) used to measure the deflection of the cantilever beam of the probe in the liquid. In order to realize the system mentioned above, we design an adaptive Quality-Factor-controller (Q-controller) to modulate the interaction force between the tip and the sample. And, increasing the quality factor will increase the oscillation amplitude of the probe in liquid and overcome the problem with high damping ratio in the fluid which tends to make the probe hard to oscillate. It is noteworthy that the tip-sample force can be decreased if the scanning is through tapping mode whereby the sample surface will not be easily hurt due to such tip-sample contact. Hence, this type of AFM can also be used to scan soft samples, which may lead to acquire more realistic topography. To implement the above systems, we have designed a novel AFM mechanism and used an adaptive sliding-mode controller which replaces the traditional manually-tuned proportion-integration (PI) controller. By using this controller, any user can still acquire high quality AFM images easily. This AFM will be used to help to observe the continuous interaction between the biology sample and the probe tip. Through adjusting the light path system and applying the controller, we can correctly measure the displacement of the probe in vertical direction in different kinds of fluid. The use of DVD pickup head minimizes the volume of the hardware system, and thus reduces the measurement error caused by heat expansion. For testing the system capability and analyzing the biomorphic change of the sample in liquid, we have conducted a series of experiments, and the results can help us to understand more about the mechanism of the sample in liquid.