原子力顯微儀輕敲模式操作最佳化之理論、方法、條件與實證(下)

A New Approach of Optimizing the Operation for Atomic Force Microscope in Tapping Mode (Ⅱ)

林明彥(Ming Yen Lin) ； 洪紹剛(Shao Kang Hung) ； 阮基晏(Chi-Yen Juan) ； 劉瑋哲(Wei Che Liu) ； 蘇揚智(Yang Chih Su) ； 應雄(Sean Ying)

《科儀新知》 152期 (2006/06) Pp. 58-68

https://doi.org/10.29662/IT.200606.0007

摘要

原子力顯微儀所提供的「輕敲模式」，雖已被廣泛地應用於表面量測，但對於大多數非AFM專業的使用者而言，「輕敲模式」的操作與量測通常只是停留在試行錯誤的經驗法則，無法正確設定各掃描參數，達到正確取像之目的。本文根據探針尖與樣品表面原子間的作用，從探針之靈敏度及能量損耗之觀點，以數理解析之方式，詳盡說明探針尖振幅與set point 值最佳化之理論與方法。另外，導入掃描中表面形貌變化與系統回授等兩個動態因素，建立了一新的原子力顯微儀「輕敲模式」之理論解析模式，並發展出掃描取像最佳化之條件。於實際的原子力顯微儀機器之上，則做了「雜訊最小化」及「回授增益最佳化」之處理後，利用四台不同之機器，透過對四種不同樣品之實際掃圖，證明本文所提論述的正確性。對於廣泛的使用者而言，提供了一「輕敲模式」正確的操作理論、方法及條件，以達到取得最清晰影像之目的。在此實證中，意外觀察到造成艾茲海默症結晶蛋白表面上的超細微結構，對於解開艾茲海默症結晶蛋白行成的機制，相信將會有所貢獻。

並列摘要

Tapping mode, one of the imaging methods in the atomic force microscope, has been widely used in surface measurement for decades. However, most operators who do not know the nature of the AFM may probably acquire a wrong image by try-and-error or improper setup of the AFM. In this article, according to the tip-sample interaction, a theory and method of optimizing the oscillating amplitude of the probe tip and the set point of the feedback system, is analytically developed from the tip sensitivity and the tip energy dissipation. A new approach of the Tapping mode, including both dynamic factors of the surface topography variation and the system feedback in scanning, is developed for the optimum criterion for AFM operation. Furthermore, the developed theory, method and rule were proved by the images scanned from four different samples. And each sample was scanned by one of four different AFMs with the process of the noise minimization and feedback gain optimization. Therefore, a theory, method and rule of optimizing the operation for AFM in tapping mode are provided and allow users to acquire images in best quality. Finally, an image with fine structures on the surface of amyloid fibrils that cause the Alzheimer's disease was first observed coincidentally during the experiments. We believe that the discovery will definitely contribute to reveal the forming process of the deposition of protein fibrils.