應用可旋轉式探針和可變式掃描速度之新式原子力顯微鏡掃描方法

Abstract

原子力顯微鏡是一用來探究奈米世界的強力工具，於1985年由一德國物理學家所發明後，各項相關的應用便不停地被開發以及改良。與其他奈米量測儀器相比，原子力顯微鏡最特別之處在於使用物理探針作為媒介，和外界樣本進行交互作用，藉由觀測探針行為之改變，使用者得以推論出樣本之高低、粗糙度、受力以及表面機械性質等等。其泛用性，比如可以運用在不導電之樣本上，或是可在真空及液體等諸多環境中使用，更是重要優點。 然而，其缺陷亦存在。首先，由於探針本身佔有空間，它有可能對掃描本身造成阻礙進而產生失真的結果。最經典的例子之一，為掃描垂直側壁所面臨的困難。另外，一般掃描軌跡的決定和樣本本身形貌完全無關，比如常見的柵狀軌跡，是一個預先決定好掃描速度的來回式軌跡。這使得掃描中的取樣點在樣本上的分布極度不均，特別是在傾斜程度大的部分，其稀疏程度尤其嚴重。 在本篇研究中，為了同時解決這兩項問題，一套全新的原子力顯微鏡系統被設計和建立，包括嶄新的硬體和相應的掃描方式。在掃描中可旋轉的探針，可以隨時以不失真的角度掃描各種形貌。另一方面，各處的掃描速度則是適應性的調整，以較為緩慢的速度掃描傾斜程度大的部分。最後，為了解決旋轉所造成探針的偏移，一項補償方法亦被提出和運用。

Since its invention in 1986, the Atomic Force Microscope (AFM) has remained one of the most prominent tools for examining the microscopic world. Using a long cantilever with a sharp extruding tip as the medium, the AFM is capable of measuring many mechanically related properties: topography, elastic modulus, roughness, exerting force, to name a few. Recently, new techniques such as atomic manipulation and subsurface imaging are also being developed. When compared amongst other microscopes, the AFM excels in terms of its versatility, since it can scan samples of nearly every kind of material, and can operate in air, liquid or even vacuum. However, the AFM has several disadvantages. The physical tip occupies space, hence may sometimes obstruct the scanning process, creating distorted result. A classic example is the inability to image perfectly vertical sidewalls. Additionally, during most AFM scans, the tip follows a predetermined trajectory on the XY plane without taking the sample topography into consideration. This makes it so that the sampled data are distributed scarcely along surfaces with extreme local slopes. This work aims to develop a novel AFM system and a corresponding scanning method to deal with two problems mentioned above simultaneously. To alleviate the distortion, the tip is allowed to rotate. On the other hand, the scanning speed along the fast-axis in a raster scan would change, so that the data would distribute much denser along steep parts of the sample surface. Finally, to compensate for the shifts of the probe tip caused by the rotation, a thorough compensation method based on fusing the information of two images is also developed.