Abstract
This paper offers a concise survey of the most commonly used feedback loops for atomic force microscopes. In addition it proposes feedback control loops in order to minimize the effect of thermal noise on measurements of weak forces, and to improve the manipulability of the AFM. Growing requirements to study and fabricate systems of ever-shrinking size mean that ever-increasing performance of instruments like atomic force microscopes (AFM) is needed. A typical AFM consists of a micro-cantilever with a sharp tip, a sample positioning system, a detection system and a control system. Present day commercial AFMs use a standard PI controller to position the micro-cantilever tip at a desired distance from the sample. There is still a need for studies showing the optimal way to tune these controllers in order to achieve high closed-loop positioning performance. The choice of other controller structures, more suitable for dealing with the robustness/performance compromise can also be a solution.
Highlights
Description of atomic force microscopes (AFM)Atomic Force Microscopy (AFM) is an aspect of Scanning Force Microscopy, and is capable of measuring the interaction force between the sample and a sharp tip mounted on the end of a weak cantilever, see Fig. 1
This paper offers a concise survey of the most commonly used feedback loops for atomic force microscopes
Atomic Force Microscopy (AFM) is an aspect of Scanning Force Microscopy, and is capable of measuring the interaction force between the sample and a sharp tip mounted on the end of a weak cantilever, see Fig. 1
Summary
Atomic Force Microscopy (AFM) is an aspect of Scanning Force Microscopy, and is capable of measuring the interaction force between the sample and a sharp tip mounted on the end of a weak cantilever, see Fig. 1. In contact mode the cantilever is in full contact with the surface, and the interaction force (displacement of the lever) is determined by measuring the static deflection of the cantilever This technique is capable of detecting displacements on atomic scale resolution (0.1 –200 nm). The dynamic detection mode can be divided into techniques called the tapping mode and the non(pseudo)- contact mode [1] In these detection modes, the cantilever is driven, usually at its resonant frequency, with an amplitude typically less than 10 nm. Attractive long distance interaction forces affect the effective spring constant of the cantilever, and the cantilever shifts its resonance frequency This technique is used for measuring weak forces, such as the van der Waals force, and for scanning soft samples. The difference signal (A-B) is very sensitive to cantilever deflection
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