The subresonant tapping (SRT) scanning mode in atomic force microscopy (AFM) is a powerful technique for mapping surface properties simultaneously with topography. It is used for studying samples as diverse as optical thin films, silicon structures in electronics, biological materials, and even living cells. However, SRT mode does not see widespread clinical or commercial use because in many cases images can take hours to complete. This work takes a novel approach to control algorithm design which significantly reduces scan time.
In this thesis, I propose three new knowledge contributions to the areas of control systems theory and atomic force microscopy. First and primarily, I propose a contribution to atomic force microscopy by testing and fully vetting dual-stage SRT mode with windowed control called switched dual-actuation (SDA) mode. This is a new scheme that has 10 times improvement in scan speed without compromising quality of data. The design approach synthesizes classical loop-shaping methods with timed switching logic and exploitation of unique algorithmic features of SRT mode.
In support of this primary research goal, I also propose the codified expansion of the manual linear system identification and model synthesis method using complex second order transfer function structures. This is a method intended to improve intuition and ease of use in identifying high-order linear models from non-parametric data. Lastly, I detail the design, fabrication, characterization, and utility of a simple z-stage using a piezoelectric coin as the actuator. This stage shows high performance without the use of exotic materials, and is well-suited for use in SDA mode.
|Advisor:||Sokolov, Igor, Messner, Bill|
|Commitee:||Cronin-Golomb, Mark, Andersson, Sean B., Rife, Jason|
|School Location:||United States -- Massachusetts|
|Source:||DAI-B 81/12(E), Dissertation Abstracts International|
|Subjects:||Mechanical engineering, Nanoscience, Engineering|
|Keywords:||Atomic force microscopy, Control system engineering, Dual actuation, Nanopositioning, Scanning probe microscopy, System identification|
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