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O: Fachverband Oberflächenphysik

O 101: Scanning Probe Techniques: AFM

O 101.4: Vortrag

Freitag, 20. März 2015, 11:15–11:30, MA 144

A sophisticated Feedback Control algorithm for High-Speed AFM — •Anne-D. Mueller and Falk Mueller — Anfatec Instruments AG, Melanchthonstr. 28, 08606 Oelsnitz.

The need to track surface features in Scanning Probe Applications (SPM) while increasing the scan speed leads to the complication, that the feedback parameters (e.g. Ki and Kp) entered by the user become more difficult to determine. As a result, the surface is not tracked with optimum performance.

This contribution utilizes a control theory approach to determine the microscope's closed loop transfer function in Z. An algorithm to automatically determine the optimum parameter set is presented that considers a scan speed driven bandwidth. As a result, Ki and Kp become system specific, while the strength of the tracking representing the sample roughness is left as the only free user entry. This completely new approach not only simplifies the control of an AFM; it automatically leads to an optimum noise level. Surprisingly, the feature tracking bandwidth can be tuned higher than the system's bandwidth.

With the help of a simulation circuit for contact and dynamic mode AFM operation, the frequency dependence of the feature tracking on the entry parameters is simulated and studied. Finally, the method is applied to real feedback systems demonstrating unexpected performance.