Modeling and control of undesirable dynamics in atomic force microscopes

The phenomenal resolution and versatility of the atomic force microscope (AFM), has made it a widely-used instrument in nanotechnology. In this thesis, a detailed model of AFM dynamics has been developed. It includes a new model for the piezoelectric scanner coupled longitudinal and lateral dynamics, creep, and hysteresis. Models for probe-sample interactions and cantilever dynamics were also included. The models were used to improve the dynamic response and hence image quality of contact-mode AFM. An extensive parametric study has been performed to experimentally analyze in-contact dynamics. Nonlinear variations in the frequency response were observed, in addition to changes in the pole-zero structure. The choice of scan parameters was found to have a major impact on image quality and feedback performance. Further, compensation for scanner creep was experimentally tested yielding a reduction in creep by a factor of 3 to 4 from the uncompensated system. Moreover, fundamental performance limitations in the AFM feedback system were identified. These limitations resulted in a severe bound on the maximum achievable feedback bandwidth, as well as a fundamental trade-off between step response overshoot and response time. A careful analysis has revealed that a PID controller has no real advantage over an integral controller.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• El Rifai, Osamah M

Advisor dc:contributor.advisor

• Kamal Youcef-Toumi.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/38256

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/38256