U-038

On Factors Affecting the Performance of Atomic Force Microscopes in Contact-Mode

Authors: Osamah M. El Rifai and Kamal Youcef-Toumi
Affiliation: Massachusetts Institute of Technology

Abstract
The importance of the atomic force microscope (AFM), in nano-technology, demands understanding of factors affecting AFM performance and image quality. Through a simulation study, the impact of scanning parameters on AFM images acquired in contact-mode has been investigated. The performance and limitations of commercial AFM controllers was also discussed. Based on the generated images, it is seen that high speed scans may require a large force set-point to maintain probe-sample contact at the expense of higher surface deformation, contact area, and friction force. Hence, reducing resolution and increasing image distortion. The sensitivity of AFM images to scan and controller parameters, invites the development of a systematic procedure for parameter selection for a given sample and operating environment. This would greatly reduce the current guess work in parameter selection and improve image repeatability. Currently, commercial control systems do limit the capabilities of the AFM in terms of speed and data repeatability. A good controller should be able to compensate for the large uncertainty due to different cantilevers and samples that may be used, nonlinearities, and system resonances. In addition, it should provide a tight tolerance on sample surface tracking both during transient and at steady state operation. This would enable robust high-speed operation and allow small or negative force set-point to be used.

Professor Youcef-Toumi
Massachusetts Institute of Technology
77 Mass. Ave., Rm. 3-352
Cambridge, MA 02139, USA
Phone:(617) 253-2216
Fax: (617) 258-6771
youcef@mit.edu