Scanning Probe Microscopy – A Control Systems Perspective

January 31, 2014, Webb 1100

Srinivasa Salapaka

University of Illinois - Urbana-Champaign, Mechanical Engineering


This talk will focus on control systems theoretic analysis and synthesis of new modes of operations that significantly expand the range of performance specifications and capabilities of Atomic Force Microscopes. We will present a systems theory framework to study fundamental limitations on the performance of these devices. This viewpoint leads to a new generation of techniques that can potentially enable probing material at the sub-angstrom level at significantly higher bandwidths. In particular, we will characterize the inherent fundamental trade-offs between resolution, tracking-bandwidth, and reliability specifications on positioning capability of these devices. In addition to determining fundamental limitations, this framework leads to a better understanding of existing technology and in overcoming some technological hurdles that were previously thought to be fundamentally limiting. For instance, we will present the design of an alternate signal for sample profile estimation that proved false the widely held perception that sample profile estimation bandwidth was limited by the regulation bandwidth of the atomic force microscope (AFM). This talk will present recent research on robust high bandwidth nanopositioning, estimation of sample profiles, model based design ideas that achieve substantial improvements in imaging and detection bandwidths, and correcting for artifacts and misinterpretations in AFM imaging. This talk also presents a new dynamic mode of operation in an Atomic Force Microscope (AFM) where the deflection signal is used for force regulation instead of its derivatives such as the amplitude and phase. This mode is especially useful in the light of new advances that have resulted in high speed positioning systems with bandwidths of the order of one-tenth to a half of the natural frequency of the scanning probe. Also, we present a method to estimate the tip-sample interaction force and extract the sample topography information from this estimate. The overall scheme facilitates high speed imaging that can potentially exploit fast scanning devices without compromising on the bandwidth and resolution. The outcomes of this research will be corroborated with experimental results.

Speaker's Bio

Srinivasa M. Salapaka received the B.Tech. degree in Mechanical Engineering from Indian Institute of Technology in 1995, the M.S. and the Ph.D. degrees in Mechanical Engineering from the University of California at Santa Barbara, U.S.A in 1997 and 2002, respectively. During 2002-2004, he was a postdoctoral associate in the Laboratory for Information and Decision Systems, Massachusetts Institute of Technology, Cambridge, USA. Since January 2004, he has been a Faculty Member in Mechanical science and Engineering at the University of Illinois, Urbana-Champaign. He got the NSF CAREER award in the year 2005. His areas of current research interest include controls for nanotechnology, combinatorial optimization, Brownian ratchets, and numerical/dynamic-systems analysis of root solving algorithms.