Iowa State University Research Foundation Inc

Murti V Salapaka

Deepak Ranjan Sahoo

Abu Sebastian

Tathagata De

Pranav Agarwal

An observer based Q control method for a cantilever in an atomic force microscopy is provided that provides for a 'dual' Q behavior such that a particular effective Q is achieved when a sample is present and another effective Q when a sample is absent. In the control method, the transfer function from dither input to photo-diode output is independent of the observer so that the cantilever effectively behaves like a spring-mass-damper system. The effective quality factor and stiffness of the cantilever can be changed by appropriately choosing the state feedback gain. The method provides sample-imaging using transient atomic force microscopy.

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An approach to determine cantilever movement is presented. An observer based state estimation and statistical signal detection and estimation techniques are applied to Atomic Force Microscopes. A first mode approximation model of the cantilever is considered and an observer is designed to estimate the dynamic states. The cantilever-sample interaction is modeled as an impulsive force applied to the cantilever in order to detect the presence of sample. A generalized likelihood ratio test is performed to obtain the decision rule and the maximum likelihood estimation of the unknown arrival time of the sample profile and unknown magnitude of it. The use of the transient data results in sample detection at least ten times faster than using the steady state characteristics.

Method to transiently detect sample features using cantilevers

An approach to detect when a cantilever loses interaction with a sample, thereby detecting when a portion of an image obtained using a cantilever is spurious is presented. An observer based estimation of cantilever deflection is compared to the cantilever deflection and the resulting innovation is used to detect when the cantilever loses interaction. The loss of interaction is determined when the innovation is outside of and/or below a threshold level.

Real time detection of loss of cantilever sensing loss

An approach to determine cantilever movement is presented. An observer based state estimation and statistical signal detection and estimation techniques are applied to Atomic Force Microscopes. A first mode approximation model of the cantilever is considered and a Kalman filter is designed to estimate the dynamic states. The tip-sample interaction is modeled as an impulsive force applied to the cantilever in order to detect the presence of sample. A generalized likelihood ratio test is performed to obtain the decision rule and the maximum likelihood estimation of the unknown arrival time of the sample profile and unknown magnitude of it. The use of the transient data results in sample detection at least ten times faster than using the steady state characteristics.

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Ames, IA, United States of America

Murti V Salapaka