Session: MNS-01-02: Dynamics of MEMS/NEMS 2nd Session

Paper Number: 97842

97842 - Mode Coupling and Operating Regimes in Bimodal Atomic Force Microscopy 

In bimodal atomic force microscopy (AFM) multiple eigenmodes of the microcantilever are simultaneously excited and monitored.  This increases the number of experimental observables compared to the more commonly utilized single frequency tapping mode AFM, enabling the extraction of additional information about the surface.  However, bimodal AFM leads to complex nonlinear interactions between the two excited eigenmodes.  This complicates the extraction of sample properties from experimental observables and in practice limits the types of samples and operating conditions under which bimodal AFM can be used.  In this work, we explore these nonlinear coupling behaviors with both experiments and simulations to gain a deeper insight into the underlying nonlinear dynamics.   Experimentally, we observe that by increasing the second eigenmode amplitude both the location of the first eigenmode amplitude where the system transitions from the attractive to repulsive regime and the phase in the repulsive regime increases. Simulations that numerically solve the partial differential equations describing the motion of the AFM cantilever reproduce both observations when utilizing tip-sample contact mechanics models that include both viscoelastic and adhesive forces.  We hypothesize that both behaviors are explained by the increased second eigenmode amplitude causing more indentation into the sample leading to larger repulsive and viscoelastic forces on the tip.

Presenting Author: Ryan Wagner Purdue

Presenting Author Biography: Ryan Wagner is a Research Assistant Professor in the School of Mechanical engineering at Purdue University. He received his B.S. and Ph.D. both in Mechanical Engineering from Purdue in 2008 and 2014 respectively. His graduate research topic was the application of AFM to study the mechanics of cellulose-based nanomaterials. Ryan was awarded a National Research Council postdoctoral fellowship at the National Institute of Standards and Technology where he worked on AFM metrology and cavity optomechanics. After this postdoc, Ryan was employed as a Research and Development Scientist at Asylum Research, an AFM instrument manufacturing company. Ryan’s research interests include metrology, microscopy, interferometry, spectrometry, vibrations, and dynamics.

Authors:

Ryan Wagner Purdue
Uidam Jung Purdue University
Anil Bajaj Purdue University
Arvind Raman Purdue University