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MNMDL is interested in various multiphysical dynamics problems at micro/nanoscales, broadly divided into three main areas:(i) Exploiting nonlinear characteristics in micro/nano-electro-mechanical systems (MEMS/NEMS); (ii) Advancing the state-of-art Atomic Force Microscopy (AFM) techniques to achieve better material characterizations beyond topography; and (iii) Applying the capabilities of advanced AFM and microsystems for various material science researches.

Developing Nonlinear MEMS/NEMS

During the last decades, we have witnessed that MEMS/NEMS revolutionized fundamental and applied science. However, due to small size and low damping, these devices often exhibit significant nonlinearity and thus the operational range of these impressive applications shrinks. Therefore, understanding the mechanisms leading to nonlinearity in such systems will eliminate obstacles to their further development and significantly enhance their performance. Motivated by the need to advance current capabilities of MEMS/NEMS, our research has been focused on the implementation of intentional intrinsic nonlinearity in the design of MEMS/NEMS and proved that harnessing intentional strong nonlinearity enables exploiting various nonlinear phenomena, not attainable in linear settings, such as broadband resonances,dynamic instabilities, nonlinear hysteresis, and passive targeted energy transfers. 

            With the financial support from DARPA, we developed a comprehensive analytical, numerical, and experimental methodology to consider structural nonlinearity as a main design factor enabling to tailor mechanical resonances and achieve targeted performance. We investigated the mechanism of geometric nonlinearity in a non-prismatic microresonator and suggested strategies to tailor the nonlinear hardening resonance. We also utilized the parametric nonlinearity originating from the base excitation to make a broadband resonance. 

  • Asadi, K.; Li, J.;Peshin, S.; Yeom, J.; Cho, H.(2017). Mechanism of Geometric Nonlinearity in a Nonprismatic and Heterogeneous Microbeam Resonator. Physical Review B, 96(11), doi:10.1103/PhysRevB.96.115306
  • Asadi, K.;Peshin, S.; Yeom, J.; Cho, H. (2016).Experimental and Theoretical Studies of Nonlinear Resonances in a Si Microcantilever Constrained by a Polymer Attachment. ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference (IDETC/CIE).Paper presented at: Charlotte, NC, United States.
  • Potekin, R.;Kim, S.; McFarland, D.M.; Bergman, L.A.; Cho, H.; Vakakis, A.F. (2018). A Micromechanical Mass Sensing Method Based on Amplitude Tracking Within an Ultra-Wide Broadband Resonance. Nonlinear Dynamics, 92(2), 287-304. doi:10.1007/s11071-018-4055-y
  • Potekin, R.; Asadi, K.;Kim, S.; Bergman, L.A. et al. (2018). Ultra-broadband Microresonators with Geometrically Nonlinear Stiffness and Dissipation. Manuscript Submitted to Physical Review Applied, Jan 2019. Revision & Rebuttal Submitted, May 2019.
  • Asadi, K.;Babayemi, E.;Li, J.;Peshin, S. et al. Tailoring Geometric Nonlinearity in a Silicon Double Microcantilever System with Polymer Coupling. Manuscript to be Submitted to Nonlinear Dynamics, June 2019.

            Our more recent works focus on exploitingnonlinearityand multimodalitysimultaneouslyby internally coupling two or more modes through the mechanism of internal resonance or combination resonance. We experimentally realized the strong 1:2 internal resonance in a non-prismatic microbeam resonator by enforcing the 1:2 relationship between the second and third flexural mode frequencies. Through the analytical model based on the energy method, we demonstrated that the intermodal coupling between the second and third flexural modes in an asymmetric structure provides an optimal condition to easily implement the strong internal resonance with a high energy transfer to the internally resonated mode.

            We also experimentally demonstrated that the mechanism of strong 1:2 internal resonance can stabilize the frequency fluctuations of MEMS oscillators with high robustness over a wide range of operation (see Figure 1). We presented the results at IEEE Inertial 2019 and won the Best Student Paper Award. We also experimentally and theoretically studied the combination resonance and demonstrated the nonlinear energy transfer during combination resonance can pump energies into three resonant modes to expand the resonance bandwidth. The details of these works will be published in journals in a very near future:

  • Asadi, K.; Yu, J.;Cho, H. (2018). Nonlinear Couplings and Energy Transfers in Micro- and Nano-Mechanical Resonators: Intermodal Coupling, Internal Resonance and Synchronization. Philosophical Transactions of The Royal Society A-Mathematical Physical and Engineering Sciences, 376(2127), doi:10.1098/rsta.2017.0141
  • Asadi, K.;Peshin, S.; Li, J.; Yeom, J.; Cho, H.Realization and Optimization of Internal Resonance in a Nonlinear Micromechanical Resonator. Submitted to Nature Microsystems & Nanoengineering, May 2019.
  • Asadi, K.;Peshin, S.; Li, J.; Yeom, J. et al. Sustenance of Energy in Three Resonant Modes via Combination Resonance. Manuscript to be submitted to Physical Review Letters, June 2019.  
  • Yu, J.;Asadi, K.; Brahmi, H.; Cho, H. Frequency Stabilization in a MEMS Oscillator via Tunable Internal Resonance. Manuscript to be submitted to Nature Communications, June 2019.  

Advancing Atomic Force Microscopy

Since the development in the early 1980s, atomic force microscopy (AFM) has been one of the most useful tools in the field of nano- and bio-science. AFM is capable of imaging and characterizing various materials with nanometer-scale spatial resolution under any environmental conditions including in air and liquid. Our group is interested in applying our understanding of cantilever dynamics to advance the state of art AFM by (i) interpreting the signal generated by a cantilever’s motion; (ii) designing a new cantilever system to obtain more information about material properties; and (iii) developing new (or advanced) techniques to measure multiphysical properties such as piezoelectricity and IR absorptivity.

With the financial support from NSF, we invented a new AFM probe, the so-called inner-paddled cantilever, which enables two independent transduction channels to extend AFM’s capability of material characterization beyond topographic imaging. The current state of the art AFM probe is a single-body system, in the shape of a rectangular or triangular beam, which is not ideal for carrying more than one type of information. In contrast, the new AFM probe is reshaped to have a two-field microcantilever design with a considerable dimensional discrepancy in the component part of base cantilever and inner paddle. By doing so, this mechanical transducer provides two discrete transduction channels such that they respond independently to the variations in surface topography and material properties/functionality. 

When the contact resonance mode of AFM is used for simultaneous characterization of topological and functional properties of a material (e.g., piezoresponse force microscopy), the conventional unitary probe system has continuously suffered from the crosstalk between the observables, causing undesirable artifacts and complicated interpretations (see the upper row in Figure below). The inner-paddled cantilever addresses this issue by integrating two discrete pathways such that they respond independently to the variations in surface topography and material functionality (see the lower row in Figure below). Hence, this new design allows reliable and potentially quantitative determination of functional properties. The details of this work are published in:

  • Dharmasena, S.;Yang, Z.; Kim, S.; Bergman, L.A.; Vakakis, A.F.; Cho, H.(2018). Ultimate Decoupling Between Surface Topography and Material Functionality in Atomic Force Microscopy Using an Inner-Paddled Cantilever. ACS Nano, 12(6), 5559-5569. doi:10.1021/acsnano.8b01319
  • Dharmasena S.; Potekin R; Bergman LA; Vakakis AF; Cho H. (2019). Inner-Paddled Microcantilever for Multi-Modal and Nonlinear Atomic Force Microscopy. (Altenbach, H.; Irschik, H.; Matveenko, V.) (Eds.), Advanced Structured Materials Series. Location: Springer publisher. 
  • Dharmasena, S.;Cho, H.(2018). Dynamics of an Inner-Paddled Cantilever in Contact Resonance-Atomic Force Microscopy. Manuscript submitted to Physics Review Applied, Jan 2019. Revision & Rebuttal Submitted, April 2019.
  • [Patent] Cantilever for atomic force microscopy. 2018-02-14 (Published). Ohio State University. Application number: 15/896,199, Publication number: US-2018-0231581-A1

When the tapping mode AFM is applied, a considerable dimensional discrepancy in this two-field microcantilever design achieves a nonlinear 1:n internal resonance by simply tailoring the length of the inner paddle. When the 1:n internal resonance is triggered by nonlinear tip-sample interaction forces during tapping mode, low- to high-frequency energy transfer amplifies the higher harmonic in a passive way. In our theoretical and experimental study, this higher harmonic signal turns out to be sensitive to variations of mechanical properties of a sample. The theoretical and experimental demonstration of the inner-paddled cantilever for multi-frequency AFM is found in the publications of:

  • Potekin, R.; Dharmasena, S.;Keum, H.; Jiang, X.; Lee, J.; Kim, S.; Bergman, L.A.; Vakakis, A.F.; Cho, H.*(2018). Multi-Frequency Atomic Force Microscopy Based on Enhanced Internal Resonance of an Inner-Paddled Cantilever. Sensors and Actuators, A: Physical, 273, 206-220. doi:10.1016/j.sna.2018.01.063
  • Potekin, R.; Dharmasena, S.;McFarland, D.M.; Bergman, L.A.; Vakakis, A.F.; Cho, H.(2017). Cantilever Dynamics in Higher-Harmonic Atomic Force Microscopy for Enhanced Material Characterization. International Journal of Solids and Structures, 110-111, 332-339. doi:10.1016/j.ijsolstr.2016.11.013
  • Jeong, B.; Pettit, C.;Dharmasena, S.;Keum, H.; Lee, J.; Kim, J.; Kim, S.; McFarland, M.D.; Bergman L.A.; Vakakis, A.F.; Cho, H.*(2016). Utilizing Intentional Internal Resonance to Achieve Multi-Harmonic Atomic Force Microscopy. Nanotechnology, 27(12), doi:10.1088/0957-4484/27/12/125501
  • Pettit, C.;Jeong, B.; Keum, H.; Lee, J.; Kim, J.; Kim, S. et al. (2015). Microcantilever System Incorporating Internal Resonance for Multi-Harmonic Atomic Force Microscopy. 28th IEEE International Conference on Micro Electro Mechanical Systems (MEMS).Paper presented at: Estoril, Portugal.

We are currently developing a batch fabrication process to commercialize this AFM probe design, which is supported by NSF-PFI through the Industrial Innovation and Partnerships (IIP) office.


Material Research Using Advanced AFM

Our advanced capabilities of material characterization using AFM are actively applied to various areas in material research through collaborations. Our research team is building expertise in these new research areas of energy, bio, and environment, of which efforts have been supported by OSU Materials Research Seed Grant. By leveraging the internal seed grant, our team was recently granted an external fund from LG Chem to support a battery project. I am enthusiastic to continue this research endeavors to expand my research expertise to make a real societal impact on the following areas. 

1) Energy area: In-situ measurement of battery electrodes in collaboration with Jung Hyun Kim. (Supported by OSU Material Research Seed Grant & LG Chem.)

  • O'Meara, C.; Polozhentceva, I.A.; Karushev, M.P.; Dharmasena, S.; Cho, H.; Yurkovich, B.J.; Kogan, S., Kim, J.-H.* (2019). Nickel-Salen Type Polymer as Conducting Agent and Binder for Carbon-Free Cathodes in Lithium-Ion Batteries. ACS Applied Materials & Interfaces, 11(1), 525–533. doi:10.1021/acsami.8b13742
  • Lee, M., Reddi, R., Choi, J., Liu, J., Huang, X. Cho, H., Kim, J.H., Huang, X. (2020). In-Operando Characterization of Si Anode Binders in Liquid Electrolyte, ACS Applied Energy Materials.


2) Bio area: Investigate the role of collagen piezoelectricity as a stiffness modulator of bone. In collaboration with Prof. Soheil Soghrati and Prof. Do-Gyoon Kim at the College of Dentistry. (Supported by OSU Material Research Seed Grant)

  • Kwon, J.; Kim, D.; Cho, H. Piezoelectric Heterogeneity in Collagen Type I Fibrils Quantitatively Characterized by Piezoresponse Force Microscopy. (submitted)

3) Environment area: Characterize the interaction between cyanobacteria and cyanophage. In collaboration with Prof. Jiyoung Lee at the College of Environmental Health Science.

  • Potekin, R.; Dharmasena, S.;Keum, H.; Jiang, X.; Lee, J.; Kim, S.; Bergman, L.A.; Vakakis, A.F.; Cho, H.*(2018). Multi-Frequency Atomic Force Microscopy Based on Enhanced Internal Resonance of an Inner-Paddled Cantilever. Sensors and Actuators, A: Physical, 273, 206-220. doi:10.1016/j.sna.2018.01.063
  • Jiang, X.; Ha, C.;Lee, S.; Kwon, J.;Cho, H.; Gorham, T.; Lee, J. Discovery of lytic cyanophages in Lake Erie: Interaction mechanisms and structure damage of toxic cyanobacteria. Submitted to Environmental Science & Technology Letters, May 2019.


We greatly acknowlege the following agencies for funding our research.