Dr. Ryan C. Tung received the B.S. degree in mechanical engineering from the University of Nevada, Reno, NV, USA, in 2006, and the M.S. and Ph.D. degree in mechanical engineering from Purdue University, West Lafayette, IN, USA, in 2008 and 2012, respectively. He completed a National Research Council Postdoctoral Fellowship at the National Institute of Standards and Technology, Boulder, CO, USA in 2014. He is currently an assistant professor in mechanical engineering at the University of Nevada, Reno. His current research interests include the dynamics of contact resonance atomic force microscopy, fluid-structure interactions in microsystems, and novel metrology techniques.
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Viscoelastic property measurements made at the solid− liquid interface are key to characterizing materials for a variety of biological and industrial applications. Further, nanostructured materials require nanoscale measurements. Here, material loss tangents (tan δ) were extracted from confounding liquid effects in nanoscale contact resonance force microscopy (CR-FM), an atomic force microscope based technique for observing mechanical properties of surfaces.
Abstract Contact resonance atomic force microscopy (CR-AFM) methods currently utilize the eigenvalues, or resonant frequencies, of an AFM cantilever in contact with a surface to quantify local mechanical properties. However, the cantilever eigenmodes, or vibrational shapes, also depend strongly on tip–sample contact stiffness. In this paper, we evaluate the potential of eigenmode measurements for improved accuracy and sensitivity of CR-AFM.
We present a method to correct for surface-coupled inertial and viscous fluid loading forces in contact resonance (CR) atomic force microscopy (AFM) experiments performed in liquid. Based on analytical hydrodynamic theory, the method relies on experimental measurements of the AFM cantilever's free resonance peaks near the sample surface. The free resonance frequencies and quality factors in both air and liquid allow reconstruction of a continuous hydrodynamic function that can be used to adjust the CR data in liquid.
Electrostatically operated RF-MEMS switches are known to suffer from discrete switch bounce events during switch closure that increase wear and tear and lead to increased switching times. Here, we use laser Doppler vibrometer to analyze the switch response of three types of cantilevered dc-contact switches at a 200 ns time resolution. We find that bounce events are multiple time scale events with distinct motion occurring at 10-1 and 10 1 s timescales in effect high frequency bounces within a bounce.
We present a method to improve accuracy in measurements of nanoscale viscoelastic material properties with contact resonance atomic force microscope methods. Through the use of the two-dimensional hydrodynamic function, we obtain a more precise estimate of the fluid damping experienced by the cantilever-sample system in contact resonance experiments, leading to more accurate values for the tip-sample damping and related material properties.
Structural parameters of doubly clamped microfabricated beams such as initial curvature, boundary compliance, thickness and mean residual stress are often critical to the performance of microelectromechanical systems (MEMS) and need to be estimated as a part of quality control of the microfabrication process. However, these parameters couple and influence many metrics of device response and thus are very difficult to disentangle and estimate using conventional methods such as the M-test, static mechanical tests, pull-in ...
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April 27, 2017
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