Research

Our research interests include microelectromechanical systems (MEMS), nanomechanics and device applications of nanostructures. Below is a list of some of the active projects in the group.

1. MEMS-based Instrumentation for Nanomechanical Testing
MEMS have potential to impact the nanomechanical characterization through controlled actuation, high-resolution force/displacement measurements, integrated multi-functions and tiny size for in-situ electron microscopy testing. We pioneered in developing a MEMS-based testing stage that enabled in-situ SEM/TEM tensile testing of one-dimensional (1D) nanostructures. Recently my group has conducted a systematic investigation on the temperature distribution in MEMS thermal actuators using a combined experiment/modeling approach (e.g., using micro‐Raman and multiphysics FEA). In addition, we have developed a novel MEMS thermal actuator, which possess self-sensing capability based on piezoresistivity.

Representative publications:
Q. Qin and Y. Zhu, “Temperature Control in Thermal Microactuators with Applications to in-situ Nanomechanical Testing”, Applied Physics Letters 102, 013101 (2013).
J. Ouyang and Y. Zhu, “Z-Shaped MEMS Thermal Actuators: Piezoresistive Self-Sensing and Preliminary Results for Feedback Control,” Journal of Microelectromechanical Systems 21, 596-604 (2012).

2. Mechanical Behavior of Crystalline Nanostructures
In the last several years exciting progress has been made in exploring the extrinsic length scale (e.g., sample dimensions) in addition to the intrinsic length scale (e.g., grain size). Chemically synthesized crystalline NWs (in addition to the micro/nano-pillars) represent an excellent model system to probe size effects and deformation mechanisms at the nanoscale. Recent advance in NW synthesis, atomistic simulations and nanomechanical testing offers exciting opportunities for us, as a community, to investigate mechanical behavior of NWs. Our group has quite extensive experience with in-situ SEM/TEM mechanical testing of NWs. For example, we found when the diameter decreases, the elastic modulus of Si NWs decreases and the fracture strength increases reaching >12 GPa; Si NWs fracture in a brittle fashion at room temperature. We also found that yield strain of Ag NWs scales reasonably well with the surface area, which suggests that yielding of Ag NWs is due to dislocation nucleation from surface sources.

Representative publications:
Q. Qin, F. Xu, Y. Cao, P.I. Ro and Y. Zhu, “Measuring True Young’s Modulus of a Cantilevered Nanowire: Effect of Clamping on Resonance Frequency”, Small 8 (16), 2571-2576 (2012).
Y. Zhu, Q. Qin, F. Xu, F. Fan, Y. Ding, T. Zhang, B.J. Wiley and Z.L. Wang, “Size effects on elasticity, yielding and fracture of silver nanowires: in situ experiments,” Physical Review B 85, 045443 (2012).

3. Nanostructure-Enabled Wearable Devices for Healthcare
Stretchable electronics enables unconventional applications such as implantable biosensors, wearable electronics and flexible RFID. My group has explored a new route in the field of stretchable electronics, which is enabled by 1D nanostructures instead of the nano-ribbons that have been successfully demonstrated by other researchers. The key premise of using 1D nanostructures is based on two of our recent findings: 1) 3D coils exhibit superior stretchability; and 2) an interface-mediated buckling strategy, instead of the prestrain-then-buckling strategy, could lead to scalable manufacturing of 1D nanomaterials for stretchable electronics. Our group is part of the recently funded NSF-nanoERC at NC State to create body-powered, wearable health monitoring systems.

Representative publications:
F. Xu and Y. Zhu, “Highly Conductive and Stretchable Silver Nanowire Conductors,” Advanced Materials 24 (37), 5117-5122 (2012).
F. Xu, W. Lu and Y. Zhu, “Controlled 3D buckling of silicon nanowires for stretchable electronics,” ACS Nano 5, 672-678 (2011).