Figure 1 (Top) SEM image of a MEMS-based material testing system (Bottom) TEM images and diffraction patterns obtained during in-situ testing of a zinc oxide nanowire.

We have developed a unique MEMS-based nanoscale-Material Testing System (n-MTS), which is interfaced with scanning and transmission electron microscopes (SEM/TEM) for in-situ (electro) mechanical characterization in uniaxial loading. The displacement-controlled loading is applied using the thermal actuator and load is measured from the displacement of the load sensor shuttle based on a differential capacitive sensing scheme. As the actuator and the sensor are both controlled electronically, high resolution imaging of the specimen can be performed during the tension/compression testing. For instance, nanodiffraction patterns can be obtained at different stages of loading to obtain direct atomic level strain. Likewise, mechanically induced defects such as dislocation and fracture are imaged in real time. This testing set-up has been employed to study the mechanical and electromechanical response of semiconducting nanowires and carbon nanotubes.

We have employed this set-up (i) to experimentally prove the theoretical strength of carbon nanotubes as predicted by quantum mechanics simulations; (ii) to characterize elasticity size effects in semiconducting zinc oxide (ZnO) nanowires and (iii) to investigate the failure modes in ZnO NWs.

Figure 2 (Top) TEM image revealing defects on the surface of a ZnO nanowire. (Bottom) Post-mortem HRTEM image of fracture plane.

Complementing the MEMS testing platforms, we have developed extensive expertise in precision-manipulation of individual 1-D nanostructures. Nanomanipulation is a critical component of nanoscale testing because in order to test the properties of individual nanostructures they must be carefully manipulated and placed on the testing platforms. We use a piezoelectric nanomanipulator with nanometer resolution inside a SEM or dual beam FIB/SEM to carefully position nanostructures. Combining controlled electron beam induced deposition of carbon or platinum, focused ion or electron beam cutting and know-how accumulated over years of experimentation, we are able to place nanowires, nanotubes and nanotube bundles in many configurations suitable for testing.

Our current efforts include investigating nanowires made of other materials like gallium nitride (GaN), silver and gold. We investigate size effects in mechanical properties such as the Young’s Modulus and electrical and electromechanical properties such as conductivity and piezoelectricity. Recently, we have performed in-situ TEM tests on GaN nanowires revealing their mechanical properties. These results were coupled with simulations to give an unambiguous picture of the mechanical properties of these nanowires.

Projects 

• Effect of axis orientation and doping on GaN NWs
• Piezoelectric properties of semiconducting nanowires (GaN, ZnO)
• Mechanical properties of metallic nanowires (Ag, Au)

Personnel 

• H.D. Espinosa (PI)
• T. Filleter (Postdoc)
• M. Minary (Postdoc)
• R. Bernal (Graduate Student)

Publications 

• R.A. Bernal, R. Agrawal, B. Peng, K.A. Bertness, N.A. Sanford, A.V. Davydov and H.D. Espinosa "Effect of Growth Orientation and Diameter on the Elasticity of GaN Nanowires. A Combined in Situ TEM and Atomistic Modeling Investigation" Nano Letters, Vol. 11, No. 2, p. 548–555, 2011.

• M.A. Haque, H.D. Espinosa, and H.J. Lee "MEMS for In Situ Testing—Handling, Actuation, Loading, and Displacement Measurements" MRS Bulletin, Vol. 35, No. 5, p. 375-381, 2010.

• R. Agrawal, B. Peng and H.D. Espinosa, "Experimental-Computational Investigation of ZnO Nanowires Strength and Fracture" Nano Letters, Vol. 9, No. 12, p 4177-4183, 2009.

• R. Agrawal and H.D. Espinosa, "Multiscale Experiments; State of the Art and Remaining Challenges" Journal of Engineering Materials and Technology, Vol. 131, No. 4, Art. No. 041208, 2009.

• B. Peng, M. Locascio, P. Zapol, S. Li, S. Mielke, G. Schatz, H.D. Espinosa, "Measurements of near-ultimate strength for multiwalled carbon nanotubes and irradiation-induced crosslinking improvements," Nature Nanotechnology, Vol. 3, No. 10, p. 626-631, 2008.
• Commentary by Eric Stach, "Nanotubes reveal their true strength," Nature Nanotechnology, Vol. 3, No. 10, p. 586-587, 2008.

• Y. Zhu, C-H. Ke and H.D. Espinosa. "Experimental Techniques for the Mechanical Characterization of Thin Films and One-Dimensional Nanostructures" Experimental Mechanics, Vol. 47, No. 1, p. 7-24, 2007.

• Y. Zhu, A. Corigliano and H.D. Espinosa. "A thermal actuator for nanoscale in-situ microscopy testing: design and characterization" Journal of Micromechanics and Microengineering, Vol. 16, No. 2, p. 242-253, 2006.

• Y. Zhu, N. Moldovan and H.D. Espinosa. "A microelectromechanical load sensor for in situ electron and x-Ray microscopy tensile testing of nanostructures," Applied Physics Letters, Vol. 86, No. 1, Art. No. 013506, 2005.

• Y. Zhu and H.D. Espinosa. " An electromechanical material testing system for in situ electron microscopy and applications " Proceedings of the National Academy of Sciences, Vol. 102, No. 41, p. 14503-14508, 2005.