2013 Theses Doctoral

Batch-compatible Integration of Nanowires with Uniaxial Micro Tensile Testing Platforms

Yilmaz, Mehmet

Nanoscale materials often have stochastic material properties due to random distribution of material defects and lack of sufficient number of defects to ensure a consistent average. Current methods to measure the mechanical properties employ microelectromechanical systems based tensile loading platforms. The nanoscale specimens are typically mounted manually onto the loading platforms with external integration techniques so the boundary conditions have random variations, complicating the experimental measurement of the stochasticity in the natural state of the material properties. In this Ph. D. thesis, we show methods for batch-compatible (i.e. monolithic) integration of nanoscale specimens cofabricated with the tensile loading platforms. The specimens are gold nanowires of 40 nm thickness, 350 nm to 410 nm width (depending on the specimen), and 7-micrometer length. The uniaxial micro tensile loading platforms are interdigitated electrode electrostatic actuators. The experiments are performed in a scanning electron microscope and digital image correlation is employed to measure displacements to determine nominal stress and nominal strain. The ultimate tensile strength of the nanocrystalline gold nanowires approach 1 GPa, consistent with the smaller-is-stronger paradigm. The batch-compatible integration method is designed to microfabricate uniaxial micro tensile testing platforms that are suitable for transmission electron microscope experiments. This batch-compatible integration method is designed also to create nominally identical nanoscale specimens and boundary conditions for a broad range of nanoscale materials provided the nanoscale materials of interest are compatible with the etchants used in the microfabrication processes. Furthermore, in addition to the batch-compatible integration method, a generalized external integration method that can be applied to free-standing thin-films is developed. Using this method, mechanical behavior of single crystal gold metal, and single crystal gold-silver alloy nanoscale specimens are extracted. For the extraction of the mechanical properties, similar procedures followed for batch-compatible integrated nanoscale specimens are followed. For single crystal gold nanoscale specimen, a Young's modulus of 33.42 GPa, and ultimate tensile strength of 0.48 GPa is obtained. For single crystal gold-silver alloy nanoscale specimen, a Young's modulus of 64.47 GPa, and ultimate tensile strength of 0.67 GPa is obtained.