High-Throughput Screening of Shape Memory Alloy Thin-Film Spreads using Nanoindentation

We have demonstrated the utility of nanoindentation as a rapid characterization tool for mapping shape memoryalloy compositions in combinatorial thin-film libraries. Nanoindentation was performed on Ni–Mn–Al ternary composition spreads. The indentation hardness and the reduced elastic modulus were mapped across a large fraction of the ternary phase diagram. The large shape memoryalloy composition region, located around the Heusler composition (Ni2MnAl), was found to display significant departure in these mechanical properties from the rest of the composition spread. In particular, the modulus and the hardness values are lower for the martensite region than those of the rest of the phase diagram

\u3cem\u3eIn Situ\u3c/em\u3e Nanomechanical Testing in Focused Ion Beam and Scanning Electron Microscopes

The recent interest in size-dependent deformation of micro- and nanoscale materials has paralleled both technological miniaturization and advancements in imaging and small-scale mechanical testing methods. Here we describe a quantitative in situ nanomechanical testing approach adapted to a dualbeam focused ion beam and scanning electron microscope. A transducer based on a three-plate capacitor system is used for high-fidelity force and displacement measurements. Specimen manipulation, transfer, and alignment are performed using a manipulator, independently controlled positioners, and the focused ion beam. Gripping of specimens is achieved using electron-beam assisted Pt-organic deposition. Local strain measurements are obtained using digital image correlation of electron images taken during testing. Examples showing results for tensile testing of single-crystalline metallic nanowires and compression of nanoporous Au pillars will be presented in the context of size effects on mechanical behavior and highlight some of the challenges of conducting nanomechanical testing in vacuum environments

Structural characterization of B-doped diamond nanoindentation tips

We report on the electrical and structural properties of boron-doped diamond tips commonly used for in-situ electromechanical testing during nanoindentation. The boron dopant environment, as evidenced by cathodoluminescence (CL) microscopy, revealed significantly different boron states within each tip. Characteristic emission bands of both electrically activated and nonelectrically activated boron centers were identified in all boron-doped tips. Surface CL mapping also revealed vastly different surface properties, confirming a high amount of nonelectrically activated boron clusters at the tip surface. Raman microspectroscopy analysis showed that structural characteristics at the atomic scale for boron-doped tips also differ significantly when compared to an undoped diamond tip. Furthermore, the active boron concentration, as inferred via the Raman analysis, varied greatly from tip-to-tip. It was found that tips (or tip areas) with low overall boron concentration have a higher number of electrically inactive boron, and thus non-Ohmic contacts were made when these tips contacted metallic substrates. Conversely, tips that have higher boron concentrations and a higher number of electrically active boron centers display Ohmic-like contacts. Our results demonstrate the necessity to understand and fully characterize the boron environments, boron concentrations, and atomic structure of the tips prior to performing in situ electromechanical experiments, particularly if quantitative electrical data are required.This research was supported by an Australian Research Council Linkage project. JB is the recipient of an Australian Research Council QEII Fellowship