Nano-Scale Tensile Testing and Sample Preparation Techniques for Silicon Nanowires

In this paper, we describe an experimental technique to achieve a highly reliable characterization of the mechanical properties of silicon (Si) nanowires (NWs). A reusable on-chip Si device consisting of comb-drive electrostatic actuator for generating tensile force and capacitive sensors for measuring tensile force and displacement was designed and developed for quasi-static tensile test of Si NWs. The combination of focused ion beam (FIB) fabrication, FIB-assisted chemical vapor deposition, and probe manipulation enabled us to directly fabricate the NWs on the device. This sampling technique led to high yielding percentage of nano-scale tensile testing. The NWs were made from 200-nm-thick Si membranes that were produced by using silicon-on-nothing membrane fabrication technique. Several Si NWs were annealed at 700 °C in ultrahigh vacuum (UHV) for 5 min in order to examine the influence of annealing on the mechanical characteristics. The mean Young's modulus for nonannealed NWs was 129.1±10.1 GPa. After UHV annealing, the mean value was improved to be 168.1±1.3 GPa, comparable to the ideal value for Si(001)[110]. The annealing process gave rise to improving the Young's modulus, whereas it degraded the strength. Transmission electron microscopy suggested that recrystallization and gallium nanoclusters formation by annealing would have changed the mechanical characteristics.