Mechanical Characterization of High Aspect Ratio Silicon Nanolines

In this study, we performed nanoindentation experiments on two sets of silicon nanolines (SiNLs) of widths 24 nm and 90 nm, respectively, to investigate the mechanical behavior of silicon structures at tens of nanometer scale. The high height-to-width aspect ratio (∼15) SiNLs were fabricated by an anisotropic wet etching (AWE) method, having straight and nearly atomically flat sidewalls. In the test, buckling instability was observed at a critical load, which was fully recoverable upon unloading. It was found that friction at the contact between the indenter and SiNLs played an important role in the buckling response. Based on a finite element model (FEM), the friction coefficient was estimated to be in a range of 0.02 to 0.05. The strain to failure was estimated to range from 3.8% for 90 nm lines to 7.5% for 24 nm lines.

Buckling of Single-Crystal Silicon Nanolines under Indentation

Atomic force microscope-(AFM-) based indentation tests were performed to examine mechanical properties of parallel single-crystal silicon nanolines (SiNLs) of sub-100-nm line width, fabricated by a process combining electron-beam lithography and anisotropic wet etching. The SiNLs have straight and nearly atomically flat sidewalls, and the cross section is almost perfectly rectangular with uniform width and height along the longitudinal direction. The measured load-displacement curves from the indentation tests show an instability with large displacement bursts at a critical load ranging from 480 μNto 700 μN. This phenomenon is attributed to a transition of the buckling mode of the SiNLs under indentation. Using a set of finite element models with postbuckling analyses, we analyze the indentation-induced buckling modes and investigate the effects of tip location, contact friction, and substrate deformation on the critical load of mode transition. The results demonstrate a unique approach for the study of nanomaterials and patterned nanostructures via a combination of experiments and modeling.