In situ observation of tensile behavior in a single silicon nano-helix grown by glancing angle deposition

In order to investigate the mechanical properties of amorphous silicon helical nanoelements (nano-helices), grown by the glancing angle deposition (GLAD) technique, we conducted tensile testing experiments on single nano-helices, which focused on the proof-of-principle. Three isolated nano-helices were prepared from the same GLAD layer by the removal of adjacent nano-helices using a nano-probe, and the top end was adhered to the loading tip with an electron beam curing adhesive. In situ observation by scanning electron microscopy revealed that the single nano-helix underwent a large longitudinal elastic elongation until fracture (about 40% of the fracture displacement) owing to its helical shape. In the early stage of deformation, there was a jump in the load-displacement relationship, due to partial breaking of the connecting leg at the root of the nano-helix. The tension induced plastic deformation and fracture in the bottom zone where the wire diameter was smaller. Examination based on element geometry at local zones indicated that deformation in the elastic stage was governed by the element shape. The yield stress of the amorphous silicon for the nano-helix was estimated to be approximately 0.8 GPa.