Plastic deformation of nanometric single crystal silicon wire in AFM bending test at intermediate temperatures

This paper focuses on revealing specimen size and temperature effects on mechanical properties of nanometric single crystal silicon (SCS) wires at intermediate temperatures. Mechanical properties of the nanometric SCS wires were characterized by bending tests with an atomic force microscope (AFM). The fixed-fixed SCS wires with widths from 200 nm to 800 nm and a thickness of 255 nm were fabricated on a silicon diaphragm by means of field-enhanced anodization with AFM and anisotropic wet etching. The AFM bending tests of the SCS wires were carried out at temperatures ranging from 295 K to 573 K in high vacuum. Elastic moduli of the SCS wires showed temperature dependence, but had no size effect. However, plastic properties such as critical resolved shear stress and plastic deformation range showed a clear dependence on both of specimen size and temperature. The critical resolved shear stress ranged from 4.2 GPa to 7.2 GPa, which was 10 times higher than that in a millimeter scale specimen. Force-displacement curves and AFM observations of the slip line also showed that plastic flow in the nanometric SCS wires was induced at 373 K, which was very close to room temperature. A dislocation model is proposed on the basis of the AFM observation, which was able to rationalize that the nanometric specimen had a large influence on the activation Gibbs free energy in the thermal activated process