Size-dependent plasticity and activation parameters of lithographically-produced silicon micropillars
Résumé
Silicon is brittle at ambient temperature and pressure, but using micro-scale samples fabricated by focused ion
beam (FIB) plasticity has been observed. However, typical drawbacks of this methodology are FIB-damage and
surface amorphization. In this study, lithographic etching was employed to fabricate a large number of 〈100〉-oriented Si pillars with various diameters in the micro-scale. This allowed quantitative study of plasticity and the
size effect of FIB-free Si in the brittle temperature range (25–500 °C) by conducting monotonic and transient
microcompression in situ in the scanning electron microscope (SEM). Lithographic pillars achieved the ideal
strength in temperature range of 25–100 °C and displayed significantly higher strengths (30–60%) than FIBmachined pillars because of the undamaged surface and the oxide layer confinement. The activation energy of
deformation revealed a transition in dislocation mechanisms as a function of temperature. Strain rate sensitivity
and activation volume measured from strain rate jump and stress relaxation tests indicated the surface nucleation of kink-pairs associated with the constricted dislocation motion in Si during deformation at temperatures
below the brittle-ductile transition. A modified analytical model is proposed to accurately evaluate the sizedependent strength of covalent crystalline Si. The weak size effect observed in Si is attributed to the surface nucleation of dislocations and high lattice friction during their motion.
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