Size effects in the deformation of sub-micron Au columns

TLDR

The study performed uniaxial compression on single‑crystal Au columns (180 nm–8 µm) fabricated by focused‑ion‑beam milling into a large‑grained Au sheet and tested with a nanoindenter equipped with a flat diamond punch. Compression produced localized shear on the most favorably oriented slip systems, yielding discrete strain bursts; the yield stress scales inversely with the square root of column diameter, strain hardening rises sharply with decreasing size, reaching stresses up to 1 GPa, all attributed to dislocation source‑limited behavior.

Abstract

Uniaxial compression tests have been performed on single crystal Au columns ranging in diameter from 180 nm to 8 µm. The columns were machined into the surface of a large-grained Au sheet using a focused ion beam microscope and then mechanically tested using a nanoindenter outfitted with a flat diamond punch. Images of the compressed columns show that deformation occurs by localized shear on the slip systems with the largest resolved shear stresses. After an elastic loading regime, the columns exhibit yielding in discrete strain bursts. The compressive yield stress scales roughly as the inverse square root of the column diameter. The apparent strain hardening rate also increases strongly with decreasing column diameter and stresses as large as 1 GPa are reached. Both of these size effects are attributed to dislocation source-limited behaviour in small volumes.