Deformation behavior of silver submicrometer-pillars prepared by nanoimprinting

Abstract

Scaling in material properties is of great importance in microsystems and microelectronics where the device dimensions continuously shrink. Recently, compression tests of micron-sized pillars produced using a focused-ion beam (FIB) have become standard in the investigation of scaling effects. The influence of the fabrication process on the mechanical properties of the samples has, however, not been conclusively resolved. In this study, 130 silver pillars were fabricated using a novel embossing technique that does not pose the issues associated with FIB milling, i.e. surface amorphization and gallium contamination. Displacement-controlled compression tests on pillars with diameters of 130–3000 nm reveal for submicrometer samples an inverse proportionality of flow strength to diameter, which is associated with a wide strength distribution and a deformation taking place in large discrete strain bursts. The largest pillars show instead near bulk-like behavior. Unlike studies on other fcc materials, mechanical twinning is also an important deformation mechanism in Ag due to its very low stacking fault energy. In addition, occasional preexisting twin boundaries constituted preferential planes for localized deformation if favorably sloped. Despite the absence of ion-induced artifacts, scaling laws and absolute values of strength are comparable to those obtained via FIB milling.

Keywords:

• microforming
• direct nanoimprinting
• size effects
• mechanical properties
• dislocation slip
• EBSD
• yield strength

Acknowledgements

We thank Franck Robin, Faouzi Khechana and Cyrille Hibert for their help with the mold microstructuring, Erwin Fischer for invaluable technical support, and Peter Uggowitzer for helpful discussions. This work was supported by the ETH Zurich Initiative on Composite Doped Metamaterials (CDM) and by an ETH Research Grant TH-29/07-3.