Multipurpose nanomechanical testing machines revealing the size-dependent strength and high ductility of pure aluminium submicron films

Fabregue, D. [UCL] André, Nicolas [UCL] Coulombier, Michaël [UCL] Raskin, Jean-Pierre [UCL] Pardoen, Thomas [UCL]

The mechanical properties measurement of materials with submicron dimensions is extremely challenging, from the preparation and manipulation of specimens, to the application of small loads and extraction of accurate stresses and strains. A novel, versatile concept of micro and nano-machines to test films or beams with characteristic dimensions ranging between 10 and 1000 nm, allowing multiple loading configurations and geometries, is described. This new nanotesting method has been applied to thin, pure aluminium films. The yield strength linearly increases with the inverse of the film thickness, reaching 625 MPa for 150 nm thickness which is ten times larger than for macroscopic samples. The strain hardening rate is large, similar to what is measured with macroscopic specimens. Unexpectedly, large strains equal to about 75% have been measured before the initiation of a stable ductile failure mode. This nanomechanical laboratory involves thousands of micromachines built onto a single silicon wafer, providing a unique platform for investigating the elementary mechanisms of deformation and fracture in nanoscale metal, polymer or ceramic samples.