Achieving the ideal strength in annealed molybdenum nanopillars

The theoretical strength of a material is the stress required to deform an infinite, defect-free crystal. Achieving the theoretical strength of a material experimentally is hindered by the ability to create and mechanically test an absolutely defect-free material. Here we show that through annealing it is possible to employ the versatility of the focused ion beam (FIB) but recover a mechanically pristine limited volume. Starting with FIB-milled molybdenum pillars, we anneal them in situ in a transmission electron microscope (TEM) producing a molybdenum pillar with a spherical cap. This geometry allows for the maximum stress to occur in the interior of the spherical cap and is ideally suited for experimentally achieving the ideal strength. During in situ compression testing in the TEM the annealed pillars show initial elastic loading followed by catastrophic failure at, or very near, the calculated theoretical strength of molybdenum.