Comparing the strength of f.c.c. and b.c.c. sub-micrometer pillars: Compression experiments and dislocation dynamics simulations

We compare mechanical strength of f.c.c. gold and b.c.c. molybdenum single crystal pillars of sub-micrometer diameter in uniaxial compression ests. Both crystals show an increase of flow stress with decreasing diameter, but the change is more pronounced in Au than in Mo. The ratio etween the observed maximum flow stress and the theoretical strength is much larger in Au pillars than in Mo pillars. Dislocation dynamics imulations also reveal different dislocation behavior in these two metals. While in a f.c.c. crystal a dislocation loop nucleated from the surface imply moves on its glide plane and exits the pillar, in a b.c.c. crystal it can generate multiple new dislocations due to the ease of screw dislocations o change slip planes. We postulate that this difference in dislocation behavior is the fundamental reason for the observed difference in the plastic eformation behavior of f.c.c. and b.c.c. pillars.