Effect of deposition rate on the microstructure of electron beam evaporated nanocrystalline palladium thin films

• Fraction of twinned grains and twin boundary density increase with deposition rate.
• Clear increase of dislocation density was observed for the highest deposition rate.
• A moderate increase of the mean grain size with increase of deposition rate is found.
• For the highest deposition rate, the twin boundaries lose their coherency.
• Fraction of high angle grain boundary (55–65˚) increases with deposition rate.

The influence of the deposition rate on the formation of growth twins in nanocrystalline Pd films deposited by electron beam evaporation is investigated using transmission electron microscopy. Statistical measurements prove that twin boundary (TB) density and volume fraction of grains containing twins increase with increasing deposition rate. A clear increase of the dislocation density was observed for the highest deposition rate of 5 Å/s, caused by the increase of the internal stress building up during deposition. Based on crystallographic orientation indexation using transmission electron microscopy, it can be concluded that a {111} crystallographic texture increases with increasing deposition rate even though the {101} crystallographic texture remains dominant. Most of the TBs are fully coherent without any residual dislocations. However, for the highest deposition rate (5 Å/s), the coherency of the TBs decreases significantly as a result of the interaction of lattice dislocations emitted during deposition with the growth TBs. The analysis of the grain boundary character of different Pd films shows that an increasing fraction of high angle grain boundaries with misorientation angles around 55–65° leads to a higher potential for twin formation.