60 seconds on...nanoscale films of copper
 Credit: Zhang Xiaopu. Perspective view of the STM topography of nanocrystalline copper film, which shows a valley with dissociated dislocations and a ridge with recombined dislocations. The size of the image is 50nm by 50nm.
Until now, grain boundaries in nanocrystalline copper films have been thought to be perpendicular to the material’s surface. But new research shows that these grains are often rotated, forming ridges that cause surface roughness.
This discovery is detailed in Nanocrystalline copper films are never flat by a team of researchers from AMBER, the Science Foundation Ireland-funded materials science centre based in Trinity College Dublin, Ireland, the University of Pennsylvania, USA, Imperial College London, UK, and the Intel Corporation Components Research Group, USA.
What did the research involve?
The researchers used scanning tunnelling microscopy to study the grain boundaries of copper, finding that the presence of these boundaries creates a misaligned surface, with ridges and valleys formed by grain rotation. The rotation is created by reduced grain boundary energy.
While the team focused on copper films, Professor John Boland, Investigator at AMBER and corresponding author of the paper, claims the findings will also apply to silver, gold and potentially nickel. As nanocrystalline copper and other nanocrystalline metals are used in integrated circuits as electrical contacts and interconnects, this improved understanding of grain structure can aid the development of more efficient circuits and devices that last longer. Â
To read more on this topic see page 13 of the upcoming September issue of Materials World.