Kirkendall effect

Kirkendall effect refers to the rate of diffusion of components of alloy and a metal. Eg. if molybdenum signifies as marker of diffusion between copper and brass (copper-zinc alloy) – molybdenum will direct diffusion toward the alloy brass, since zinc is more rapidly diffused than copper. This effect has significant effects on creation of voids that are formed at the interfaces of alloys and metals, and are called kirkendall voids. Kirkendall effect in wire bonding technology was demonstrated to show importance of impurities. And that was for the rate of impurities in forming precipitation at the wire bonds, where voids in intermetallics were formed following the difference between diffusion rates of two metals. These voids would cause weakness and would develop in numbers when heat applied. Nanoscale hollow structures can grow according to Kirkendall effect that demonstrates the influence of surface diffusion on the morphology evolution. The influence is based on counterdiffusion at the reaction interfaces. There was observation that after formation of voids the second stage of surface diffusion follows that show rapid growth of fast diffusing material along the pore surface.

Fan Influence of surface diffusion on the formation of hollow nanostructures induced by the Kirkendall effect: the basic concept, Nano letter, 2007 Apr. vol 7 (4): pp993-7
http://www.ncbi.nlm.nih.gov/pubmed/17381161
Yin, Formation of hollow nanocrystals through the nanoscale Kirkendall effect, Science, 2004 Apr 30, 304 (5671), pp 711-4

http://nepp.nasa.gov/wirebond/horsting%20analysis.htm

http://www.wikipedia.com

The Discovery and Acceptance of the Kirkendall Effect: The Result of a Short Research Career, http://www.tms.org/pubs/journals/JOM/9706/Nakajima-9706.html