His team created its nanotrees specifically by applying a slight variation of a synthesis technique called chemical vapor deposition to the material lead sulfide. But the chemists believe the new mechanism will be applicable to many other materials, as well.
We think these findings will motivate a lot of people to do this purposefully, to design dislocation and try to grow nanowires around it, Jin says. Or perhaps people who have grown a structure and were puzzled by it will read our paper and say, Hey, we see something similar in our system, so maybe now we have the solution.
What initially puzzled Jin and his students about their pine tree structures was the long length of the trunks compared with the branches, a difference that indicated the trunks were growing much faster. The result was surprising because when complex, branching nanostructures are grown with metal catalysts, the branches are usually all of similar length because of similar growth rates, leading to boxy shapes rather than the cone-shapes of the trees.
Another oddity was the twist to the trunks, which sent the branches spiraling.
The long and twisting trunks were telling us we had a new growth mode, says Jin. Suspecting dislocation, the team set about refining their technique for growing the pine trees they soon learned to produce entire forests with ease and then confirmed the presence of dislocations with a special type of transmission electron microscopy.
Upon closer examination, the twisting trunks and spiraling branches also turned out to embody a well-known general theory about the mechanical deformation of crystalline materials caused by screw dislocations. Although this so-called Eshelby twist was first calculated back in 1953 and is discussed in many textbooks, Jins experimental results likely offer the best support yet for the theory.
These are beautiful, truly intriguing structures, but behind them is also a really beautiful, i
|Contact: Song Jin|
University of Wisconsin-Madison