Recently, two different formation mechanisms of five-fold twinning via repeated oriented attachment of ~3 nm gold, platinum, and palladium nanoparticles were clarified by in situ high-resolution transmission electron microscopy and molecular dynamics simulations. Related research findings were published online in Science on January 3.
The work was jointly done by Dr. ZHOU Gang and Dr. WANG Hao from the Institute of Metal Research (IMR) of the Chinese Academy of Sciences and international collaborators from Pacific Northwest National Laboratory and University of Michigan.
Five-fold twins have been widely employed in crystal growth, mechanical engineering, optics, and catalysis. For example, the stress of five-fold twins substantially increases the Young’s modulus of nanowires, while multi-twinned Cu nanowires exhibit excellent methane selectivity during reduction of carbon dioxide. The formation mechanism of five-fold twinned nanoparticles is a difficult issue which has puzzled material scientists for a long time.
In this study, the researchers discovered two different mechanisms to form five-fold twinned nanoparticles, both of which are driven by the accumulation and elimination of strain. Mechanism I operated via oriented attachment and atomic surface diffusion, following the nucleation and growth of zero-strain twin. And Mechanism II operated via oriented attachment and partial dislocation slipping.
The occurrence of the two mechanisms depends on the surface structure of the nanoparticles after oriented attachment. With the concave surface angle close to 90° and 150° after oriented attachment, the five-fold twinned nanoparticles are formed by Mechanism I and II, respectively.
Their findings place disparate systems into the context of well-developed theories for multiple twin formation mechanisms, hence providing a guide for interpreting and controlling twinned crystal structures and morphologies, and hopefully will result in the advances in materials design and synthesis for diverse applications.
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