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 result was published online on January 3rd in Science.
The work was done jointly by Dr. ZHOU Gang (joint first author) and Dr. WANG Hao from Division of Titanium Alloys, Institute of Metal Research, Chinese Academy of Sciences, Prof. Dongsheng Li (corresponding author) and Dr. Miao Song (joint first author) from Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, and Dr. Ning Lu (joint first author) from Department of Materials Science and Engineering, 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 the paper, the authors discovered two different mechanisms to form five-fold twinned nanoparticles, both of which are driven by the accumulation and elimination of strain. Mechanism I operates via oriented attachment and atomic surface diffusion, following the nucleation and growth of zero-strain twin. And Mechanism II operates 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 90o and 150o after oriented attachment, the five-fold twinned nanoparticles form 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.
