Dresden 2009 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 42: Nanostructured Materials III

MM 42.2: Talk

Thursday, March 26, 2009, 14:15–14:30, IFW A

Segregation-induced near-surface lattice strain in CuAu nanoparticles — •Darius Pohl¹, Elias Mohn¹, Juri Barthel², Karsten Albe³, Ludwig Schultz¹, and Bernd Rellinghaus¹ — ¹IFW Dresden, D-01171 Dresden, Germany — ²FZ Jülich, D-52425 Jülich, Germany — ³TU Darmstadt, D-64287 Darmstadt, Germany

For binary nanoparticles, experimental findings indicate the segregation of one alloy constituent towards the particle surface which leads to a surface-near relaxation of the lattice. Due to a difference in the surface free energies between copper and gold, a gold segregation for nanoparticles is expected. In the case of CuAu nanoparticles, Au segregation towards the surface is suggested to lead to a lattice expansion. Through aberration-corrected HRTEM imaging with minimum delocalisation is achieved, and the position of individual atom columns can be determined with unrivalled precision.

Molecular dynamic (MD) simulations of CuAu nanoparticles are conducted under the constraint that the particle surface is terminated with either Cu or Au. A comparison between HRTEM contrast simulations of the simulated structures and experimental HRTEM images then allows to distinguish between the different possible scenarios. It is hereby proven that single crystal CuAu nanoparticles with a mean diameter of 3 nm exhibit a lattice relaxation due to a segregation of Gold atoms. This finding is in agreement with previous results obtained for multiply twinned FePt nanoparticles and thus corroborates that the surface-near expansion of the lattice is due to a segregation rather than to internal stress within the particle structure itself.