Phase boundary effects on the mechanical deformation of core/shell Cu/Ag nanoparticles
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Elissa H. Williams Department of Chemistry and Biochemistry, George Mason University, Fairfax, Virginia 22030 (Received 23 October 2008; accepted 17 February 2009)
The uniaxial compressive deformation of core/shell-type Cu/Ag nanoparticles and naked Cu nanoparticles were simulated by molecular dynamics, revealing the role of nanophase boundaries in the mechanical deformation. The simulations show that single type of partial dislocations glide across the entire slip planes of the Cu cores, resulting in elongated Cu cores compared with circular Cu cores of naked Cu nanoparticles. The phase boundary is the nucleation source of dislocations, and the ultrahigh atomic level stress of part atoms in the phase boundary can ensure the movement of the single type of dislocations under compressed.
I. INTRODUCTION
Nanostructured materials have been investigated extensively during the past decade due to their unique properties, which are often affected by the limited size and microstructures of nanostructured materials. One issue concerning nanostructured materials is how to effectively control the surface and/or interface in nanosystems. A solution to this problem is the special “core/ shell” type nanoparticles (NPs) with heterogeneous interfaces, which can improve the oxidation resistance and the dispersive ability of naked metallic NPs. For example, the enhanced dual-frequency microwave absorption of core/shell-type metal/C,1,2 Ni/Polyaniline3 NPs due to the polarization action between the core/shell interfaces were reported recently. The antiwear ability of Cu/dialkyldithiophosphate is increased due to the protective film from the core/shell interfaces.4,5 Therefore, it is reasonable to speculate that the core/shell NPs are promising materials for the controlled surface and/or interface in nanosystems. However, little theoretical work in relation to the nanoscale-interface effects on the mechanical properties of the core/shell NPs has been reported to date. II. SIMULATION METHOD
The purpose of this study is to reveal the role of phase boundary effects in mechanical deformation using a classic molecular dynamics (MD) simulation. Based on exa)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0263
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J. Mater. Res., Vol. 24, No. 7, Jul 2009
perimental observation, we have reasonably constructed the core/shell Cu/Ag NPs with an epitaxial relationship between the core and the shell.6 Cu/Ag NPs with a Cu core diameter of 4, 6, and 8 nm and an Ag shell of 1 nm were prepared for the simulations. Two slabs, which were copper atoms with a face-centered-cubic (FCC) structure and which had several layers where the atoms can move and the layer furthest from the particle were rigid, were added on the top and bottom of the NP perpendicular to [001] crystal orientation (z-axis). The effect between the slabs and the NPs led to an increase of atomic repulsive force when the slabs approached the NPs. The large repulsive force between atoms is the driving force of the compressive deformation of
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