Strain Distribution Of Confined Metal Nanoparticles

For the core-shell nanoparticles confined in a host matrix, a substantial strain is induced, which can be used to tune the interplay between the core and shell layers, the morphology and optical properties. In this thesis, the relation between the strain distributions and the morphology of the Au/Ag and Ag/Au core-shell nanoparticles has been investigated, respectively. The simulation results have significant influences on the preparation and the applications of the metal core-shell nanoparticles.1、Au and Ag nanoparticles embedded in amorphous Al2O3 matrix are fabricated by the pulsed laser deposition(PLD) method and rapid thermal annealing(RTA) technique, which are confirmed by the experimental high-resolution transmission electron microscope(HRTEM) results, respectively. The strain distribution of Au and Ag nanoparticles embedded in the Al2O3 matrix is investigated by the finite-element(FE) calculations.The simulation results clearly indicate that both the Au and Ag nanoparticles incur compressive strain by the Al2O3 matrix. However, the compressive strain existing on the Au nanoparticle is much weaker than that on the Ag nanoparticle. This phenomenon can be attributed to the reason that Young’s modulus of Au is larger than that of Ag.2、The matrix-dependent strain distributions of Au and Ag nanoparticles in metaloxide-semiconductor based nonvolatile memory device are investigated by the finite element calculations. The simulation results clearly indicate that both the Au and Ag nanoparticles are incurred compressive strain by the high-k Al2O3 and the conventional Si O2 dielectrics. The strain distribution of the nanoparticles is closely related to the surrounding matrix. Nanoparticles embedded in different matrices experience different compressive stresses, which provide the opportunities to tailor the microstructure of Au and Ag nanoparticles.3、On the basis of the above research, the strain distributions of core/shell nanoparticles composed of Au and Ag with different core and shell sizes and confined in the Al2O3 matrix are investigated. The study indicate that because of the Young’s modulus of Au is larger than that of Ag, with the increase of the core size, the strain gradient existing in Au/Ag nanoparticle becomes larger, while the strain gradient existing in Ag/Au nanoparticle keeps constant. And the strain gradient existing in Au/Ag nanoparticle is bigger than that in Ag/Au nanoparticle under the same core sizes. Both of Au/Ag and Ag/Au nanoparticle, the strain is enhanced with the increasing of the shell thickness. However, the strain gradient in the shell decreases gradually with the increasing of the shell thickness for both of Ag/Au ad Au/Ag nanoparticles. However, the strain gradient in the shell decreases faster for Au/Ag than that for Ag/Au nanoparticles. These results demonstrate an effective method to manipulate the strain distributions of the Au/Ag and Ag/Au nanoparticles by tuning the morphology, which have significant influences on the microstructure and the physical properties of the nanoparticles with core-shell structure.