Microstructure of precipitated Au Nanoclusters in Single Crystal MgO
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Microstructure of precipitated Au Nanoclusters in Single Crystal MgO C. M. Wang, S. Thevuthasan, V. Shutthanandan, A. Cavanagh, J. Walton, W. Jiang, W. J. Weber, L. E. Thomas, L. M. Wang1, and Jie Lian1 Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA 1 Department of Nuclear Engineering and Radiological Sciences, The University of Michigan, Ann Arbor, Michigan 48109, USA ABSTRACT Gold nanoclusters dispersed in single crystal MgO were prepared by ion implantation and subsequent annealing at 1000 °C. The morphological feature, size, crystallographic orientation of the Au nanoclusters with respect to the MgO matrix, and the interface structure between the Au nanoclusters and MgO were investigated using transmission electron microscopy. During annealing, the Au clusters nucleate coherently in the MgO lattice, leading to an epitaxial orientation relationship of [010]MgO// [010]Au and (200)MgO//(200)Au that is maintained for all the Au clusters. A critical size for the coherent-semicoherent interface transition is observed to be in the range from ~5 to 8 nm for Au clusters in MgO. Au clusters larger than this critical size exhibit faceting on the {001} planes. The precipitated Au also exhibits internal dislocations. Introduction Recently, considerable research efforts have been made on investigating the optical properties of Au nanoclusters dispersed in single crystal MgO [1-3], which were prepared by MeV ion implantation and subsequently high temperature annealing. Using positron spectroscopy, Xu et al. [4,5] have found that quantum antidots (a subnanometer scale vacancy cluster) in single crystal MgO dispersed with Au nanoclusters are localized at the surface of the Au nanoclusters. They have proposed that the transfer of the electrons from the Au cluster surfaces to the quantum antidotes may account for the observed redshift of the gold surface plasmon resonance for Au nanoparticles dispersed in the single crystal MgO. However, the structural nature of the precipitated Au nanoclusters has not been systematically investigated as a function of ion fluence, particularly with regard to size and morphology, crystallographic orientation with respect to the matrix, and the interface structure between the Au nanoclusters and the MgO matrix has not been systematically investigated. In this paper, transmission electron microscopy (TEM) have been used to characterize the microstructural features of Au nanoclusters dispersed in single crystal MgO, providing a comprehensive understanding of the size, morphology, orientation, and interface structure of Au clusters in the MgO matrix prepared by the MeV ion implantation and subsequent high temperature annealing. EXPERIMENTAL DETAILS The Au2+ ions were implanted into (100) MgO at 975 K and an angle of 30° relative to the surface using a 3.0 MeV tandem accelerator within the Environmental Molecular Sciences Laboratory (EMSL) at the Pacific Northwest National Laboratory. Two ion fluences were used, 7 x 1016 Au2+ ions/cm2 and 1.4 x 1017 Au2+ ions/cm2.
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