Ion-beam synthesis of epitaxial Au nanocrystals in MgO
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J. Lian and L.M. Wang Department of Materials Science Engineering and Geological Sciences, The University of Michigan, Ann Arbor, Michigan 48109 (Received 20 October 2003; accepted 29 January 2004)
The formation of Au nanoclusters in MgO using ion implantation and subsequent annealing was investigated. Approximately 1200 and 1400 Au2+ ions/nm2 were implanted in MgO(100) substrates at 300 and 975 K, respectively. Subsequent annealing in air for 10 h at 1275 K promoted the formation of Au nanostructures in MgO. The sample implanted at 300 K showed severe radiation damage. In addition, two-dimensional plateletlike structures with possible composition of Au and MgO were formed during implantation in the sample that was implanted at 300 K. In contrast, Au implantation at 975 K promoted the nucleation of Au nanostructures during implantation. Subsequent annealing of both samples show three-dimensional clusters in MgO. However, the 975 K implanted sample shows clean, high-quality, single-crystal Au clusters that have an epitaxial relationship to MgO(100). Nucleation and growth of two and three-dimensional nanostructures show unique structural, optical, electronic, and vibrational properties due to the quantum confinement of charge carriers. When the size is sufficiently small, the three-dimensional quantum dot structures show atomlike discrete energy levels, and several recent investigations have focused on tailoring these size effects in semiconductor technology, especially in electronic and optoelectronic applications.1–9 Although spontaneous self-assembled island formation due to lattice mismatch between two materials provides the basis for the nucleation of these quantum dots, many aspects of the formation of these structures are still unknown. In many cases, molecular-beam epitaxy and metal oxide chemical vapor deposition methods have been used to generate these conventional semiconductor quantum dots on suitable substrates.3–6,8,9 Most of these quantum dots are very sensitive to the environment in which they are stored, and as such, special attention is needed in the direction of either passivating those surfaces or keeping the structures in an inert environment. Recently, ion implantation and subsequent thermal annealing has been effectively used to generate various embedded nanoparticles in the near surface region of oxide materials.10–17 Formation of nanostructures using
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Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http:// www.mrs.org/publications/JMR/policy.htm DOI: 10:1557/JMR.2004.0174 J. Mater. Res., Vol. 19, No. 5, May 2004
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this method within nonmetallic media has generated several new types of active surfaces. Linear and nonlinear optical properties of optically active surfaces can be changed and controlled by incorporating nanoparticles of semicond
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