Vertically Self-Organized Gold Nanoparticles in Amorphous Alumina Matrices
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Vertically Self-Organized Gold Nanoparticles in Amorphous Alumina Matrices Chunming Jin1, Honghui Zhou2, Wei Wei2, and Roger J. Narayan1 1 Biomedical Engineering, North Carolina State University, 3030 Engineering Building I, 911 Partners Way, Raleigh, NC, 27695-7115 2 Materials Science and Engineering, North Carolina State University, 3030 Engineering Building I, 911 Partners Way, Raleigh, NC, 27695-7907 Abstract In this study, self-organized growth of gold nanoparticles dispersed in amorphous alumina matrices was investigated. Au/Al2O3 multilayered structures were grown on silicon (001) substrates using pulsed laser deposition. Vertical ordering of particles was examined with cross-sectional transmission electron microscopy and image Fourier transformation. Selforganization of gold nanoparticles along the vertical direction was observed in the samples grown at room temperature and 320 °C. This process occurred through two-different growth modes, known as top-on-top growth and top-on-middle growth. The driving force for the vertical ordering was attributed to long-range elastic interactions among nanoparticles during the film deposition process. Introduction Vertical organization of nanostructured multi-layered systems is a key step for creating ordered three-dimensional nanoparticle arrays.1 The driving force for vertical correlation growth has previously been attributed to the long-range elastic interaction among the growing particles and the particles buried in the matrix.1-3 Vertical correlation growth has been investigated extensively in heteroepitaxial systems such as SiGe/Si,4 and InAs/GaAs.5 In these situations, the matrix material has the same structure as the nanoparticle material. However, it is possible to realize vertically coherent growth in amorphous media as long as the specific growth conditions or parameters are achieved and the underlying nanoparticle layers are able to provide the strain field modulations. In this article, we report on vertical correlation growth of gold nanoparticles in amorphous alumina matrices. These materials, in which metallic nanoparticles are dispersed in amorphous matrice,s have several opto-electronic and magnetoelectronic device applications.6-7 Experimental Gold nanoparticle samples were prepared using pulsed laser deposition with alternate growth of nanoparticles and alumina buffer layers. A KrF excimer laser operated at λ=248 nm was used to ablate a high purity gold target and a commercial hot-pressed alumina target. Three samples were investigated, which were prepared at different substrate temperatures and different deposition parameters. The deposition parameters were shown in Table 1. For all the samples, alumina buffer layers were first deposited on the substrates to keep the same initial surface morphology and substrate structure. Silicon (001) was used as the substrate material. The native silicon dioxide layer was not removed in order to maintain an amorphous substrate surface.
Table 1. Deposition parameters for Au/Al2O3 multilayered structure
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