Epitaxial Growth Of Nickel Nanocrystals By Domain Matching Epitaxy
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S4.7.1
EPITAXIAL GROWTH OF NICKEL NANOCRYSTALS BY DOMAIN MATCHING EPITAXY
Jagdish Narayan National Science Foundation Center for Advanced Materials and Smart Structures, Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, NC 27695-7916, USA. ABSTRACT
We show that epitaxial nickel (fcc structure, lattice constant of 0.3528nm) nanocrystals are formed inside magnesium oxide (sodium chloride structure, lattice constant of 0.4201nm) matrix, where the misfit ranges from 3.0% to 31.3% on different interfaces. By controlling the annealing conditions, we obtained two distinct epitaxial morphologies: (1) cube-on-cube with Ni // MgO with a misfit of about 18.0%; and (2) morphology with // MgO (misfit 31.3%); Ni // MgO (misfit 3.0%); and Ni // MgO (misfit 17.0%). These results on epitaxial growth of nickel on MgO with misfit ranging from 3.0% to 31.3% are consistent with the domain matching epitaxy paradigm (DME), where integral multiple of lattice planes match across the film-substrate interface. The lattice planes include all the planes in a crystal structure, not just the diffraction planes involved in the X-ray, electron and neutron scattering. The residual misfit away from the integral multiples is accommodated by the principle of domain variation, where two or three sets of domains alternate with a certain frequency to minimize the misfit close to zero. The epitaxy in the DME paradigm is defined as the film having a fixed orientation which could be the same under certain conditions. From these results on Ni epitaxy, the dominant role of planes and matching of integral multiples of planes to accommodate small to large misfit are clearly established according to the DME paradigm.
S4.7.2
Introduction
Metallic colloids or nanocrystals in the size range 1 to 100nm inside wide bandgap materials such as ceramics are known to modify the physical properties of these materials in a useful way (1-4). Selective absorption of solar energy, and cathodochromic, photochromic and data storage represent a few examples of the modifications of physical properties. By changing the size distribution of nanocrystals, optical properties and mechanical properties (enhanced fracture toughness and ductility) can be tailored precisely for various applications. For the optical and mechanical properties, the epitaxial alignment is not as crucial. However, for nanomagnetics and information storage, the epitaxial growth and alignment of easy magnetization axis play a critical role. Our previous studies have shown that, by controlling the orientation of magnetic nanoparticles, we can enhance coercivity, blocking temperature and saturation magnetization and optimize information storage capability(5). Thus, epitaxial growth of magnetic nanoparticles such as Ni, Fe, Co and its alloys inside nonmagnetic matrices such as MgO and TiN, which have a large lattice misfit, offers a major challenge for fabrication of solid state devices(5-6). In this paper, we show that epitaxy of magnetic Ni nanocrystal
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