engleski

Self-organization of nickel nanoparticles in dielectric matrices

Ni nanoparticles (NPs) attract lot of interest as catalyst for carbon nanotube growth, as particles forming interacting or noninteracting ensembles, optoelectronic entities, etc. We have produced self-ordered Ni NPs either on surface or embedded into the alumina or silica matrix starting from three types of nickel and alumina multilayered structures prepared by magnetron sputtering. The structure and morphology of the prepared materials have been examined by grazing-incidence small- angle scattering (GISAXS), wide-angle X-ray scattering (WAXS), atomic force microscopy (AFM), and transmission electron microscopy (TEM), while magnetic properties were measured by SQUID magnetometer. Thin Ni films deposited onto dielectric's surface exhibit markedly different particle size distribution at room temperature and at elevated temperatures. The effect of temperature on NP formation has been employed for formation of 3-dim arrays of Ni NPs in dielectric matrix. Two types of precursor materials have been used: a) multilayers consisting od alternating pure Ni and pure alumina layers, and b) multilayers consisting od alternating mixed Ni+alumina and pure alumina layers. Both types of precursor material were deposited at room temperature and at elevated temperature, and subsequently annealed. The size of the Ni NPs and their average lateral distance was controlled by the amount of Ni in the Ni- containing layer, while their cross-layer interaction was governed by the thickness of intervening dielectric spacer. That way, the magnetic properties could be controlled, as well. An example of the effects of alumina dielectric spacer thickness (6 & 2 nm) and annealing temperature (RT & 500°C) upon Ni NPs sizes and spatial distribution is shown in composite GISAXS Fig. 1. The size and spatial distributions of Ni NPs govern the supermagnetic properties of such an ensemble. An example of the blocking phenomena of superparamagnets is shown in Fig. 2 for Ni NP array in silica.

self-organization; nickel nanoparticles; multilayers; magnetron sputtering

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