This paper presents the method for fabricating size-selected nickel nanoparticles (diameter:  5−20 nm) coated with nickel oxide shells (thickness:  about 2 nm). The core−shell particles were synthesized by a series of sequential gas-phase processes including pulsed laser ablation, aerosol postannealing, size-classification, compulsory oxidation, and aerosol-jet deposition. The change in the size distribution of the generated particles due to postannealing was measured by a low-pressure differential mobility analyzer (LP-DMA) coupled with a Faraday cup electrometer. The peak size decreased as the postannealing temperature rose, indicating that a sintering and restructuring of the agglomerates was taking place. In the high-resolution TEM (HRTEM) observation, the Ni particles of less than 15 nm in diameter were found to be spherical and single crystal after the annealing at 1073 K. The 20 nm particles were also spherical, but they remained polycrystalline due to insufficient annealing treatment required for recrystallization. The change in the surface morphology due to the compulsory oxidation was analyzed by the HRTEM and electron diffraction. Finally, monodispersed (geometric standard deviation < 1.2) Ni/NiO core−shell particles with oxidized surface layers of 2 nm and particle diameters ranging from 5 to 20 nm were successfully fabricated.

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Deposition and Properties of Reactively Sputtered Ruthenium Dioxide Films.-Thin stoichiometric RuO2 films, useful as diffusion barrier layers, are deposited onto Si wafers by reactive sputtering of Ru at 1.0 kW and 12 mtorr in O2/Ar at an oxygen partial pressure (P(O2)) above 4.8 mtorr or at lower P(O2) by sputtering at lower power or higher pressure. The grain size of the film increases with increasing pressure and P(O2) By annealing of stoichiometric RuO2 films (101) RuO2 grains are grown, whereas annealing of films in H2 deposited at lower P(O2) leads to a thin RuO2 surface layer where the oxygen results from the Ru/Si interface and grain boundary. The resistivity of the RuO2 film decreases with increasing annealing temp.; at 900 . degree.C, a resistivity of 63.5 ω-cm is attained. -(SAKIYAMA, K.; ONISHI, S.; ISHIHARA, K.; ORITA, K.; KAJIYAMA, T.; HOSODA, N.; HARA, T.; J.

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