Formation of Size-Selected Ni/NiO Core−Shell Particles by Pulsed Laser Ablation

Abstract

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.

Synthesis of Nanoparticles by Laser Ablation: A Review

“…4) is significantly more capable of controlling nanoparticle morphologies. Sakiyama et al (2004) fabricated Ni particles of a select size coated with a NiO shell with the laser ablation method. They also applied the aerosol process, i.e., LPDMA size classification, and gas phase annealing to improve Ni nanoparticle morphology.…”

“…Since laser-generated particles have a very clean surface, agglomerated particles create chemical bonds at the contact point (neck), which significantly compromise the properties of primary particles ( Fig. 3(d), Sakiyama et al, 2004). The low-pressure gas process is advantageous not only for reducing the size of the primary particles but also for preventing coagulation.…”

Structural investigations of oxidative behavior on nanocrystalline nickel

“…Ni and/or NiO are receiving increased attention for not only their interesting chemical characteristic, such as catalysts, fuel cell electrodes, gas sensors and supercapacitors/battery hybrids but also for their magnetic properties since NiO is antiferromagnetic and Ni is ferromagnetic [1][2][3][4][5][6][7][8][9][10]. In addition, metal-ceramic materials are also interesting since they typically exhibit enhanced mechanical properties [6].…”

“…The frequently encountered obstacle during the preparation of nanoscale metal particles is the spontaneous production of oxides due to very high surface to volume ratio of the particles. As a result, metal particles are being encapsulated within a spontaneous surface oxide (SSO) layer, which is known as a 'core-shell' structure [7,8]. For example, in many solar absorbing coatings, the presence of a dielectric/insulating shell at least part of the metallic core severely delays the oxidation and appears to be the main reason for their high stability [9].…”

Frequency response analysis of the constant molar flow semi-batch adsorption vessel containing core-shell composites

“…Composite particles with core-shell structure may be useful in many applications, such as development of adsorbents, catalysts, calorimetric sensors, optoelectronic devices, and bioprocessing devices [13][14][15][16][17][18]. When the inner core is impermeable, the composite is called an inert-core adsorbent, since this composite was reported to be suitable as an adsorbent for stable expansion at high flow rates in expanded-bed.…”