Anisotropic growth of NiO nanorods from Ni nanoparticles by rapid thermal oxidation

Abstract

NiO nanorods with extremely high crystallinity were grown by rapid thermal oxidation through exposure of Ni nanoparticles (NPs) heated above 400° C to oxygen. Oxidation proceeds by nucleation of a NiO island on a Ni NP that grows anisotropically to produce a NiO nanorod. This process differs completely from that under mild oxidation conditions, where the surface of the NPs is completely covered with an oxide film during the early stage of oxidation. The observed novel behaviour strongly suggests an interfacial oxidation mechanism driven by the dissolution of adsorbed oxygen into the Ni NP sub-surface region, subsequent diffusion and reaction at the NiO/Ni interface. The early oxidation conditions of metal NPs impose a significant influence on the entire oxidation process at the nanoscale and are therefore inherently important for the precise morphological control of oxidized NPs to design functional nanomaterials.

Growth of semi-coherent Ni and NiO dual-phase nanoparticles using hollow cathode sputtering

“…The Ni-O phase diagram shows that (below1 700 K), there exists only two phases, Ni and NiO (Kowalski and Spencer 1995). In the case of Koga et al, the oxidation is shown to take place not only at 400°C and P O 2 = 533 Pa but also at 900°C and 1.6 Pa (Koga and Hirasawa 2013). These numbers can be compared with the present work where 0.08 sccm results in P O 2 = 0.2 Pa, if an ideal gas mixture is assumed.…”

“…This has important consequences for the synthesis and structure evolution of nanoparticles of Ni and NiO in oxygen environments. This was described elegantly by Koga and Hirasawa (2013) in post-oxidation of spherical Ni nanoparticles into short NiO rods.…”

“…There are several different methods for producing Ni/ NiO nanoparticles. For example, oxidizing pure Ni nanoparticles (Koga and Hirasawa 2013), or using chemical reactive processes to grow Ni (Gang Wu et al 2010) or NiO (El-Kemary et al 2013). A common issue is the difficulty in precisely controlling the level of oxidation of the nanoparticles (i.e., the relative composition of Ni and NiO) or to have a structure other than a metallic core and oxide shell in a single-step approach (Spadaro et al 2015).…”

Wire-shaped ultraviolet photodetectors based on a nanostructured NiO/ZnO coaxial p–n heterojunction via thermal oxidation and hydrothermal growth processes

“…At the initial stage of thermal oxidation under the above conditions, the bulk Ni surface was formed into NiO shells by contacting with oxygen at high temperature and it transformed into a p-type semicon-ductor with Ni 2+ vacancies. 39 As the thermal oxidation further progressed, the NiO NSs were grown mainly by the cationic diffusion (that is, the Ni 2+ ions are diffused outward through NiO shells) and the size of NiO was increased. After that, as shown in Fig.…”

Catalytic steam methane reforming enhanced by CO2 capture on CaO based bi-functional compounds

“…The analyses of MayIM at higher magnification ( Fig. 15 ) show darker spherical Ni 0 particles [24] and some plates structure of the matrix ( Fig. 15 a).…”