Synthesis of metal oxide nanomaterials by plasma treatment – A SEM investigation of Nb2O5 nanowires

Plasma techniques for rapid synthesis of large quantities of metal oxide nanoparticles are presented. Suitable metal foils are exposed to cold oxygen plasma with a large density of neutral oxygen atoms of the order of 1021 m−3 and the ion density of the order of 1016 m−3. Depending on the flux of neutral atoms onto the sample surface as well as other plasma parameters, such as the positive ion kinetic energy and the sample temperature, different types of nanoparticles are synthesized, such as nanowires, nanocones and nanobelts. Nanowires are synthesized at extremely large flux of neutral oxygen atoms on the sample surface, often exceeding 1 × 1024 m−2 s−1. Other features are synthesized at moderate flux of atoms of the order of 1023 m−2 s−1. The phenomenon is explained by rapid nucleation of metal oxide on the sample surface followed by a one -dimensional growth of the nanowires due to balanced supply of neutral atoms and ions to the surface. Controlling the plasma parameters, a fair control on the nanostructure size as well as shape is achieved. The technique allows for synthesis of nanowires at the rate of almost 1 g/h, and therefore assures huge quantities of this material. The synthesis of niobium oxide nanowires is studied to some details by scanning electron microscopy.

► This paper is the first report on origin of Nb2O5 nanowires. ► An original experimental setup allows for monitoring all structures on one sample. ► Formation of scarce as well as dense nanowires are observed.