Invited: Controlled Growth of Hierarchical Metal Oxide Nanoarchitectures by an Atmospheric Pressure Micro-Afterglow

Metal oxide nanostructures with controlled shapes and size distribution have stimulated interest in fundamental scientific research owing to their morphology-dependent properties that offer potential wide-ranging applications. Plasma-assisted processing is one of the emerging processes used for the production of various metal oxide nanostructures [1]. In this study, we present an innovative strategy to synthesize different metal oxide nanostructures. This very simple process consists in exposing a metal surface directly to the afterglow of an argon-oxygen micro-plasma at atmospheric pressure [2].

            Different metals are treated by the afterglow (Cu, Zn, Fe). For example in the case of copper, this flexible process makes it possible to design in a single treatment step, hierarchical nanostructures, which are not obtained by classical thermal oxidation like nanowalls or nanoflowers (figure 1). The growth mechanism is driven by stress-induced migration due to the development of stress gradients caused by the formation of copper oxide layers CuO and Cu₂O. A specific study based on the local stress evolution measurement is proposed to determine accurately its influence on the growth of copper oxide nanostructures.

            In this work, we present also the possibility to obtain the localized growth of ruthenium oxide nanostructures by applying the afterglow on a ruthenium substrate [3]. The mechanism is two-fold. First, a nanostructure made of lamellae covers the whole surface. Second, localized bunches of nanowires are distributed randomly, their growth being driven by the local stress that depends on the presence of emerging defects. We study also the influence of two alkali salts: NaCl and KCl. The presence of these crystals on the surface enhances the growth of nanowires all around them, created a circular area where nanowires are found (figure 2). The different existing growth models are considered to interpret these new results. This nanowire growth mechanism can be another important way to control the location of the metal oxide nanostructures.

Reference

[1] K. Ostrikov, U. Cvelbar, A. Murphy “Plasma nanoscience: setting directions, tackling grand challenges”, J. Phys. D: Appl. Phys. 44 (2011) 174001.

[2] G. Arnoult, R.P. Cardoso, T. Belmonte, G. Henrion “Flow transition in a small scale microwave plasma jet at atmospheric pressure”, Appl. Phys. Let. 93 (2008) 191507.

[3] D. Kuete Saa, R.P. Cardoso, F. Kosior, A. Altaweel, T. Gries, S. Laminsi, T. Belmonte “Growth of ruthenium dioxide nanostructures by micro-afterglow oxidation at atmospheric pressure”, Surf. & Coat. Technol. DOI: 10.1016/j.surfcoat.2013.10.040 (in press).