Ni- Assisted Growth of Nanowires and Nanoplates Based on Mn-Oxides

In this work, Mn-based oxides, mainly Mn₃O₄ and MnO, micro- and nanostructures in form of wires, rods, nanoplates and brush-like structures have been grown following a one-step vapor-solid process [1] using a controlled mix of Mn and Ni powders as precursors. These precursor powders have been treated at 1000 – 1500 ^oC under a controlled Ar flow using a NiO pellet as a substrate. Following this method, a high yield of elongated micro- and nanostructures have been fabricated, with variable morphology, dimensions and properties as a function of the parameters used during the thermal treatment. These structures have been analyzed by means of x-ray diffraction (XRD), electron microscopy (SEM, TEM, HRTEM), energy dispersive x-ray spectroscopy (EDS), Raman spectroscopy and x-ray photoelectron spectroscopy (XPS). When necessary, the elongated structures have been detached from the pellet for their individual analysis. The microwires and rods present a terraced appearance with lengths up to hundreds of microns and widths of few microns. Moreover, most of them exhibit secondary growth in forms of nanowires hundreds of nm lengths and tens of nm width, occasionally decorated with nanoplates and 2D structures. Electron microscopy confirms the morphology and dimensions of the structures, while EDS indicates that the presence of Ni assisted the growth of secondary growths and nanoplates. XRD and Raman spectroscopy, confirms that these wires mainly consist of Mn₃O₄, while HAADF images confirm the presence of metallic Ni acting as nucleation areas for the growth of the Mn₃O₄ nanowires, 2D structures and plates. XPS spectra confirm variations mainly in the Mn(2p) and O(1s) core levels as a function of the probed regions along the elongated structures. Based on this analysis, the properties of the micro- and nanostructures were studied and the Ni-assisted growth process has been discussed.<br/>The achievement of low dimensional structures, including 2D and quasi 2D forms, based on Mn- oxides will improve the applicability of these materials in diverse fields of technological research [2].<br/><br/><br/>[1] M. Taeño, D. Maestre, A. Cremades. <i>J. Alloys and Compounds</i>, 881, 160654 (2021)<br/>[2] N. Palaniyandy, F.P. Nkosi, K. Raju, K.I. Ozoemena. <i>J. Eletr. Chem</i>. 833 (2019), 79-92