MRS Meetings and Events

 

NM07.09.08 2022 MRS Fall Meeting

Micro-and Nanowires of Ni and Mn Oxides and Their Heterostructures Synthesized by a One-Step Vapor Solid Method

When and Where

Dec 1, 2022
10:15am - 10:30am

Hynes, Level 2, Room 203

Presenter

Co-Author(s)

David Maestre1,Javier Garcia-Alonso1,Ana Cremades1

Universidad Complutense de Madrid1

Abstract

David Maestre1,Javier Garcia-Alonso1,Ana Cremades1

Universidad Complutense de Madrid1
The synthesis of transition metal oxide micro- and nanostructures with controlled dimensions, morphology and composition have gained increasing relevance in recent years due to their wide range of applications in many fields of research such as photocatalysis, spintronics, optoelectronics, and energy storage [1]. The achievement of controlled doping and the fabrication of heterostructures based on these oxides at the micro- and nanoscale are go-to topics that can broaden the field of applications of these materials. Different synthesis processes have been explored so far to obtain elongated structures of Mn and Ni oxides with controlled morphology, composition and structural properties, however in most cases the growth of heterostructures formed by these oxides require of more complex synthesis routes with different steps.<br/>In this work, we present the synthesis and characterization of Mn and Ni oxides in form of elongated microstructures, nanowires, and hierarchical structures. Combination of NiO with metallic Mn and Ni powders were used as precursors. After thermal treatments at 1000 – 1500<sup>o</sup>C under a controlled Ar flow the growth of high yield of elongated micro- and nanostructures through a one-step vapor – solid method is promoted. The elongated microstructures present a square base with dimensions usually in the range of tenths of microns and lengths up to hundreds of microns. Most of these elongated microstructures show the growth of nanowires with lower dimensions at their apex, leading to brush-like morphologies, as confirmed by electron microscopy. These nanowires, in some cases following hierarchical growths, show diameters from tens to hundreds of nanometers and tend to grow from nucleation points related to variations in the Ni/Mn composition. The bigger microrods show Mn-rich areas mainly related to Mn<sub>3</sub>O<sub>4</sub> while the bunch of nanowires at the apex is associated with Ni-rich areas mostly formed by NiO and diverse Mn-oxides, as demonstrated by XRD and micro-Raman spectroscopy. Considering that NiO is one of the few p-type oxides, this one-step growth can lead to the formation of p-n heterostructures at the micro- and nanoscale. Moreover, Ni doped Mn<sub>2</sub>O<sub>3</sub> and Mn doped NiO are also promoted during the growth, as confirmed by energy dispersive x-ray spectroscopy (EDS).<br/>X-ray photoelectron spectroscopy (XPS) spectra confirm variation mainly in the Mn(2p) and O(1s) core levels as a function of the probed regions along the elongated structures. Finally, photoluminescence acquired with a 325 nm laser indicates the presence of a broad visible emission centered around 500 nm at the region with nanowires, which can be related to the presence of Ni vacancies in the NiO areas.<br/>The achievement of low dimensional elongated structures presenting a hierarchical growth based on transition metal oxides will improve the applicability of these materials in diverse fields of technological research.<br/><br/>[1] J. García-Alonso, D. Maestre, E. Nogales, A. Cremades, B. Mendez. "Study of NiGa2O4 microneedles grown by a thermal-evaporation method". J. García-Alonso, D. Maestre, E. Nogales, A. Cremades, B. Méndez. Journal of Alloys and Compounds, 919 (2022), 165718

Keywords

crystal growth | nanostructure | spectroscopy

Symposium Organizers

Jeehwan Kim, Massachusetts Institute of Technology
Sanghoon Bae, Washington University in Saint Louis
Deep Jariwala, University of Pennsylvania
Kyusang Lee, University of Virginia

Publishing Alliance

MRS publishes with Springer Nature