Crystalline phase control and growth selectivity of β-MnO2 thin films by remote plasma assisted pulsed laser deposition

Abstract

In this paper, we exploit the effect of coupling an oxygen remote plasma source to Pulsed Laser Deposition (PLD) for the growth of pure and well crystallized β-MnO2 films. Films were grown on Si substrates by laser ablation of a MnO target in oxygen ambient and remote plasma. X-Ray Diffraction, Fourier Transform Infra-Red spectroscopy and Raman scattering were used to determine the crystalline structure and bonding in the grown layers, whereas Atomic Force Microscopy was used to study their morphology and surface roughness. Deposition at 500 °C and high oxygen pressure (33.3–66.6 Pa) resulted in the formation of films with roughness of 12 nm consisting of nsutite γ-MnO2, a structure characterized by the intergrowth of the pyrolusite β-MnO2 in a ramsdellite R-MnO2 matrix. Deposition at the same temperature but low pressure (1.33–3.33 Pa) in oxygen ambient lead to the formation of Mn2O3 whereas plasma activation within the same pressure range induced the growth of single phase highly crystalline β-MnO2 having smooth surfaces with a roughness value of 0.6 nm. Such results underline the capability of remote plasma assisted PLD in selecting and controlling the crystalline phase of manganese oxide layers. © 2016 Elsevier B.V.