Plasma-Assisted Chemical Vapor Deposition of F-Doped MnO2 Nanostructures on Single Crystal Substrates.

Lorenzo Bigiani,Chiara Maccato,Elza Bontempi,Alberto Gasparotto,Davide Barreca,Cinzia Sada

doi:10.3390/nano10071335

Abstract

MnO2 nanostructures were fabricated by plasma assisted-chemical vapor deposition (PA-CVD) using a fluorinated diketonate diamine manganese complex, acting as single-source precursor for both Mn and F. The syntheses were performed from Ar/O2 plasmas on MgAl2O4(100), YAlO3(010), and Y3Al5O12(100) single crystals at a growth temperature of 300 °C, in order to investigate the substrate influence on material chemico-physical properties. A detailed characterization through complementary analytical techniques highlighted the formation of highly pure and oriented F-doped systems, comprising the sole β-MnO2 polymorph and exhibiting an inherent oxygen deficiency. Optical absorption spectroscopy revealed the presence of an appreciable Vis-light harvesting, of interest in view of possible photocatalytic applications in pollutant degradation and hydrogen production. The used substrates directly affected the system structural features, as well as the resulting magnetic characteristics. In particular, magnetic force microscopy (MFM) measurements, sensitive to the out-of-plane magnetization component, highlighted the formation of spin domains and long-range magnetic ordering in the developed materials, with features dependent on the system morphology. These results open the door to future engineering of the present nanostructures as possible magnetic media for integration in data storage devices.

Highlights

Manganese oxides have attracted considerable interest thanks to their diversity of oxidation states and crystal structures, yielding broadly tunable characteristics as a function of the adopted preparation conditions [1,2,3,4,5,6,7,8,9,10,11]
When the 3s electron is photoejected from a paramagnetic center like manganese, the exchange coupling between the 3s hole created after photoemission and the 3d electrons results in a signal splitting, whose magnitude is a fingerprint of the metal oxidation state [3,6,8,44]
Two components contributed to the O1s signal (Figure 1b and Figure S2a–c), a major one at 529.6 eV (I), attributed to lattice Mn–O–Mn moieties, and a second one at higher Binding energy (BE) (II), centered at 531.5 eV, due to the presence of hydroxyl groups/oxygen chemisorbed on surface O defects [13,39,42,43]

Summary

Introduction

Manganese oxides have attracted considerable interest thanks to their diversity of oxidation states and crystal structures, yielding broadly tunable characteristics as a function of the adopted preparation conditions [1,2,3,4,5,6,7,8,9,10,11]. The interest in β-MnO2 has been promoted by its screw-type magnetic structure with an important spin-lattice coupling, as well as by the large room temperature magnetoresistance and ferromagnetism. These features are of considerable importance from both a fundamental and a technological point of view, since they can give rise to applications in recording devices and contribute to new studies on electronic-magnetic interactions in the target systems [16,24,25,35,37]

Methods

Results

Conclusion