Structure and properties of Mn3O4 thin films grown on single crystal substrates by chemical vapor deposition

Abstract

Mn3O4 thin films were fabricated on SrTiO3(111) and Y3Al5O12 (100) substrates by chemical vapor deposition (CVD) under O2 atmospheres, starting from a fluorinated Mn(II) diketonatediamine adduct. The obtained systems were investigated by a multi-technique characterization in order to elucidate the interplay between preparation conditions and their chemico-physical properties. The results highlighted the formation of phase-pure and homogeneous -Mn3O4 (haussmannite) films, characterized by a smooth morphology, an appreciable Vis light absorption and structural features directly dependent on the used substrate. The target systems were uniformly doped with fluorine, due to the used Mn compound acting as a single-source precursor for both Mn and F. In addition, magnetic force microscopy measurements revealed the formation of spin domains and long-range magnetic order in the target materials, paving the way to their future implementation as magnetic media toward device integration for data storage.

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

“…As can be observed in Figure 6, right column, the recorded micrographs revealed an even in-plane distribution of magnetic domains. The reversing of MFM contrast from bright to dark can be associated to the switch from repulsive to attractive surface-tip interactions, corresponding, in turn, to upward and downward orientations of magnetic moments, respectively [42]. The lack of single-color large areas enabled to discard the presence of magnetic impurities in appreciable amounts, confirming thus the obtainment of pure MnO 2 nanostructures with homogeneous characteristics.…”

“…As a matter of fact, the occurrence of oxygen defects in the target nanomaterials can favorably influence the system functional behavior for (photo)catalytic end-uses [23,34]. In particular, the present Vis-light harvesting might be beneficial for eventual photocatalytic applications for environmental protection and energy production, as already mentioned [40,42,48]. Irrespective of the substrate nature, Tauc plot analysis (see Figure 5b) yielded a mean energy gap value of E G = (2.0 ± 0.1) eV, which was blue-shifted with respect to that reported for various MnO 2 polymorphs [7,9,23].…”

“…The latter conclusion was further corroborated by the energy difference between the Mn2p 3/2 and O1s lattice components (112.7 eV; see below) [ 23 , 32 , 34 ]. In fact, two components contributed to the O1s signal ( Figure 1 b 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 BE (II), centered at 531.5 eV, due to the presence of hydroxyl groups/oxygen chemisorbed on surface O defects [ 13 , 39 , 42 , 43 ]. The occurrence of the latter, already reported in previous literature studies on various manganese dioxide polymorphs [ 8 , 16 , 25 , 37 ], is in line with optical absorption results (see below).…”

“…In this regard, one of the valuable means to modulate MnO 2 nanosystem properties involves its controlled anionic doping, far less explored than the conventional cationic one. In particular, fluorine doping can be a useful tool to enhance the surface reactivity and tune both electrical and optical characteristics, a key issue for eventual photocatalytic, energy storage, and gas sensing applications [34,[39][40][41][42]. In addition, the obtained system characteristics are directly affected by the electronic structure and properties of surfaces and interfaces, as well as on the nature of the used deposition substrate, which may influence the nucleation kinetics and the subsequent structural and morphological evolution [3,21].…”

“…These include reactive sputtering on Si [ 22 ], pulsed laser deposition on stainless steel [ 30 ], thermal evaporation on glass and quartz [ 9 ], hydrothermal routes on Si, carbon cloth, and Ni foams [ 14 , 33 , 43 ], electrodeposition on stainless steel, glass, carbon fibers, and Ni sheets [ 7 , 8 , 10 , 11 ], chemical bath deposition on stainless steel [ 13 , 30 ], spray pyrolysis on glass and steel [ 15 ], atomic layer deposition on Si [ 6 , 31 , 32 ], and chemical vapor deposition (CVD) on Si and glass [ 23 , 34 , 44 ]. Nevertheless, the use of single crystal substrates can not only stabilize specific polymorphs, but also affect morphology, structure, and crystal quality [ 21 , 41 , 42 , 45 ]. To date, different studies have reported on the atomic layer deposition (ALD) of α -MnO 2 on NaCl(100), KCl(100), and KBr(100) and of ε -MnO 2 on Al 2 O 3 (001) [ 1 , 21 ].…”