Atomistic growth phenomena of reactively sputtered RuO₂ and MnO₂ thin films

Abstract

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

“…The presence of the sole (101) reflection irrespective of the used substrate suggested the occurrence of a (101) preferential orientation and/or of anisotropic crystallite growth [23,34,44]. The relatively weak and broad diffraction peaks, as often observed in the case of supported MnO 2 films/nanosystems [9,10,13,14,22,33], suggested the formation of defective nanocrystallites, whose average dimensions were comprised between 25 and 35 nm ( Figure S3).…”

“…Repeated growth experiments under the same conditions enabled to ascertain the full reproducibility of material chemico-physical characteristics. The use of higher growth temperatures was avoided in order to prevent MnO 2 transformation into Mn 2 O 3 or Mn 3 O 4 [ 22 , 28 , 30 , 36 ]. For the same reason, the obtained samples were analyzed as-prepared, without any ex-situ thermal treatment.…”

“…MnO 2 exhibits at least six different structurally related crystalline modifications ( α , β , γ , δ , ε , and λ ) [ 1 , 2 , 4 , 7 , 10 , 16 , 17 , 18 , 19 ]. All these polymorphs are semiconductors with low resistivity [ 2 , 20 , 21 ], and have emerged as attractive candidates for several end-uses, including electrodes in Li- and Na-ion batteries and supercapacitors, thermoelectric materials, chemical sensors, photo- and electrocatalysts for pollutant degradation and hydrogen production, and magnetic devices useful for information storage [ 5 , 8 , 11 , 12 , 13 , 14 , 15 , 18 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ]. Among MnO 2 polymorphs, the most stable and abundant, i.e., rutile-type β -MnO 2 ( pyrolusite ) [ 16 , 34 , 35 ], is composed of MnO 6 octahedra linked by corner-shared oxygens into tunnel-containing frameworks [ 4 , 9 , 23 , 36 ].…”

“…Whereas bulk manganese oxide crystals and, especially, powdered materials with different morphologies have been widely investigated [ 3 , 12 , 16 , 17 , 27 , 29 , 35 , 37 , 38 ], the fabrication and tailoring of supported thin films and nanostructures, that may yield significant changes in the system behavior, deserves further attention [ 6 , 14 , 15 , 22 ]. 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.…”

“…So far, the preparation of MnO 2 thin films/nanosystems has been performed on polycrystalline substrates by various techniques. 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 ].…”