Rapid Growth of Crystalline Mn5O8 by Self-Limited Multilayer Deposition using Mn(EtCp)2 and O3
2016
Young, Matthias J. | Hare, Christopher D. | Cavanagh, Andrew S. | Musgrave, Charles B. | George, Steven M.
This work investigates the use of ozone as a post-treatment of ALD-grown MnO and as a coreactant with bis(ethylcyclopentadienyl)manganese (Mn(EtCp)₂) in ALD-like film growth. In situ quartz crystal microbalance measurements are used to monitor the mass changes during growth, which are coupled with ex situ materials characterization following deposition to evaluate the resulting film composition and structure. We determined that during O₃ post-treatment of ALD-grown MnO, O₃ oxidizes the near-surface region corresponding to a conversion of 22 Å of the MnO film to MnO₂. Following oxidation by O₃, exposure of Mn(EtCp)₂ results in mass gains of over 300 ng/cm², which exceeds the expected mass gain for reaction of the Mn(EtCp)₂ precursor with surface hydroxyls by over four times. We attribute this high mass gain to adsorbed Mn(EtCp)₂ shedding its EtCp ligands at the surface and releasing Mn(II) ions which subsequently diffuse into the bulk film and partially reduce the oxidized film back to MnO. These Mn(EtCp)₂ and O₃ reactions are combined in sequential steps with (a) Mn(EtCp)₂ reacting at the surface of an O-rich layer, shedding its two EtCp ligands and freeing Mn(II) to diffuse into the film followed by (b) O₃ oxidizing the film surface and withdrawing Mn from the subsurface to create an O-rich layer. This deposition process results in self-limiting multilayer deposition of crystalline Mn₅O₈ films with a density of 4.7 g/cm³ and an anomalously high growth rate of 5.7 Å/cycle. Mn₅O₈ is a metastable phase of manganese oxide which possesses an intermediate composition between the alternating MnO and MnO₂ compositions of the near-surface during the Mn(EtCp)₂ and O₃ exposures.
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