Molecular Layer Deposition of “Magnesicone”, a Magnesium-based Hybrid Material

Molecular layer deposition (MLD) offers the deposition of ultrathin and conformal organic or hybrid films which have a wide range of applications. However, some critical potential applications require a very specific set of properties. For application as desiccant layers in water barrier films, for example, the films need to exhibit water uptake and swelling and be overcoatable. For application as a backbone for a solid composite electrolyte for lithium ions on the other hand, the films need to be stable against lithium and need to be transformable from a hybrid MLD film to a porous metal oxide film. Magnesium-based MLD films, called “magnesicone”, are promising on both these aspects, and thus, an MLD process is developed using Mg(MeCp)2 as a metal source and ethylene glycol (EG) or glycerol (GL) as organic reactants. Saturated growth could be achieved at 2 to 3 Å/cycle in a wide temperature window from 100 to 250 °C. The resulting magnesicone films react with ambient air and exhibit water uptake, which is in the case of the GL-based films associated with swelling (up to 10%) and in the case of EG-based magnesicone with Mg(CO)3 formation, and are overcoatable with an ALD of Al2O3. Furthermore, by carefully tuning the annealing rate, the EG-grown films can be made porous at 350 °C. Hence, these functional tests demonstrate the potential of magnesicone films as reactive barrier layers and as the porous backbone of lithium ion composite solid electrolytes, making it a promising material for future applications.