Molecular layer deposition (MLD) offers the deposition of ultra-thin 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, 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 1 Page 1 of 51 ACS Paragon Plus Environment Chemistry of Materials aspects and thus an MLD process is developed using Mg(MeCp) 2 as metal source and ethylene glycol (EG) or glycerol (GL) as organic reactants. Saturated growth could be achieved at 2Å/cycle to 3Å/cycle in a wide temperature window from 100 • C 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 ALD of Al 2 O 3 . 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.
Novel coating materials are constantly
needed for current and future
applications in the area of microelectronics, biocompatible materials,
and energy-related devices. Molecular layer deposition (MLD) is answering
this cry and is an increasingly important coating method for organic
and hybrid organic–inorganic thin films. In this study, we
have focused on hybrid inorganic–organic coatings, based on
trimethylaluminum, monofunctional aromatic precursors, and ring-opening
reactions with ozone. We present the MLD processes, where the films
are produced with trimethylaluminum, one of the three aromatic precursors
(phenol, 3-(trifluoromethyl)phenol, and 2-fluoro-4-(trifluoromethyl)benzaldehyde),
ozone, and the fourth precursor, hydrogen peroxide. According to the
in situ Fourier-transform infrared spectroscopy measurements, the
hydrogen peroxide reacts with the surface carboxylic acid group, forming
a peroxyacid structure (C(O)–O–OH), in the case of all
three processes. In addition, molecular modeling for the processes
with three different aromatic precursors was carried out. When combining
these modeling results with the experimental research data, new interesting
aspects of the film growth, reactions, and properties are exploited.
Developing higher capacity electrode materials is a key challenge in battery advancement. Metal oxides undergoing conversion and/or alloying reactions offer high capacities, but suffer from volumetric changes and poor conductivities. However, combining several of these oxides can induce a synergistic effect, enhancing electrode characteristics. Using atomic layer deposition (ALD), carefully controlled model thin-film electrodes comprised of SnO2 and Fe2O3, and mixtures thereof are deposited to investigate length scales at which intermixing of the oxides is required to maximize this effect. ALD enables the synthesis of both intermixed structures and oxides where Fe, Sn, and O are mixed at the atomic scale and nanolaminated structures where Fe2O3 layer and SnO2 layers form a structure with well-defined interfaces. These model systems reduce the complexity of electrodes by eliminating the need for binders and additives and ensuring one-dimensional charge carrier diffusion. Using ALD enables us to study the influence of interfaces on electrode characteristics. It was found that intermixing of Fe2O3 and SnO2 at the atomic scale kinetically suppresses the alloying of Sn. In the nanolaminated superstructure, however, Sn alloying does take place, causing the well-defined interfaces to break down due to the volume changes brought about by alloying. As a consequence, the electrode capacity is rapidly fades, and thus, this structure type should be avoided. Here, the authors demonstrate that ALD is a unique tool with great potential for unraveling complex mechanisms in battery materials.
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