Molecular Layer Deposition of Alucone Polymer Films Using Trimethylaluminum and Ethylene Glycol

Abstract

Polymeric films can be grown by a sequential, self-limiting surface chemistry process known as molecular layer deposition (MLD). The MLD reactants are typically bifunctional monomers for stepwise condensation polymerization and can yield completely organic films. The MLD of organic–inorganic hybrid polymers can also be accomplished using a bifunctional organic monomer and a multifunctional inorganic monomer. In this work, the growth of a poly(aluminum ethylene glycol) polymer is demonstrated using the sequential exposures of trimethylaluminum (TMA) and ethylene glycol (EG). These hybrid polymers, known as alucones, were grown over a wide range of temperatures from 85 to 175 °C. In situ quartz crystal microbalance and ex situ X-ray reflectivity experiments confirmed linear growth of the alucone film versus number of TMA/EG reaction cycles at all temperatures. The alucone growth rates decreased at higher temperatures. Growth rates varied from 4.0 Å per cycle at 85 °C to 0.4 Å per cycle at 175 °C. In situ Fourier transform infrared spectroscopy was used to monitor the surface reactions during alucone MLD. Ex situ FTIR spectroscopy, X-ray photoelectron spectroscopy, and X-ray reflectivity measurements were also employed to determine the chemical composition, thickness, and density of the alucone films. These ex situ studies revealed that the alucone films grown on Al2O3 ALD surfaces evolved under ambient conditions before reaching a stable state. Alucone films capped with rapid SiO2 ALD displayed much more stability than alucone films grown on Al2O3 ALD surfaces. These results indicated that H2O may facilitate the chemical transformation of the alucone MLD films. The alucone films represent a new class of organic–inorganic hybrid polymers. Modification of this basic alucone MLD chemistry with use of other diols or other bifunctional monomers can produce different alucone polymers with variable properties.

Tunable optical properties of hybrid inorganic–organic [(TiO2)m(Ti–O–C6H4–O–)k]n superlattice thin films

“…This is in line with the previously reported values 3.39-3.76 g/cm 3 for ALD-fabricated TiO2 films 30 and is in agreement with our XRD data that confirmed growth of anatase phase TiO2. The value 1.6 g/cm 3 for the m=0 hybrid indicates a dramatic decrease in density compared to the purely inorganic films and compares well with the values of around 1.5-2.0 g/cm 3 reported previously for similar types of hybrid films 14,20,21,27 . Such changes in the density values for the present films indicate modification of mechanical properties typically searched for hybrid inorganic-organic films, e.g., for flexible applications.…”

“…10,11 Molecular layer deposition can be used to fabricate thin films of organic polymers, such as polyamides and polyimides. 12,13 Most interestingly, use of metal precursors together with organic precursors enables hybrid inorganic-organic thin films to be fabricated with combined ALD/MLD processes, 14,15 where the organic precursors can be, e.g., organic alcohols 14,16 or carboxylic acids. 17,18 Such combined ALD/MLD processes also allow for fabrication of hybrid inorganic-organic materials in the form of nanolaminates [19][20][21] and superlattices [22][23][24] in an elegant manner.…”

Progress and future directions for atomic layer deposition and ALD-based chemistry

“…One of the fi rst hybrid organic-inorganic fi lms was an aluminum alkoxide polymer fi lm grown using trimethylaluminum (TMA) and ethylene glycol (EG). 22 This hybrid organic-inorganic is just one of a large family of aluminum alkoxides known as "alucones." 23 A schematic showing the surface chemistry of alucone growth using TMA and EG is shown in Figure 2 .…”

Atomic-Level Structural and Electronic Properties of Hybrid Inorganic–Organic ZnO:Hydroquinone Superlattices Fabricated by ALD/MLD

“…ALD (Atomic Layer Deposition), for inorganic materials. [1][2][3] For the inorganicorganic hybrids, ALD cycles are combined with MLD (Molecular Layer Deposition) cycles based on purely organic precursors, [4][5][6][7] as schematically shown in Figure 1. This enables the atomic/molecular layer-by-layer production of inorganic-organic hybrid thin films through sequential self-limiting gas-surface reactions with high precision for the film thickness and composition like in the case of inorganic ALD thin films.…”