Combination Of Atomic Layer Deposition Research Articles

Plasma-enhanced atomic layer deposition of titania on alumina for its potential use as a hydrogen-selective membrane

As a clean energy carrier, hydrogen has attracted global attention in recent years, because it could address issues that are related to reducing global climate change. It has to be stipulated that to date's processes for hydrogen production using fossil fuels need to be coupled with CO 2 separation and storage. Thermally and hydrothermally stable microporous membranes with intrinsic high H 2/CO 2 selectivity are highly demanded in steam-reforming and water gas-shift processes for H 2 gas separation. In this study a composite alumina–titania membrane was synthesized by the combination of atomic layer deposition (ALD) and sol–gel processes. By adjusting the number of ALD cycles (280 cycles), a thin TiO 2 layer corresponding to a thickness of ∼10 nm was deposited on the surface of γ-Al 2O 3 membranes. The gas permeation was tested to assess the membranes’ gas separation performance. The membranes exhibited a good balance between H 2 permeance and separation properties. At 450 K, the H 2 permeance is approximately 12.5 × 10 −8 mol m −2 s −1 Pa −1 and the separation factor is 5.8 for a H 2/CO 2 mixture. The results clearly demonstrate that the studied deposition method ALD is a promising route to prepare ceramic microporous membranes for hydrogen separation.

Surface Chemistry for Molecular Layer Deposition of Organic and Hybrid Organic−Inorganic Polymers

The fabrication of many devices in modern technology requires techniques for growing thin films. As devices miniaturize, manufacturers will need to control thin film growth at the atomic level. Because many devices have challenging morphologies, thin films must be able to coat conformally on structures with high aspect ratios. Techniques based on atomic layer deposition (ALD), a special type of chemical vapor deposition, allow for the growth of ultra-thin and conformal films of inorganic materials using sequential, self-limiting reactions. Molecular layer deposition (MLD) methods extend this strategy to include organic and hybrid organic-inorganic polymeric materials. In this Account, we provide an overview of the surface chemistry for the MLD of organic and hybrid organic-inorganic polymers and examine a variety of surface chemistry strategies for growing polymer thin films. Previously, surface chemistry for the MLD of organic polymers such as polyamides and polyimides has used two-step AB reaction cycles using homo-bifunctional reactants. However, these reagents can react twice and eliminate active sites on the growing polymer surface. To avoid this problem, we can employ alternative precursors for MLD based on hetero-bifunctional reactants and ring-opening reactions. We can also use surface activation or protected chemical functional groups. In addition, we can combine the reactants for ALD and MLD to grow hybrid organic-inorganic polymers that should display interesting properties. For example, using trimethylaluminum (TMA) and various diols as reactants, we can achieve the MLD of alucone organic-inorganic polymers. We can alter the chemical and physical properties of these organic-inorganic polymers by varying the organic constituent in the diol or blending the alucone MLD films with purely inorganic ALD films to build a nanocomposite or nanolaminate. The combination of ALD and MLD reactants enlarges the number of possible sequential self-limiting surface reactions for film growth. Extensions to three-step ABC reaction cycles also offer many advantages to avoid the use of homo-bifunctional reactants and incorporate new functionality in the thin film. The advances in ALD have helped technological development in many areas, including semiconductor processing and magnetic disk-drive manufacturing. We expect that the advances in MLD will lead to innovations in polymeric thin-film products. Although there are remaining challenges, effective surface chemistry strategies are being developed for MLD that offer the opportunity for future advances in materials and device fabrication.