ALD Based Surface Functionalization and Porosity Control
LaboratoryLawrence Livermore National Laboratory (LLNL)
Capability ExpertMonika Biener
Node Readiness Category3: Photoelectrochemical (PEC)
This capability involves 1) the development of catalytically active and corrosion resistant high surface area electrodes for photoelectrolysis 2) fine tuning the porosity of porous materials and 3) templating of porous materials to yield freestanding ALD coatings that are fully tunable in density and porosity.
We have long-term experience in using atomic layer deposition (ALD) to increase the catalytic activity and long-term stability of high-surface area materials. Even ultra-high (>104) aspect ratio materials have been successfully coated with uniform and conformal metal oxide coatings as thin as one monolayer (one Angstrom). The resulting hybrid materials combine the structural properties of the substrate (such as ultra-high surface area) with the catalytic properties and corrosion resistance of the ALD coating . For example, ultrathin and pin-hole free oxide coatings have the potential to stabilize semiconductor photoelectrodes that otherwise would be unstable in aqueous acid or base. In addition, one Angstrom thick metal oxide coatings are thin enough to warrant fast electron transport through the oxide layer. Using high surface area (high aspect ratio) photoelectrodes opens the door to compensate low electrocatalytic activity (due to low turnover frequencies or low catalyst mass loadings) with high surface area. ALD coatings on nanoporous materials with unimodal feature/pore sizes can also be used to fine tune the pore size of the material. To generate these ultrathin, conformal and uniform coatings on ultra-high aspect ratio bulk materials we are using a customized ALD reactor technology. If the substrate is removed through an etch process, the technology yields freestanding and transparent ultra-high surface area bulk materials with fully tunable pore size, composition, and density .
Samples up to 4 inch diameter and half inch thickness can be coated. Standard ALD processes include Al2O3, TiO2, ZnO, Fe2O3, Ta2O5 and Pt, other processes can be installed on demand.
The ALD capability has been funded by LLNL's materials science program for >10 years. Our customized ALD system is specifically designed to uniformly coat ultra-high aspect ratio materials with uniform and conformal coatings. Using this capability, we have developed a proprietary ALD-based technology to fabricate highly active and thermally stable nanoporous catalysts.
Our customized ALD system is capable of simultaneous coating many samples. Using predefined deposition protocols makes it easy to train postdocs and to reproducibly generate large amounts of samples. State of the art materials characterization techniques (SEM, TEM, micro-Raman) are available for quality control.
This capability can improve the stability and efficiency of photoelectrode materials by applying an ultra-thin protective and catalytically active surface coating by atomic layer deposition.
Conformal ultrathin TiO2 ALD coating on bulk Nanoporous gold 
1. Biener, M.M., et al., ALD functionalized nanoporous gold: Thermal stability, mechanical properties, and catalytic activity. Nano Letters, 2011. 11: p. 3085–3090.
2. Biener, M.M., et al., Ultra-strong and Low-Density Nanotubular Bulk Materials with Tunable Feature Sizes. Advanced Materials, 2014. 26(28): p. 4808–4813.
3. Ye, J.C., et al., Structural Optimization of 3D Porous Electrodes for High-Rate Performance Lithium Ion Batteries. Acs Nano, 2015. 9(2): p. 2194-2202.