Single-Cycle Atomic Layer Deposition on Bulk Wood Lumber for Managing Moisture Content, Mold Growth, and Thermal Conductivity

Abstract

Wood is a universal building material. While highly versatile, many of its critical properties vary with water content (e.g., dimensionality, mechanical strength, and thermal insulation). Treatments to control the water content in wood have many technological applications. This study investigates the use of single-cycle atomic layer deposition (1cy-ALD) to apply <1 nm Al₂O₃, ZnO, or TiO₂ coatings to various bulk lumber species (pine, cedar, and poplar) to alter their wettability, fungicidal, and thermal transport properties. Because the 1cy-ALD process only requires a single exposure to the precursors, it is potentially scalable for commodity product manufacturing. While all ALD chemistries are found to make the wood's surface hydrophobic, wood treated with TiO₂ (TiCl₄ + H₂O) shows the greatest bulk water repellency upon full immersion in water. In situ monitoring of the chamber reaction pressure suggests that the TiCl₄ + H₂O chemistry follows reaction-rate-limited processing kinetics that enables deeper diffusion of the precursors into the wood's fibrous structure. Consequently, in humid or moist environments, 1cy-ALD (TiCl₄ + H₂O) treated lumber shows a 4 times smaller increase in thermal conductivity and improved resistance to mold growth compared to untreated lumber.