Room Temperature and Atmospheric Pressure Atomic Layer Deposition of SiO ₂ Thin Films Mediated by a Molecular Water Layer

Silicon dioxide (SiO2) is commonly used in optoelectrical devices and encapsulation technologies because of its high transparency, chemical resistance, and excellent barrier properties. In this work, we demonstrate the room-temperature deposition of SiO2 thin films using atmospheric-pressure spatial atomic layer deposition (AP-SALD) from SiCl4 and water. Uniform coatings were obtained on silicon and sapphire substrates, also on silver nanowire (AgNW) networks, confirming the compatibility of the coating process with thermally sensitive materials. In contrast to conventional ALD, which often relies on surface hydroxyl groups at elevated temperatures, growth proceeds here through a pathway in which SiCl4 reacts with physisorbed H2O molecules transiently retained on the substrate surface. First-principle calculations support this water-mediated mechanism, which enables film formation under ambient conditions. As a proof of concept, AgNW networks were conformally encapsulated with SiO2, demonstrating preserved morphology, suppressed degradation due to Joule heating, and enhanced thermal stability. These findings establish an ALD regime for SiO2 growth at low temperature for thermally sensitive substrates.