Deposition of Ultrathin Polythiourea Films by Molecular Layer Deposition

Molecular layer deposition (MLD) is a film growth technique which utilizes self-saturating surface chemistry to deposit organic films layer-by-layer. In this study we report a new MLD coupling chemistry to grow oxygen-free films with polythiourea groups. 1,4-Phenylene diisothiocyanate and ethylenediamine are reacted to form thiourea moieties. The films exhibit a constant growth rate and show saturation behavior in dosing each of the precursor molecules. The chemical composition of the films is probed by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and density functional theory, which confirm that the expected polythiourea films are formed by the MLD process. Transmission electron micrographs demonstrate conformal coating of SiO 2 nanoparticles. Thermal stability studies reveal that the thiourea films are stable to 200 °C, and indicate that desorption likely occurs at the SiO 2 /organic interface.