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 SiO2 nanoparticles. Thermal stability studies reveal that the thiourea films are stable to 200 degrees C, and indicate that desorption likely occurs at the SiO2/organic interface.