Designing molecular complex for improved atomic economy in initiated chemical vapor deposition
Improving the atomic economy is important for thin film fabrication processes. Initiated chemical vapor deposition (iCVD) is considered as one of the most promising methods for polymer film fabrication due to its abundant material library, flexible design, solvent-less and substrate-independent features. For iCVD, surface adsorption of monomers determines the surface concentration, and in turn the deposition rate, conversion efficiency, and film properties. The surface adsorption in the iCVD process is predominantly regulated by diluting the monomer vapor with the inert carrier gas. Nevertheless, controllability and the atomic economy are restricted by the inherent molecular features for high-volatility valuable chemicals. Here, we proposed a universal strategy to enhance the monomer adsorption by forming molecular complex to improve the atomic economy. We exemplified the strategy using 4-vinyl pyridine (4VP) as a model system. By replacing the carrier gas from inert argon into active hexafluoro-2-propanol (HFIP) that interacts with various polar monomers via strong hydrogen bond to form molecular complex, a 310% deposition rate or 56% less monomer supply was achieved under typical fabrication condition. By systematically changing the polarity of monomer and the interaction between carrier gas and monomers, intermolecular interaction is proved as the key to enhanced adsorption. Polymer films deposited under active carrier gas revealed higher surface roughness, 4-times higher molecular weight and 25% higher hardness for the same polymer composition. Given its universality, this strategy is broadly applicable for enhanced adsorption for polar monomers, which in turn improves the film quality, cost-effectiveness and environmental friendliness of chemical vapor deposition.