Methods and apparatus for preparing a protective coating are described. In one example aspect, an apparatus for preparing a protective coating includes a chamber, a substrate positioned within the chamber configured to hold at least a target object, an inlet pipe configured to direct a monomer vapor into the chamber, and one or more electrodes configured to perform a chemical vapor deposition process to produce a multi-layer coating. The chemical vapor deposition process comprises multiple cycles, each cycle comprising a pretreatment phase and a coating phase to produce a layer of the multi-layer coating.