Multi-layer protective coating

A method for preparing a protective coating, comprising:

• adding a monomer vapor into a chamber, wherein the chamber includes a movable substrate having a target object positioned on the movable substrate;
• and
• performing a chemical vapor deposition process using one or more electrodes surrounding the movable substrate such that the monomer vapor forms a multi-layer protective coating on surfaces of the target object, wherein the one or more electrodes are each positioned substantially perpendicular to the movable substrate so as to surround the movable substrate,
• wherein the chemical vapor deposition process comprises multiple cycles, each cycle comprising a pretreatment phase and a coating phase to prepare a layer of the multi-layer coating, wherein, in the pretreatment phase, a first type of a discharge is applied at a first power level for a first time, and, in the coating phase, a second type of a discharge is applied at a second power level for a second time duration, the second power level being lower than the first power level, the method further comprising:
• adjusting, for different cycles in the chemical vapor deposition process, at least one parameter of the chemical vapor deposition process to produce layers having different densities or thicknesses, the at least one parameter including the first type of discharge, the second type of discharge, the first power level, the second power level, the first time duration, or the second time durations.