Adsorption properties of fluorocarbon thin films prepared by physical vapor deposition methods

To investigate their potential as gas sensors, fluorocarbon thin films were deposited onto the gold electrode of a quartz crystal microbalance by vacuum evaporation (VE), plasma assisted vacuum evaporation (PE-VE) and RF sputtering (RF-SP). The adsorption properties of these thin films for water, ethanol, acetone, acetaldehyde, toluene and methyl salicylate were then evaluated and compared to their surface morphologies. These fluorocarbon thin films have low sensitivities to non-polar solvents which contain methyl and aromatic groups, and high sensitivities to polar solvents which contain carbonyl and hydroxyl groups. The adsorbed mass of all gases besides water was found to increase with increasing film surface free energy. The adsorbed mass of water was largest for the film prepared by PE-VE, which is thought to be the result of the larger polar component of its surface free energy. In addition, the film prepared by RF-SP was shown to have a high sensitivity for polar solvents such as ethanol, acetone and acetaldehyde.