Petroleum pollution sensing at ppb level using quartz crystal resonators sputtered with porous polyethylene under photo-excitation

Radio-frequency (r.f.) sputtering of a porous polyethylene (PE) disk made by sintering PE granules can be used to form hydrocarbon-polymer films applied as the chemical-sensing overlayers of quartz crystal resonator sensors that can detect petroleum hydrocarbon vapors at low parts-per-billion (ppb) levels. The vapor-sorption capabilities of these films are profoundly affected by the sputtering method used; they are enhanced by photo-excitation through irradiation using ultraviolet (UV) light, and reduced by carbonization induced by long-term processing or by water-treatment. The PE films, especially photo-excited PE film, are characterized by a smooth surface, a high atomic density with a high hydrogen content, and dangling-bond longevity. Photo-excited PE film are capable of detecting linear hydrocarbon (>C12) vapors below the ppb level. Pre-sorption with water vapor at 9% relative humidity (RH) can enhance the sensing abilities of sensors for petroleum hydrocarbons. The effect of this water treatment on petroleum hydrocarbon sorption is especially prominent for d-phenylalanine-sputtered film.