Organic vapor detection using quartz crystal sensors coated by sputtering of porous sintered-polymer targets

Abstract

A lipophilic hydrocarbon–polymeric film applicable to hydrocarbon gas sensing at the ppm level was prepared by radiofrequency sputtering of a porous sintered-polyethylene (PE) disk on to an AT-cut quartz crystal resonator as a mass transducer. The hydrocarbon polymeric structure was confirmed by hydrogen forward scattering–Rutherford backscattering spectroscopy and X-ray photoelectron spectroscopy. This thickness-shear mode acoustic wave sensor was also sensitive to polar organic vapors owing to the incorporation of 8% of oxygen. Fluoropolymer films without oxygen can also be produced by rf sputtering of a porous sintered-poly(vinylidene fluoride) (PVDF) disk. The sorption behaviors of the PE and PVDF films for 20 ppm primary alcohols showed proportional and inversely proportional relationships, respectively, with the polarizabilities of solute molecules. Although 100 ppm toluene vapor did not induce mechanical damping of the PE film owing to its swelling or softening, its sorption capacity strongly decreased during iterative sorption tests. However, 100 ppm ethanol vapor did not cause such an abrupt decrease in sorption capacity over 10-cycle iterative tests.