DC Magnetron Sputtered\nPolyaniline-HCl Thin Films\nfor Chemical Sensing Applications

Abstract

Thin films of conducting polymers exhibit unique chemical\nand physical\nproperties that render them integral parts in microelectronics, energy\nstorage devices, and chemical sensors. Overall, polyaniline (PAni)\ndoped in acidic media has shown metal-like electronic conductivity,\nthough exact physical and chemical properties are dependent on the\npolymer structure and dopant type. Difficulties arising from poor\nprocessability render production of doped PAni thin films particularly\nchallenging. In this contribution, DC magnetron sputtering, a physical\nvapor deposition technique, is applied to the preparation of conductive\nthin films of PAni doped with hydrochloric acid (PAni-HCl) in an effort\nto circumvent issues associated with conventional thin film preparation\nmethods. Samples manufactured by the sputtering method are analyzed\nalong with samples prepared by conventional drop-casting. Physical\ncharacterization (atomic force microscopy, AFM) confirm the presence\nof PAni-HCl and show that films exhibit a reduced roughness and potentially\npinhole-free coverage of the substrate. Spectroscopic evidence (UV–vis,\nFT-IR, and X-ray photoelectron spectroscopy (XPS)) suggests that structural\nchanges and loss of conductivity, not uncommon during PAni processing,\ndoes occur during the preparation process. Finally, the applicability\nof sputtered films to gas-phase sensing of NH₃ was investigated\nwith surface plasmon resonance (SPR) spectroscopy and compared to\nprevious contributions. In summary, sputtered PAni-HCl films exhibit\nquantifiable, reversible behavior upon exposure to NH₃ with\na calculated LOD (by method) approaching 0.4 ppm NH₃ in\ndry air.