Heterostructured Layer Growth of Polyaniline by Vacuum Thermal Evaporation and Fabrication of Thin-Film Capacitors

Thin films of conducting polymers find applications in many emerging areas, such as packaging, sensing, coating, thin-film capacitors, organic integrated circuits, organic thin wires, and electroluminescent devices. The success of thin-film-based devices relies on precisely controlled thickness (∼100 nm) and surface characteristics. Tailored-made properties can be harnessed by preparing thin films by multiple coatings (namely, layer-by-layer deposition), which results in heterogeneity within the film required for special applications. In spite of excellent electrical conductivity of Polyaniline (PANI), the fabrication of thin-film-based devices is restricted because of its brittleness. Herein, we report the preparation of bilayer thin films of PANI along with the individual thin films of PANI-emeraldine salt (ES) and PANI-emeraldine base (EB) using the vacuum thermal evaporation method. Detailed structural and morphological analysis shows the formation of well-organized PANI thin films with a roughness of ≈ 10 nm and the thickness ranging from 50 to 100 nm. PANI-ES shows the highest electrical, dielectric, and electrostatic charge properties, which is attributed to the crystalline structure as revealed by X-ray diffraction analysis. All the thin films show semiconducting behavior as revealed by the band gap analysis (1.7-2.2 eV). The optical constants of the bilayer film measured from spectroscopic ellipsometry show a marginal deviation from the individual films, which is attributed to the interfacial interaction between the layers of PANI-ES and PANI-EB. Thin-film capacitors based on PANI-ES show the highest current and energy density compared to those based on PANI-EB and bilayer films.