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.