Structural and electrical properties of Ni films sputter-deposited on HCl-doped polyaniline substrates

• Ni films were sputter-deposited on HCl-PANI substrates.
• Ni/HCl-PANI composites were obtained.
• Ni/HCl-PANI composites exhibit a metal–semiconductor transition.
• The transition temperature lowers with decreasing film thickness.
• Ni films grow with columnar grains.

Ni films with a thickness of 45–240 nm were sputter-deposited on HCl-doped polyaniline (HCl-PANI) substrates at 300 K, forming the Ni/HCl-PANI composites. All the Ni films grow with columnar grains. The grain size increases with increasing film thickness. A temperature dependence of the resistance within 5–300 K reveals that all the Ni/HCl-PANI composites exhibit a metal–semiconductor transition. The transition temperature lowers with decreasing film thickness. The composite shows a metallic conduction behavior at temperatures below the transition temperature and a semiconducting behavior at temperatures over the transition temperature. A temperature coefficient of resistance increases with film thickness in the temperature range of the metallic conduction. A decrease of the resistance with temperature becomes more significant with decreasing film thickness in the temperature range of the semiconducting behavior.