Effects of dodecylamine and dodecanethiol on the conductive properties of nano-Ag films

Nano-Ag particles, with dodecylamine (DDA) and dodecanethiol (DDT) as the protective agent, were prepared and studied in order to investigate the effect of protective agent in the post heat-treatment of nano-Ag films. Results of electrical resistivity, micro-structural evolution and thermal analysis showed that the Ag–DDA films require a lower treatment temperature to convert into conductive materials compared to that of the Ag–DDT films. And the Ag–DDA films also have lower final electrical resistivity as well as more uniform and dense microstructure in comparison with the Ag–DDT films. Further study indicated that Ag–DDA films are thermodynamically unstable and the sinter of Ag–DDA particles could occur spontaneously even at room temperature. FT-IR, 1H NMR and X-ray diffraction determinations revealed that both DDA and DDT molecules coordinate to the surface of nano-Ag particles through their head-groups. The bonding energy of Ag–S is higher than that of Ag–N and the alkyl chains ordering of chemisorbed DDT is also higher than that of chemisorbed DDA. It is implied that the post heat-treatment temperature and final resistivity of nano-Ag films are associated with the bonding energy and configuration of different capping molecules. Finally the conductive ink was prepared with well dispersed Ag–DDA nanoparticles and the ink-jet printed patterns on PI films show a sheet resistance of 166 mΩ/□ after heat-treating at 140 °C for 60 min.