Investigation of sintering behavior of octanethiol-coated copper nano ink under various atmospheres

In this study, octanethiol-coated, nonoxidized 10 wt.% copper (Cu) nano ink was examined under different gas atmospheres during sintering. The Cu nanoparticles, 100 ± 10 nm in size, were coated with 1-octanethiol using a vapor self-assembled multilayer coating technique, under ultra-high vacuum and variable atmospheric conditions. 10 μL of the octanethiol-coated (surface-modified) nano ink was dropped onto a glass substrate to form a Cu pattern. The Cu pattern was sintered at 350 °C in a tube furnace under various gas atmospheres: hydrogen gas (H2), ammonia (NH3), an Ar/H2 gas mixture (Ar 95% : H2 5%), and Ar gas. The effect of sintering in different gas atmospheres on the octanethiol-coated Cu thin-film patterns was investigated by high-resolution transmission electron microscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and resistivity analysis. The resistivity of the fabricated thin films after sintering was 5.8 × 10− 6, 3.82 × 10− 5, 1.15 × 10− 3, and 8.64 × 10− 3 Ω cm for the H2, NH3, Ar/H2 gas mixture, and Ar gas atmospheres, respectively. The H2 atmosphere exhibited the lowest resistivity, which was close to that observed for bulk Cu. XPS analysis confirmed that the H2 and NH3 atmospheres completely removed the octanethiol coating from the Cu surface, due to their high reactivity. Additionally, the grain growth observed in the SEM images under H2 conditions was significantly better than that observed for the other gases. The technique used in this study to produce octanethiol-coated Cu nano ink provides an effective, environmentally friendly fabrication method for the electronic printing of materials.