Synthesis and characterization of copper sulfide nanocrystallites with low sintering temperatures

Abstract

To study nano-inks with relatively low sintering temperatures for fabrication of functional electronics on paper by inkjet printing technology, we have successfully prepared copper sulfide nanocrystallites protected by self-assembled monolayers. Systematic characterization was performed on as-prepared nanoparticles by FTIR, NMR, thermogravimetric analysis (TGA), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and wide-angle X-ray scattering (WAXS) with heating. The copper sulfide nanocrystallites with crystal sizes <1.5 nm show a hexagonal Cu₂S phase at low temperatures but undergo significant consolidation/crystallization from 100 to 240 °C, accompanying a transformation from the hexagonal Cu₂S phase to the cubic Cu_1.8S phase when heated up to ca. 150 °C. The protective ligand burnout during heating is closely associated with the nanocrystallite consolidation. Further, the copper sulfide nanoparticles were deposited on paper and sintered at 240 °C in air. The sintered particles are composed of large crystals of cubic Cu_1.8S with no serious degradation due to oxidation. The resistivity of the sintered particles was of the order of 1 × 10⁻⁵ (Ω m).