Surface Chemistry of Copper Nanoparticles and Direct Spray Printing of Hybrid Particle/Metallorganic Inks

Copper films have been direct written on heated substrates using both neat metallorganic and two-component, copper nanoparticle/copper metallorganic inks. Commercial nanoparticle copper (nano-Cu) was characterized by transmission electron microscopy and powder X-ray diffraction (PXRD) and found to consist of Cu/Cu₂O spherical particles measuring 100-500 nm in diam. The Cu₂O was etched away using an excess of hexafluoroacetylacetone (Hhfa) and vinyltrimethylsilane (VTMS) yielding pure Cu by PXRD. Hhfa etching in the absence of VTMS led to the formation of millimeter-sized Cu particles at room temperature. Neat (hexafluoroacetylacetonato)Cu(1)-(VTMS) (Cu(hfa)·VTMS) was spray printed in a nitrogen ambient on glass microscope slides and Kapton at 210-230°C to give dense, adherent films. Hhfa/VTMS-etched nano-Cu was mixed with (Cu(hfa)·VTMS) and spray printed in a nitrogen ambient on glass microscope slides and Kapton at 210-220°C. Copper films produced by both approaches were characterized by scanning electron microscopy and standard four-probe resistivity techniques.