High-Purity Copper Structures from a Perfluorinated Copper Carboxylate Using Focused Electron Beam Induced Deposition and Post-Purification

The electron-induced modification of volatile physisorbed metal-organic molecules is the key process in focused electron beam induced deposition (FEBID). In this work, the perfluorinated copper carboxylate [Cu-2(mu-O2CC2F5)(4)], (Cu-2(pfp)(4)), was implemented in FEBID, as it has the highest metal-to-carbon ratio Cu/C = 1:6 compared to other Cu precursors used so far. FEBID was obtained within a small temperature window of 120-130 degrees C. Transmission electron microscopy verified the presence of metal(oxide) nanocrystals within a carbonaceous matrix. The chemical composition analysis revealed the loss of about 80% of ligand material during the electron-induced dissociation. The copper nanocrystals oxidized within a few minutes in films <80 nm upon exposure to ambient conditions, while they were protected by a carbon-fluorine-containing matrix in thicker areas of the deposits. A two-step post-growth annealing procedure with subsequent oxidizing and reducing atmosphere was used to purify the deposits. Pure copper crystals were formed in this step.