Electron-induced deposition using Fe(CO)₄MA and Fe(CO)₅ - effect of MA ligand and process conditions

The electron-induced decomposition of Fe(CO)₄MA (MA = methyl acrylate), which is a potential new precursor for focused electron beam-induced deposition (FEBID), was investigated by surface science experiments under UHV conditions. Auger electron spectroscopy was used to monitor deposit formation. The comparison between Fe(CO)₄MA and Fe(CO)₅ revealed the effect of the modified ligand architecture on the deposit formation in electron irradiation experiments that mimic FEBID and cryo-FEBID processes. Electron-stimulated desorption and post-irradiation thermal desorption spectrometry were used to obtain insight into the fate of the ligands upon electron irradiation. As a key finding, the deposits obtained from Fe(CO)₄MA and Fe(CO)₅ were surprisingly similar, and the relative amount of carbon in deposits prepared from Fe(CO)₄MA was considerably less than the amount of carbon in the MA ligand. This demonstrates that electron irradiation efficiently cleaves the neutral MA ligand from the precursor. In addition to deposit formation by electron irradiation, the thermal decomposition of Fe(CO)₄MA and Fe(CO)₅ on an Fe seed layer prepared by EBID was compared. While Fe(CO)₅ sustains autocatalytic growth of the deposit, the MA ligand hinders the thermal decomposition in the case of Fe(CO)₄MA. The heteroleptic precursor Fe(CO)₄MA, thus, offers the possibility to suppress contributions of thermal reactions, which can compromise control over the deposit shape and size in FEBID processes.