Electron Beam Induced Reactions of Adsorbed Cobalt Tricarbonyl Nitrosyl (Co(CO)₃NO) Molecules

Abstract

This study focuses on elucidating the bond breaking steps involved in the electron beam induced deposition (EBID) of nanostructures created from the organometallic precursor cobalt tricarbonyl nitrosyl (Co(CO)3NO) by studying the effect of 500 eV incident electrons on nanometer scale films of Co(CO)3NO. Experiments were performed under ultrahigh vacuum conditions, using a suite of surface analytical techniques, principally X-ray photoelectron spectroscopy and mass spectrometry. The purely electron stimulated reactions of Co(CO)3NO adsorbed on gold or amorphous carbon substrates at low temperatures (−168 °C) occurs in two distinct steps. The first step involves a one electron process that initiates decomposition of the nitrosyl (NO) ligand to form a nitride, accompanied by the simultaneous desorption of at least one CO ligand to create a partially decarbonylated intermediate. This first step decomposes Co(CO)3NO into a nonvolatile Co-containing compound and therefore initiates the EBID process. In the second step, the residual CO ligands in the partially decarbonylated fragments undergo electron stimulated decomposition as opposed to desorption, leading to the formation of adsorbed carbon and oxidized cobalt atoms. However, carbon atoms in the partially decarbonylated species formed during the first step are thermally labile below room temperature. This provides a rationale for the observation that EBID nanostructures created from Co(CO)3NO under steady state deposition conditions, at ambient temperatures, typically contain very low levels of carbon contamination. Results from this study highlight the importance that both electron and thermally stimulated processes can play in determining the ultimate chemical composition of nanostructures created by EBID.