Electron induced reactions of surface adsorbed tungsten hexacarbonyl (W(CO)6)

Abstract

Tungsten hexacarbonyl (W(CO)₆) is frequently used as an organometallic precursor to create metal-containing nanostructures in electron beam induced deposition (EBID). However, the fundamental electron stimulated reactions responsible for both tungsten deposition and the incorporation of carbon and oxygen atom impurities remain unclear. To address this issue we have studied the effect of 500 eV incident electrons on nanometer thick films of W(CO)₆ under Ultra-High Vacuum (UHV) conditions. Results from X-ray Photoelectron Spectroscopy, Mass Spectrometry, and Infrared Spectroscopy reveal that the initial step involves electron stimulated desorption of multiple CO ligands from parent W(CO)₆ molecules and the formation of partially decarbonylated tungsten species (W_x(CO)_y). Subsequent electron interactions with these W_x(CO)_y species lead to ligand decomposition rather than further CO desorption, ultimately producing oxidized tungsten atoms incorporated in a carbonaceous matrix. The presence of co-adsorbed water during electron irradiation increased the extent of tungsten oxidation. The electron stimulated deposition cross-section of W(CO)₆ at an incident electron energy of 500 eV was calculated to be 6.50 × 10⁻¹⁶ cm⁻². When considered collectively with findings from previous precursors (MeCpPtMe₃ and Pt(PF₃)₄), results from the present study are consistent with the idea that the electron induced reactions in EBID are initiated by low energy secondary electrons generated by primary beam–substrate interactions, rather than by the primary beam itself.