The reactions of low energy (<100 eV) electrons with organometallic precursors underpin the fabrication of metalcontaining nanostructures using focused electron beam-induced deposition. To understand these reactions at a molecular level, we have studied the electron-induced reactions of Ru(CO) 4 I 2 in three different environments: as isolated molecules in the gas phase, adsorbed as thin films on surfaces, and as used in electron beaminduced deposition (EBID) in an Auger spectrometer. Gas-phase studies show that dissociative electron attachment (DEA) to Ru(CO) 4 I 2 predominantly results in the loss of two CO ligands, while dissociative ionization (DI) of Ru(CO) 4 I 2 leads to significantly more extensive fragmentation. Surface science studies of thin films of Ru(CO) 4 I 2 adsorbed on gold at −100 °C and irradiated with 500 eV electrons show that decomposition proceeds in two distinct steps: (1) an initial loss of two CO ligands, followed by (2) a slower step, where the residual two CO ligands desorb, leaving RuI 2 on the surface. EBID using Ru(CO) 4 I 2 and its brominated analogue, Ru(CO) 4 Br 2 , produced deposits with a ruthenium-to-halide ratio of ≈1:2 and minimal carbon and oxygen contamination. These results suggest that DEA is dominant over DI in the initial deposition step on the surface. This step produces a partially decarbonylated Ru(CO) 2 I 2 species, which is then subject to CO desorption under further electron irradiation, findings likely generalizable to other Ru(CO) 4 X 2 species (X = halide). The desorption of CO from the partially decarbonylated intermediate differs markedly from the results obtained for other metal carbonyls (e.g., W(CO) 6 ), a difference tentatively ascribed to the presence of M− X bonds.

Focused electron beam-induced deposition (FEBID) and focused ion beam-induced deposition (FIBID) are direct-write fabrication techniques that use focused beams of charged particles (electrons or ions) to create 3D metal-containing nanostructures by decomposing organometallic precursors onto substrates in a low-pressure environment. For many applications, it is important to minimize contamination of these nanostructures by impurities from incomplete ligand dissociation and desorption. This spotlight on applications describes the use of ultra high vacuum surface science studies to obtain mechanistic information on electron- and ion-induced processes in organometallic precursor candidates. The results are used for the mechanism-based design of custom precursors for FEBID and FIBID.

A combination of in situ X-ray photoelectron spectroscopy and mass spectrometry has been used to elucidate the elementary surface reactions initiated by the interaction of low-energy (860 eV) argon ions with three organometallic precursors [Ru­(CO)4I2, Co­(CO)3NO, and WN­(NMe2)3]. The effects of ion exposure on each precursor can be described by a largely sequential series of surface reactions. The initial step involves ion-induced decomposition of the precursor to create a nonvolatile deposit, followed by physical sputtering of the atoms in the deposit. For the precursors that contain CO ligands [Ru­(CO)4I2 and Co­(CO)3NO], ion-induced decomposition is accompanied by desorption of the majority of the CO groups. This is in marked contrast to previous studies of low-energy electron-induced reactions with the same precursors where precursor decomposition yielded only partial desorption of the CO ligands. Conversely, argon ion bombardment of WN­(NMe2)3 led to decomposition without ligand loss. For all three precursors, the initial ion-induced decomposition step was not accompanied by significant desorption of intact precursor molecules, while during subsequent physical sputtering of the deposited atoms, ligand-derived organic and inorganic contaminants were removed at higher rates than the metals. This indicates that controlled ion beam deposition conditions could be used to produce deposits with high metal contents from all three precursors. Comparison of low-energy electron-induced reactions of these three precursors with results of this investigation indicates that secondary electrons do not play an important role in the deposition process, but rather precursor decomposition occurs via efficient ion–molecule energy transfer. These reactions are discussed in the context of focused ion beam-induced deposition.

We investigated the focused electron beam induced deposition (FEBID) of Ru-containing deposits on SiO2 and sputter-cleaned Si in an ultra-high vacuum. The precursor Ru(CO)4I2 was held at 340 to 345 K, and the applied electron doses were varied from 1.56 to 9.36 C/cm 2 , using a focused electron beam (5 keV, 1.5 nA, 10 nm diameter). Local Auger electron spectroscopy (AES) along with subsequent sophisticated fitting procedures not only revealed the elemental composition but also enabled to determine the thickness of the fabricated deposits. Ru contents of up to 60% can be achieved at lower electron doses; at higher doses, the Ru content decreases to 45% and simultaneously the I content increases. The initially lower iodine content is attributed to simultaneous focused electron beam induced etching (FEBIE), which is found to be competing with the deposition process. The etching is evidenced by atomic force 2 microscopy, where the structures are observed to have negative apparent height for low electron doses. Upon increasing the electron doses, the deposits exhibit positive apparent heights. Hence, the etching is less pronounced at higher electron doses, once the ruthenium surface coverage has increased. The high Ru content and the difficile balance between electron induced deposition and etching considerably expand the possibilities to engineer nanostructured materials.