Toward the goal of better understanding the elementary steps involved in the electron beam-induced deposition (EBID) of organometallic precursors, the present study is aimed at understanding the sequence of electronstimulated reactions of surface-bound η 3 -allyl ruthenium tricarbonyl bromide [(η 3 -C 3 H 5 )Ru(CO) 3 Br], an organometallic complex with three different ligands: carbonyl (CO), halide (Br), and η 3 -allyl (η 3 -C 3 H 5 ). X-ray photoelectron spectroscopy and mass spectrometry were used in situ to probe the effects of 500 eV electrons on nanometer scale films of [(η 3 -C 3 H 5 )Ru-(CO) 3 Br]. Initially, electron irradiation decomposes the precursor, reducing the central Ru atom and causing the ejection of CO ligands into the gas phase. Experimental evidence points to the inability of electron irradiation to remove the carbon atoms of the η 3 -allyl (η 3 -C 3 H 5 ) ligand from the resulting EBID deposits. Although the Br atoms are not labile in the initial molecular decomposition step, they are removed from the film after exposure to higher electron doses as a result of a slower, electron-stimulated desorption process. Comparative studies with [(η 3 -C 3 H 5 )Ru(CO) 3 Cl] reveal that the identity of the halogen does not influence the elementary reaction steps involved in the decomposition process. Collectively, results from these studies suggest that sufficiently volatile organometallic precursors with a small number of carbonyl and halide ligands could be used to generate deposits in EBID with significantly higher metal concentrations (and correspondingly lower levels of organic contamination) compared to existing EBID precursors.

Here we describe in detail low energy electron induced fragmentation of a potential focused electron beam induced deposition (FEBID) precursor, π-allyl ruthenium tricarbonyl bromide, i.e. (η-CH)Ru(CO)Br, specially designed to allow comparison of the effect of different ligands on the efficiency of low energy electron induced fragmentation of FEBID precursors. Specifically, we discuss the efficiency of dissociative electron attachment (DEA) and dissociative ionization (DI) with respect to electron-induced removal of the allyl, bromide and carbonyl ligands. We place this in perspective with a previous surface study on the same precursor and we propose a design strategy for FEBID precursor molecules to increase their susceptibility towards DEA.

Chemical vapor deposition (CVD) is an attractive technique for the metallization of organic thin films because it is selective and the thickness of the deposited film can easily be controlled. However, thermal CVD processes often require high temperatures which are generally incompatible with organic films. In this paper, we perform proof-of-concept studies of photochemical CVD to metallize organic thin films. In this method, a precursor undergoes photolytic decomposition to generate thermally labile intermediates prior to adsorption on the sample. Three readily available Ru precursors, CpRu(CO)Me, (η-allyl)Ru(CO)Br, and (COT)Ru(CO), were employed to investigate the role of precursor quantum yield, ligand chemistry, and the Ru oxidation state on the deposition. To investigate the role of the substrate chemistry on deposition, carboxylic acid-, hydroxyl-, and methyl-terminated self-assembled monolayers were used. The data indicate that moderate quantum yields for ligand loss (φ ≥ 0.4) are required for ruthenium deposition, and the deposition is wavelength dependent. Second, anionic polyhapto ligands such as cyclopentadienyl and allyl are more difficult to remove than carbonyls, halides, and alkyls. Third, in contrast to the atomic layer deposition, acid-base reactions between the precursor and the substrate are more effective for deposition than nucleophilic reactions. Finally, the data suggest that selective deposition can be achieved on organic thin films by judicious choice of precursor and functional groups present on the substrate. These studies thus provide guidelines for the rational design of new precursors specifically for selective photochemical CVD on organic substrates.