A combined gas phase and surface study on electron induced decomposition of the heteronuclear FEBID precursor; CpFe(CO)2Mn(CO)5

Here we percent a combined gas phase and surface study on electron induced decomposition of the heteronuclear FEBID precursor; CpFe(CO)2Mn(CO)5. Dissociative electron attachment and dissociative ionization of this compound in the gas phase is explored and discussed in context to controlled deposition experiments where the same compound is exposed to high-energy electrons, when adsorbed on a surface.


Synopsis
Here we percent a combined gas phase and surface study on electron induced decomposition of the heteronuclear FEBID precursor; CpFe(CO) 2 Mn(CO) 5 . Dissociative electron attachment and dissociative ionization of this compound in the gas phase is explored and discussed in context to controlled deposition experiments where the same compound is exposed to high-energy electrons, when adsorbed on a surface.
In recent years, a number of gas phase studies on the interaction of low energy electrons with organome-tallics have been conducted in conjunction with sur-face studies on deposit formation from thin layers of the same compounds adsorbed on surfaces and ex-posed to high--energy electrons [1]. The aim of these studies has primarily been to evaluate the potential of these compounds as precursor molecules in focused electron beam induced deposition (FEBID) [2] and to unravel the mechanisms behind deposit formation [1]. In this context, the combination of gas phase and surface experiments is advantageous as the former can deliver information on the extent and energy de-pendency of individual processes, while the latter elucidates the surface interactions and exposure to secondary electrons with an energy distribution simi-lar to what is expected in FEBID instruments. The use of heteronuclear precursors is an attractive alterna-tive to mixed gas or multiple gas inlet systems for the fabrication of alloy nanostructures, and recent exper-iments with HFeCo3(CO)12 [3] achieved a typical met-al purity of 80% with 1:3 FeCo ratio, clearly demon-strating the viability of this approach.
To follow this path and explore further heteronuclear precursor candidates, we have conducted gas phase studies on dissociative ionization and dissociative electron attachment to the heteronuclear organome-tallic CpFe(CO)2Mn(CO)5 [5], a compound specifically synthesized for this purpose. Furthermore, the com-bination of the multiply coordinated cyclopentadienyl group, which is known to be a poor leaving group (see ref. 4 and refs therein), and the more labile CO ligands offers an excellent opportunity to compare these ligands in a heteronuclear architecture.
The two most intense fragments produced in DEA to by CpFe(CO)2Mn(CO)5 are both formed via a low-lying resonance leading to a maximum in the ion yield near 0 eV. These channels are the loss of one CO, and the cleavage of the iron--manganese bond to form Mn(CO)5 − . Hence, both these channels are associated with a single bond rupture. Further CO loss is also observed in DEA, covering the formation of [M − nCO] − over the range from n = 2 to n = 6. These chan-nels are, however, orders of magnitude less efficient than the primary single bond rupture channels. No cyclopentadienyl loss is observed in DEA to this com-pound. In dissociative ionization, the fragmentation pattern observed are very different to these observed in DEA. At about 70 eV, the DI spectra is dominated by fragments formed through the loss of 5 and 6 CO ligands, the formation of the iron cyclopentadienyl fragments FeCp and FeCp(CO)2 + and the bare metal Fe + and Mn + . Hence, the fragmentation through DI is much more extensive than through DEA.
Recently, surface science experiments were per-formed in the Fairbrother lab, wherein CpFe(CO)2Mn(CO)5 was physisorbed onto gold and highly ordered pyrolytic carbon (HOPG) substrates under ultra--high vacuum (UHV) and irradiated with varying electron dose, while the surface composition was monitored using X--ray photoelectron spectros-copy (XPS). These studies show that the primary dep-osition pathway is through carbonyl loss, while no cyclopentadienyl loss is observed.
In the current contribution we discuss the efficiency of the DI vs. the DEA channels in conjunction with the decomposition pathways and deposit formation from thin layers of CpFe(CO)2Mn(CO)5 at surfaces.