Speaker
Description
Focused electron beam-induced deposition (FEBID) is a direct-write technique for depositing nanostructures on the surface in the sub-10 nm regime [1]. Due to their magnetic properties, iron nanostructures have the potential to be used in magnetic storage devices, and nano-sensing [2]. For use in FEBID, the iron atoms are surrounded by suitable ligands to ensure the volatility of the precursor. In an ideal situation, after a local irradiation by a focused electron beam, the metal is expected to be deposited and the other fragments should desorb from the surface. However, the resulting structures often have a high amount of contamination coming from the non-metalic fragmetns. These other fragments are formed by the interaction of precursor with low-energy secondary electrons generated from the interaction of high-energy electron beam (keV) with the substrate. Processes like dissociative ionization (DI), neutral dissociation (ND), and dissociative electron attachment (DEA) break the parent molecule. To improve the purity of the deposited iron, different types of precursor molecules are used [3, 4] or are still in the developed. Before using compound as a FEBID precursor, it is essential to characterize its dissociation induced by low-energy electrons.
We used the CLUB (CLUster Beam) and TEM-QMS (Trochoidal Electron Monochromator) setups [4] to study the fragmentation pattern of a newly synthesised precursor molecule, iron tetracarbonyl acrolein (Fe(CO)$_{4}$-C$_{3}$H$_{4}$O) via DI and DEA processes. At 70 eV incident electron energy (CLUB setup), the presence of the parent cation (mass 224) is negligible. The fragments with m/z (mass to charge) ratios 84 and 112 have the highest abundance. When the data is accumulated over 5-80 eV electron energy range, m/z 56 becomes the most dominating fragment followed by 84 and 112. For the negative ions, which are mostly formed by resonant processes, we did the measurement on the TEM-QMS setup which has a better resolution, it shows the m/z 196 and 168 are present close to 0 eV and have a very narrow spread of 0.5 eV, whereas the other fragments are mostly present for electron energy above 2 eV and have a broad distribution. Using the DFT, we have calculated the thresholds for different fragmentation channels. We discuss possible mechanisms that can lead to the observed fragmentation patterns.
Reference
[1] Huth et al., O. V. Microelectron. Eng. 2018,
185–186, 9–28.
[2] Fernández-Pacheco et al., O. V. Materials 2020, 13,
3774.
[3] Boeckers et al. P. Beilstein J. Nanotechnol. 2024, 15, 500–516.
[4] Lyshchuk et al. P. Beilstein J. Nanotechnol. 2024, 15, 797–807.
