Experimental and Theoretical Study on Electron Ionization and Fragmentation of Propylene Oxide─the First Chiral Molecule Detected in the Interstellar Medium.

Propylene oxide, CHCHOCH, is the first chiral molecule detected in space and the third C3 oxide detected toward the Sagittarius B2 (Sgr B2 (N)) molecular cloud, the others being propanal, CHCHCHO, and acetone, (CH)CO. With homochirality being ubiquitous in the building blocks of living matter, the formation and decay paths of propylene oxide in space are of specific interest. Motivated by the significant role of photo- and secondary electrons in astrochemistry, we have studied electron ionization and fragmentation of propylene oxide.

A combined gas-phase dissociative ionization, dissociative electron attachment and deposition study on the potential FEBID precursor [Au(CH)Cl].

Motivated by the potential of focused-electron-beam-induced deposition (FEBID) in the fabrication of functional gold nanostructures for application in plasmonic and detector technology, we conducted a comprehensive study on [Au(CH)Cl] as a potential precursor for such depositions. Fundamental electron-induced dissociation processes were studied under single collision conditions, and the composition and morphology of FEBID deposits fabricated in an ultrahigh-vacuum (UHV) chamber were explored on different surfaces and at varied beam currents. In the gas phase, dissociative ionization was found to lead to significant carbon loss from this precursor, and about 50% of the chlorine was on average removed per dissociative ionization incident.

Low-energy electron interaction with 2-(trifluoromethyl)acrylic acid, a potential component for EUVL resist material.

Motivated by the current introduction of extreme ultraviolet lithography (EUVL) into chip manufacturing processes, and thus the transition to electron-induced chemistry within the respective resist materials, we have studied low energy electron-induced fragmentation of 2-(trifluoromethyl)acrylic acid (TFMAA). This compound is chosen as a potential resist component, whereby fluorination enhances the EUV adsorption and may at the same time promote electron-induced dissociation. Dissociative ionization and dissociative electron attachment are studied, and to aid the interpretation of the observed fragmentation channels, the respective threshold values are calculated at the DFT and coupled cluster level of theory.

On the Electron-Induced Reactions of (CH)AuP(CH): A Combined UHV Surface Science and Gas-Phase Study.

Focused-electron-beam-induced deposition (FEBID) is a powerful nanopatterning technique where electrons trigger the local dissociation of precursor molecules, leaving a deposit of non-volatile dissociation products. The fabrication of high-purity gold deposits via FEBID has significant potential to expand the scope of this method. For this, gold precursors that are stable under ambient conditions but fragment selectively under electron exposure are essential.

Dissociative ionization and electron beam induced deposition of tetrakis(dimethylamino)silane, a precursor for silicon nitride deposition.

Motivated by the use of tetrakis(dimethylamino)silane (TKDMAS) to produce silicon nitride-based deposits and its potential as a precursor for Focused Electron Beam Induced Deposition (FEBID), we have studied its reactivity towards low energy electrons in the gas phase and the composition of its deposits created by FEBID. While no negative ion formation was observed through dissociative electron attachment (DEA), significant fragmentation was observed in dissociative ionization (DI). Appearance energies (AEs) of fragments formed in DI were measured and are compared to the respective threshold energies calculated at the DFT and coupled cluster (CC) levels of theory.

HF Formation through Dissociative Electron Attachment-A Combined Experimental and Theoretical Study on Pentafluorothiophenol and 2-Fluorothiophenol.

In chemoradiation therapy, dissociative electron attachment (DEA) may play an important role with respect to the efficiency of the radiosensitizers used. The rational tailoring of such radiosensitizers to be more susceptive to DEA may thus offer a path to increase their efficiency. Potentially, this may be achieved by tailoring rearrangement reactions into the DEA process such that these may proceed at low incident electron energies, where DEA is most effective.

Low-energy electron interaction and focused electron beam-induced deposition of molybdenum hexacarbonyl (Mo(CO)).

Motivated by the potential role of molybdenum in semiconductor materials, we present a combined theoretical and experimental gas-phase study on dissociative electron attachment (DEA) and dissociative ionization (DI) of Mo(CO) in comparison to focused electron beam-induced deposition (FEBID) of this precursor. The DEA and DI experiments are compared to previous work, differences are addressed, and the nature of the underlying resonances leading to the observed DEA processes are discussed in relation to an earlier electron transmission study. Relative contributions of individual ionic species obtained through DEA and DI of Mo(CO) and the average CO loss per incident are calculated and compared to the composition of the FEBID deposits produced.

The Role of Low-Energy Electron Interactions in cis-Pt(CO)Br Fragmentation.

Platinum coordination complexes have found wide applications as chemotherapeutic anticancer drugs in synchronous combination with radiation (chemoradiation) as well as precursors in focused electron beam induced deposition (FEBID) for nano-scale fabrication. In both applications, low-energy electrons (LEE) play an important role with regard to the fragmentation pathways. In the former case, the high-energy radiation applied creates an abundance of reactive photo- and secondary electrons that determine the reaction paths of the respective radiation sensitizers.

Electron-induced fragmentation mechanisms in organic monomers and their implications for photoresist optimization for EUV lithography.

Secondary electrons generated during the Extreme Ultraviolet Lithography (EUVL) process are predominantly responsible for inducing important patterning chemistry in photoresist films. Therefore, it is crucial to understand the electron-induced fragmentation mechanisms involved in EUV-resist systems to improve their patterning performance. To facilitate this understanding, mechanistic studies were carried out on simple organic EUV-resist monomers, methyl isobutyrate (MIB) and methacrylic acid (MAA), both in the condensed and gas phases.

Electron-Transfer-Induced Side-Chain Cleavage in Tryptophan Facilitated through Potassium-Induced Transition-State Stabilization in the Gas Phase.

Fragmentation of transient negative ions of tryptophan molecules formed through electron transfer in collisions with potassium atoms is presented for the first time in the laboratory collision energy range of 20 up to 100 eV. In the unimolecular decomposition process, the dominating side-chain fragmentation channel is assigned to the dehydrogenated indoline anion, in contrast to dissociative electron attachment of free low-energy electrons to tryptophan. The role of the collision complex formed by the potassium cation and tryptophan negative ion in the electron transfer process is significant for the mechanisms that operate at lower collision energies.

Dissociation of the FEBID precursor cis-Pt(CO)Cl driven by low-energy electrons.

In this study, we present experimental and theoretical results on dissociative electron attachment and dissociative ionisation for the potential FEBID precursor cis-Pt(CO)Cl. UHV surface studies have shown that high purity platinum deposits can be obtained from cis-Pt(CO)Cl. The efficiency and energetics of ligand removal through these processes are discussed and experimental appearance energies are compared to calculated thermochemical thresholds.

The role of the dihedral angle and excited cation states in ionization and dissociation of mono-halogenated biphenyls; a combined experimental and theoretical coupled cluster study.

We present a combined theoretical and experimental study on the ionization and primary fragmentation channels of the mono-halogenated biphenyls; 2-chlorobiphenyl, 2-bromobiphenyl and 2-iodobiphenyl. The ionization energies (IEs) of the 2-halobiphenyls and the appearance energies (AEs) of the principal fragments are determined through electron impact ionization, while quantum mechanical calculations at the coupled cluster level of theory are used to elucidate the observed processes and the associated dynamics. The primary fragmentation channels are the direct loss of the halogen upon ionization, the loss of the respective hydrogen halides (HX) as well as loss of the hydrogen halide and an additional hydrogen.

Electron interactions with the heteronuclear carbonyl precursor HFeRu(CO) and comparison with HFeCo(CO): from fundamental gas phase and surface science studies to focused electron beam induced deposition.

In the current contribution we present a comprehensive study on the heteronuclear carbonyl complex HFeRu(CO) covering its low energy electron induced fragmentation in the gas phase through dissociative electron attachment (DEA) and dissociative ionization (DI), its decomposition when adsorbed on a surface under controlled ultrahigh vacuum (UHV) conditions and exposed to irradiation with 500 eV electrons, and its performance in focused electron beam induced deposition (FEBID) at room temperature under HV conditions. The performance of this precursor in FEBID is poor, resulting in maximum metal content of 26 atom % under optimized conditions. Furthermore, the Ru/Fe ratio in the FEBID deposit (≈3.

Electron induced surface reactions of (η-CH)Fe(CO)Mn(CO), a potential heterobimetallic precursor for focused electron beam induced deposition (FEBID).

Electron-induced surface reactions of (η-CH)Fe(CO)Mn(CO) were explored in situ under ultra-high vacuum conditions using X-ray photoelectron spectroscopy and mass spectrometry. The initial step involves electron-stimulated decomposition of adsorbed (η-CH)Fe(CO)Mn(CO) molecules, accompanied by the desorption of an average of five CO ligands. A comparison with recent gas phase studies suggests that this precursor decomposition step occurs by a dissociative ionization (DI) process.

Low energy electron-induced decomposition of (η-Cp)Fe(CO)Mn(CO), a potential bimetallic precursor for focused electron beam induced deposition of alloy structures.

The production of alloyed nanostructures presents a unique problem in focused electron beam induced deposition (FEBID). Deposition of such structures has historically involved the mixing of two or more precursor gases in situ or via multiple channel gas injection systems, thereby making the production of precise, reproducible alloy compositions difficult. Promising recent efforts to address this problem have involved the use of multi-centred, heterometallic FEBID precursor species.

Amplified cross-linking efficiency of self-assembled monolayers through targeted dissociative electron attachment for the production of carbon nanomembranes.

The determination of the negative ion yield of 2'-chloro-1,1'-biphenyl (2-Cl-BP), 2'-bromo-1,1'-biphenyl (2-Br-BP) and 2'-iodo-1,1'-biphenyl (2-I-BP) upon dissociative electron attachment (DEA) at an electron energy of 0 eV revealed cross section values that were more than ten times higher for iodide loss from 2-I-BP than for the other halogenides from the respective biphenyls (BPs). Comparison with dissociative ionization mass spectra shows that the ratio of the efficiency of electron impact ionization induced fragmentation of 2-I-BP, 2-Br-BP, and 2-Cl-BP amounts to approximately 1:0.7:0.

Electron beam induced deposition of silacyclohexane and dichlorosilacyclohexane: the role of dissociative ionization and dissociative electron attachment in the deposition process.

We present first experiments on electron beam induced deposition of silacyclohexane (SCH) and dichlorosilacyclohexane (DCSCH) under a focused high-energy electron beam (FEBID). We compare the deposition dynamics observed when growing pillars of high aspect ratio from these compounds and we compare the proximity effect observed for these compounds. The two precursors show similar behaviour with regards to fragmentation through dissociative ionization in the gas phase under single-collision conditions.

Formation and decay of negative ion states up to 11 eV above the ionization energy of the nanofabrication precursor HFeCo(CO).

In single electron collisions with the heteronuclear metal carbonyl compound HFeCo(CO) we observe the formation of long-lived negative ion states up to about 20 eV, 11 eV above its ionization energy. These transient negative ions (TNIs) relax through dissociation (dissociative electron attachment, DEA), losing up to all 12 CO ligands, demonstrating their resilience towards reemission of the captured electron - even at such very high energies. This is unique in DEA and we hypothesize that this phenomenon is rooted in the orbital structure enabling a scaffold of multi-particle, electronically excited resonances.

Proton Shuttling and Reaction Paths in Dissociative Electron Attachment to o- and p-Tetrafluorohydroquinone, an Experimental and Theoretical Study.

Here we present a combined experimental and theoretical study on the fragmentation of o- and p-tetrafluorohydroquinone upon low energy electron attachment. Despite an identical ring-skeleton and identical functional groups in these constitutional isomers, they show distinctly different fragmentation patterns, a phenomenon that cannot be explained by distinct resonances or different thermochemistry. Using high-level quantum chemical calculations with the computationally affordable domain localized pair natural orbital approach, DLPNO-CCSD(T), we are able to provide a complete and accurate description of the respective reaction dynamics, revealing proton shuttling and transition states for competing channels as the explanation for the different behavior of these isomers.

Low energy electron-induced decomposition of (η-CH)Ru(CO)Br, a potential focused electron beam induced deposition precursor with a heteroleptic ligand set.

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.

The role of low-energy electrons in focused electron beam induced deposition: four case studies of representative precursors.

Focused electron beam induced deposition (FEBID) is a single-step, direct-write nanofabrication technique capable of writing three-dimensional metal-containing nanoscale structures on surfaces using electron-induced reactions of organometallic precursors. Currently FEBID is, however, limited in resolution due to deposition outside the area of the primary electron beam and in metal purity due to incomplete precursor decomposition. Both limitations are likely in part caused by reactions of precursor molecules with low-energy (<100 eV) secondary electrons generated by interactions of the primary beam with the substrate.

State selectivity and dynamics in dissociative electron attachment to CF₃I revealed through velocity slice imaging.

In light of its substantially more environmentally friendly nature, CF3I is currently being considered as a replacement for the highly potent global-warming gas CF4, which is used extensively in plasma processing. In this context, we have studied the electron-driven dissociation of CF3I to form CF3(-) and I, and we compare this process to the corresponding photolysis channel. By using the velocity slice imaging (VSI) technique we can visualize the complete dynamics of this process and show that electron-driven dissociation proceeds from the same initial parent state as the corresponding photolysis process.

NCO(-), a key fragment upon dissociative electron attachment and electron transfer to pyrimidine bases: site selectivity for a slow decay process.

We report gas phase studies on NCO(-) fragment formation from the nucleobases thymine and uracil and their N-site methylated derivatives upon dissociative electron attachment (DEA) and through electron transfer in potassium collisions. For comparison, the NCO(-) production in metastable decay of the nucleobases after deprotonation in matrix assisted laser desorption/ionization (MALDI) is also reported. We show that the delayed fragmentation of the dehydrogenated closed-shell anion into NCO(-) upon DEA proceeds few microseconds after the electron attachment process, indicating a rather slow unimolecular decomposition.

Stabilization, fragmentation and rearrangement reactions in low-energy electron interaction with tetrafluoro-para-benzoquinone: a combined theoretical and experimental study.

Quinones are a class of organic compounds whose extraordinary electron transfer properties are fundamental in ubiquitous processes such as the ATP production and the photosynthesis. Here, we report a combined theoretical and experimental study to shed some light on low-energy electron interaction with tetrafluoro-para-benzoquinone (TFQ) and para-benzoquinone (p-BQ). Similar to it's native counterpart; p-BQ, TFQ forms a metastable molecular anion at unusually high incident energies in electron attachment under single collision conditions.

Quantum superposition of target and product states in reactive electron scattering from CF4 revealed through velocity slice imaging.

Exploiting the technique of velocity slice imaging, we have performed a detailed study of reactive electron scattering with CF4. We have measured the electron impact energy dependence of both the angular and kinetic energy distributions of the channels yielding F- and CF3(-) anions. These data provide an unprecedented insight into the quantum superposition of the target state and product channels, respectively, of Td and C3v symmetry, and shed new light on the dissociation dynamics.