W. Barszczewska

Bio: W. Barszczewska is an academic researcher from Siedlce University of Natural Sciences and Humanities. The author has contributed to research in topics: Electron & Electron capture. The author has an hindex of 7, co-authored 15 publications receiving 154 citations.

Low‐energy electron interactions with tungsten hexacarbonyl – W(CO)6

Abstract: RATIONALE Low-energy secondary electrons are formed when energetic particles interact with matter. High-energy electrons or ions are used to form metallic structures from adsorbed organometallic molecules like W(CO)6 on surfaces. We investigated low-energy electron attachment to W(CO)6 in the gas phase to elucidate possible reactions during surface modification. METHODS Two crossed electron/molecular beam setups were utilised: (i) a high-resolution electron monochromator combined with a quadrupole mass spectrometer which was used for the measurement of relative cross sections as a function of the electron energy, and (ii) a double focusing mass spectrometer used for measurements of metastable decays of anions. RESULTS The study was performed in the electron energy range between ~0 and 14 eV. W(CO)6 efficiently decomposed upon attachment of a low-energy electron and no stable W(CO)6– anion was observed on mass spectrometric time scales. The transient negative ion formed lost instead sequentially CO ligands. The fragment anions W(CO)5–, W(CO)4–, W(CO)3–, and W(CO)2– were observed. However, no W– was detectable. CONCLUSIONS Dissociative electron attachment (DEA) to W(CO)6 led to strong dissociation but a complete loss of all CO ligands was not observed in DEA. Deposit contaminations might be a direct result of DEA reactions close to the irradiation spot in beam deposition techniques. Copyright © 2012 John Wiley & Sons, Ltd.

Electron ionization of W(CO)6: Appearance energies

Abstract: The electron ionization (EI) of W(CO)6 has been studied in detail using a high resolution crossed electron-molecular beams technique. We have detected singly (W+, CW+, (CO)xW+ (x = 1–6), (CO)yCW+ (y = 1–3), CO+) and doubly charge positive ions (W2+, CW2+, (CO)xW2+ (x = 1–6) and (CO)yCW2+ (y = 1–3)). The relative partial cross sections for formation of particular ions have been measured and the breakdown curves constructed. The ionization energies (IE) for single (8.47 ± 0.06 eV) and double ionization (22.90 ± 0.08 eV) of the molecule, as well as the appearance energies (AEs) for the dissociative ionization channels for singly and doubly charged ions have been estimated from experimental ion efficiency curves. On the basis of the IEs and AEs values we have calculated sequential bond dissociation energies (BDEs) of different bonds in the positive ions formed from W(CO)6.

Low-Energy Electron Attachment by Chloroalkanes

Abstract: Thermal electron attachment rate constants for 1,1,2-trichloroethane, 1,1,2,2-tetrachloroethane, 1- and 2-chloropropanes, and 1,1-, 1,2-, 2,2-, and 1,3-dichloropropanes have been measured using an electron swarm method. It has been found that all the investigated compounds attach electrons only in a two-body process. Corresponding rate constants are equal to 1.4 x 10 - 1 0 , 3.2 x 10 - 8 , 2.7 × 10 - 1 3 , 3.8 × 10 - 1 2 , 5.7 × 10 - 1 1 , 8.1 × 10 - 1 2 , 6.3 × 10 - 1 2 , and 1.2 x 10 - 1 1 cm 3 molecule - 1 s - 1 , respectively. The dependence of the electron capture rate constants on the electronic polarizability of the accepting center of the molecule and the vertical attachment energy has been demonstrated.

Low energy electron attachment by bromoalkanes

Abstract: Electron attachment process in three halopropanes, CH3CH2CH2Br, CH3CHBrCH3 and CH3CHBrCF3, have been investigated using an electron swarm and electron capture negation mass spectrometry techniques. All compounds attach electrons in dissociative process, and the main product is bromine ion. The rate constants for thermal electron attachment are equal to 1.1·10−1, 1.4·10−12 and 4.1·10−10 cm3molec.−1 s−1 for CH3CH2CH2Br, CH3CHBrCH3 and CH3CHBrCF3, respectively.

Electron attachment to oxygen in nitrogen buffer gas at atmospheric pressure

Abstract: We have carried out experimental and theoretical studies of three body electron attachment (TBEA) to O2 in N2/O2 mixtures. We have applied three different experimental methods to determine the apparent rate constant k for TBEA to O2 for reduced electric fields E/ n from 0.5 Td up to 4.5 Td and O2 concentrations from 0.02% up to 3%. From the apparent rate constant k we have evaluated three body rate constant for electron attachment to O2 in pure O2 $$\left( {k_{O_2 } } \right)$$ and in pure N2 $$\left( {k_{N_2 } } \right)$$ . The comparison of present data with former studies shows that the former values of $$k_{N_2 }$$ overestimated the efficiency of this reaction, while in case of $$k_{O_2 }$$ we have found agreement with earlier studies. We have solved numerically the Boltzmann equation of the electrons and calculated the values of k, $$k_{N_2 }$$ and $$k_{O_2 }$$ using well established cross sections. Using the known collision cross section set for TBEA to O2, very good agreement between calculated and measured results for $$k_{O_2 }$$ was found, while in the case of k and $$k_{N_2 }$$ we had to introduce a scaling function, which describes the decrease of the efficiency of TBEA to O2 in presence of N2 and the dependence of the scaling function on E/n was determined.

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

Abstract: 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. These low-energy electrons are abundant both inside and outside the area of the primary electron beam and are associated with reactions causing incomplete ligand dissociation from FEBID precursors. As it is not possible to directly study the effects of secondary electrons in situ in FEBID, other means must be used to elucidate their role. In this context, gas phase studies can obtain well-resolved information on low-energy electron-induced reactions with FEBID precursors by studying isolated molecules interacting with single electrons of well-defined energy. In contrast, ultra-high vacuum surface studies on adsorbed precursor molecules can provide information on surface speciation and identify species desorbing from a substrate during electron irradiation under conditions more representative of FEBID. Comparing gas phase and surface science studies allows for insight into the primary deposition mechanisms for individual precursors; ideally, this information can be used to design future FEBID precursors and optimize deposition conditions. In this review, we give a summary of different low-energy electron-induced fragmentation processes that can be initiated by the secondary electrons generated in FEBID, specifically, dissociative electron attachment, dissociative ionization, neutral dissociation, and dipolar dissociation, emphasizing the different nature and energy dependence of each process. We then explore the value of studying these processes through comparative gas phase and surface studies for four commonly-used FEBID precursors: MeCpPtMe3, Pt(PF3)4, Co(CO)3NO, and W(CO)6. Through these case studies, it is evident that this combination of studies can provide valuable insight into potential mechanisms governing deposit formation in FEBID. Although further experiments and new approaches are needed, these studies are an important stepping-stone toward better understanding the fundamental physics behind the deposition process and establishing design criteria for optimized FEBID precursors.

Recent Progress in Dissociative Electron Attachment: From Diatomics to Biomolecules

Abstract: Dissociative electron attachment (DEA) processes occur in many important applied contexts, particularly gas discharges, plasmas, biological systems, and astrophysical environments. In this review, we survey the basic physics of DEA and the progress that has been made during past 14 years since the last important review on DEA (Hotop et al., Adv. At. Mol. Opt. Phys. 49, 86). This progress includes studies of DEA to simple diatomic and polyatomic molecules with high energy resolution revealing vibrational Feshbach resonances and threshold structures, studies of angular distribution of the fragmentation products allowing analysis of the symmetries of the resonances involved, and theoretical developments in investigating the dynamics of nuclear motion in DEA processes. Particular attention is paid to recent advances in DEA to biological molecules as the process is important for understanding radiation damage. Recent progress in understanding electron attachment to van der Waals clusters and the influence of cluster environments on DEA is also reviewed. The review concludes with a forward look and suggestions for new research directions.

Electron induced reactions of surface adsorbed tungsten hexacarbonyl (W(CO)6)

Abstract: Tungsten hexacarbonyl (W(CO)6) is frequently used as an organometallic precursor to create metal-containing nanostructures in electron beam induced deposition (EBID). However, the fundamental electron stimulated reactions responsible for both tungsten deposition and the incorporation of carbon and oxygen atom impurities remain unclear. To address this issue we have studied the effect of 500 eV incident electrons on nanometer thick films of W(CO)6 under Ultra-High Vacuum (UHV) conditions. Results from X-ray Photoelectron Spectroscopy, Mass Spectrometry, and Infrared Spectroscopy reveal that the initial step involves electron stimulated desorption of multiple CO ligands from parent W(CO)6 molecules and the formation of partially decarbonylated tungsten species (Wx(CO)y). Subsequent electron interactions with these Wx(CO)y species lead to ligand decomposition rather than further CO desorption, ultimately producing oxidized tungsten atoms incorporated in a carbonaceous matrix. The presence of co-adsorbed water during electron irradiation increased the extent of tungsten oxidation. The electron stimulated deposition cross-section of W(CO)6 at an incident electron energy of 500 eV was calculated to be 6.50 × 10−16 cm−2. When considered collectively with findings from previous precursors (MeCpPtMe3 and Pt(PF3)4), results from the present study are consistent with the idea that the electron induced reactions in EBID are initiated by low energy secondary electrons generated by primary beam–substrate interactions, rather than by the primary beam itself.

Absolute cross sections for dissociative electron attachment and dissociative ionization of cobalt tricarbonyl nitrosyl in the energy range from 0 eV to 140 eV.

Abstract: We report absolute dissociative electron attachment (DEA) and dissociative ionization (DI) cross sections for electron scattering from the focused electron beam induced deposition (FEBID) precursor Co(CO)3NO in the incident electron energy range from 0 to 140 eV. We find that DEA leads mainly to single carbonyl loss with a maximum cross section of 4.1 × 10−16 cm2, while fragmentation through DI results mainly in the formation of the bare metal cation Co+ with a maximum cross section close to 4.6 × 10−16 cm2 at 70 eV. Though DEA proceeds in a narrow incident electron energy range, this energy range is found to overlap significantly with the expected energy distribution of secondary electrons (SEs) produced in FEBID. The DI process, on the other hand, is operative over a much wider energy range, but the overlap with the expected SE energy distribution, though significant, is found to be mainly in the threshold region of the individual DI processes.

Ionization of large homogeneous and heterogeneous clusters generated in acetylene–Ar expansions: Cluster ion polymerization

Abstract: Pure acetylene and mixed Ar-acetylene clusters are formed in supersonic expansions of acetylene/argon mixtures and analysed using reflectron time-of-flight mass spectrometer with variable electron energy ionization source. Acetylene clusters composed of more than a hundred acetylene molecules are generated at the acetylene concentration of ≈8%, while mixed species are produced at low concentrations (≈0.7%). The electron energy dependence of the mass spectra revealed the ionization process mechanisms in clusters. The ionization above the threshold for acetylene molecule of 11.5 eV results in the main ionic fragment progression (C2H2)n(+). At the electron energies ≥21.5 eV above the CH+CH(+) dissociative ionization limit of acetylene the fragment ions nominally labelled as (C2H2)nCH(+), n ≥ 2, are observed. For n ≤ 7 these fragments correspond to covalently bound ionic structures as suggested by the observed strong dehydrogenation [(C2H2)n - k × H](+) and [(C2H2)nCH - k × H](+). The dehydrogenation is significantly reduced in the mixed clusters where evaporation of Ar instead of hydrogen can stabilize the nascent molecular ion. The C3H3(+) ion was previously assigned to originate from the benzene molecular ion; however, the low appearance energy of ≈13.7 eV indicates that a less rigid covalently bound structure of C6H6(+) ion must also be formed upon the acetylene cluster electron ionization. The appearance energy of Arn(C2H2)(+) fragments above ≈15.1 eV indicates that the argon ionization is the first step in the fragment ion production, and the appearance energy of Arn≥2(C2H2)m≥2(+) at ≈13.7 eV is discussed in terms of an exciton transfer mechanism.