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. However, while DCSCH shows appreciable cross sections with regards to dissociative electron attachment, SCH is inert with respect to this process. We discuss our deposition experiments in context of the efficiency of these different electron-induced fragmentation processes. With regards to the deposition dynamics, we observe a substantially faster growth from DCSCH and a higher saturation diameter when growing pillars with high aspect ratio. However, both compounds show similar behaviour with regards to the proximity effect. With regards to the composition of the deposits, we observe that the C/Si ratio is similar for both compounds and in both cases close to the initial molecular stoichiometry. The oxygen content in the DCSCH deposits is about double that of the SCH deposits. Only marginal chlorine is observed in the deposits of from DCSCH. We discuss these observations in context of potential approaches for Si deposition.CWH likes to thank Luc van Kessel, Kerim Arat and Sebastiaan Lokhorst for their assistance with the Monte Carlo simulations of Figure 10. OI acknowledges supported from the Icelandic Center of Research (RANNIS) Grant No. 13049305(1-3) and the University of Iceland Research Fund. RKTP acknowledges a doctoral grant from the University of Iceland Research Fund and financial support from the COST Action CM1301; CELINA, for short term scientific missions (STSMs)Peer Reviewe

Relating purple back flying squid (Sthenoteuthis oualaniensis) abundance to environmental parameters using GIS and GAM in south eastern Arabian Sea

Relating purple back flying squid (Sthenoteuthis oualaniensis) abundance to environmental parameters using GIS and GAM in south eastern Arabian Se

Negative ion formation through dissociative electron attachment to the group IV tetrachlorides: Carbon tetrachloride, silicon tetrachloride and germanium tetrachloride

© 2018 Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license:http://creativecommons.org/licenses/by-nc-nd/4.0/ This author accepted manuscript is made available following 24 month embargo from date of publication (Jan 2018) in accordance with the publisher’s archiving policyThe current contribution constitutes the third and final part of our trilogy of papers on electron attachment reactions of the group IV tetrahalides; XY4 (X = C, Si, Ge and Y = F, Cl, Br). In this context we extend our previous studies on XF4 and XBr4 and report results for electron attachment to the tetrachlorides: CCl4, SiCl4 and GeCl4 in the incident electron energy range from about 0 to 10 eV. At the same time we give a summary of the currently available literature on electron interactions with those latter compounds. Upon electron attachment the formation of Cl−, XCl3−, XCl2− and Cl2− is observed from all the tetrachlorides, and additionally the molecular anion SiCl4− is observed from SiCl4. The main DEA contributions are observed through narrow, threshold peaks (at 0 eV) and we attribute these features to single particle resonances associated with the a1 symmetry LUMOs of those compounds. Contributions from another low-lying resonance, which we assign as a 2T2 shape resonance associated with the t2 symmetry LUMO+1, is also observed in the ion yield curves for all the tetrachlorides. The energy of the peak position of those contributions varies in the range from about 1 to 2 eV, depending on the compound and the fragment formed. In addition to these low energy contributions, higher energy, fairly broad, features are observed for all the tetrachlorides. These contributions exhibit a peak in the energy range between 5 and 8 eV, again depending on the compound and the fragment formed. Further to the experimental data, we report DFT and coupled cluster calculations on the thermochemical thresholds for the individual fragments as well as the respective bond dissociation energies and electron affinities. These calculated values are compared with the experimental appearance energies and literature values, where they are available

Electron interactions with the heteronuclear carbonyl precursor H2FeRu3(CO)13 and comparison with HFeCo3(CO)12: 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 H2FeRu3(CO)13 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 (≈3.5) is higher than the 3:1 ratio predicted. This is somewhat surprising as in recent FEBID studies on a structurally similar bimetallic precursor, HFeCo3(CO)12, metal contents of about 80 atom % is achievable on a routine basis and the deposits are found to maintain the initial Co/Fe ratio. Low temperature (≈213 K) surface science studies on thin films of H2FeRu3(CO)13 demonstrate that electron stimulated decomposition leads to significant CO desorption (average of 8–9 CO groups per molecule) to form partially decarbonylated intermediates. However, once formed these intermediates are largely unaffected by either further electron irradiation or annealing to room temperature, with a predicted metal content similar to what is observed in FEBID. Furthermore, gas phase experiments indicate formation of Fe(CO)4 from H2FeRu3(CO)13 upon low energy electron interaction. This fragment could desorb at room temperature under high vacuum conditions, which may explain the slight increase in the Ru/Fe ratio of deposits in FEBID. With the combination of gas phase experiments, surface science studies and actual FEBID experiments, we can offer new insights into the low energy electron induced decomposition of this precursor and how this is reflected in the relatively poor performance of H2FeRu3(CO)13 as compared to the structurally similar HFeCo3(CO)12.The authors acknowledge the fruitful and productive environment provided by the COST Action CELINA CM1301 and we would like to take the opportunity to extend our thanks to Prof. Petra Swiderek for running this Action exceptionally well. Marc Hanefeld and Michael Huth acknowledge financial support by the Deutsche Forschungsgemeinschaft (DFG) through Priority Program SPP 1928, project HU 752/12-1. DHF thanks the National Science Foundation for support of this work through the linked collaborative grants CHE-1607621 and CHE-1607547. OI acknowledges supported from the Icelandic Center of Research (RANNIS) Grant No. 13049305(1-3) and the University of Iceland Research Fund. RKTP acknowledges a doctoral grant from the University of Iceland Research Fund and financial support from the COST Action CM1301; CELINA, for short term scientific missions (STSMs).Peer Reviewe

Hlutverk lágorkurafeinda í niðurbroti kísil innihaldandi efna til notkunar í örprentun yfirborða með skörpum rafeindasgeislum: HFeCo3(CO)12, H2FeRu3(CO)13, SiC5H10Cl2, SiC5H12 and Si3C3H12

Focused electron beam induced deposition (FEBID) is a direct-write 3D nanofabrication technique, which works on the principle of electron-induced molecular decomposition. In FEBID, a high-energy focused electron beam dissociates the precursor molecules adsorbed on a substrate into volatile and non-volatile species. The volatile species can be pumped away from the substrate by vacuum pumps and the non-volatile species will be deposited on top of the substrate. Although FEBID is a potentially useful 3-D direct write nanofabrication technique, it still faces some critical challenges such as deposit impurity and lateral broadening of deposited structures. These challenges are mainly due to the spatial distribution of secondary electrons (SEs, electrons with energy < 50 eV) outside the focal point of the primary electron beam and the incomplete electron- induced decomposition of precursor molecules. Several dissociation mechanisms are active in the low-energy SE energy range: dissociative electron attachment (DEA), dissociative ionization (DI), dipolar dissociation (DD) and neutral dissociation (ND). In particular, DEA and DI have been shown to be relevant to the deposition of several FEBID precursors. Understanding electron interactions with precursor molecules in this low-energy SEs range can therefore aid in addressing the challenges facing FEBID. One potential approach to realize this is combining gas phase and surface studies of FEBID precursor molecules. In gas phase studies, an electron beam of variable energy (0 - 80 eV) is crossed with an effusive molecular beam of FEBID precursor molecules under single electron- molecule collision conditions, and the subsequently formed ionic species are detected using a quadrupole mass spectrometer. In surface studies, FEBID precursor molecules are adsorbed onto a cold substrate (at -120 0C) under ultrahigh vacuum (UHV) condi- tions and irradiated with a broad beam of electrons (energy ~500 eV) from a flood gun. Different changes occur in the adsorbed precursor film due to electron-induced reactions can be monitored using X-ray photoelectron spectrometry (XPS), while the species desorbed from the film can be detected using a Mass spectrometer (MS) attached to the UHV chamber. This thesis focuses on gas phase and surface studies of the bimetallic precursor molecules HFeCo3(CO)12 and H2FeRu3(CO)13. The bimetallic nanostructures have many applications mainly in the semiconductor industry. The conventional method to fabricate bimetallic nanostructures in FEBID is mixing two different metal centered precursor molecules using a dual or multichannel gas injection system. However, this method has difficulties in reproducing the exact deposited structure and there is only limited control over the composition of the deposits. These difficulties in FEBID can be overcome by using bimetallic precursor molecules like HFeCo3(CO)12 and H2FeRu3(CO)13. Although these are both bimetallic and structurally similar precur- sor molecules, their performance in FEBID is significantly different. This different behavior of HFeCo3(CO)12 and H2FeRu3(CO)13 in FEBID motivated us to conduct gas phase and surface studies of their electron-induced dissociation behavior. Gas phase studies presented in this thesis mainly contain DEA and DI of HFeCo3(CO)12 and H2FeRu3(CO)13. Gas phase studies also included quantum chemical calculations to identify most probable electron attachment fragmentation channels in HFeCo3(CO)12 and H2FeRu3(CO)13. The surface study part mostly discussed the electron induced bond breaking reactions of surface adsorbed HFeCo3(CO)12 and H2FeRu3(CO)13. The observations made from gas phase and surface study are used in this thesis to discuss why these two bimetallic precursor molecules behaved differently in FEBID reactions. Furthermore, in this thesis, the gas phase study of trisilacyclohexane (TSCH) and the FEBID study of TSCH, dichlorosilacyclohexane (DCSCH) and silacyclohexane (SCH) are discussed in relation to their different behaviour towards DEA and DI. The precursor molecules SCH and TSCH are completely inert to DEA within the sensitivity of our experimental set up, however DCSCH is active to DEA and all these precursor molecules are active to DI. How the inert behaviour of SCH towards DEA compared to DCSCH reflects in the electron beam induced deposition of these precursor molecules will be discussed in this thesis. The questions like ’does this inert behaviour of SCH compared to DCSH influence significantly to the electron induced growth dynamics of these precursor molecules?, comparatively more silicon content in the TSCH precursor will have any advantage in FEBID?’ will be addressed in this thesis.Örprentun með skörpum rafeindageisla (e. Focused Electron Beam Induced Deposition, FEBID) er aðferð sem nota má til að prenta þrívíða strúktúra á yfirborð með rafeindahvötuðu niðurbroti svokallaðra forverasameinda. Það eru þó enn þónokkrar hindranir sem standa ı vegi fyrir notkun FEBID, þar á meðal óhreinindi í útfellingum og og breikkun þeirra. Þessar hindranir má að stúru leyti rekja til dreifingar lágorkurafeinda (rafeinda með hreyfiorku undir 50 eV) út fyrir brennipunkt rafeindageislans og ófullkomið niðurbrot á forverasameindunum. Nokkrar rafeindadrifnar niðurbrotsleiðir eru mögulegar á lágorkusviðinu: rjúfandi rafeindarálagning (Dissociative Electron Attchment, DEA), rjúfandi jónun (e. Dissociative Ionization, DI), tvískautssundrun (Dipolar Dissociation, DD) og hlutlaus sundrun (e. Neutral Dissociation, ND). Við hagnýtingu á FEBID getur vitneskja um hvörf drifin af lágorkurafeindum skipt sköpum. Ein möguleg nálgun við rannsóknir á þessum ferlum er samtvinnaðar mælingar á forverasamendum í gasfasa og á yfirborðum. Tilraunir í gasfasa eru svokallaðar þvergeislatilraunir þar sem rafeindageisli (hreyfi- orka rafeindanna er 0-80 eV) og sameindageisli mætast undir réttu horni. Þessar mælingar eru gerðar við lágan þrýsting, sem tryggir að hver sameind víxlverkar einungis við eina rafeind. Jónir sem myndast við þessa víxlverkan eru greindar með massagreini. Í yfirborðsmælingum aðsogast forverasameindir á kalt yfirborð (við 153 K) við mjög lágan þrýsting og eru síðan geislaðar með breiðum rafeindageisla (~500 eV). Þær breytingar sem eiga sér stað á efnunum á yfirborðinu eru reyndar með Röntgen ljósröfunarmæli (X-ray Photoelectron Spectrometer, XPS) og þau efni sem losna frá yfirborðinu eru mæld með massagreini. Í thessari ritgerð er sjónum beint að gasfasa- og yfirborðsmælingum á forverasameindunum HFeCo3(CO)12 and H2FeRu3(CO)13. thó báðar sameindirnar séu tvímálmar, með svipaða uppbyggingu og lögun, hefur reynslan af þeim í FEBID verið gjörólík. Því er samanburður milli þeirra í gasfasa- og yfirborðsmælingum áhugaverður. Gasfasatilraunirnar sem hér eru kynntar eru aðallega DEA og DI á HFeCo3(CO)12 and H2FeRu3(CO)13. Að auki voru skammtafræðilegir útreikningar á sameindunum framkvæmdir til að meta líklegustu niðurbrotsleiðir. Yfirborðsmælingarnar voru síðan notaðar til að athuga hvaða áhrif yfirborðið hefur tengjarof á sameindunum. Niðurstöður mælinganna sýna hvers vegna þessar tvær sameindir eru svo ólíkar í FEBID. Að auki eru FEBID mælingar á trisilacyclohexane (TSCH), dichlorosilacyclohexane (DCSCH) og silacyclohexane (SCH) og niðurbrot þeirra í DEA og DI borið saman. Forverasameindirnar SCH og TSCH sýna ekkert niðurbrot í DEA en DCSCH sýnir talsvert niðurbrot. Allar sameindirnar brotna niður við DI. Athyglinni er beint að spurningum eins og "hefur óhvarfgirni TSCH m.t.t. DEA samanborið við DCSH áhrif á FEBID?og "Hefur aukið kísilsinnihaldi í TSCH einhver áhrif í FEBID?".University of Iceland research fund, CELINA COST action 1301Thesi

Structure and energetics in dissociative electron attachment to HFeCo

Here we report structural parameters on the heteronuclear transition metal complex HFeCo3(CO)12 and its anion formed upon electron attachment, as well as the thermochemical thresholds for sequential CO loss and the loss of the apical group (as Fe(CO)-3 and Fe(CO)-4). Geometrical parameters from single crystal X-ray diffraction are compared with calculated values from density functional theory calculations, for the neutral and anionic ground state of this transition metal cluster. Further, experimental appearance energies for sequential CO loss and the formation of Fe(CO)-3 and Fe(CO)-4 are compared to the respective calculated threshold values. Geometry optimizations were performed at the BP86/def2-TZVP level of theory while the threshold energies were calculated at the PBE0/ma-def2-TZVP level of theory. The SOMO of the anion is found to have a clear Fe-Co anti-bonding character resulting in elongation of the Fe-Co bonds and the transformation of one of the terminal Co-CO groups to a bridging Co-CO-Fe group upon electron attachment. The thermochemical threshold PBE0 calculations are concordant with the observed appearance energies and structural parameters from single crystal X-ray diffraction for the neutral molecule are well reproduced at the BP86/def2-TZVP level of theory

Formation and decay of negative ion states up to 11 eV above the ionization energy of the nanofabrication precursor HFeCo3(CO)12

In single electron collisions with the heteronuclear metal carbonyl compound HFeCo3(CO)12 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. We support this with calculated MO-diagrams revealing dense bands of energy levels near the HOMO–LUMO gap. HFeCo3(CO)12 is a promising focused electron beam induced deposition (FEBID) precursor and we argue that its unusual DEA behavior relates to its exceptional performance in FEBID. This may be general to a class of molecules with high potential for nano-fabrication by FEBID.This work was supported by the Icelandic Center of Research (RANNIS) Grant No. 13049305(1-3) and the University of Iceland Research Fund. RKTP acknowledges a doctoral grant from the University of Iceland Research Fund and nancial support from the COST Action CM1301; CELINA, for short term scientic missions (STSMs). R. B. acknowledges support from the Icelandic Research Fund, Grant No. 141218051.Peer Reviewe

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. 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

Spectroscopic signatures of states in the continuum characterized by a joint experimental and theoretical study of pyrrole

We report a combined experimental and theoretical investigation of electron-molecule interactions using pyrrole as a model system. Experimental two-dimensional electron energy loss spectra (EELS) encode information about vibrational states of the molecule as well as position and structure of electronic resonances. The calculations using non-Hermitian extensions of equation-of-motion coupled-cluster theory facilitate the assignment of all major EELS features. We confirm the two previously described π* resonances at about 2.5 and 3.5 eV (the calculations place these two states at 2.92 and 3.53 eV vertically and 2.63 and 3.27 adiabatically). The calculations also predict a low-lying resonance at 0.46 eV, which has a mixed character---of a dipole-bound state and σ* type. This resonance becomes stabilized at one quanta of the NH excitation, giving rise to the sharp feature at 0.9 eV in the corresponding EELS. Calculations of Franck-Condon factors explain the observed variations in the vibrational excitation patterns. The ability of theory to describe EELS provides concrete illustration of the utility of non-Hermitian quantum chemistry, which extends such important concepts as potential energy surfaces and molecular orbitals to states embedded in the continuum

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. However, while DCSCH shows appreciable cross sections with regards to dissociative electron attachment, SCH is inert with respect to this process. We discuss our deposition experiments in context of the efficiency of these different electron-induced fragmentation processes. With regards to the deposition dynamics, we observe a substantially faster growth from DCSCH and a higher saturation diameter when growing pillars with high aspect ratio. However, both compounds show similar behaviour with regards to the proximity effect. With regards to the composition of the deposits, we observe that the C/Si ratio is similar for both compounds and in both cases close to the initial molecular stoichiometry. The oxygen content in the DCSCH deposits is about double that of the SCH deposits. Only marginal chlorine is observed in the deposits of from DCSCH. We discuss these observations in context of potential approaches for Si deposition.ImPhys/Imaging PhysicsImPhys/Charged Particle Optic