Decomposition of Iron Pentacarbonyl Induced by Singly and Multiply

Subscriber access provided by UNIV OF LOUISIANA

C: Physical Processes in Nanomaterials and Nanostructures

Decomposition of Iron Pentacarbonyl Induced by Singly and Multiply Charged Ions and Implications for Focused Ion Beam Induced Deposition Suvasthika Indrajith, Patrick Rousseau, Bernd Huber, Chiara Nicolafrancesco, Alicja Domaracka, Kateryna Grygoryeva, Pamir Nag, Barbora Sedmidubská, Juraj Fedor, and Jaroslav Ko#išek J. Phys. Chem. C, Just Accepted Manuscript • Publication Date (Web): 27 Mar 2019 Downloaded from http://pubs.acs.org on March 27, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Decomposition of Iron Pentacarbonyl Induced by Singly and Multiply Charged Ions and Implications for Focused Ion Beam Induced Deposition Suvasthika Indrajith,

†,‡

Nicolafrancesco,

†

Patrick Rousseau,

∗,†

Alicja Domaracka,

¶,§

Barbora Sedmidubská,

†

Bernd Huber,

†

Kateryna Grygoryeva,

¶

Juraj Fedor,

¶

Chiara

Pamir Nag,

¶

∗,¶

and Jaroslav Ko£i²ek

†Normandie Univ., ENSICAEN, UNICAEN, CEA, CNRS, CIMAP, 14000 Caen, France ‡Synchrotron SOLEIL, L'Orme des Merisiers, Saint Aubin, B.P. 48, 91192 Gif-sur-Yvette,

France ¶J. Heyrovský Institute of Physical Chemistry v.v.i., The Czech Academy of Sciences,

Dolej²kova 3, 18223 Prague, Czech Republic §Deptartment of Nuclear Chemistry, Faculty of Nuclear Sciences and Physical Engineering,

Czech Technical University in Prague,B°ehová 7,115 19 Prague, CZ. E-mail: [email protected]; [email protected]

1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 23

Abstract Focused ion beams are becoming important tools in nanofabrication. The underlying physical processes in the substrate were already explored for several projectile ions. However, the studies of ion interaction with precursor molecules for beam assisted deposition are almost non-existent. Here we explore the interaction of various projectile ions with iron pentacarbonyl. We report fragmentation patterns of isolated gas phase iron pentacarbonyl after interaction with 4 He+ at a collision energy of 16 keV, 4 He2+ at 16 keV, 84 Kr3+

20 Ne+

at 6 keV,

at 12 keV and

20 Ne4+

84 Kr17+

at 40 keV,

40 Ar+

at 3 keV,

40 Ar3+

at 21 keV,

at 255 keV. These projectiles cover interaction regimes

ranging from collisions dominated by nuclear stopping through collisions dominated by electronic stopping to soft resonant electron capture interactions. We report a surprising eciency of Ne+ in the Fe(CO)5 decomposition. The interaction with multiply charged ions results in a higher content of parent ions and slow metastable fragmentation due to electron capture process. The release of CO groups during the decomposition process seems to take o a signicant amount of energy. The fragmentation mechanism may be described as Fe being trapped within a CO cluster.

Introduction Focused particle beam processing is a novel technique, which is rapidly developing in the eld of nanofabrication. 14 A straightforward use of electron and ion beams for nanopatterning led to extensive studies of electron and ion beam interactions with substrate materials, which are now fairly well understood. 5 The situation is dierent for beam assisted deposition techniques where precursor molecules (often metal-containing) are introduced to the vicinity of a substrate by a gas-injection system. While the possible role of secondary electrons in the deposition process has recently inspired a large number of studies on low-energy electron interactions with deposition precursors, 6 there are practically no data concerning the interaction of these precursors with primary ions. The spread of secondary electrons interacting 2


Page 3 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


with precursor molecules during the Focused Ion Beam Induced Deposition (FIBID) is low 1 increasing the relative importance of precursor decomposition by primary ions, as studied in the present work. The ion beam - surface interaction is usually characterized by the energy transfer from the projectile to the deposit and can be described by the concept of stopping power. 5,7 Here we explore dierent regimes of ion - molecule interaction showing that stopping power alone may not be sucient to describe the underlying fragmentation mechanisms. The ion-induced fragmentation of complex molecules, like in the present case Fe(CO)5 , is based on dierent processes and mechanisms depending on the fact whether the ion interacts with the electronic cloud of the molecule (individual or collective electron excitation and electron capture) or with the heavy particle system (elastic collisions with the molecular nuclei). The relative importance of both types of interactions depends on the velocity of the projectile, on its charge state as well as on the ion mass. Fragmentation can be induced either by populating dissociative electronically excited states or by the transfer of electronic excitation energy (multiply excited states) which is transferred later on into the degrees of vibrational motion and causes molecular decay. Furthermore, when the charge state of the projectile is high, the created multiply charged molecular ions become unstable due to the repelling Coulomb forces and energetic fragments are formed. When binary collisions between the projectile ion and the target nuclei are important a local vibrational excitation can occur, which can at suciently high energy transfer provoke the emission of a nucleus in a so-called knockout process. In the case of very light projectiles like He+ the possible energy transfer to the heavy nuclei (Fe, O, C) is very low due to the unfavorable mass ratio and the energy transfer will mainly occur via the so-called electronic stopping power. When the mass of the projectile is increased nuclear collisions become more important and the energy transfer may overcome that obtained by the interaction with the electronic system. However, also the projectile velocity is an important parameter which favors at high values the probability for electronic 3



Figure 1: Projectile energy loss by nuclear (blue dot-dashed line) and electronic (red dotted line) stopping for projectiles (H+ , C+ and Ar+ ) passing through a C60 fullerene molecule at an impact parameter of 2 atomic units. The data are taken from. 8 excitation, whereas the nuclear stopping probability has a maximum at rather low velocities. As a typical example we show in Figure 1 theoretical results, based on non-adiabatic quantum molecular dynamics (NA-QMD) calculations, which have been obtained by Kunerth and Schmidt for collisions of H+ , C+ and Ar+ projectiles with C60 fullerenes in the gas phase. 8 One can clearly see the increase of the nuclear stopping in its maximum with the projectile mass. The electronic enery loss increases as well with mass and kinetic energy up to velocities of about v=1 au. Similar results have been obtained for ions colliding with pyrene and coronene molecules. 911 When the excitation energy is distributed over all vibrational degrees of freedom, statistical fragmentation occurs. 12 The hot system can be described as an evaporative ensemble, which will lead to an evaporative chain showing maxima when the binding energy of a certain species is higher than that of their neighbors. An example are magic number peaks showing up at shell closures in evaporating metallic clusters. 13 A second important issue treated in this work is the interaction with multiply charged ions. Higher charge states enable higher impact velocities of ions at much lower acceleration voltages. Additionally, higher charge states open new modes of interaction with molecules 4


Page 4 of 23

Page 5 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and surfaces (see e.g. 14,15 ). This concerns mainly resonant electron capture, where the target can be eciently ionized in spite of a large impact parameter in the collision. An appropriate ion source may then allow to apply new interaction regimes in the conventional ion microscopes. Iron pentacarbonyl, which was selected for the present study, is a common and well explored deposition precursor. 1619 The structure and bonding of the molecule are well known. 2025 In the context of focused particle beam deposition, it has been studied in collisions with electrons at low and medium energies in the gas phase, 24,2632 in clusters 33,34 and deposited on surfaces. 3537 However, we are not aware of any study concerning the behavior of Fe(CO)5 , or a dierent FIBID precursor, after ion irradiation at relevant kinetic energies. This eld is largely unexplored. To our knowledge, the only relevant work is that of Martin et al. 38 on tungsten hexacarbonyl in collisions with ions at very low energies ∼3 keV.

Methods The experiments were carried out using the COLIMACON experimental setup. 39 Fe(CO)5 passed from a glass bulb kept at 303 K through a metal capillary kept at 323 K into the interaction zone. The sample was purchased from Sigma Aldrich with stated purity of 99.99% and was used without further purication. Before the measurements, the bulb volume above the liquid sample was pumped to remove possible impurities or decomposition products. The formed eusive beam of Fe(CO)5 was crossed by an ion beam delivered by the ARIBE 40 facility at GANIL. 41 The used projectiles were 16 keV 4 He+ , 16 keV 4 He2+ , 6 keV 40 keV

20

3 keV

Ar+ projectiles produced by a Perkin Elmer ion gun.

40

Ne4+ , 21 keV

40

Ar3+ , 12 keV

84

Kr3+ and 255 keV

84

20

Ne+ ,

Kr17+ . Additionally, we used

Cationic products of the interaction were analyzed using a Wiley-McLaren time-of-ight (TOF) spectrometer with a spatially extended extraction region. 42 In the present paper, we will discuss inclusive mass spectra (MS), i.e. spectra which include all ions created in

5



individual detected collision events. As the signals are registered in an event-by-event mode, the stored data can be separated with respect to the number n of created ions per collision event, leading to so-called n-stop spectra. The inclusive spectrum contains signals from all n-values. The ion pulse length was 500 ns for He and Ne projectiles, 1 µs for Kr and Ar3+ projectiles and 3 µs for Ar+ . The ion extraction pulse length was in all cases 4 µs. The extraction eld of 240 V/cm was applied immediately after the ion bunch has left the interaction zone (∼10 ns).

Results and Discussion Fragmentation patterns

Here we discuss the fragmentation patterns, i.e. mass spectra for Fe(CO)5 decomposition after the interaction with studied rare gas projectiles. The comparison of the spectra enables identication of dierent interaction regimes described in the introduction. The spectra are plotted in Figures 2 and 3. The common characteristics of all the spectra is an evaporation series where various numbers of neutral CO molecules are emitted from the Fe(CO)+ 5 reaching the nal fragment of pure Fe+ . The intensity distribution of this series depends strongly on the projectile ion and on the energy, which is transferred during the collision to the molecule. For very low excitation energies the parent molecular ion Fe(CO)+ 5 should be dominant in the mass spectrum, for high energy transfers (>6 eV) we expect the Fe+ fragment to play an important role. In several cases, a U-shape form of the intensity distribution is observed indicating a wide energy distribution caused by interplay of dierent interaction mechanisms. The smooth intensity distribution may be also perturbed by the fragments with increased stability as described in the introduction. The appearance energies for the FeCO+ n (n=0 to 5) ions, which have been determined in experiments where electrons were collided with the 6


Page 6 of 23

Page 7 of 23

neutral parent molecule, 29 increase from 8.45 eV to 14.65 eV above the ground state of the neutral molecule for n=0 to 5, respectively. The bond dissociation energies for (CO)n Fe+ -CO were estimated to be 1 eV for n=3 to 5 and about 2 eV for n=1 and 2. +

CO /Fe

2+

4

100

Fe

+

O

+

He

+

16 keV

+

50

C

Fe(CO)

FeCO

2+

FeCO

+

Fe(CO) +

+ 2

FeC

Fe(CO)

0 Intensity (arb. units)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


100

0

20

40

60

80

100 20

120

Ne

+

140

+

Fe(CO)

+ 5

+ 4

3

160

180

200

160

180

200

160

180

200

6 keV

50 0 100

0

20

40

60

80

100 40

Ar

50

+

120 +

Ar

140

3 keV

0 0

20

40

60

80

100

120

140

m/z

Figure 2: Mass spectra of Fe(CO)5 fragmentation by the impact of singly charged projectiles. Figure 2 shows the spectra obtained in collisions with singly charged projectiles. For He+ projectiles (upper panel), the intensity of the intact molecular ion is rather low, whereas the intensity of the Fe+ fragment, the end point of the CO loss chain is rather high, indicating that a large amount of energy is transferred to the target. As mentioned in the introduction, for He+ ions electronic excitation and electron capture are the dominant underlying processes. The recombination energy of He+ ions is rather high with 24.59 eV and it is well above the ionization potential of Fe(CO)5 , which is 8.45 eV. Thus, the ground state electron capture process is highly exothermic (∼+16 eV) and has a very low probability. The capture of 7



lower lying electrons will be more probable, resulting in highly electronically excited states of Fe(CO)+∗ 5 . In agreement with these statements, the experimental spectrum shows a low signal for the intact singly charged molecule and intense fragmentation. Although the fragmentation primarily results in the evaporation of neutral CO, also singly charged CO+ fragments are observed. Their intensity decreases for the Ne+ and Ar+ projectiles. This again indicates the high electronic excitation in the case of interaction with He+ . Fe(CO)5 is a low-spin d8 complex with a trigonal bipyramidal structure. In this form, ve highest occupied molecular orbitals of Fe(CO)5 are dominated by iron d orbitals. 43 Electron transfer from these orbitals will therefore primarily result in the formation of Fe+ containing fragments while electron transfer from lower lying orbitals will result in a more uniform distribution of the charge in between CO+ and Fe+ parts of the molecule. Finally, the formation of highly electronically excited Fe(CO)+∗ 5 is also supported by the increased intensity of small fragments in the He+ spectra. The FeC+ and FeCO2+ fragments are correlated with higher appearance energies of about 22 eV and 30 eV. 29 The C+ and O+ fragments may be formed in fast direct dissociation rather than after the redistribution of the excitation energy as the dissociation of the CO bond requires 11 eV compared to 1.5 eV for the dissociation of the Fe-C bond. 29,44 For Ne+ (shown in the middle panel of Figure 2) with recombination energy of 21.6 eV, we can still observe the low mass fragments as a result of electron transfer from low lying molecular orbitals of Fe(CO)5 . The projectile is heavier and slower in comparison to He+ , what results in a higher energy transfer to the target (see Figure 1). As a result, the fragment intensity distribution has its maximum at the Fe+ fragment and the intact molecular ion is hardly observed. The relative importance of elastic nuclear collisions also increases and contributes to the localized heating of the target molecule. The nuclear stopping is becoming even more dominant for collisions with 3 keV Ar+ ions shown in the bottom panel of Figure 2. In this case, the fragmentation is non statistical, dominated by the FeCO+ fragment. Similar non-statistical fragmentation after collisions dominated by nuclear excitation was 8


Page 8 of 23

Page 9 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


also observed for other systems. 10,11 It may indicate the localized character of the primary excitation. The additionally observed Ar+ peak is due to the residual gas contamination from the Ar ion gun and the symmetric electron capture Ar+ +Ar, which has a very high cross section. In Figure 3, spectra obtained in collisions with multiply charged projectiles are shown. When comparing collisions of He2+ with those of He+ projectiles at the same velocity, single electron capture occurs at much larger inter-nuclear distances. 45 Hence, the energy transfer is much smaller. As a consequence, the intensity of the intact molecular ion increases and that of the Fe+ fragment decreases, becoming lower than that of the intact molecule. With heavier multiply charged projectiles (Ne, Ar, Kr) one might expect a similar, extensive fragmentation as for the Ne+ . However, due to their higher charge state, single electron capture with a low energy transfer becomes very likely occurring at large inter-nuclear distances. Thus, the intensity of intact molecular ions becomes higher than for singly charged ions. For example when comparing the spectra for Ne+ and Ne4+ projectiles, in both cases the Fe+ fragment is dominant, but in the latter case also the contributions from intact + molecular ions Fe(CO)+ 5 as well as that from Fe(CO)4 become comparable.

For Ne4+ , Ar3+ and Kr3+ projectiles, with similar momentum and charge state, we can see the increase of the Fe(CO)+ fragment intensity with increasing mass and decreasing velocity of the projectile. As discussed for the singly charged ions, this may be caused by more localized character of the nuclear excitation. With low intensities, we can also observe doubly charged ions like Fe(CO)2+ 3 (m/z =70), FeCO2+ (m/z =42) or FeC(CO)2+ 3 (m/z =48). However, some of them are overlapping with singly charged ion signals as CO+ and Fe2+ at m/z =28. In addition to direct nuclear collisions or single capture events, these may be formed in multi-electron capture processes resulting in stable doubly charged systems. Multi-electron capture processes can also result in charge instabilities and Coulomb explosion forming fragments with high kinetic energies (e.g. C+ , O+ , CO+ ) as will be discussed further below. 9



4 +

CO /Fe

100

0 100

2+

Fe

C

+

100

100

Fe(CO)

+

+

Fe(CO)

+

+

4

2

2+

FeCO

Fe(CO)

+

3

0

20

40

60

80

100 120 140 160 180 200 20

0

20

40

60

80

Ne

40

0

20

40

60

80

4+

40 keV

100 120 140 160 180 200

50 0

16 keV

FeCO

50 0

2+

Fe(CO)

+

O

He

5

+

50

Intensity (arb. units)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 23

3+

Ar

21 keV

100 120 140 160 180 200 84

50

3+

Kr

12 keV

0 100

0

20

40

60

80

100 120 140 160 180 200 84

17+

Kr

255 keV

50 0

0

20

40

60

80

100 120 140 160 180 200 m/z

Figure 3: Mass spectra of Fe(CO)5 fragmentation by the impact of multiply charged projectiles.

10


Page 11 of 23

for Fe(CO)

x

+

ions (x=0-5)

4 Number of CO groups per Fe

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3

2.7

2.2

2

2

1.9

2

1.3

1

1.1

1

0.3

He+ Ne+ Ar+ He2+ Ne4+ Ar3+ Kr3+ Kr17+ eProjectile

Figure 4: Fragmentation eciency by dierent projectiles demonstrated on the number of iron atoms per CO groups in the Fe(CO)+ x ions, calculated from integrals of appropriate peaks in the time-of-ight spectra. Ratio for e− calculated from MS available from NIST database. 46 A comparison of the ion spectra with that obtained by electron impact ionization at an electron energy of 70 eV 29 shows clear dierences. Although one might expect that the EI spectrum should be similar to that of He, dominated by electronic excitation, the spectra are dierent. Whereas in the rst case the clearly dominating fragments are Fe+ and Fe(CO)+ , the intensity of which overcomes the intensity of the other fragments by a factor of 10, in the He+ case the dierence is not so large. The higher m/z part of the EI spectrum, which has very low intensity, indicates a high energy transfer in single ionization collisions with 70 eV electron. Another observation concerns the low yield of CO+ fragments in the EI case. This indicates that electron impact ionization favors population of excited electronic states of Fe(CO)+ 5 , which are dierent than those from ion impact. One of the goals of the FIBID technique is the preparation of pure metallic deposits. Concerning this point, we can see that the interaction with Ne+ projectiles results in the most eective fragmentation and nearly exclusively to the Fe+ ion formation. In order to obtain a more quantitative picture, we integrated all Fe(CO)+ x (x=0-5) peaks in the mass spectra and calculated the total number of CO groups remaining on Fe for particular projectiles. The result is shown in Figure 4. We select only iron containing ions for two reasons. First, these 11



are the "heavy" fragments that may be more involved in the deposition, while gas phase fragments such as CO can easily evaporate. Second, we can see that for some projectiles, the kinetic energies of small fragments are high so that we are not able to detect all of them (see discussion below). The value of the ratio is ∼2, for all the multiply charged projectiles. For singly charged projectiles, the ratio is slightly lower (∼1), except for the case of Ne+ with the ratio of only 0.3. This again demonstrates the eciency of Ne+ in the Fe(CO)5 decomposition discussed above, which can not be described by a simple increase in the fragmentation with higher nuclear stopping power. According to such trend, Ar+ should be much more eective, which is not the case. As a consequence, Ne+ should be very eective in the creation of pure deposits in FIBID.

Prompt vs. metastable fragmentation

As mentioned above, projectiles in higher charge states enable resonant electron capture processes. Due to the long range character of the interaction, they may result in soft ionization with low energy transfer. Such ionization is then accompanied by a redistribution of energy into molecular degrees of freedom and formation of metastable molecular cations, with lifetimes in the range of µs. In our instrument, these cations can be analyzed due to the spatially extended TOF extraction system. 42,47,48 Fragment ions formed by metastable decay in this part of the spectrometer are time-delayed in comparison to the fragment ions formed directly during the ionization event, forming a typical tail of the fragment mass peak shape towards longer drift times and hence masses. In the present case, the most intense contributions are observed for Fe(CO)+ 4 fragments, which are visualized in Figure 5. These are formed by the delayed emission of one CO unit from the intact molecular ion Fe(CO)+ 5 . We can see that the metastable decay occurs only for the multiply charged projectiles. The slope of the tail can be used to estimate the lifetime of the metastable ions which are similar for all projectiles of the order of ∼4µs. 12


Page 12 of 23

Page 13 of 23

Fe(CO)

+


5

Fe(CO)

4

+

+ CO

10

y=11*e

-x/3.74

5

1 100

2

3

Residence Time in the Extraction Region (

4

s) 2+

He

3+

Kr

10

17+

Kr


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3+

Ar

4+

Ne

1

+

He

+

Ne

+

Ar

0.1

0.01

165

170

175

180

185

m/z

Figure 5: Metastable parent ion decay in the extraction region of the spectrometer by release of one CO group. Top gure shows the TOF transformed into the residence time in the extraction region and the corresponding t to the data, which is used to estimate the ion lifetime. In the present case, the decay for all multiply charged projectiles, which is shown in the bottom part of the gure, follows a similar shape. Therefore, the t is made for an average of the spectra for all multiply charged projectiles. Also shown is the signal for interaction with singly charged projectiles, show such a metastble decay to a much lower extent. The prominent peaks on the left side of the gure, in the mass range between m/z = 165-170, correspond to the Fe(CO)+ 4 and its isotopes. As the ion signal is spread out over a long time, the integral contribution for a particular ion can add up to several percents. Additionally, the tail does not contain all the metastable ions. We can see a drop in the intensity at the time, which corresponds to the TOF of the parent cation through the rst extraction eld. Decay occurring during the passage of the ions through the second eld of the extraction region leads to further contributions up to the mass of the parent ion, although with lower intensity as the ion velocity is higher in this region. The relative contribution of the metastable decay process may be even higher on the long timescales of deposition experiments.

13



Fast fragments

When several electrons are captured by the passage of highly charged ions, the target molecule is left behind multiply charged. If the charge is localized on one atom, we often end up with stable multiply charged cations in MS. In the case of iron pentacarbonyl, these cations contain iron as a large atom with high contribution to valence orbitals, enabling formation of multiply charged ions at a relatively low energy input. When the charge is localized on several neighbored atoms, the electrostatic repulsion typically results in a rapid bond cleavage and molecular explosion, which can lead to fragments with high kinetic energies. Another process that can lead to energetic fragments is the direct knock out of atoms as described in the introduction and in the works concerning complex hydrocarbons. 9,11 100

100 CO

of the Fragment (eV)

Maximum Observed Kinetic Energy

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 23

10

+

10

+

Fe

1

1

0.1

0.1

0.01

0.01 He+ Ne+ Ar+ He2+ Ne4+ Ar3+ Kr3+ Kr17+ Projectile

Figure 6: Maximum kinetic energies of CO+ and Fe+ fragments for dierent projectiles. In FIBID, such energetic fragments may produce unwanted deposit broadening. Therefore, we analyzed the kinetic energies of the fragments for dierent projectiles. In the linear TOF setup, the initial kinetic energy of fragments causes a broadening of the mass peaks. The maximum kinetic energy of the fragments, can be estimated analytically from the parameters of the extraction eld and the TOF geometry used in the experiment. In Figure 6, we show the maximum kinetic energies for the two fragments CO+ and Fe+ for dierent projectile ions. Among the iron containing fragments, contributing to the deposit broadening, Fe+ ions are the lightest and therefore can posses highest kinetic energies. 14


Page 15 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


For collisions dominated by electronic excitation, the kinetic energy of the fragments is low (0.2 eV-0.5 eV), in good agreement with our expectation of eective energy redistribution and ergodic dissociation. For collisions dominated by nuclear stopping and multiple electron capture, the maximum kinetic energy of CO+ fragments rises dramatically from 2.6 eV for Ne+ to about 27 eV for Kr17+ . These high energies can be reached in Coulombic explosion of multiply charged molecules, by dissociation of highly excited states or by direct knockout. However, the last option will be quite surprising as we are discussing molecular fragments. On the other side, the kinetic energies of Fe+ fragments change only slightly from 0.2 eV to 0.8 eV. The reasonable explanation seems to be that CO groups act protectively on the Fe core. As a central atom, Fe does not participate in the Coulomb explosion. Also, the direct "knockout" collision may result only in the energy redistribution to the motion of CO groups instead of Fe+ release. The structure of Fe(CO)5 is therefore surprisingly well designed to produce Fe fragments with low kinetic energies.

Conclusions In conclusion, we report experimental results on the fragmentation of the deposition precursor iron pentacarbonyl after interaction with eight ion projectiles, which enabled the identication of dierent interaction regimes. We focused on the characteristics relevant for the FIBID technique. The collisions with light projectiles such as He results in electronic excitation. The kinetic energies of fragments formed in this regime are low which will result in a weak deposit broadening in FIBID. On the other hand, the fragmentation eciency is low, with an average of two CO groups remaining on the iron. Formation of high purity deposits may therefore require further processing. The most eective fragmentation with an average of only ∼0.3 CO groups remaining at the iron atom was observed for Ne+ projectile impact.

15



Collisions with multiply charged Kr projectiles result in CO+ fragments with extremely high kinetic energies up to tens of eV while the kinetic energy of Fe+ fragments varies around a value of ∼0.5 eV. We suggest that CO groups have a strong protective and trapping eect during the interaction with ions. Two aspects of the present work should be stressed at this point. The rst is that we are limited to detection of charged fragments and do not detect products of the neutral dissociation, which may lead to dierent numbers of evaporated ligands (see e.g. 49 ). The second aspect is that in the present experiments the precursor molecules are completely isolated, while in the realistic FIBID conditions the interaction primary happens at the vicinity of the substrate. One of the eects of the substrate's presence may be that it represents a heat bath leading to a cooling of the 'hot' molecule, the fragmentation of which is mediated by vibrational excitation. This may become important for the projectiles with higher charge state producing parent cations with lifetimes in the microsecond range via resonant electron capture process. Reduction of the internal energy of the molecular ions on the surface may then reduce also the fragmentation yield.

Acknowledgement The project was supported by the Czech Science Foundation grant no. 16-10995Y; the Czech Ministry of Youth, Sports and Education mobility program Barrande, project number 7AMB17FR047. JK and JF acknowledge the support by European Regional Development Fund; OP RDE; Project "CARAT" No. CZ.02.1.01/0.0/0.0/16_026/0008382. We also acknowledge the support from Ministéres de l'Europe et des Aaires étrangéres (MEAE) et de l'Enseignement supérieur, de la Recherche et de l'Innovation (MESRI) project number 38079PL (FR). Research was conducted in the framework of the International Associated Laboratory (LIA) Fragmentation DYNAmics of complex MOlecular systemsDYNAMO funded by the Centre National de la Recherche Scientique. CN is co-funded by

16


Page 16 of 23

Page 17 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Région Normandie and Synchrotron SOLEIL. The experiments were performed at Grand Accélérateur National d'Ions Lourds (GANIL) by means of the CIRIL Interdisciplinary Platform, part of the CIMAP laboratory, Caen, France, beamtime proposal no 1109A.

References (1) Alkemade, P. F. A.; Miro, H. Focused Helium-Ion-Beam-Induced Deposition. Applied

Physics A 2014, 117, 17271747. (2) Huth, M.; Gölzhäuser, A. Focused Particle Beam-Induced Processing. Beilstein J. Nan-

otechnol. 2015, 6, 1883. (3) Jesse, S.; Borisevich, A. Y.; Fowlkes, J. D.; Lupini, A. R.; Rack, P. D.; Unocic, R. R.; Sumpter, B. G.; Kalinin, S. V.; Belianinov, A.; Ovchinnikova, O. S. Directing Matter: Toward Atomic-Scale 3D Nanofabrication. ACS Nano 2016, 10, 56005618. (4) Stanford, M. G.; Lewis, B. B.; Mahady, K.; Fowlkes, J. D.; Rack, P. D. Review Article: Advanced Nanoscale Patterning and Material Synthesis with Gas Field Helium and Neon Ion Beams. Journal of Vacuum Science & Technology B 2017, 35, 030802. (5) Hlawacek, G.; Gölzhäuser, A. Helium Ion Microscopy ; Springer International Publishing: Switzerland, 2016. (6) Swiderek, P.; Marbach, H.; Hagen, W. C. Chemistry for Electron-Induced Nanofabrication. Beilstein J. Nanotechnol. 2018, 9, 1317. (7) Wilhelm, R. A.; El-Said, A. S.; Krok, F.; Heller, R.; Gruber, E.; Aumayr, F.; Facsko, S. Highly Charged Ion Induced Nanostructures at Surfaces by Strong Electronic Excitations. Progress in Surface Science 2015, 90, 377 395.

17



(8) Kunert, T.; Schmidt, R. Excitation and Fragmentation Mechanisms in Ion-Fullerene Collisions. Phys. Rev. Lett. 2001, 86, 52585261. (9) Delaunay, R.; Gatchell, M.; Rousseau, P.; Domaracka, A.; Maclot, S.; Wang, Y.; Stockett, M. H.; Chen, T.; Adoui, L.; Alcamí, M. et al. Molecular Growth Inside of Polycyclic Aromatic Hydrocarbon Clusters Induced by Ion Collisions. The Journal of Physical

Chemistry Letters 2015, 6, 15361542. (10) Chen, T.; Gatchell, M.; Stockett, M. H.; Alexander, J. D.; Zhang, Y.; Rousseau, P.; Domaracka, A.; Maclot, S.; Delaunay, R.; Adoui, L. et al. Absolute Fragmentation Cross Sections in Atom-Molecule Collisions: Scaling Laws for Non-Statistical Fragmentation of Polycyclic Aromatic Hydrocarbon Molecules. The Journal of Chemical Physics 2014,

140, 224306. (11) Gatchell, M.; Zettergren, H. Knockout Driven Reactions in Complex Molecules and Their Clusters. Journal of Physics B: Atomic, Molecular and Optical Physics 2016,

49, 162001. (12) Alvarado, F.; Bernard, J.; Li, B.; Brdy, R.; Chen, L.; Hoekstra, R.; Martin, S.; Schlathölter, T. Precise Determination of 2-Deoxy-D-Ribose Internal Energies after keV Proton Collisions. ChemPhysChem 2008, 9, 12541258. (13) Knight, W. D.; Clemenger, K.; de Heer, W. A.; Saunders, W. A.; Chou, M. Y.; Cohen, M. L. Electronic Shell Structure and Abundances of Sodium Clusters. Phys. Rev.

Lett. 1984, 52, 21412143. (14) Cederquist, H. Highly Charged Ions Colliding with Atoms, Surfaces and Clusters. Phys-

ica Scripta 1999, 1999, 4651. (15) Burgdörfer, J.; Lemell, C.; Schiessl, K.; Solleder, B.; Reinhold, C.; T®kési, K.; Wirtz, L. Collisions of Slow Highly Charged Ions with Surfaces. Photonic, Electronic and Atomic Collisions. 2006; pp 1645. 18


Page 18 of 23

Page 19 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(16) Lukasczyk, T.; Schirmer, M.; Steinrück, H.-P.; Marbach, H. Generation of Clean Iron Structures by Electron-Beam-Induced Deposition and Selective Catalytic Decomposition of Iron Pentacarbonyl on Rh(110). Langmuir 2009, 25, 1193011939. (17) Wen, J. Z.; Goldsmith, C. F.; Ashcraft, R. W.; Green, W. H. Detailed Kinetic Modeling of Iron Nanoparticle Synthesis from the Decomposition of Fe(CO)5 . The Journal of

Physical Chemistry C 2007, 111, 56775688. (18) Utke, I.; Homann, P.; Melngailis, J. Gas-Assisted Focused Electron Beam and Ion Beam Processing and Fabrication. J. Vac. Sci. Technol. B 2008, 26, 11971276. (19) Aviziotis, I. G.; Duguet, T.; Vahlas, C.; Boudouvis, A. G. Combined Macro/Nanoscale Investigation of the Chemical Vapor Deposition of Fe from Fe(CO)5 . Advanced Materials

Interfaces 2017, 4, 1601185. (20) Lewis, K. E.; Golden, D. M.; Smith, G. P. Organometallic Bond Dissociation Energies: Laser Pyrolysis of Iron Pentacarbonyl, Chromium Hexacarbonyl, Molybdenum Hexacarbonyl, and Tungsten Hexacarbonyl. Journal of the American Chemical Society

1984, 106, 39053912. (21) Sunderlin, L. S.; Wang, D.; Squires, R. R. Metal (Iron and Nickel) Carbonyl Bond − Strengths in Fe(CO)− n and Ni(CO)n . Journal of the American Chemical Society 1992,

114, 27882796. (22) Jang, J. H.; Lee, J. G.; Lee, H.; Xie, Y.; III, H. F. S. Molecular Structures and Vibrational Frequencies of Iron Carbonyls: Fe(CO)5 , Fe2 (CO)9 , and Fe3 (CO)1 2. J. Phys.

Chem. A 1998, 102, 52985304. (23) Persson, B. J.; Taylor, P. R. Calculation of Accurate Binding Energies for the Transition-Metal Carbonyls Ni(CO)4 , Fe(CO)5 and Cr(CO)6 . Theor. Chem. Acc. 2003,

110, 211217. 19



(24) Shchukin, P. V.; Muftakhov, M. V.; Khatymov, R. V. Parametric Model of Decomposition of Metastable Fragmentary Negative Ions From Iron Pentacarbonyl. Issled. Russ.

2005, 16721681. (25) Atkins, A. J.; Bauer, M.; Jacob, C. R. High-Resolution X-ray Absorption Spectroscopy of Iron Carbonyl Complexes. Phys. Chem. Chem. Phys. 2015, 17, 1393713948. (26) Compton, R. N.; Stockdale, J. A. D. Formation of Gas Phase Negative Ions in Fe(CO)5 and Ni(CO)4 . Int. J. Mass. Spectrom. Ion Phys. 1976, 22, 4755. (27) George, P. M.; Beauchamp, J. L. Dissociative Electron Attachment Reactions of Transition Metal Carbonyls and Their Apparent Inuence on the Thermalization of Electrons by CO. J. Chem. Phys. 1982, 76, 29592964. (28) Shuman, N. S.; Miller, T. M.; Friedman, J. F.; Viggiano, A. A. Electron Attachment to Fe(CO)n (n=0-5). J. Phys. Chem. A 2012, 117, 1102. (29) Lacko, M.; Papp, P.; Wnorowski, K.; . Matej£ík, Electron-Induced Ionization and Dissociative Ionization of Iron Pentacarbonyl Molecules. Eur. Phys. J. D. 2015, 69, 84. (30) Ribar, A.; Danko, M.; Országh, J.; da Silva, F. F.; Utke, I.; . Matej£ík, Dissociative Excitation Study of Iron Pentacarbonyl Molecule. Eur. Phys. J. D 2015, 69, 117. (31) Buathong, S.; Kelley, M.; Dunning, F. B. Probing Dissociative Electron Attachment Through Heavy-Rydberg Ion-Pair Production in Rydberg Atom Collisions. J. Chem.

Phys. 2016, 145, 134309. (32) Allan, M.; Lacko, M.; Papp, P.; Matej£ík, .; Zlatar, M.; Fabrikant, I. I.; Ko£i²ek, J.; Fedor, J. Dissociative Electron Attachment and Electronic Excitation in Fe(CO)5 . Phys.

Chem. Chem. Phys. 2018, 20, 1169211701.

20


Page 20 of 23

Page 21 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(33) Lengyel, J.; Fedor, J.; Fárník, M. Ligand Stabilization and Charge Transfer in Dissociative Ionization of Fe(CO)5 Aggregates. J. Phys. Chem. C 2016, 120, 1781017816. (34) Lengyel, J.; Papp, P.; . Matej£ík,; Ko£i²ek, J.; Fárník, M.; Fedor, J. Suppression of Low-Energy Dissociative Electron Attachment in Fe(CO)5 Upon Clustering. Beilstein.

J. Nanotechnol. 2017, 8, 22002207. (35) Hauchard, C.; Rowntree, P. A. Low-Energy Electron-Induced Decarbonylation of Fe(CO)5 Films Adsorbed on Au(111) Surfaces. Can. J. Chem. 2011, 89, 11631173. (36) Massey, S.; Bass, A. D.; Sanche, L. Role of Low-Energy Electrons (

Decomposition of Iron Pentacarbonyl Induced by Singly and Multiply

Recommend Documents