Unraveling the Atomic Structure of Fe Intercalated under Graphene on

Subscriber access provided by University of Sunderland

Article

Unraveling the Atomic Structure of Fe Intercalated under Graphene on Ir(111): a Multi-Technique Approach Rodrigo Cezar de Campos Ferreira, Luis Henrique de Lima, Lucas Barreto, Caio C. Silva, Richard Landers, and Abner de Siervo Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.8b03186 • Publication Date (Web): 24 Sep 2018 Downloaded from http://pubs.acs.org on September 29, 2018

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 10 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

Chemistry of Materials

Unraveling the Atomic Structure of Fe Intercalated under Graphene on Ir(111): a Multi-Technique Approach Rodrigo Cezar de Campos Ferreira,† Luis Henrique de Lima,‡ Lucas Barreto,‡ Caio C. Silva,† Richard Landers,† and Abner de Siervo∗,† †Instituto de F´ısica “Gleb Wataghin”, Universidade Estadual de Campinas, Campinas, 13083-859, SP, Brazil ‡Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André, 09210-580, SP, Brazil Received September 23, 2018; E-mail: [email protected]

Abstract: The interaction of Fe deposited on graphene grown on Ir(111) was studied in detail to better understand the growth, intercalation, and oxidation of Fe ultrathin films on and under graphene. The study has combined a multiple technique approach that allows extracting at once the chemical, topographic and the precise atomic structure of the system submitted to different conditions of growth and atmospheric environment. For instance, scanning tunneling microscopy (STM) measurements allowed us to follow the formation of Fe nanostructures during Fe deposition and intercalation. Synchrotron-based high-resolution X-ray photoelectron spectroscopy (HR-XPS) untangled the different chemical environments for C-Fe bonds. We have also used photoelectron diffraction experiments to unravel sitespecifically the atomic structure of the intercalated Fe under graphene. Oxidation experiments were also performed for samples prepared under different conditions which revealed that indeed one can set the sample temperature to selectively protect or oxidize the intercalated/supported materials which open interesting possibilities to engineer complex metal-oxide graphene-based devices.

1. INTRODUCTION Since the synthesis of graphene (Gr) and the study of its peculiar electronic and structural properties, 1 there has been a huge growth of fundamental and applied research related to this material and, more recently, on two-dimensional materials (2D-materials). 2 The 2D structural configuration induces electronic, chemical, optical and magnetic properties very different from their three-dimensional counterparts. 3 Consequently, special attention and efforts have been given to the synthesis, characterization and functionalization of these new materials with the aim to control specific properties (e.g., gap opening and doping). Graphene undoubtedly emerged as a fundamental candidate and pioneer material 4,5 for future generations of electronics, magnetic and photonic devices. Beyond the electronic and photonic structure of the material, its combination with other 2D materials, oxides, and nanoparticles have opened a playground to engineer promising materials with new and exotic properties for future technologies.

Epitaxial growth of graphene on metallic substrates by the chemical vapor deposition (CVD) method results in large areas of graphene with high structural order and quality. 6–8 The nature and intensity of graphene-substrate interaction vary from substrate to substrate and it is dependent on the degree of hybridization between the electrons of the graphene π band and the electronic states of the substrate as well as is directly related to the difference between the lattice parameters. The superposition typically results in a moiré superstructure with periodic adsorption sites distributed over the entire surface, introducing in these locations sites with different interactions to the substrate, i.e., some with a covalent-bonding character and others van der Waals character. For example, graphene on Ir(111) (Gr/Ir(111)) presents predominantly van der Waals interactions modulated by a weak covalent bond formation on some specific sites 7 that induces a corrugated structure as described previously in literature. 7,9 Furthermore, if performed under specific conditions of temperature and pressure, graphene grows on Ir(111) in a single crystallographic domain having large regions with lowdensity of structural defects and showing a quasi-free standing electronic structure. 10,11 In order to promote electronic doping and gap control of supported graphene, the intercalation of different elements 12–20 is recurrent. In fact, beyond the modifications of the electronic characteristics, structural changes like suppression or complete removal of the graphene sheet corrugation, 21 or even its physical decoupling has already been reported. 17,22,23 The procedure can also protect the intercalated element from the external chemical reaction at moderate temperatures and pressures as demonstrated by previous results, for instance, for intercalated Co clusters between the graphene and buffer-layer on SiC(0001). 20 One might speculate the possibility of engineering complex magnetic nanostructures by selective intercalation controlled by temperature. For instance, one can first intercalate ferromagnetic materials under graphene at a certain temperature, cool the sample down and cover it, without intercalation, with another material, for example, an antiferromagnetic oxide to create magnetic heterojunctions. In fact, there are several examples in the literature where intercalated protected ferromagnetic elements can also affect the magnetic properties like inducing magnetic polarization on graphene 24 or display tunneling magneto-resistance in complex nanostructured patterns, 25 opening interesting possibilities in the study of anisotropic magnetic thin films, magnetic heterostructures, and spintronics for applications on data storage devices. For some applications, such as heterogeneous catalysis, instead of in-

ACS Paragon Plus Environment 1


2. RESULTS AND DISCUSSIONS 2.1. Clean graphene on Ir(111). A representative STM overview of the surface after graphene growth is shown in Fig.1-a, as well as the characteristic moiré low-energy electron diffraction (LEED) pattern (inset). 10 STM was exhaustively performed in different areas and no uncovered regions were detected. Fig.1-b shows a magnified area close to a step edge which reveals that graphene has grown in a single domain and continuously over the step edge as “a carpet”, which in principle, would not allow atomic intercalation at these regions. Fig.1-c shows STM with atomic resolution and a line profile displaying the unit cell dimensions of the moiré superstructure (∼ 25 Å) and lattice corrugation of about 0.3 Å in good agreement with the reported literature. 9,28 It is possible to find a few point defects on close inspection in selected areas. One possible explanation might be carbon vacancies with one or two atoms missing, as shown in Fig.1-d. The binding energies (BE) for the bulk component (BC) and surface state (SS) in Ir 4f (Fig.1-e) are in perfect agreement with those reported in the literature. 29,30 A careful fitting procedure was used and will be detailed here for a comprehensive understanding of the impact of Fe growth presented in the next sections. In our fitting procedure, the intrinsic linewidths are kept the same for both bulk and surface states, being fitted to Γ=0.15 eV and Γ=0.19 eV respectively for the Ir 4f7/2 and Ir 4f5/2 ; while the asymmetry parameter α=0.11 was the same for all components. The bulk components for Ir 4f are well determined at BE=60.78±0.02 eV (Ir 4f7/2 ) and BE=63.77±0.02 eV (Ir 4f5/2 ). Due to the beamline highresolution, the pronounced surface states (SS) are well resolved

a)

b)

c)

d)

40 20 0 0

e)

2

3

4

Distance (nm)

Ir 4f h= 190 eV

66

64 62 60 Binding Energy (eV)

5

f) C 1s h= 400 eV

C1

C2

285

284

283

Binding Energy (eV)

Figure 1. STM, LEED and XPS characterization of Gr/Ir(111). (a) Representative (150 × 150) nm2 STM image (Vt =0.13 V @ It =0.6 nA) and inset showing the characteristic LEED pattern (E0 =78 eV) (b) (50 × 50) nm2 STM image including a step edge showing a single oriented graphene layer as “a carpet”. (c) STM with atomic resolution showing the characteristic moiré pattern with a corrugation of about 30 pm. (d) Selected area (150 × 150) nm2 showing point defects that might be carbon vacancies. (e) HR-XPS for Ir 4f (solid-line is BC and dash-line is SS) and (f) C 1s corelevels for the clean Gr/Ir(111) (details in the text).

at BE=60.24±0.02 eV and BE=63.26±0.02 eV. It is important to mention that these values are virtually the same before and after graphene growth, i.e., the graphene layer does not affect the position or intensity of the surface state due to the low interaction with Ir. Graphene on Ir(111) is almost flat, but different regions showing depression and hills can be clearly distinguished by STM which have a clear impact on its electronic structure that might be disentangled with the photoemission spectra. Due to the constrains on linewidths and instrumental broadening obtained by our fitting procedure from Ir 4f peaks, we have been able to distinguish two C 1s components in the Gr/Ir(111). The components C1 and C2 of C 1s core level (Fig. 1-f) represent the different adsorption sites of graphene interacting with the Ir substrate: C1 at 284.12±0.02 eV represent carbon atoms interacting less with the Ir substrate while C2 at BE=284.27±0.02 eV describes the depressions in which the C atoms are closer to Ir surface. The linewidth Γ=0.10 eV and asymmetry parameter α=0.03 were identical for both C components. The relative small energy splitting between these two components are in good agreement with a small corrugation observed by STM as well as with the reported electronic structure measured


~25 Å 1

Photoemission Intensity (arb. units)

z (pm)

tercalating 2D films, the goal is to use corrugated graphene as a template to grow ordered nanoparticles with special reactivity and selectivity for some reactions as already described in literature. 26,27 Therefore it is clear that a deep understanding of the mechanisms and the driving forces involved in growing materials (metals, oxides, alloy films, nanoparticles, clusters, and molecules) intercalated or supported by graphene is a very important issue. Considering this context, the aim of this work is to study the process of Fe intercalation in Gr/Ir(111) and determine site-specifically the chemical changes and the atomic structure during the initial stage of Fe growth. Two types of samples were prepared in which the evaporation of Fe was done at room temperature (sample RT) and at a moderate temperature of ∼700 K (sample HT). The chemical properties of the graphene, Fe and the first layers of Ir, before and after each stage of sample preparation, were monitored by high-resolution X-ray photoelectron spectroscopy (HR-XPS) at the Brazilian Synchrotron Light Laboratory (LNLS). In parallel, scanning tunneling microscopy (STM) measurements allowed us to follow the formation of Fe nanostructures during the evaporation cycles and intercalation. STM can provide a good topographic understanding of the sample, but very few information can be obtained regarding distances between the Ir, Fe and graphene layers. An interesting and effective technique for this investigation is the X-ray photoelectron diffraction (XPD) which is an element and chemical selective technique able to provide accurate information about the local atomic structure surrounding an emitter atom. The combined information from STM, XPS, and XPD, have allowed us to precisely and unambiguously determine the atomic structure of intercalated metals (Fe) under corrugated graphene. Oxidation experiments were also performed for samples prepared under different conditions which revealed that indeed one can set sample temperature and oxygen pressure to selectively protect or oxidize the intercalated/supported materials that opens interesting possibilities to engineering complex graphene-based devices.


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 10

Page 3 of 10 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


by angle-resolved photoelectron spectroscopy (ARPES). 31 Following the Gr/Ir(111) sample preparation, the next step was to investigate two conditions of Fe deposition: 1- deposition performed with the substrate at room temperature (sample RT) and 2deposition performed with the substrate at ∼700K (sample HT). 2.2. Fe deposited on Gr/Ir(111) at RT. Figure 2 displays STM images of representative areas where we find 2D triangular structures growing mainly from the substrate step edges. These islands show a Moiré pattern with the same periodicity of ∼ 25 Å as in the Gr/Ir(111), however, they present a larger corrugation (∼ 1 Å) as previously described in literature. 25 Some isolated nanoparticles can be also found as indicated in Fig. 2-a by a dashed circle, suggesting an additional formation of iron 3D islands. Here, it is worth discussing more deeply the intercalation. The mechanism of intercalation involves complex diffusion processes along and across the layer, interactions with graphene itself and with the substrate that are not well understood. Several mechanisms of intercalation are considered in the literature: (1) One of the most accepted mechanisms is the diffusion through edges of graphene flakes. 14,19,23,32 (2) Another possibility is the penetration through domain boundaries, as for example in the case of Gr/SiC(0001), or nanoscale fissures formed by large compressive forces (wrinkles). 33–36 In such places, the distance between graphene and substrate could facilitate the migration of the material like in a “subway tube”. (3) Intercalation is also commonly attributed to pointlike defects, which is a good explanation in very large graphene sheets epitaxially grown on metals, as for example in Gr/Ir(111), Gr/Ru(111), and Gr/Ni(111). 37–40 (4) Another explanation would involve an exchange mechanism in which the C-C bonds are broken, resulting in a transition phase between carbon and suspending atoms, followed by the intercalation and self-healing of the graphene sheet. 19,41,42 This mechanism (4) involves very high energy barriers that, in theory, cannot be overcome with the common preparation temperatures used in the experiments, i.e, typical temperatures used are not enough to break C-C bond (∼5.7 eV) 43 or to enable the metal-carbon exchange process, that requires ∼3 eV. 41 It is worth mentioning that, in most of the cases, the metal deposition is done with conventional e-beam evaporators and there are few studies in the literature addressing the effect of energetic ions compared to neutral atoms to promote the intercalation. 44 In this situation, the ions are energetic enough to promote mechanisms (3) and (4). In all suggested mechanisms and through examples from literature, 15 the temperature and the deposition rate are critical parameters, hence the experimental conditions play an important role favoring one or another mechanism of intercalation. For example, the intercalation of oxygen on Gr/Ir(111) can happen only above a certain temperature and at high O2 pressure (∼mbar range) as demonstrated by Larciprete and co-workers. 22 In a previous study of Gr/Fe/Ir(111), the intercalation is performed completely when Fe is deposited while the sample is held at ∼500 K. 45 Bazarnik and co-workers 45 have attributed intercalated islands in the middle of terraces to mechanism (3), which was also observed in the present work. The Ir 4f core level clearly shows a suppression of the surface states as a function of coverage (Fig. 3-a), which is expected as the iron covers the surface and the most reasonable assumption is the intercalation and strong interaction with the first Ir atomic layer. Notwithstanding, there was no appreciable binding energy shift in the Ir 4f core levels, leading us to conclude that no Ir-Fe alloying formation occurred at RT temperature. To fit the intensities presented in Fig. 3-a, the same model applied to Fig. 1-e was used. The surface states (SS) have all fitting parameters, i.e, position, linewidths, and asymmetry unchanged, which characterizes regions not covered by Fe. On another hand, the ”bulklike” com-

ponent (BC) is now representing regions with 2D intercalated Fe islands and 3D supported Fe nanoparticles, as well as the clean regions. To take into account such different contributions linewidth for the BC components have to increase to Γ=0.19 eV and Γ=0.21 eV, respectively, for the Ir 4f7/2 and Ir 4f5/2 . Assuming such a model we have been able to characterize the surface coverage as a function of deposition time using the normalized fraction of SS contribution to the Ir 4f spectrum (Fig. 3-c).

a)

b)

Figure 2. STM results for Fe deposited on Gr/Ir(111) at RT. (a) Representative STM image of (200 × 200) nm2 (Vt =1.1 V @ It =60 pA) for the first stage of growth, i.e., after 5 minutes of Fe deposition (∼0.1 ML) showing 2D intercalated islands (triangles) and 3D nanoparticles (dash circle). (b) Magnified STM image of (100 × 100) nm2 (Vt =1.1V @ It =80 pA) showing the intercalated Fe islands at the step edges and at the middle of the terraces. The inset display the line profiles for the intercalated islands showing the pattern with the same ∼2.5 nm periodicity, but with a stronger corrugation compared to the clean Gr/Ir(111).

The C 1s core level has significant spectrum changes upon Fe deposition. The components C1 and C2 reduce their intensities as a function of Fe coverage (evaporation time), as shown in Fig. 3-d. Similar behavior was reported for the Gr/Co/Ir(111) system by Presel and co-workers. 16 In the present work, we have been able to find three new components due to the intercalated Fe, here named, C3 (284.48±0.02 eV), C4 (284.90±0.02 eV) and C5 (285.00±0.02 eV) arising with higher binding energies than C1 and C2, indicating a stronger chemical interaction between Fe and graphene. The characteristic peak fitting parameters are Γ=0.15 eV, α=0.02 for C3 and Γ=0.24, α=0.07 for C4 and C5. The interpretation for these components comes from regions with stronger (C4,C5) and weaker (C3) interactions between graphene and Fe, and we expect smaller distances between C and Fe when compared to the case of C and Ir as the following: C3 component is related to the center of the graphene carbon ring sitting on top of the intercalated Fe atom. This peak is



C 1s

h= 400 eV data fit C1 C2 C3 C4 C5

a) C5

C4 C1 C3

C2

66

64

62

Binding Energy (eV)

c) 60

286

60

C1 + C2 C3 C4 or C5 C4 + C5 C3 + C4 + C5

50 80 Relative intensity (%)

30 20 10 0

284

5 10 15 20 25 Deposition time (min)

40 20

0

5 10 15 20 25 Deposition time (min)

Figure 3. High-resolution XPS after 26 minutes of Fe deposition (∼0.5 ML) at RT for Ir 4f (a) and C 1s (b) core-levels (details in the text). (c) Percent of the surface covered by Fe as a function of time deposition obtained from the Ir 4f SS. (d) Evolution of the C 1s components upon Fe deposition.

shifted only + 0.36 eV to a higher BE compared to the C1 component. This corroborates a corrugated region of graphene on top of Fe that shows the lowest C-Fe interaction compared to the regions related to C4 and C5 components. This region will be named “top-site”. As observed by the STM images there is an almost continuous distribution of C-Fe distances for the C atoms neighboring the “top-site” which cannot be solved in XPS that is translated by a slightly higher linewidth compared to the C1 and C2 components. Complementary, C4 and C5 regions are describing carbon atoms over the Fe islands that present strong C-Fe interaction (shift of about +1.0 eV from C1), i.e., the lowest C-Fe distances. Considering only one component to interpret C4 + C5 region results in a worse fitting agreement upon Fe deposition. Thus, as indicated by STM, C4 and C5 have relatively similar, but not identical, C-Fe distances that are much smaller than in C3. From now, we named C4 the “fcc-site” and C5 the “hcp-site”. Such stronger interactions are also reflected in the linewidth of C4 and C5. These conclusions based on the chemical shifts are confirmed by precise atomic structure determination using XPD measurements presented later. In order to further verify whether or not intercalation occurred, we carried out an oxidation attempt, subjecting the chamber to 5×10−5 mbar of oxygen gas pressure for 5 minutes in a static pumping regime and with the sample at RT in the XPS/STM system (see experimental methods section). The XPS for Fe 2p core level display an iron oxide component around 711.0 eV, but still showing a metallic Fe component at ∼707.0 eV as can be seen in Fig. 4-a. A similar procedure was performed in the XPD system (see experimental methods section) (Fig. 4-b), but using much higher O2 pressure (10−3 mbar). A very similar behavior was obtained for both experiments. The experimental results indicate that 3D islands on

h= 1486.6 eV Fe0 (706.8 eV)

FexOy

715

b)

710

Fe 2p

as grown oxidized

h= 800 eV

Fe0 (707.0 eV)

FexOy (711 eV)

705

Binding Energy (eV)

715

710

705

Binding Energy (eV)

2.3. Fe deposted on Gr/Ir(111) at 700K. To further test if is possible to intercalate Fe completely at moderate temperatures and what is the impact on its electronic and atomic structure as well as the ability of graphene to protect the intercalated material, the sample was held at approximately 700 K during Fe deposition. This temperature demonstrates to be high enough to promote the complete intercalation without inducing Fe-Ir alloying and avoiding the nucleation of 3D Fe nanoparticles as shown in Fig. 5-a and 5-b. The interesting behavior of the intercalated Fe growth in a 2D fashion might be an indication that graphene is acting as a surfactant layer to promote a layer-by-layer growth of Fe as proposed in previous results in the literature. 46–48 The equivalent experiment was repeated at the synchrotron to perfom HR-XPS and XPD. Fig. 5-d shows the Ir 4f core level XPS with a large suppression of surface states, indicating almost 1 ML of Fe intercalated under graphene. The linewidths and positions remained almost unchanged with respect to the sample RT. Thus the careful peak fitting analysis, strongly indicates no important Fe-Ir alloying formation for the present preparation procedure. 49 Such finding was corroborated by the STM result with no changes in the corrugation height and periodicity, as well as by XPD results (discussed in the next section). In Fig. 5-e, C1s spectrum does not show C1 and C2, which corroborates the assertion that iron is homogeneously covering almost the complete surface. Remarkably, C3, C4 and C5 remain with the same width and energy positions as compared to Sample RT, which is another point that corroborates the absence of Fe-Ir alloy or carbide. Subsequently the XPD experiments were carried out to precisely address the atomic structure of the intercalated Gr/Fe/Ir(111) system. It is worth mentioning that in a previous experiment 45 involving Fe multilayer intercalation on Gr/Ir(111), authors reported very similar images to the present work, but also some other structures were the typical high corrugated moiré pattern is lost. That might be related to prolonged annealing which were not addressed in the present work. The attempts of oxidation were again performed in both experimental stations, STM system as well as in the synchrotron, XPD system. For the same sample presented in Fig. 5-a and 5-b, the oxidation was tried using 10−5 mbar of O2 for 10 minutes. STM from Fig. 5-c reveals no topographic changes after oxygen exposure, however a higher density of defects seems to be more visible compared to the previous case, which might be attributed to an oxygen etching. 40,50 Additionally XPS from Fig. 5-f demonstrates no Fe oxidation at all (normal (θ = 0◦ ) or grazing (θ = 75◦ ) emission).


Fe 2p

Figure 4. XPS for the Fe 2p3/2 after 26 minutes of Fe deposition (∼0.5 ML) on Gr/Ir(111) at RT as grown and after oxidation performed in the STM/XPS system (a) and in the XPD system (b) (details in text).

60

0 0

as grown oxidized

(711 eV)

100

40

285

Binding Energy (eV)

d)

top of graphene can be completely oxidized under these conditions; however, the intercalated Fe islands are protected by graphene.



Ir 4f


b) h= 190 eV


a)

Surface covered by 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

Page 4 of 10

a)

c)

b)

h= 190 eV

e)

66

64

62

60

Binding Energy (eV)

58

C 1s

h= 400 eV


Ir 4f

287

data fit C3 C4 C5 BG

f)

C5 C4 C3

Fe 2p

h= 1486.6 eV


d) Photoemission 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


g) Photoemission Intensity (arb. units)

Page 5 of 10

as grown (=0) after O2 (=0) as grown (=75) after O2 (=75)

FexOy (711 eV)

Fe0

as grown after O2 @ RT

286

285

284

715

710

705

Binding Energy (eV)

Fe0

h= 800 eV

(707.0 eV)

FexOy

(706.8 eV)

Binding Energy (eV)

Fe 2p

after O2 @ 500K

(711 eV)

715

710

705

Binding Energy (eV)

Figure 5. STM images and XPS spectra for Fe deposited on Gr/Ir(111) at 700K. (a) Representative STM image of (500 × 500) nm2 (Vt =0.130 V @ It =0.48 nA) showing almost only 2D intercalated Fe islands under graphene. (b) Magnified STM image of (90 × 90) nm2 (Vt =0.130 V @ It =0.95 nA) detailing the intercalated Fe islands at the step edges as well as clean graphene regions. (c) STM image of (50 × 50) nm2 (Vt =0.420 V @ It =0.18 nA) after oxygen exposure(detail in text) showing the protected Fe islands and point defects on graphene, may be due to oxygen etching. HR-XPS for Ir 4f (d), C 1s (e), and Fe 2p (f,g) (details in text).

The oxidation attempts at synchrotron used even higher pressures that are resumed in Fig. 5-g. Initially, the sample was exposed to an oxygen pressure of 1.3×10−3 mbar for 5 minutes at RT and the XPS exhibits no feture suggesting oxide formation (Fig. 5-g). In a final attempt to oxidize the intercalated Fe, following the results of Larciprete et al, 22 a partial oxidation was obtained with the sample at ∼500 K and 1.0×10−3 mbar of oxygen pressure for 5 minutes, as can be seen on Fe 2p XPS (Fig. 5-g). These results demonstrate that the intercalated metal is protected at RT and probably up to intermediate temperatures. The ability for selective intercalation of metal without oxidation is a key step to engineer complex magnetic metal-oxide heterostructures. 2.4. Photoelectron diffraction results. From the combined experiments of STM, XPS and oxidation, the surface topography as well as the chemical environment of Ir, Fe and C are well characterized. However, the exact atomic distances between Ir, Fe and graphene layers cannot be completly explored by these techniques. For instance Mart´ın-Recio et al. 51 conducted a STM and DFT study demonstrating the difficulty to describe graphene-corrugated systems. From one hand, DFT calculations can be very dependent on functionals. On another hand, the correct interpretation of STM images are very difficult due to the interplay between electronic and geometric contributions in the STM contrast. Therefore, since XPD is based on photoemission, it has the unique capability to be a chemical-specific structural technique able to explore the first few atomic layers at the surface. Furthermore, due to the low inelastic mean-free path (λim f p ) for the photoelectrons with low kinetic energies, it is very sensitive to short-range ordering, thus it is able to explore different adsorption sites even when the resolution is not

high enough to separate very close chemical states, as exemplified in previous works. 52–54 The Fe-3p core-level was used to probe the atomic structure around the Fe atoms, and hν = 200 eV as the photon energy. Therefore, the kinetic energy (KE) of the emitted photoelectrons is only 147 eV and, consequently, a λim f p in the order of 3 monolayers. It implies that the information contained in the Fe-3p XPD pattern results basically from the forward scattering processes in the C atoms and the backscattering process in the top layer of the Ir substrate, allowing the determination of the distances between the graphene and Fe layers (dGr-Fe) and the Fe layer and Ir substrate (dFe-Ir). The angle-scanned XPD pattern was recorded over a polar angle ranging from 12 ≤ θ ≤ 72◦ , and over a full 360◦ azimuthal range (φ), in steps of 3◦ for both angles. The polar angle θ = 0 corresponds to normal emission. The Fe-3p XPD experimental pattern is shown in the Fig. 6-a. The percentage value displayed in the diffraction patterns represents the diffraction anisotropy, as defined elsewhere. 55,56 The atomic structure around the emitter atoms is obtained from the simulation of a XPD pattern for a proposed structural model and the comparison with the experimental result. A paraboloid cluster of ∼ 400 atoms was used in the simulations, with a surface radius of 11 Å. The simulations demonstrated that the best model consists of only a Fe monolayer intercalated between the graphene and the Ir substrate. Moreover, the Fe layer follows the fcc stacking of the substrate with the √ same in-plane lattice parameter of 2.714 Å for the Ir structure ( 2/2 × 3.839 Å), a result that agrees with the STM measurements, since the superstructure periodicity remains the same after the Fe intercalation process (∼ 25 Å). We conclude


Chemistry of Materials 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

a)

b)

a)

Page 6 of 10

CA CB

EXP

SIM

b) c)

d) HCP

FCC

[111]

e)

f)

c)

FCC

HCP TOP

FCC

TOP TOP

Figure 6. X-ray Photoelectron Diffraction (XPD) patterns for Fe-3p corelevel (KE = 147 eV): experimental a) and best model b) obtained by the sum of three distinct simulations. The patterns for the three models are presented in c), d) and e). f) shows the dependence of C-1s binding energies with the distance between graphene and the Fe layer.

that the superstructure is formed by (10 × 10) unit cells of Gr on top of (9×9) unit cells of Fe (or Ir). In this way, the Fe-3p photoelectron diffraction pattern contains information from all the non-equivalent positions between C and Fe atoms within the superstructure unit cell. It is impracticable, from the computational point of view, to use such a large unit cell to simulate the diffraction pattern. However, the XPD simulations show that the experimental diffraction pattern can be obtained, with excellent agreement, from the incoherent sum of three simulated patterns, 57,58 where each pattern is obtained from a single Fe emitter atom located in the center of the paraboloid cluster and occupying one of the three positions of higher symmetry between the C atoms in the graphene and the Fe layer: “top-site”, “hcp-site” and “fcc-site” (see structure model in Fig. 7). 59 In order to have the best theory-experiment agreement, the main parameters optimized were the perpendicular distance between the graphene and the Fe intercalated layer (dGr-Fe), the distance between the Fe layer and the Ir substrate (dFe-Ir) and the perpendicular distance between the two sublattices (CA and CB ) that form the honeycomb structure of graphene (see Fig. 7), which we will call “buckling”. 52–54 The distances were varied using a grid approach for all the three models (fcc, hcp and top) and all the possible combinations between them were made to obtain the model with the

HCP

Figure 7. Structure model for the Gr/Fe/Ir(111). a) Graphene with two carbons atoms (CA and CB ) in the unit cell. b) Side-view detailing the elements and interlayer distances. c) Top-view of the a moiré unit cell indicating the “hcp”, “top” and “fcc” sites.

lowest Ra . The error bars were determined using the procedure reported in the literature. 60 The results are presented in table 1. Table 1. Interlayer distances (in Å) obtained from the multiple scattering simulations for the three main carbon sites within the superstructure unit cell.

dist\site buckling dGr-Fe dFe-Ir

hcp 0.16±0.05 1.70±0.03 1.79±0.05

top 0.20±0.09 3.20±0.07 1.80±0.04

The Fig. 6-b shows the simulated pattern for the best model. The excellent agreement between the experiment and the simulation can be observed visually from the patterns and by the low value in the reliability factor Ra = 0.162. The Fig. 6-c, 6-d and 6-e show the patterns obtained for each one of the three models which sum up the result in the pattern of Fig. 6-b. It is important to note that these are not the best individual models for each site that result in the best agreement with the experimental result, but the individual models that, when added, result in the best overall model. No individually tested model resulted in a better Ra factor than that obtained by the incoherent sum. It is possible to observe that certain diffraction structures present in the experimental pattern come from each one of the three models. We also tested combinations of only two of


fcc 0.16±0.15 2.12±0.13 2.06±0.07

Page 7 of 10 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 three models and it was observed that the inclusion of the three models is essential for a good agreement with the experimental result. Fig. 6-f shows the dependence of the C-1s binding energy of the components C3 (top), C4 (fcc) and C5 (hcp) with the distances obtained by the XPD simulations. This experimental finding obtained here from the correlation of the independent XPS and XPD results can be also corroborated by others similar results obtained, for instance by DFT calculations, for several intercalated metals (Rh, Ru, Co) between Gr and Ir(111). 16 The results show that the total corrugation within the unit cell of the superstructure is of the order of 1.5 Å, much larger than the values of 0.3 Å observed for Gr/Ir(111). This is a consequence of the stronger interaction between the C atoms and the Fe atoms compared to the Ir case, in agreement with the XPS results. In addition, the interaction of the Fe single layer with the graphene and the Ir substrate results in a small corrugation also in the Fe layer of the order of 0.3 Å. 3. CONCLUSIONS This work has addressed the structure and chemistry of a single atomic layer of Fe intercalated between graphene and Ir(111) as well as explored the Fe growth regime at different sample temperatures and its stability when subjected to oxygen pressures. The results have shown that it is possible to grow a thin film of Fe under Gr/Ir(111) when it is carried out at moderate temperatures of approximately 700 K avoiding the formation of 3D Fe islands observed when the Fe growth is performed at RT. The intercalated 2D islands epitaxially grow mostly from the substrate step edges and are fully protected by the graphene layer without evidence of Fe-Ir alloy formation. The experiments performed at different temperatures (RT and HT) demonstrate the ability to control by sample temperature the metal intercalation as well as the metal oxidation. Such selectivity for intercalation of metal and gases is a key step to engineer complex magnetic metal-oxide heterostructures using graphene plataform. The XPD approach have unambiguously determined site-specifically the atomic structure of the intercalated Fe corroborating the STM and XPS experimental data. XPD shows that Fe is strongly bonded to carbon atoms in the hcp and fcc moiré sites, while the top region interacts more weakly. The variation of these intensities is reflected in a large corrugation with amplitudes of 1.5 Å compared to 0.3 Å in the bare Gr/Ir(111) while the moiré unit cell (25 Å) remains identical to that of Gr/Ir(111). This highly corrugated and well-ordered network may eventually serve as templates for depositing nanoparticles or molecules in order to study different possible arrangements on the surface. 4. EXPERIMENTAL METHODS The experiments were performed in two different ultra-high vacuum (UHV) systems. The first is an STM/XPS system located at UNICAMP and the second one is a XPD system connected to the PGM beamline 61 at the Brazilian Synchrotron Light Laboratory (LNLS). The STM/XPS system has two connected chambers. One chamber is equipped with an STM and the other one with an XPS, low energy electron diffraction (LEED), e-beam evaporators, and standard cleaning and sample preparation facilities. The homemade manipulator allows sample heating (RT-1400◦ C) by direct e-bombardment in the back side of the crystal. Temperature was controlled by a pyrometer using 10% for the emissivity. The base pressures were in the low 10−10 mbar range and in the middle 10−11 mbar range in the XPS and STM chambers, respectively. The STM microscope used was a SPECS Aarhus 150 equipped with a SPECS SPC 260 Controller. The STM measurements were performed in a constant current mode with a tungsten tip cleaned in situ

by Ar+ sputtering. STM bias voltages were applied to the sample and the images were analyzed using the WSxM software. 62 XPS was performed with a SPECS Phoibos 150 hemispherical analyzer with multi-channeltron detection. The photons employed in XPS were obtained from an non-monochromatic Al-Kα source. The Ir(111) single crystal was prepared by several cycles of Ar+ sputtering (1200V @ ∼5 µA.cm−2 ) for 30 minutes with subsequent annealing at 1300 ◦ C for 10 min following a slow cooling ramp to ensure large and well-ordered terraces. The manipulator was exhaustively degassed to ensure that residual pressure during the whole annealing stays below 1.0 × 10−9 mbar to avoid the formation of amorphous carbon at the surface. The graphene growth was performed by the CVD method by keeping the crystal temperature at 1300 ◦ C with a propylene (99.9%) gas pressure of 6 × 10−7 mbar for 6 minutes, assuring the epitaxial growth of a single graphene layer in the R0◦ domain 10,63 over the whole surface. After that, the propylene was pumped out and the sample was slowly cooled to RT. Fe was evaporated from a 1 mm Fe rod (99.999%) which was previously well-degassed in an e-beam evaporator. The Fe deposition rate was ∼0.02 ML/min calibrated by the analysis of STM images and XPS. The high-resolution XPS (HR-XPS), as well as XPD experiments, were performed in the XPD system which was connected to the PGM beamline at LNLS. The system is equipped with an Omicron EA125 high-resolution electron analyzer with multichanneltron detection, LEED optics, e-beam evaporator, conventional Al/Mg X-ray source and a five axis manipulator that allows performing angle-scanned XPD measurements as described elsewhere. 52 The base pressure in the UHV chamber was in the low 10−10 mbar range. The graphene growth and Fe deposition followed the same procedure described above which were also calibrated using conventional XPS. The HR-XPS with synchrotron light were performed always in normal emission, pass energy of 5 eV and the photon energy for Ir 4f was hν=190 eV, whereas for C 1s it was hν=400 eV. All photoemission peaks were fitted with the DoniachSunjic 64 line shape characterized by a Lorentzian width Γ, which takes into account the finite core-hole lifetime, and by the asymmetry parameter α that describes low-energy electron-hole pair excitations near the Fermi level. All peaks were convoluted to a Gaussian distribution (fixed width) that describes the instrumental broadening, phonon contributions, and sample inhomogeneities. The inelastic background contribution was removed using the Shirley type background. 65 The XPD pattern of the emitted photoelectrons of the sample for various angles (azimutal and polar) relatively to the analyzer gives information about both the emitting atoms and the relative position of the surrounding scattering atoms. With this information in hand, the experimental pattern collected can be compared with a comprehensive computional model in which the relative atoms positions of the sample surface are specified. In this work, we used the MSCD (Multiple Scattering Calculation of Diffraction) package 66 to simulate the experimental patterns. The structure is determined in a search process for the best set of parameters that describes the agreement between theory and experiment through minimization of the reliability factor (Ra ), as described elsewhere. 55 5. AUTHOR INFORMATION Corresponding Author *E-mail (Prof. Abner de Siervo): [email protected]. Author Contributions R.C.C.F., L.H.L, L.B., C.S.S, and A. S. performed the measurements. R.C.C.F., L.H.L and A.S. analyzed the data. R.C.C.F, L.H.L and A.S. co-wrote the paper. A.S. conceived the study. All authors have read, and given approval to the final version of the manuscript.



Notes The authors declare no competing financial interest.

(22)

6. ACKNOWLEDGMENT Authors thanks LNLS for beamtime at PGM beamline as well as PGM staff for technical support during the experiments. This work was financially supported by Fundaça˜ o de Amparo a Pesquisa do Estado de São Paulo (FAPESP) under project number 2007/548295, 2007/08244-5 and 2016/21402-8 and by CNPq under project number 455807/2014-0. RCCF acknowledge CAPES for studentship and LHL and LB acknowledge CNPq for the studentship funding.

(23) (24)

(25)

(26) (27)

REFERENCES (1) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric Field Effect in Atomically Thin Carbon Films. Science 2004, 306, 666–669. (2) Butler, S. Z.; Hollen, S. M.; Cao, L.; Cui, Y.; Gupta, J. A.; Gutiérrez, H. R.; Heinz, T. F.; Hong, S. S.; Huang, J.; Ismach, A. F.; Johnston-Halperin, E.; Kuno, M.; Plashnitsa, V. V.; Robinson, R. D.; Ruoff, R. S.; Salahuddin, S.; Shan, J.; Shi, L.; Spencer, M. G.; Terrones, M.; Windl, W.; Goldberger, J. E. Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene. ACS Nano 2013, 7, 2898–2926. (3) Wallace, P. R. The Band Theory of Graphite. Phys. Rev. 1947, 71, 622–634. (4) Castro Neto, A. H.; Guinea, F.; Peres, N. M. R.; Novoselov, K. S.; Geim, A. K. The electronic properties of graphene. Rev. Mod. Phys. 2009, 81, 109–162. (5) Han, W.; Kawakami, R. K.; Gmitra, M.; Fabian, J. Graphene spintronics. Nat. Nanotechnol. 2014, 9, 794–807. (6) Bae, S.; Kim, H.; Lee, Y.; Xu, X.; Park, J. S.; Zheng, Y.; Balakrishnan, J.; Lei, T.; Kim, R. H.; Song, Y. I.; Kim, Y. J.; Kim, K. S.; Ozyilmaz, B.; Ahn, J. H.; Hong, B. H.; Iijima, S. Roll-to-roll production of 30-inch graphene films for transparent electrodes. Nat. Nanotechnol. 2010, 5, 574– 578. (7) Busse, C.; Lazić, P.; Djemour, R.; Coraux, J.; Gerber, T.; Atodiresei, N.; Caciuc, V.; Brako, R.; N’Diaye, A. T.; Blügel, S.; Zegenhagen, J.; Michely, T. Graphene on Ir(111): Physisorption with Chemical Modulation. Phys. Rev. Lett. 2011, 107, 036101. (8) Coraux, J.; N’Diaye, A. T.; Engler, M.; Busse, C.; Wall, D.; Buckanie, N.; zu Heringdorf, F.-J. M.; van Gastel, R.; Poelsema, B.; Michely, T. Growth of graphene on Ir(111). New J. Phys. 2009, 11, 023006. (9) Hämäläinen, S. K.; Boneschanscher, M. P.; Jacobse, P. H.; Swart, I.; Pussi, K.; Moritz, W.; Lahtinen, J.; Liljeroth, P.; Sainio, J. Structure and local variations of the graphene moiré on Ir(111). Phys. Rev. B 2013, 88, 201406. (10) Hattab, H.; N’Diaye, A. T.; Wall, D.; Jnawali, G.; Coraux, J.; Busse, C.; van Gastel, R.; Poelsema, B.; Michely, T.; zu Heringdorf, F.-J. M.; von Hoegen, M. H. Growth temperature dependent graphene alignment on Ir(111). Appl. Phys. Lett. 2011, 98, 141903. (11) Starodub, E.; Bostwick, A.; Moreschini, L.; Nie, S.; Gabaly, F. E.; McCarty, K. F.; Rotenberg, E. In-plane orientation effects on the electronic structure, stability, and Raman scattering of monolayer graphene on Ir(111). Phys. Rev. B 2011, 83, 125428. (12) Tontegode, A. Carbon on transition metal surfaces. Prog. Surf. Sci. 1991, 38, 201 – 429. (13) Dedkov, Y. S.; Shikin, A. M.; Adamchuk, V. K.; Molodtsov, S. L.; Laubschat, C.; Bauer, A.; Kaindl, G. Intercalation of copper underneath a monolayer of graphite on Ni(111). Phys. Rev. B 2001, 64, 035405. (14) Grånäs, E.; Knudsen, J.; Schröder, U. A.; Gerber, T.; Busse, C.; Arman, M. A.; Schulte, K.; Andersen, J. N.; Michely, T. Oxygen Intercalation under Graphene on Ir(111): Energetics, Kinetics, and the Role of Graphene Edges. ACS Nano 2012, 6, 9951–9963, PMID: 23039853. (15) Liu, X.; Han, Y.; Evans, J. W.; Engstfeld, A. K.; Behm, R. J.; Tringides, M. C.; Hupalo, M.; Lin, H.-Q.; Huang, L.; Ho, K.-M.; Appy, D.; Thiel, P. A.; Wang, C.-Z. Growth morphology and properties of metals on graphene. Prog. Surf. Sci. 2015, 90, 397 – 443. (16) Presel, F.; Jabeen, N.; Pozzo, M.; Curcio, D.; Omiciuolo, L.; Lacovig, P.; Lizzit, S.; Alfè, D.; Baraldi, A. Unravelling the roles of surface chemical composition and geometry for the graphene-metal interaction through C1s core-level spectroscopy. Carbon 2015, 93, 187–198. (17) Lizzit, S.; Larciprete, R.; Lacovig, P.; Dalmiglio, M.; Orlando, F.; Baraldi, A.; Gammelgaard, L.; Barreto, L.; Bianchi, M.; Perkins, E.; Hofmann, P. Transfer-Free Electrical Insulation of Epitaxial Graphene from its Metal Substrate. Nano Lett. 2012, 12, 4503–4507. (18) Ulstrup, S.; Andersen, M.; Bianchi, M.; Barreto, L.; Hammer, B.; Hornekaer, L.; Hofmann, P. Sequential oxygen and alkali intercalation of epitaxial graphene on Ir(111): enhanced many-body effects and formation of pn-interfaces. 2D Mater. 2014, 1, 025002. (19) Sutter, P.; Sadowski, J. T.; Sutter, E. A. Chemistry under Cover: Tuning Metal-Graphene Interaction by Reactive Intercalation. J. Am. Chem. Soc. 2010, 132, 8175–8179, PMID: 20527937. (20) de Lima, L. H.; Landers, R.; de Siervo, A. Patterning Quasi-Periodic Co 2D-Clusters underneath Graphene on SiC(0001). Chem. Mater. 2014, 26, 4172–4177. (21) Huang, L.; Pan, Y.; Pan, L.; Gao, M.; Xu, W.; Que, Y.; Zhou, H.; Wang, Y.; Du, S.; Gao, H.-J. Intercalation of metal islands and films at the interface of

(28) (29) (30)

(31)

(32)

(33)

(34)

(35)

(36) (37) (38)

(39)

(40)

(41) (42)

(43)

(44)

(45) (46) (47)

epitaxially grown graphene and Ru(0001) surfaces. Appl. Phys. Lett. 2011, 99, 163107. Larciprete, R.; Ulstrup, S.; Lacovig, P.; Dalmiglio, M.; Bianchi, M.; Mazzola, F.; Hornekaer, L.; Orlando, F.; Baraldi, A.; Hofmann, P.; Lizzit, S. Oxygen Switching of the Epitaxial Graphene-Metal Interaction. ACS Nano 2012, 6, 9551–9558, PMID: 23051045. Sutter, P.; Albrecht, P.; Tong, X.; Sutter, E. Mechanical Decoupling of Graphene from Ru(0001) by Interfacial Reaction with Oxygen. J. Phys. Chem. C 2013, 117, 6320–6324. Weser, M.; Rehder, Y.; Horn, K.; Sicot, M.; Fonin, M.; Preobrajenski, A. B.; Voloshina, E. N.; Goering, E.; Dedkov, Y. S. Induced magnetism of carbon atoms at the graphene/Ni(111) interface. Appl. Phys. Lett. 2010, 96, 012504. Decker, R.; Bazarnik, M.; Atodiresei, N.; Caciuc, V.; Blügel, S.; Wiesendanger, R. Local tunnel magnetoresistance of an iron intercalated graphene-based heterostructure. J. Phys.: Condens. Matter 2014, 26, 394004. Fan, X.; Zhang, G.; Zhang, F. Multiple roles of graphene in heterogeneous catalysis. Chem. Soc. Rev. 2015, 44, 3023–3035. Gotterbarm, K.; Bronnbauer, C.; Bauer, U.; Papp, C.; Steinrück, H.-P. Graphene-Supported Pd Nanoclusters Probed by Carbon Monoxide Adsorption. J. Phys. Chem. C 2014, 118, 25097–25103. Batzill, M. The surface science of graphene: Metal interfaces, CVD synthesis, nanoribbons, chemical modifications, and defects. Surf. Sci. Rep. 2012, 67, 83 – 115. Hüfner, S.; Wertheim, G. K. Core-line asymmetries in the x-rayphotoemission spectra of metals. Phys. Rev. B 1975, 11, 678–683. Lacovig, P.; Pozzo, M.; Alfè, D.; Vilmercati, P.; Baraldi, A.; Lizzit, S. Growth of Dome-Shaped Carbon Nanoislands on Ir(111): The Intermediate between Carbidic Clusters and Quasi-Free-Standing Graphene. Phys. Rev. Lett. 2009, 103, 166101. Kralj, M.; Pletikosić, I.; Petrović, M.; Pervan, P.; Milun, M.; N’Diaye, A. T.; Busse, C.; Michely, T.; Fujii, J.; Vobornik, I. Graphene on Ir(111) characterized by angle-resolved photoemission. Phys. Rev. B 2011, 84, 075427. Bignardi, L.; Lacovig, P.; Dalmiglio, M. M.; Orlando, F.; Ghafari, A.; Petaccia, L.; Baraldi, A.; Larciprete, R.; Lizzit, S. Key role of rotated domains in oxygen intercalation at graphene on Ni(111). 2D Mater. 2017, 4, 025106. Vlaic, S.; Kimouche, A.; Coraux, J.; Santos, B.; Locatelli, A.; Rougemaille, N. Cobalt intercalation at the graphene/iridium(111) interface: Influence of rotational domains, wrinkles, and atomic steps. Appl. Phys. Lett. 2014, 104, 101602. Sicot, M.; Leicht, P.; Zusan, A.; Bouvron, S.; Zander, O.; Weser, M.; Dedkov, Y. S.; Horn, K.; Fonin, M. Size-Selected Epitaxial Nanoislands Underneath Graphene Moiré on Rh(111). ACS Nano 2012, 6, 151–158, PMID: 22214768. Petrovic, M.; Srut Rakic, I.; Runte, S.; Busse, C.; Sadowski, J. T.; Lazic, P.; Pletikosic, I.; Pan, Z.-H.; Milun, M.; Pervan, P.; Atodiresei, N.; Brako, R.; Sokcevic, D.; Valla, T.; Michely, T.; Kralj, M. The mechanism of caesium intercalation of graphene. Nat. Commun. 2013, 4, 2772. Jinsung, K.; Se-Yang, K.; Yongsu, J.; Yeon, K. N.; Youb, K. S.; Zonghoon, L.; Soon-Yong, K. Unraveling the Water Impermeability Discrepancy in CVD-Grown Graphene. Adv. Mater. 30, 1800022. Pan, Y.; Zhang, H.; Shi, D.; Sun, J.; Du, S.; Liu, F.; Gao, H.-j. Highly Ordered, Millimeter-Scale, Continuous, Single-Crystalline Graphene Monolayer Formed on Ru (0001). Adv. Mater. 2009, 21, 2777–2780. O’Hern, S. C.; Boutilier, M. S. H.; Idrobo, J.-C.; Song, Y.; Kong, J.; Laoui, T.; Atieh, M.; Karnik, R. Selective Ionic Transport through Tunable Subnanometer Pores in Single-Layer Graphene Membranes. Nano Lett. 2014, 14, 1234–1241. Owais, C.; James, A.; John, C.; Dhali, R.; Swathi, R. S. Selective Permeation through One-Atom-Thick Nanoporous Carbon Membranes: Theory Reveals Excellent Design Strategies! J. Phys. Chem. B 2018, 122, 5127– 5146. Romero-Muñiz, C.; Mart´ın-Recio, A.; Pou, P.; Gómez-Rodr´ıguez, J. M.; Pérez, R. Unveiling the atomistic mechanisms for oxygen intercalation in a strongly interacting graphene-metal interface. Phys. Chem. Chem. Phys. 2018, 20, 13370–13378. Cui, Y.; Gao, J.; Jin, L.; Zhao, J.; Tan, D.; Fu, Q.; Bao, X. An exchange intercalation mechanism for the formation of a two-dimensional Si structure underneath graphene. Nano Res. 2012, 5, 352–360. Li, G.; Zhou, H.; Pan, L.; Zhang, Y.; Huang, L.; Xu, W.; Du, S.; Ouyang, M.; Ferrari, A. C.; Gao, H.-J. Role of Cooperative Interactions in the Intercalation of Heteroatoms between Graphene and a Metal Substrate. J. Am. Chem. Soc. 2015, 137, 7099–7103, PMID: 25961327. Girit, C.; Meyer, J. C.; Erni, R.; Rossell, M. D.; Kisielowski, C.; Yang, L.; Park, C.-H.; Crommie, M. F.; Cohen, M. L.; Louie, S. G.; Zettl, A. Graphene at the Edge: Stability and Dynamics. Science 2009, 323, 1705– 1708. Standop, S.; Lehtinen, O.; Herbig, C.; Lewes-Malandrakis, G.; Craes, F.; Kotakoski, J.; Michely, T.; Krasheninnikov, A. V.; Busse, C. Ion Impacts on Graphene/Ir(111): Interface Channeling, Vacancy Funnels, and a Nanomesh. Nano Lett. 2013, 13, 1948–1955, PMID: 23570261. Bazarnik, M.; Decker, R.; Brede, J.; Wiesendanger, R. Multi-layer and multi-component intercalation at the graphene/Ir(111) interface. Surf. Sci. 2015, 639, 70–74. Wang, Z.; Dong, A.; Wei, M.; Fu, Q.; Bao, X. Graphene as a surfactant for metal growth on solid surfaces: Fe on graphene/SiC(0001). Appl. Phys. Lett. 2014, 104, 181604. Vlaic, S.; Rougemaille, N.; Kimouche, A.; Burgos, B. S.; Locatelli, A.; Coraux, J. Intercalating cobalt between graphene and iridium (111): Spatially dependent kinetics from the edges. Phys. Rev. Mater. 2017, 1, 053406.


Page 8 of 10

Page 9 of 10 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


(48) Vlaic, S.; Rougemaille, N.; Artaud, A.; Renard, V.; Huder, L.; Rouviere, J.L.; Kimouche, A.; Santos, B.; Locatelli, A.; Guisset, V.; David, P.; Chapelier, C.; Magaud, L.; Canals, B.; Coraux, J. Graphene as a Mechanically Active, Deformable Two-Dimensional Surfactant. J. Phys. Chem. Lett. 2018, 9, 2523–2531. (49) Brede, J.; Slawinska, J.; Abadia, M.; Rogero, C.; Ortega, J. E.; PiqueroZulaica, I.; Lobo-Checa, J.; Arnau, A.; Cerdá, J. I. Tuning the Graphene on Ir(111) adsorption regime by Fe/Ir surface-alloying. 2D Mater. 2016, 4, 015016. (50) Schröder, U. A.; Grånäs, E.; Gerber, T.; Arman, M. A.; MartinezGalera, A. J.; Schulte, K.; Andersen, J. N.; Knudsen, J.; Michely, T. Etching of graphene on Ir(111) with molecular oxygen. Carbon 2016, 96, 320– 331. (51) Mart´ın-Recio, A.; Romero-Muñiz, C.; Mart´ınez-Galera, A. J.; Pou, P.; Pérez, R.; Gómez-Rodr´ıguez, J. M. Tug-of-war between corrugation and binding energy: revealing the formation of multiple moiré patterns on a strongly interacting graphene-metal system. Nanoscale 2015, 7, 11300– 11309. (52) de Lima, L. H.; de Siervo, A.; Landers, R.; Viana, G. A.; Goncalves, A. M. B.; Lacerda, R. G.; Häberle, P. Atomic surface structure of graphene and its buffer layer on SiC(0001): A chemical-specific photoelectron diffraction approach. Phys. Rev. B 2013, 87, 081403. (53) de Lima, L. H.; Handschak, D.; Schonbohm, F.; Landers, R.; Westphal, C.; de Siervo, A. The atomic structure of a bare buffer layer on SiC(0001) chemically resolved. Chem. Commun. 2014, 50, 13571–13574. (54) de Lima, L. H.; Barreto, L.; Landers, R.; de Siervo, A. Surface structure determination of black phosphorus using photoelectron diffraction. Phys. Rev. B 2016, 93, 035448. (55) de Siervo, A.; Soares, E.; Landers, R.; Fazan, T. A.; Morais, J.; Kleiman, G. Pd on Cu(111) studied by photoelectron diffraction. Surf. Sci. 2002, 504, 215 – 222. (56) Soares, E.; de Siervo, A.; Landers, R.; Kleiman, G. Photoelectron diffraction from random surface alloys: critique of calculational methods. Surf. Sci. 2002, 497, 205 – 213. (57) Sagurton, M.; Bullock, E.; Fadley, C. The analysis of photoelectron diffraction data obtained with fixed geometry and scanned photon energy. Surf. Sci. 1987, 182, 287 – 361. (58) Krüger, P.; Da Pieve, F.; Osterwalder, J. Real-space multiple scattering method for angle-resolved photoemission and valence-band photoelectron diffraction and its application to Cu(111). Phys. Rev. B 2011, 83, 115437. (59) N’Diaye, A. T.; Coraux, J.; Plasa, T. N.; Busse, C.; Michely, T. Structure of epitaxial graphene on Ir(111). New J. Phys. 2008, 10, 043033. (60) Bondino, F.; Comelli, G.; Baraldi, A.; Rosei, R.; Lizzit, S.; Goldoni, A.; Larciprete, R.; Paolucci, G. Photoelectron diffraction study of the lowtemperature low-coverage oxygen layer on Rh(110). Phys. Rev. B 2002, 66, 075402. (61) Cezar, J. C.; Fonseca, P. T.; Rodrigues, G. L. M. P.; de Castro, A. R. B.; Neuenschwander, R. T.; Rodrigues, F.; Meyer, B. C.; Ribeiro, L. F. S.; Moreira, A. F. A. G.; Piton, J. R.; Raulik, M. A.; Donadio, M. P.; Seraphim, R. M.; Barbosa, M. A.; de Siervo, A.; Landers, R.; de Brito, A. N. The U11 PGM beam line at the Brazilian National Synchrotron Light Laboratory. J. Phys.: Conf. Ser. 2013, 425, 072015. (62) Horcas, I.; Fernández, R.; Gómez-Rodr´ıguez, J. M.; Colchero, J.; GómezHerrero, J.; Baro, A. M. WSXM: A software for scanning probe microscopy and a tool for nanotechnology. Rev. Sci. Instrum. 2007, 78, 013705. (63) Liu, X.; Wang, C. Z.; Hupalo, M.; Lu, W. C.; Tringides, M. C.; Yao, Y. X.; Ho, K. M. Metals on graphene: correlation between adatom adsorption behavior and growth morphology. Phys. Chem. Chem. Phys. 2012, 14, 9157– 9166. (64) Doniach, S.; Sunjic, M. Many-electron singularity in X-ray photoemission and X-ray line spectra from metals. J. Phys. C: Solid State Phys. 1970, 3, 285. (65) Shirley, D. A. High-Resolution X-Ray Photoemission Spectrum of the Valence Bands of Gold. Phys. Rev. B 1972, 5, 4709–4714. (66) Chen, Y.; Garc´ıa de Abajo, F. J.; Chassé, A.; Ynzunza, R. X.; Kaduwela, A. P.; Van Hove, M. A.; Fadley, C. S. Convergence and reliability of the Rehr-Albers formalism in multiple-scattering calculations of photoelectron diffraction. Phys. Rev. B 1998, 58, 13121–13131.



Page 10 of 10

Graphical TOC Entry

Cold = Protection

O2 Hot = Oxidation


Unraveling the Atomic Structure of Fe Intercalated under Graphene on

Recommend Documents