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[Ryotaro Sakakibara](https://orcid.org/0000-0001-7150-2831), [Tomo‐o Terasawa](https://orcid.org/0000-0003-3027-6780), [Taizo Kawauchi](https://orcid.org/0000-0001-6346-2059), [Katsuyuki Fukutani](https://orcid.org/0000-0002-6270-3620), [Takahiro Ito](https://orcid.org/0000-0003-2234-7315), [Wataru Norimatsu](https://orcid.org/0000-0002-7866-1154)

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[2D Iron Oxide at the Graphene/SiC(0001) Interface](https://mdr.nims.go.jp/datasets/a1f56975-f251-4a88-860b-c9b7728a6bd7)

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2D Iron Oxide at the Graphene/SiC(0001) InterfaceSmall Methods www.small-methods.comRESEARCH ARTICLE2D Iron Oxide at the Graphene/SiC(0001) Interface Ryotaro Sakakibara1 Tomo-o Terasawa2 , 3 Taizo Kawauchi4 Katsuyuki Fukutani2 , 3 Takahiro Ito5 , 6 Wataru Norimatsu7 1 Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Tsukuba, Japan 2 Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Japan 3 Institute of Industrial Science, The University of Tokyo, Tokyo, Japan 4 Isotope Science Center, The University of Tokyo, Tokyo, Japan 5 Department of Materials Science and Engineering, Nagoya University, Nagoya, Japan 6 Nagoya University Synchrotron Radiation Research Center (NUSR), Nagoya University, Nagoya, Japan 7 Faculty of Science and Engineering, Waseda University, Tokyo, Japan Correspondence: Ryotaro Sakakibara ( sakakibara.ryotaro@nims.go.jp) Received: 20 September 2025 Revised: 22 February 2026 Accepted: 3 March 2026 Keywords: 2D materials | graphene | intercalation | iron oxide | Mössbauer spectroscopy | silicon carbide | transmission electron microscopy ABSTRACT Fabrication of two-dimensional (2D) transition-metal oxides has gained considerable attention due to their unique crystal struc- tures and physical properties distinct from their bulk counterparts. Intercalation of foreign elements into the graphene/SiC(0001) interface is a possible approach for achieving this, as it enables the confinement and arrangement of atoms within the 2D interface. However, while various 2D metals and their compounds have been synthesized at the graphene/SiC interface, the fabrication of 2D transition-metal compounds remains challenging. This difficulty arises from the high reactivity of transition metals such as Fe, Co, and Ni, which readily form carbides and silicides with the host material. In this work, the fabrication of a 2D iron oxide at the graphene/SiC interface is demonstrated through the simultaneous intercalation of Fe and O. Direct observation using atomic-resolution electron microscopy revealed that the crystalline 2D iron oxide is encapsulated by graphene and forms a sharp interface with the SiC substrate. Structural analysis and Mössbauer spectroscopy suggest that the 2D iron oxide exhibits a wüstite- like structure. These findings provide another strategy for synthesizing 2D transition-metal oxides, opening new avenues for the advancement of 2D magnetic materials. 1T  i  t  o  t  a  W  [  g  t  e  [                Tw©Sh Introduction wo-dimensional (2D) metals and their compounds can exhibitntriguing properties distinct from their bulk counterparts. Dueo their potential applications in catalysis, electronics, andther fields, various methodologies have been developed forheir synthesis and structural control [ 1–10 ]. One promisingpproach involves utilizing the 2D space between van deraals (vdW) materials, such as graphene, and their substrates 5–10 ]. For example, intercalation of a Au monolayer into theraphene/Ni(111) interface [ 5 ] defines a path for the exploration ofhe electronic states of elements confined in a 2D space. A morextensively studied system is epitaxial graphene on SiC(0001) 10–21 ]. Foreign elements such as Au [ 11 ] and Ca [ 12 ] can inter-his is an open access article under the terms of the Creative Commons Attribution-NonCommercial Liork is properly cited and is not used for commercial purposes. 2026 The Author(s). Small Methods published by Wiley-VCH GmbH mall Methods , 2026; 10:e01889 ttps://doi.org/10.1002/smtd.202501889calate into the vdW gap between graphene and the buffer layer,a carbon reconstruction layer formed by thermal decompositionof SiC(0001). Intercalation into the buffer layer/SiC interface hasattracted much more attention [ 10, 13–21 ]. In this case, foreignelements saturate the topmost Si atoms of SiC, while the bufferlayer is decoupled from SiC and converted into quasi-freestandingmonolayer graphene (QFMLG). So far, various elements havebeen stabilized at this QFMLG/SiC interface [ 13 ], such as H[ 14 ], O [ 15, 16 ], Sn [ 17 ], Sb [ 18 ], Au [ 19 ], Ag [ 20 ], and Pb[ 21 ]. Furthermore, leveraging this approach, the synthesis of 2Dcompounds has been reported. For example, Al Balushi et al.synthesized graphene-encapsulated 2D GaN by intercalating Gainto the buffer layer/SiC interface, followed by nitridation [ 22 ].Also, Kakanakova-Georgieva et al. synthesized 2D AlN [ 23 ],cense, which permits use, distribution and reproduction in any medium, provided the original 1 of 12http://www.small-methods.comhttps://doi.org/10.1002/smtd.202501889https://orcid.org/0000-0001-7150-2831https://orcid.org/0000-0003-3027-6780https://orcid.org/0000-0001-6346-2059https://orcid.org/0000-0002-6270-3620https://orcid.org/0000-0003-2234-7315https://orcid.org/0000-0002-7866-1154mailto:sakakibara.ryotaro@nims.go.jphttp://creativecommons.org/licenses/by-nc/4.0/https://doi.org/10.1002/smtd.202501889http://crossmark.crossref.org/dialog/?doi=10.1002%2Fsmtd.202501889&domain=pdf&date_stamp=2026-03-142  u  2  a  t  eI  t  l  i  m  a  [  i  s  m  t  c  c  e  p  dH  t  i  t  b  a  l  i  s  u  c  t  a  m  g  m22W  t  s  [  h  S  4  a  m  d  t  i  s  a  t                                                    2 23669608, 2026, 8, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smtd.202501889 by National Institute For, Wiley Online Library on [23/04/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable CreativD InN [ 24 ], and 2D InO [ 25 ] at the graphene/SiC interfacesing a metal-organic chemical vapor deposition process. TheseD compounds exhibit structures and physical properties thatre not observed in their bulk forms [ 22, 24 ], and therefore,he graphene/SiC interface provides an excellent platform forxploring novel 2D materials. n this context, the fabrication of 2D compounds based on transi-ion metals such as Fe, Co, and Ni is of great interest, as it couldead to the development of 2D magnetic materials and proximity-nduced spin injection into graphene [ 26, 27 ]. In recent years, 2Dagnetic materials have been shown to exhibit strong magneticnisotropy and thickness-dependent modulation of magnetism 28, 29 ], highlighting the importance of dimensional reductionn magnetic materials. At the graphene/SiC interface, a possibletrategy for their synthesis is to first intercalate a transitionetal, followed by its oxidation or nitridation. However, theseransition metals readily react with graphene and SiC to formarbides [ 30, 31 ] or silicides [ 32, 33 ], which makes intercalationhallenging. As a result, despite several attempts [ 34–36 ], directvidence for the fabrication of 2D transition metals and their com-ounds at the graphene/SiC interface has not been provided toate. ere, we report the formation of a 2D iron oxide layer athe graphene/SiC interface by the intercalation technique. Wenvestigated the optimal conditions for intercalation and foundhat intentional oxidation of the Fe thin film deposited on theuffer layer/SiC surface before the intercalation is effective. Thispproach facilitates the intercalation of Fe and O, and the bufferayer is transformed into QFMLG. As a result, a crystalline 2Dron oxide layer is formed at the graphene/SiC interface. Thetructure of this interfacial 2D iron oxide was analyzed in detailsing atomic-resolution electron microscopy and theoreticalalculations. Mössbauer spectroscopy measurements revealedhat the interfacial iron oxide exhibits a magnetic transition at low temperature. Our approach enables the synthesis of 2Dagnetic materials at a large scale and their stabilization byraphene encapsulation, which facilitates the study of nanoscaleagnetism at the 2D limit.  Results and Discussion .1 Comparison of Two Annealing Methods e first investigate the optimal condition for intercalation. Ashe initial sample, we prepared the buffer layer on a SiC(0001)ubstrate with a size of 5 × 5 mm2 by thermal decomposition 37–42 ]. The buffer layer/SiC sample was loaded into an ultra-igh vacuum (UHV) chamber and degassed at around 700◦C.ubsequently, an Fe thin film with a nominal thickness of about nm was deposited on the sample surface. Two annealingpproaches were compared, as illustrated in Figure 1 . In the firstethod, the sample was annealed in UHV immediately after theeposition of metallic Fe (upper part of the figure). Althoughhis is a typical approach for metal intercalation [ 17–21, 34–36 ],t resulted in the formation of multilayer graphene and ironilicide. In the second method, the deposited Fe was oxidized byir exposure and subsequently annealed in UHV (lower part ofhe figure). We found that this approach leads to the formationof 12of QFMLG and interfacial 2D iron oxide, as a consequence ofintercalation. In both methods, the annealing temperature andduration were set to 660◦C–710◦C and 20 min, respectively. Inthe following, we compare spectroscopic evidence for the twomethods to demonstrate that annealing with pre-oxidized Feenables intercalation. 2.1.1 Evolution of Raman Spectrum Raman spectroscopy was employed to investigate the structuralevolution of the buffer layer. The Raman spectrum of the initialsample, shown in Figure 2a , exhibits a broad feature in the 1300–1600 cm− 1 range. This spectral feature arises from the vibrationaldensity of states of the buffer layer and differs from the Ramanmodes of sp2 -hybridized graphene [ 43, 44 ]. A weak signatureof the graphene 2 D band is also observed near 2720 cm− 1 [ 45,46 ], suggesting the presence of excess graphene formed duringthermal decomposition. To examine the spatial uniformity of thesample, the median Raman spectrum obtained from 100 spectrais presented in Figure S1 . The median spectrum exhibits a largelyflat 2 D -band region, indicating that the surface is mainly coveredby the buffer layer, with minor contributions from overgrownmonolayer graphene. This interpretation is further supported byan atomic force microscopy (AFM) observation (Figure S2 ). Thetopography image reveals the step-terrace structure of the SiCsubstrate, with step heights of 2–4 nm. Phase contrast imagingindicates that the sample is predominantly covered by the bufferlayer, with additional graphene strips nucleated at the step edges[ 38, 40–42 ]. After annealing the buffer layer with metallic Fe, the D , G , and2 D bands characteristic of graphene were observed (Figure 2b )[ 45, 46 ]. In general, graphene exhibits G and 2 D bands at ∼ 1560and ∼ 2680 cm− 1 , respectively. The G band originates from thebond stretching of sp2 C atoms, while the 2 D band arises from thedouble-resonant Raman scattering process. They provide a meansto estimate the number of graphene layers. The D band, appearingat ∼ 1360 cm− 1 , indicates the presence of defects in the graphenelattice. The broad G and 2 D bands and the sharp D band suggestthe formation of defect-rich multilayer graphene. On the other hand, annealing of the buffer layer with pre-oxidizedFe resulted in sharp G and 2 D bands, with a relatively weak Dband (Figure 2c ). The full width at half maximum (FWHM) ofthe 2 D band was 38–55 cm− 1 , suggesting 1–2 layers of graphene[ 45, 46 ]. The defect density estimated from the D / G intensityratio is approximately 1.0 × 1011 cm− 2 [ 47 ]. Also, the broad featurecharacteristic of the buffer layer is absent. Mapping of the 2 Dband FWHM revealed that most of the surface is covered bymonolayer graphene, while bilayer graphene appears near thestep edges (Figure S3 ). This suggests that intercalation convertedthe buffer layer into QFMLG, and the additional graphene stripsnear the step edges into quasi-freestanding bilayer graphene[ 48, 49 ]. Statistics of the Raman mapping data reveal a linearcorrelation between the G -band and 2 D -band positions, with apronounced variation (Figure S4 ). Based on established analysesin the literature [ 50 ], the graphene layer in this sample is subjectto a wide range of compressive strain (0%–1%). This may arisefrom contributions of nonintercalated overgrown graphene orSmall Methods, 2026e Commons LicenseFIGURE 1 Schematic diagram of the two annealing methods implemented in this study. The atomic structure of the buffer layer/SiC is illustrated as a ball-and-stick model. 1000 1500 2000 2500 3000DG2DDG 2D38–55 cm−1( ytisnetnIa.u.)Raman shift (cm−1)abcSiCSiCSiCFIGURE 2 Raman spectra of (a) the initial buffer layer, (b) the sample annealed with metallic Fe, and (c) the sample annealed with pre- oxidized Fe. Note that the contribution of the SiC substrate is subtracted from all Raman spectra.                                 Small Methods, 2026 23669608, 2026, 8, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smtd.202501889 by National Institute For, Wiley Online Library on [23/04/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creativfrom interactions between the graphene layer and residual ironoxide on the surface. 2.1.2 Evolution of XPS Spectra The C 1 s X-ray photoemission spectroscopy (XPS) spectrum ofthe initial sample (Figure 3a ) is mainly explained by two peaksfrom the buffer layer (S1 and S2), one peak from overgrownmonolayer graphene (dotted line), and one peak from bulk SiC[ 16, 18, 20–21, 39–40 ]. The S1 and S2 peaks originate from Catoms in the buffer layer that are respectively bonded and notbonded to the underlying SiC substrate. As these peaks are knownto be separated by about 880 meV with a peak area ratio of1: 2, the peak fitting was carried out under these constraints.The small component at higher binding energy arises fromhydrocarbon contamination [ 51 ]. The Si 2 p spectrum (Figure 3b )shows contributions from interfacial Si and bulk SiC [ 19–21 ]. Inthe fitting of the Si 2 p spectrum, a spin-orbit splitting of 0.6 eVwas employed, and the area ratio of the 2 p1/2 to 2 p3/2 componentswas constrained to 1: 2. Fitting parameters for the C 1 s and Si 2 pspectra are summarized in Tables S1 and S2 , respectively. For theFe 2 p spectrum, no signal was identified (Figure 3c ). These resultsindicate that the surface of the initial sample is mainly covered bythe buffer layer, as illustrated in Figure 3d . After annealing the buffer layer with metallic Fe, the C 1 sspectrum exhibits the graphene-derived peak and the bulk SiCcomponent (Figure 3e ). Additionally, the Si 2 p spectrum inFigure 3f shows a new peak at around 99.8 eV, which is indicativeof Si ─Fe bonding [ 52 ]. The Fe 2 p spectrum exhibits spin-orbitsplit 2 p1/2 and 2 p3/2 peaks, each of which consists of two maincomponents (Figure 3g ). The sharp peaks at lower binding energy,indicated by the arrows, can be attributed to iron silicide [ 52 ],whereas the broad peaks at higher binding energy arise fromresidual iron(III) oxide formed after sample preparation. Note,since deconvolution of Fe 2 p spectra is nontrivial due to strongmultiplet splitting and satellite features [ 53, 54 ], we here limitedour analysis to the overall spectral shape. Together with the3 of 12e Commons License290 288 286 284 282 280 106 104 102 100 98 96 740 730 720 710 700( ytisnetnIa.u.)Binding energy (eV) Binding energy (eV) Binding energy (eV)SiCS1SiCS2Si 2pC 1s Fe 2pGraFe–SiInterfaceFe–Sib cQFMLGSiCIntercalatedFe2O3SiCMultilayer grapheneIron silicideSiCf gj kdhl2p3/22p1/2DataFitsBuffer layeraeiX XFIGURE 3 Evolution of XPS spectra. (a–c) C 1 s , Si 2 p , and Fe 2 p core-level spectra of the initial sample, with (d) its schematic illustration. (e–g) The spectra after annealing with metallic Fe, showing the formation of multilayer graphene and iron silicide, as illustrated in (h). (i–k) The spectra after annealing with pre-oxidized Fe, reflecting the conversion of the buffer layer into QFMLG via intercalation, as illustrated in (l). Fitting of the C 1 s and Si 2 p spectra was performed after Shirley’s background subtraction, while the Fe 2 p spectra are shown as raw data. R  b  r  (A  s  i  t  n  l  s  c  i  t  a  w  i  s  i  2  o  s  i  B  t  c  o  c  s                        4 23669608, 2026, 8, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smtd.202501889 by National Institute For, Wiley Online Library on [23/04/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creativaman spectroscopy results, we conclude that annealing of theuffer layer with metallic Fe led to the formation of defect-ich multilayer graphene and iron silicide on the sample surfaceFigure 3h ). fter annealing the buffer layer with pre-oxidized Fe, the C 1 spectrum also exhibits the graphene-derived peak (Figure 3i ), butts intensity relative to the SiC component is substantially lowerhan that in Figure 3e . The small component X accounts for theon-intercalated region, which was fitted by scaling down theine shape of Figure 3a . The Si 2 p spectrum in Figure 3j does nothow any indication of iron silicide. As in the C 1 s case, the smallomponent X reflects the non-intercalated region. Furthermore,n both the C 1 s and Si 2 p spectra, the bulk SiC component shiftedo lower binding energy by about 0.7 eV. This shift is commonlyssociated with the intercalation of a foreign element [ 20, 21 ],hich results from the band bending due to the termination ofnterfacial Si with other elements. Consistent with the Ramanpectroscopy results, these findings support the intercalation-nduced conversion of the buffer layer into QFMLG. In the Fe p spectrum in Figure 3k , broad peaks of iron(III) oxide werebserved. As evidenced by electron microscopy observations pre-ented later, this spectrum contains contributions from both thenterfacial component and residual surface iron oxide (Figure 3l ).y optimizing the amount of deposited Fe, further insight intohe chemical states and stoichiometry of the intercalated phaseould be obtained by XPS. Nonetheless, a tentative deconvolutionf the spectrum was performed based on assumed chemicalompositions for these two components, considering multipletplitting (Figure S5 and Table S3 ) [ 53, 54 ]. The fitting resultof 12suggests that a non-negligible amount of Fe2 O3 residue remainson the surface. 2.1.3 Atomic-Scale Observation of the Interface Figure 4a shows a cross-sectional high-resolution transmissionelectron microscopy (HR-TEM) image of the sample annealedwith metallic Fe, with electron incidence parallel to the [11 ̄2 0]SiC direction. The image reveals a layered contrast of multilayergraphene, as well as an island-like structure beneath it. Figure 4bpresents a corresponding high-angle annular dark field scanningTEM (HAADF-STEM) image. The island structure exhibits abright contrast, suggesting the presence of an element witha higher atomic number than Si and C. As indicated by theblack arrow, this island is embedded more than 1 nm below theSiC substrate surface. Such island structures were observed inmultiple regions across the sample with a variety of shapes andnumbers of graphene layers. Considering the above XPS results,these islands are suggested to be iron silicide. The iron silicideseen in this field of view was further identified as Fe3 Si based ona structural analysis of the TEM image. Figure 4c shows an HR-TEM image of the sample annealedwith pre-oxidized Fe, where the uniform graphene layer isvisible on the SiC surface. Interestingly, in the correspondingHAADF-STEM image (Figure 4d ), three layers of bright spotsare arranged at the graphene/SiC interface. The number of theseinterface layers was 2–4 in the observed area (Figure S6 ). Wenote that, although two layers of graphene are observed in thisSmall Methods, 2026e Commons LicenseMultilayer grapheneIron silicideSiC SiC2 nm 2 nmSiC SiC2 nm 2 nmGraphene 2D iron oxidee80 180 280520 620 720Fe-L3O-K( ytisnetnIa.u.)Energy loss (eV)Energy loss (eV)80 180 280520 620 720Si-LIntensity (a.u.)Energy loss (eV)Energy loss (eV)Interface layer SiC substrateAnneal with pre-oxidized FeAnneal with metallic Fea bc dFIGURE 4 Atomic-scale observation and elemental analysis of the interface. (a,b) Cross-sectional HR-TEM and HAADF-STEM images of the sample annealed with metallic Fe. In (b), the SiC surface and the bottom of the iron silicide island are indicated by a dashed line and a black arrow, respectively. (c,d) Cross-sectional HR-TEM and HAADF-STEM images of the sample annealed with pre-oxidized Fe, confirming uniform graphene formation. In (d), bright spots are arranged at the graphene/SiC interface. (e) EELS spectra acquired from the highlighted regions in (d), showing O-K and Fe-L3 absorption edges detected only at the interface layer, indicating the formation of 2D iron oxide. f  l  a  e  s  t  b  p  o  a  i  w  c              S 23669608, 2026, 8, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smtd.202501889 by National Institute For, Wiley Online Library on [23/04/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creativield of view, most of the sample surface is covered by a singleayer, as confirmed by Raman mapping (Figure S3 ). Chemicalnalysis of the sample interface was performed using electronnergy loss spectroscopy (EELS), as shown in Figure 4e . EELSpectra were selectively acquired from the interface layer andhe SiC region just beneath it, as indicated by the red andlue rectangles in Figure 4d , respectively. In the interface layer,eaks corresponding to the Fe-L3 and O-K absorption edges werebserved, while no significant signal was detected at the Si-Lbsorption edge. In contrast, in the SiC region just below thenterface layer, neither Fe nor O was detected, but a clear Si peakas observed. These results indicate that the interface layer isomposed of Fe and O, and forms a sharp interface with the SiCmall Methods, 2026substrate. Energy dispersive X-ray spectroscopy (EDS) mappingalso confirms the presence of Fe and O at the interface (FigureS7 ). Based on these analytical results, we conclude that the brightspots correspond to Fe atoms, and the intercalation of Fe andO occurred. Following many previous studies on intercalation[ 10, 13, 19–25 ], we refer to this interfacial structure as 2D ironoxide rather than an ultrathin film. Its thickness is limitedto a few atomic layers (Figure S6 ), consistent with previouslyreported 2D compounds such as 2D GaN [ 22 ] and 2D AlN [ 23 ].Note, a low-magnification TEM image reveals numerous residualiron oxide islands on the sample surface, but the graphene/2Diron oxide/SiC structure was preserved beneath these islands(Figure S8 ). 5 of 12e Commons License2A  f  a  a  t  h  a  p  d  i  R  m  o  p  aI  r  o  g  b T  −  o  i  c  i  H  m  [O  p  e  r  S  t  2  s  f  m  i  o  i  o  t  i  b  a  m  a  [                                              6 23669608, 2026, 8, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smtd.202501889 by National Institute For, Wiley Online Library on [23/04/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creat.1.4 Formation Mechanism nnealing the buffer layer with metallic Fe resulted in theormation of multilayer graphene and iron silicide, whereasnnealing with pre-oxidized Fe enabled the intercalation of Fend O. In both cases, Fe atoms penetrated the buffer layer to reachhe underlying SiC. Direct penetration of Fe atoms through theexagonal lattice of the buffer layer is unlikely, given that even H atom requires a penetration barrier of 2.55 eV [ 55 ]. Thus, theenetration of Fe atoms is most likely assisted by intrinsic vacancyefects [ 56 ] and/or local lattice disruption. This interpretations consistent with the observation of graphene D bands in theaman spectra (Figure 2b,c ). Since such defects are thought to beore abundant at step edges than on terraces, penetration mayccur preferentially at step edges [ 57 ]. Indeed, for annealing withre-oxidized Fe, a HAADF-STEM image reveals bright spots of Fetoms only at the step edges (Figure S9 ). n the following, we discuss the thermodynamics of interfacialeactions after penetration to rationalize the different outcomesf the two annealing methods. The formation of multilayerraphene and iron silicide after annealing with metallic Fe cane explained by the following solid-state reaction: 3 𝐹𝑒 + 𝑆 𝑖 𝐶 → 𝐹𝑒3 𝑆 𝑖 + 𝐶𝐺𝑟𝑎 (1)he enthalpies of formation of SiC and Fe3 Si are − 71.4 and 94.1 kJ mol− 1 , respectively, yielding a Gibbs free energy changef − 33 kJ mol− 1 at 710◦C [ 58 ]. This indicates that the reactions thermodynamically favorable under the present experimentalonditions. The released C atoms, which have low solubilityn iron silicides [ 59 ], precipitate on the surface as graphite.ere, iron carbide (Fe3 C) formation is unfavorable because it isetastable, with a positive enthalpy of formation (25.5 kJ mol− 1 ) 58 ]. n the other hand, the formation of Fe3 Si is significantly sup-ressed in the presence of oxygen [ 60, 61 ], due to the much lowernthalpy of formation of Fe2 O3 ( − 824.2 kJ mol− 1 ). In addition, theeported onset temperature for the solid-state reaction betweeniC and Fe2 O3 is approximately 950◦C [ 62 ], which is abovehe temperature in our experiment ( ∼ 710◦C). The formation ofD iron oxide after annealing with pre-oxidized Fe therefore,uggests the presence of an alternative thermodynamic drivingorce stabilizing the intercalants. A plausible origin is that the ter-ination of unsaturated Si dangling bonds at the buffer layer/SiCnterface by O atoms is energetically favorable, facilitating therdering of Fe and O atoms [ 10 ]. Moreover, the graphene/2Dron oxide/SiC structure was observed regardless of the presencer absence of residual iron oxide islands (Figure S8 ), implyinghat Fe and O intercalants underwent lateral migration along thenterface after initial penetration. Such facile lateral migration haseen theoretically demonstrated for other intercalants such as Hnd Pb, with energy barriers well below 1 eV [ 55, 63 ]. Elucidating aore detailed mechanism will require theoretical investigations,s intercalation generally involves complex elementary processes 63 ] and results in structures that do not exist in the bulk form. of 122.2 Electronic Structure of QFMLG The low-energy electron diffraction (LEED) pattern of the inter-calated sample shown in Figure 5a exhibits six-fold symmetricspots from graphene (red arrow) and a (1 × 1)SiC periodicity(green arrow), with no satellites from the (6 √3 × 6 √3) R 30◦reconstruction of the buffer layer [ 10, 14, 15, 17–21, 37, 39,40 ]. The 30◦ rotation between them indicates that grapheneinherits the crystallographic orientation of the buffer layer. The(1 × 1)SiC periodicity suggests the absence of superstructure inthe interfacial iron oxide. This observation further highlights theformation of QFMLG through intercalation. To investigate the electronic structure of this sample, weconducted angle-resolved photoemission spectroscopy (ARPES)measurements at room temperature. The sixfold symmetric bandof graphene was clearly observed in the constant energy map atthe Fermi energy (Figure 5b ). The energy-momentum ( E - k ) cut atthe K̄ point of the Brillouin zone clearly exhibits the characteristiclinear dispersion of monolayer graphene (Figure 5c ). By extrapo-lating the two bands in the figure, the Dirac point was estimatedto be approximately + 0.26 eV relative to the Fermi energy ( EF ),indicating uniform hole-doping. Here, in epitaxial graphene onSiC obtained by thermal decomposition, the Dirac point is locatedat − 0.4 eV relative to EF (Figure S10 ) [ 42 ]. This electron dopingis generally understood as the charge transfer from the bufferlayer to the overlying graphene [ 64 ]. Upon intercalation, however,the doping level can be drastically altered. For example, H-intercalation induces p-type doping [ 64 ], with the Dirac pointshifted to + 0.30 eV. These results highlight that the position ofthe Dirac point is sensitive to the chemical state at the interface,as also reported for the intercalation in graphene/metal interfaces[ 5, 65 ]. Therefore, the observed Dirac point at + 0.26 eV in oursample is likely due to charge transfer from the interfacial ironoxide layer to QFMLG. Figure 5d–e presents the second-derivative images of the obtainedband structures. In addition to the graphene’s π band, a broad fea-ture attributed to Fe 3 d electrons [ 66 ] is observed around − 1.2 eVacross the entire Brillouin zone, which has no clear dispersionrelation. A similar localized Fe state has also been reported forFe intercalation in the graphene/Ir(111) system, [ 65 ] supportingthe assignment of this feature to an interfacial component. Theabsence of hybridization between the Fe 3 d and graphene bandssuggests that QFMLG merely serves as a capping layer on the2D iron oxide. The splitting of these Fe-derived states and theirspin characteristics, as well as their possible impact on the spin ofgraphene electrons via proximity effects, remains to be clarified. 2.3 Structural Analysis of the Graphene/SiC Interface Figure 6a,b show HAADF-STEM images, together with intensityprofiles along the lateral directions highlighted by the rectangles.In Figure 6a , the bright spots of Fe atoms are aligned along the[1 ̄1 00]SiC direction, with a periodicity of approximately 0.26 nm.As illustrated in the inset, this periodicity matches the spacing ofthe Si atoms in SiC along the same direction. Figure 6b presentsSmall Methods, 2026ive Commons LicenseE−EF(eV)k (Å−1) ⊥ ΓKk (Å−1) ⊥ ΓKE−EF(eV)cHighLowE−EF(eV)a138.2 eVΓKbkx (Å−1)k y(Å−1 )0.0 1.0−1.00.01.02.0−2.0−1.0Md eHighLowK'−2−10−4−3−6−5−7Fe 3d____K K'Γ_ _ _K M K'_ _ _____FIGURE 5 (a) LEED pattern of graphene/2D iron oxide/SiC at 138.2 eV. The red and green arrows indicate the spots from graphene and a (1 × 1)SiC periodicity, respectively. (b) ARPES constant energy map at the Fermi energy acquired at a photon energy of 120 eV. (c) E - k dispersion around the K point, acquired at a photon energy of 70 eV. (d) Second derivative image of (c) with respect to energy, revealing an Fe 3 d localized state indicated by the arrow. (e) Second derivative images of the E - k cuts along the K̄ −Γ̄−K̄′ and K̄ −M̄ −K̄′ directions in (b), also showing the Fe 3 d localized state as well as the graphene’s π band. a  [  g d  a  t  2  t  i  (  s  aT  i  s  i  o  l  a  s  w  s                       S 23669608, 2026, 8, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smtd.202501889 by National Institute For, Wiley Online Library on [23/04/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creativn image taken from another electron incidence, parallel to the1 ̄1 00]SiC direction. Two layers of Fe atoms are observed at theraphene/SiC interface. The intensity profile along the [11 ̄2 0]SiCirection shows an Fe atom periodicity of about 0.15 nm, whichlso corresponds to the Si atom periodicity in SiC (inset). Thus,he Fe atoms are considered to form a triangular lattice [ 17, 19,0 ] in each layer, analogous to the arrangement of Si atoms onhe SiC(0001) plane. This is in agreement with the LEED resultsn Figure 5a , where only diffraction spots from graphene and the1 × 1)SiC periodicity were observed. It should be noted that, aseen in Figure 6a , the Fe atoms exhibit an ABA stacking sequencelong the c -axis direction. he interfacial iron oxide consists of layers of Fe atoms arrangedn a triangular lattice, with these layers forming an ABAtacking sequence. Merte et al. have proposed a similar 2Dron oxide structure [ 67 ], which is composed of two typesf building blocks shown in Figure 7a . Specifically, in eachayer of the 2D iron oxide, O atoms coordinate around Fetoms in either tetrahedral or octahedral geometry [ 67 ]. Con-idering all possible combinations of these building blocks,e explored eight structural models to explain the three-layertacking seen in our STEM observations. For each candi-mall Methods, 2026date structure, we prepared an iron oxide/4H-SiC(0001) slabmodel and optimized both the cell size and atomic posi-tions using density functional theory (DFT) calculations. Afterstructural relaxation, six structures either failed to convergeor resulted in different atomic configurations, whereas twostructures closely matching the STEM images were obtained(Figure 7b,c ). Figure 7d presents simulated STEM images basedon these structures, both of which qualitatively agree withthe experimental image. Also, in both structures, the topmostSi atoms of SiC are bonded to O atoms (Figure 7b,c ), whichis consistent with the absence of Si ─Fe bonding peaks inthe XPS Si 2 p spectrum (Figure 3j ). Accordingly, the inter-face component around 102 eV can be attributed to Si ─Obonding. A common feature of these two structures is that the ironoxide layer directly above SiC exhibits tetrahedral coordination,reflecting the crystal structure of SiC, while transitioning tooctahedral coordination closer to the surface. The octahedraliron oxide layer corresponds to the (111) plane of wüstite,an iron oxide with the NaCl-type structure (Figure 7e ). Thein-plane Si–Si interatomic distance in the SiC(0001) plane(3.07 Å ) and the in-plane Fe–Fe interatomic distance in the7 of 12e Commons License0.0 0.5 1.0 1.5 2.00.0 0.5 1.0 1.5 2.00.15 nmIntensity (a.u.)0.15 nmLateral distance (nm)2 nmbLateral distance (nm)Intensity (a.u.)0.26 nm[1100]SiC_a2 nmSiCSiC0.26 nm[1120]SiC_[1120]SiC_[1100]SiC_FIGURE 6 Structural analysis of the graphene/SiC interface. HAADF-STEM images of the same sample with electron incidence parallel to (a) [11 ̄2 0]SiC and (b) [1 ̄1 00]SiC directions. The corresponding intensity profiles along the highlighted regions in each image are shown on the right. The bright spots, namely Fe atoms, are considered to be arranged in the same manner as the Si atoms on the SiC(0001) surface. w  T  b  l  c  n  o  g  t  r  s  t  2  s2OW  2  (  b  o  s  i  m  B  o  a                                                      8 23669608, 2026, 8, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smtd.202501889 by National Institute For, Wiley Online Library on [23/04/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creativüstite (111) plane (3.11 Å ) have a mismatch of about 1.3%.hus, the tetrahedral layer above SiC may serve as a bufferetween these two structures. Note that the overlying grapheneayer was not considered in these calculations due to theomputational cost, and thus, the predicted structures mayot fully represent the true stable configurations. Structuralptimization and band structure calculations, including theraphene layer, are important for gaining further insight intohe properties of the system obtained in this study, and theseemain subjects for our future work. In addition, LEED orcanning tunnelling microscopy (STM) studies of the intercala-ion process would help clarify the structural evolution of theD iron oxide and allow a more precise identification of thetructure. .4 Magnetic Structure of the Interfacial 2D Iron xide e finally investigated the magnetic properties of the interfacialD iron oxide using conversion electron Mössbauer spectroscopyCEMS). CEMS is a powerful technique for probing the magneticehavior of 57 Fe atoms in materials, based on the observationf the excitation of 57 Fe nuclear spin from the I = 1/2 groundtate to the I = 3/2 excited state. We prepared a graphene/2Dron oxide/SiC sample using a 57 Fe source and conducted CEMSeasurements at room temperature and 100 K (Figure 8a,b ).oth spectra were fitted using two components: interfacial ironxide (red) and α-Fe (green). The α-Fe components exhibit typical Zeeman-split sextet both at room temperature andof 12100 K [ 68 ] and probably originate from residual Fe remainingon the sample surface. The persistence of metallic iron afterair exposure is attributed to the very slow oxidation rate ofthe high-purity 57 Fe source. In addition, the naturally formediron oxide on these residues is expected to contribute littleto the CEMS spectra, likely due to its low crystallinity anda resultant low Lamb-Mössbauer factor [ 68 ]. Focusing on theinterfacial iron oxide component (red) in the room-temperaturespectrum (Figure 8a ), a quadrupole-split doublet peak withan isomer shift of about 0.7 mm s− 1 was observed, while nodistinct Zeeman splitting was identified. This suggests that theinterfacial 2D iron oxide does not exhibit any magneticallyordered state at room temperature. However, when cooledto 100 K, the doublet peak changed to a Zeeman-split sex-tet with a magnetic field of 48.5 T, indicating a magneticordering (Figure 8b ). Such a characteristic magnetic phasetransition closely resembles that of wüstite, which undergoesa paramagnetic-to-an antiferromagnetic phase transition uponcooling below its Néel temperature ( ∼ 200 K) [ 69, 70 ]. TheDFT calculations described above indicate that the interfacial2D iron oxide has a wüstite-like structural aspect. Therefore,our CEMS results can be qualitatively interpreted based onthe structural similarity to wüstite. The emergence of antiferro-magnetism is also predicted in theoretical studies of 2D Fe3 O4 structures [ 67, 71 ]. The observation of clear magnetic ordering in the interfacial 2Diron oxide is intriguing from the perspective of spin injectioninto graphene [ 26, 27 ]. Spin-resolved ARPES at low temperaturesmay reveal proximity-induced spin states of graphene electrons.Such spin injection into graphene is particularly attractive forspintronic applications, as it can lead to long spin coherencelengths and high carrier mobility [ 72 ]. Finally, the methodologyof the present study provides a feasible approach for exploringother 2D magnetic systems that do not exist in the bulk form.The inherently accompanying graphene encapsulation allowsthe synthesis of otherwise air-sensitive materials. Confinementwithin the interfacial 2D space enables dimensional reductionof magnetic materials, offering a viable platform to investi-gate modified magnetic anisotropy and thickness-dependentmagnetism. 3 Conclusions We compared two approaches toward the synthesis of 2D ironoxide at the graphene/SiC(0001) interface. While the annealingof the buffer layer with metallic Fe led to the formation ofdefective multilayer graphene and iron silicide, annealing withpre-oxidized Fe intercalated Fe and O into the buffer layer/SiCinterface. The QFMLG thus obtained is large-scale and single-oriented, and the interfacial 2D iron oxide forms a sharp interfacewith the SiC substrate. A detailed analysis of the atomic structurebased on STEM observations suggests that the 2D iron oxide hasa wüstite-like structural aspect. CEMS measurements revealeda magnetic phase transition in the interfacial 2D iron oxide,which can be associated with the antiferromagnetic behav-ior of wüstite. The methodology established in the presentstudy provides an alternative route to synthesize large-scale 2Dtransition-metal oxides at a buried interface, thereby enablingSmall Methods, 2026e Commons LicenseOcta OctaOctaOctaOctaOctaTetra TetraTetraFIGURE 7 Structures of interfacial 2D iron oxide from DFT calculations. (a) Two types of building blocks compose each iron oxide layer. (b,c) Possible structural models of iron oxide on 4H-SiC(0001), obtained after structural optimization. In the top-view images, unit cells are indicated by dotted rhombuses. (d) Simulated HAADF-STEM images based on the structures of (b) and (c), superimposed on the experimental image. (e) Crystal structure of wüstite. t  m44A  S  s  e  (  p  A4T  b  7  d  e  o  T  t  t  d  w  d  i  a                    S 23669608, 2026, 8, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smtd.202501889 by National Institute For, Wiley Online Library on [23/04/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creativhe exploration and development of diverse nanoscale magneticaterials.  Experimental Section .1 Preparation of the Buffer Layer  buffer layer sample was prepared by thermal decomposition ofiC [ 37–42 ]. A nominally on-axis 4H-SiC(0001) substrate with aize of 5 × 5 mm2 was cleaned via ultrasonication in acetone andthanol, followed by immersion in a hydrofluoric acid solution20 vol.%) to remove the native oxide layer on the surface. There-treated SiC substrate was then annealed at 1500–1600◦C in anr gas flow atmosphere [ 48, 49 ]. .2 Deposition of Fe and Subsequent Annealing he buffer layer sample was loaded into a UHV chamber with aase pressure of approximately 10− 8 Pa and degassed at around00◦C for 20 min. After cooling to room temperature, Fe waseposited onto the buffer layer surface via molecular beampitaxy. The Knudsen cell temperature and deposition time wereptimized to achieve a nominal film thickness of about 4 nm.wo different annealing methods were employed to investigatehe optimal conditions for intercalation. In the first method,he sample was annealed in UHV immediately after the Feeposition. On the other hand, in the second method, the sampleas intentionally exposed to air for overnight to oxidize theeposited Fe film. After the air exposure, the sample was reloadednto the chamber for annealing in UHV. In both methods, thennealing temperature and duration were set to 660–710◦C andmall Methods, 202620 min, respectively. The ambient pressure during annealing wasaround 10− 6 Pa. The samples were transported in air for thefollowing measurements. 4.3 Raman Spectroscopy Raman spectroscopy measurements were performed at roomtemperature using a Renishaw inVia spectrometer. A 532 nmexcitation laser with a spot size of about 1 µm2 was used. Toevaluate the carbon layer on the substrate surface, the SiCsubstrate contribution is subtracted from all Raman spectra in themain text. 4.4 AFM AFM observations were carried out in dynamic force mode toobtain topography and phase images simultaneously. In phaseimaging, differences in the viscoelastic properties of the samplesurface appear as phase contrasts, allowing the buffer layer andgraphene to be distinguished by their different contrasts [ 48, 49 ].4.5 XPS XPS measurements were conducted using an Al Kα ( h ν =1486.6 eV) source with a probe diameter of approximately 500 µm.Core-level spectra for each element were acquired with an energystep of 0.05 eV and a pass energy of 50 eV. The XPS spectra wereanalyzed using Shirley’s method for background subtraction andGauss–Lorentz mixing function for peak fitting unless otherwisestated. 9 of 12e Commons License1.001.021.041.06ytisnetni evitaleRytisnetni evitaleR−10 −5 0 5 101.001.041.081.12Velocity (mm s−1)RT 100 KDataTotal fitInterfaceα-FeabFIGURE 8 CEMS spectra of the graphene/2D iron oxide/SiC sam- ple measured at (a) room temperature and (b) 100 K. The dots represent the experimental data, while the colored lines indicate the fitting results. The red component corresponds to the interfacial 2D iron oxide, which exhibits a magnetic phase transition upon cooling. 4H  a  2  w  6  f  p4T  T  u  C  s  w4T  D                                             1 23669608, 2026, 8, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smtd.202501889 by National Institute For, Wiley Online Library on [23/04/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creativ.6 Cross-Sectional TEM/STEM R-TEM and HAADF-STEM observations were carried out usingn aberration-corrected JEM-ARM200F microscope operated at00 kV. In HAADF-STEM observation, the probe diameteras approximately 70 pm and the detection angle range was8–280 mrad. Additionally, EELS and EDS were carried outor elemental analysis. Thin specimens for observation wererepared via Ar-ion milling [ 48, 49 ]. .7 LEED and ARPES he LEED pattern was taken at an electron energy of 138.2 eV.he ARPES measurements were conducted at room temperaturesing the beamline BL7U at the Aichi Synchrotron Radiationenter. Photon energies of 70 eV and 120 eV were used, with apot size of approximately 150 × 70 µm2 . The energy resolutionas about 40 meV with 0.3◦ angular resolution. .8 Theoretical Calculations and Simulations o analyze the interface structure of the obtained sample,FT calculations were performed using the ABINIT code [ 73 ].0 of 12The calculations employed the generalized gradient approxima-tion based on the Perdew-Burke-Ernzerhof exchange-correlationfunctional [ 74 ] and norm-conserving pseudopotentials. The ironoxide/4H-SiC(0001) slab models were constructed by fixing Featoms at the positions of the bright spots and placing O atomsin either tetrahedral or octahedral coordination. The thickness ofthe vacuum layer was set to 2 nm, and the bottom carbon atomsof SiC were terminated with hydrogen atoms. A cutoff energy of30 Ha and a k-point sampling of 4 × 4 × 1 were used for the self-consistent f ield calculations. Structural optimization was carriedout until the residual forces were below 2 × 10− 4 Ha Bohr− 1 . The HAADF-STEM images were simulated using the multi-slice simulation program xHREM. The simulation parametersincluded an acceleration voltage of 200 kV, a detection anglerange of 68–280 mrad, a spherical aberration coefficient of0.001 mm, and a defocus value of 0 nm. 4.9 Mössbauer Spectroscopy The magnetic properties of the sample were investigated by CEMS[ 68, 75 ]. Since this technique requires the use of the 57 Fe isotope,we first prepared a sample using a 57 Fe source following the aboveprocedure. A conventional 57 Co radioisotope emitting γ-rays withan energy of 14.413 keV was employed as the γ-ray source. The γ-rays were directed perpendicular to the sample surface. Internalconversion electrons emitted upon the excitation of the 57 Fenuclei were detected using a sealed-off proportional counter filledwith rare gases [ 75 ]. The measurements were conducted at roomtemperature and 100 K. An inhomogeneity in the magnetic fieldwas taken into consideration for the spectral fit of the iron oxidecomponent. Author Contributions R.S. designed the experiments, performed sample preparation andcharacterizations (Raman spectroscopy, AFM, XPS, and TEM/STEM),conducted DFT calculations, and analyzed data under the support anddirection of T.T. and W.N. T.K. conducted CEMS measurements andanalyzed data under the direction of K.F. T.I. conducted LEED and ARPESmeasurements. R.S. wrote the whole manuscript with input from allauthors. Acknowledgements We acknowledge K. Yaji, S. Tsuda, F. Arai, and S. Ichinokura at NIMS fortheir insightful discussions. This work was supported by JSPS KAKENHIGrants Nos. JP22KJ1535, JP25K17917, and JP21K14500. This work was alsosupported by a Doctoral Research Expense Grant by the Graduate Schoolof Engineering, Nagoya University. This work was partly carried out atthe Joint Research Center for Environmentally Conscious Technologiesin Materials Science (Project No. 02105) at ZAIKEN, Waseda University.The authors also acknowledge receipt of JAEA Funds at the President’sdiscretion. TEM and STEM observations were carried out at the HighVoltage Electron Microscope Laboratory (HVEM) in Nagoya University.The ARPES experiments using synchrotron light were conducted atAichiSR BL7U (Proposal No. 202304112). This work was carried out underthe support of the Isotope Science Center, The University of Tokyo. Conflicts of Interest The authors declare no conflicts of interest. Small Methods, 2026e Commons LicenseDT  cR C2  D13  C  N4  G5  a  R6  M  M7  R  38  T9  GA1  W  11  u  T  (1  S  G  D1  C  U1  “  I1  f1  L  71  A  P1  G  R  d1  i  G                                        S 23669608, 2026, 8, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/smtd.202501889 by National Institute For, Wiley Online Library on [23/04/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creativata Availability Statement he data that support the findings of this study are available from theorresponding author upon reasonable request. eferences 1 . J. Zhou, J. Lin, X. Huang, et al., “A Library of Atomically Thin Metalhalcogenides,” Nature 556 (2018): 355–359.  . B. Y. Zhang, K. Xu, Q. Yao, et al., “Hexagonal Metal Oxide Monolayerserived from the Metal–Gas Interface,”Nature Materials 20 (2021): 1073–078.  . Z. Zhao, Z. Fang, X. 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Small Methods, 2026ive Commons License 2D Iron Oxide at the Graphene/SiC(0001) Interface 1 | Introduction 2 | Results and Discussion 2.1 | Comparison of Two Annealing Methods 2.1.1 | Evolution of Raman Spectrum 2.1.2 | Evolution of XPS Spectra 2.1.3 | Atomic-Scale Observation of the Interface 2.1.4 | Formation Mechanism 2.2 | Electronic Structure of QFMLG 2.3 | Structural Analysis of the Graphene/SiC Interface 2.4 | Magnetic Structure of the Interfacial 2D Iron Oxide 3 | Conclusions 4 | Experimental Section 4.1 | Preparation of the Buffer Layer 4.2 | Deposition of Fe and Subsequent Annealing 4.3 | Raman Spectroscopy 4.4 | AFM 4.5 | XPS 4.6 | Cross-Sectional TEM/STEM 4.7 | LEED and ARPES 4.8 | Theoretical Calculations and Simulations 4.9 | Mössbauer Spectroscopy Author Contributions Acknowledgements Conflicts of Interest Data Availability Statement References Supporting Information