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The outstanding properties of graphene, a single graphite layer, render it a top candidate for substituting silicon in future electronic devices. The so far exploited synthesis approaches, however, require conditions typically achieved in specialized laboratories and result in graphene sheets whose electronic properties are often altered by interactions with substrate materials. The development of graphene-based technologies requires an economical fabrication method compatible with mass production. Here we demonstrate for the fist time the feasibility of graphene synthesis on commercially available cubic SiC/Si substrates of >300 mm in diameter, which result in graphene flakes electronically decoupled from the substrate. After optimization of the preparation procedure, the proposed synthesis method can represent a further big step toward graphene-based electronic technologies.

To use efficiently the magnetic functionalities emerging at the surfaces or interfaces of novel lanthanides-based materials, there is a need for complementary methods to probe the atomic-layer resolved magnetic properties. Here, we show that 4f photoelectron spectroscopy is highly sensitive to the collective orientation of 4f magnetic moments and, thus, a powerful tool for characterizing the related properties. To demonstrate this, we present the results of systematic study of a family of layered crystalline 4f-materials, which are crystallized in the body-centered tetragonal ThCr

Oxygen reduction reaction (ORR) is a crucial process that drives the operation of several energy storage devices. ORR can proceed on the neat carbon surface in the absence of a catalyst, and its electrochemical activity is determined by its microstructure and chemical composition. Oxygen functional groups unavoidably existing on the carbon surface can serve as adsorption sites for ORR intermediates; the presence of some oxygen functionalities gives rise to an increase in the density of electronic states (DOS) at the Fermi level (FL). Both factors should have a positive impact on the electron transfer rate that was demonstrated for ORR in aqueous media. To study the O-groups effect on the aprotic ORR, which is now of interest due to the extensive development of aprotic metal-air batteries, we use model oxidized carbon electrodes (HOPG and single-layer graphene). We demonstrate that oxygen functionalities (epoxy, carbonyl, and lactone) do not affect the rate of one-electron oxygen reduction in aprotic media in the absence of metal cations since their introduction practically does not increase DOS at FL. However, in Li+-containing electrolytes, oxygen groups enhance both the rate of second electron transfer and carbon degradation due to its oxidation by LiO2 yielding carbonate species.

In pnictide RbEuFe4As4, superconductivity sets in at 36 K and coexists, below 15-19 K, with the long-range magnetic ordering of Eu 4f spins. Here we report scanning tunneling experiments performed on cold-cleaved single crystals of the compound. The data revealed the coexistence of large Rb-Terminated and small Eu-Terminated terraces, both manifesting 1 × 2 and 2×2 reconstructions. On 2×2 surfaces, a hidden electronic order with a period â 5 nm was discovered. A superconducting gap of â 7 meV was seen to be strongly filled with quasiparticle states. The tunneling spectra compared with density functional theory calculations confirmed that flat electronic bands due to Eu 4f orbitals are situated â 1.8 eV below the Fermi level and thus do not contribute directly to Cooper pair formation.

We present a comparative study of oxygen intercalation under polycrystalline and highly ordered graphene samples on the Co(0001) surface, which are relevant for magnetic applications. A comprehensi...

In-plane heterostructures of hexagonal boron nitride (h-BN) and graphene (Gr) have recently appeared in the focus of material science research owing to their intriguing and tunable electronic properties. However, disclosure of the atomic structure and properties of one-dimensional heterojunctions between Gr and h-BN domains remains a largely unexplored and challenging task. Here, we report an approach to obtain a perfectly oriented and atomically thin hybrid h-BN–Gr heterolayer on the Co(0001) surface. A perfect matching of the lattice parameters ensures an epitaxial growth of both Gr and h-BN on the close-packed Co surface. High crystalline quality of the resulting interface allowed us to uncover the structural and electronic properties of the lateral h-BN/Gr heterojunctions by means of complementary microscopic and spectroscopic techniques. In particular, we established the coexistence of two types of zigzag boundaries made of B–C bonds, while the boundaries with N–C bonds were found to be unfavorable. ...

The f-driven temperature scales at the surfaces of strongly correlated materials have increasingly come into the focus of research efforts. Here, we unveil the emergence of a two-dimensional Ce Kondo lattice, which couples ferromagnetically to the ordered Co lattice below the P-terminated surface of the antiferromagnet CeCo

Spin–orbit coupling induces a unique form of Zeeman interaction in momentum space in materials that lack inversion symmetry: the electron’s spin is locked on an effective magnetic field that is odd in momentum. The resulting interconnection between the electron’s momentum and its spin leads to various effects such as electric dipole spin resonance, anisotropic spin relaxation and the Aharonov–Casher effect, but also to electrically driven and optically driven spin galvanic effects. Over the past 15 years, the emergence of topological materials has widened this research field by introducing complex forms of spin textures and orbital hybridization. The vast field of Rashba-like physics is now blooming, with great attention paid to non-equilibrium mechanisms such as spin-to-charge conversion, but also to nonlinear transport effects. This Review aims to offer an overview of recent progress in the development of condensed matter research that exploits the unique properties of spin–orbit coupling in non-centrosymmetric heterostructures., P.N. acknowledges the support of the ETH Zurich Postdoctoral Fellowship Program 19-2 FEL-61. A.M. acknowledges support from the Excellence Initiative of Aix-Marseille Université–A*Midex, a French ‘Investissements d’Avenir’ program.

New temperature scales and remarkable differences from bulk properties have increasingly placed the surfaces of strongly correlated f materials into the focus of research activities. Applying first-principles calculations and angle-resolved photoelectron spectroscopy measurements, a strong Rashba effect and spin-split surface states at the CeIn surface of the heavy-fermion superconductor CeIrIn5 are revealed. The unveiled 4f-derived electron landscape is remarkably distinct for surface and bulk Ce implying the existence of novel temperature scales near the surface region in this material. These results show that ab initio calculations can reliably predict the unusual electronic and spin structure of surfaces of strongly correlated 4f systems where Rashba spin-orbit-coupling phenomena emerge. It is suggested that the structural blocks of such materials can be combined with magnetically active layers for engineering of novel nanostructural objects with appropriate substrates where the diversity of f-driven properties can be applied for the development of novel functionalities., This work was supported by the German Research Foundation (DFG) through Grants No. KR3831/5-1, No. LA655/20-1, No. SFB1143 (Project No. 247310070), and No. 0519ODR. The authors acknowledge support from the Russian Foundation for Basic Research (Grant No. 20-32-70127) and Saint-Petersburg State University (Grant No. ID 73028629). The authors acknowledge MAX IV Laboratory for time on Beamline Bloch under Proposal 20200640. Research conducted at MAX IV, a Swedish national user facility, was supported by the Swedish Research council under contract 2018-07152, the Swedish Governmental Agency for Innovation Systems under contract 2018-04969, and Formas under contract 2019-02496. The authors acknowledge support from a government research assignment for ISPMS SB RAS (Project FWRW-2019-0032).

BiPd is a noncentrosymmetric superconductor with Dirac-like surface states on both (010) and ( 0 1 ¯ 0 ) faces. The Dirac cone on (010) surface is intense and appears at 0.66 eV binding energy. These states have drawn much attention due to contradictory reports on dimensionality and the momentum of these Dirac fermions. We have studied the properties of these Dirac fermions using varied photon energies and different experimental conditions. The behavior of the Dirac cone is found to be two-dimensional. In addition, we found few more surface states appearing at higher binding energies compared to the Dirac cone.

The f-driven temperature scales at the surfaces of strongly correlated materials have increasingly come into the focus of research efforts. Here, we unveil the emergence of a two-dimensional Ce Kondo lattice, which couples ferromagnetically to the ordered Co lattice below the P-terminated surface of the antiferromagnet CeCo2P2. In its bulk, Ce is passive and behaves tetravalently. However, because of symmetry breaking and an effective magnetic field caused by an uncompensated ferromagnetic Co layer, the Ce 4f states become partially occupied and spin-polarized near the surface. The momentum-resolved photoemission measurements indicate a strong admixture of the Ce 4f states to the itinerant bands near the Fermi level including surface states that are split by exchange interaction with Co. The temperature-dependent measurements reveal strong changes of the 4f intensity at the Fermi level in accordance with the Kondo scenario. Our findings show how rich and diverse the f-driven properties can be at the surface of materials without f-physics in the bulk., This work was supported by the German Research Foundation (DFG) through Grant Nos. KR3831/5-1, No. LA655/20-1m, Fermi-NEst, GRK1621, TRR288 (No. 422213477) project A03, and SFB1143 (No. 247310070). We acknowledge support from the Spanish Ministry of Science and Innovation (Project No. PID2020-116093RB-C44, funded by MCIN/AEI/10.13039/501100011033). We also acknowledge funding from the Austrian Science Fund (FWF) (Project No. I 5384-N). I.P.R. acknowledges support from the Ministry of Education and Science of the Russian Federation within State Task No. 0721-2020-0033 (in the part of the ab initio surface electronic structure study). D.Yu.U. acknowledges support from the Saint-Petersburg State University (Grant No. ID 90383050). We acknowledge Diamond Light Source for time on Beamline I05 under Proposal SI24339 and the Paul Scherrer Institut, Villigen, Switzerland for provision of synchrotron radiation beamtime at beamline SIS-ULTRA of the SLS.

Boron Nitride Nanostripes In article number 2101455, Khadiza Ali, J. Enrique Ortega, Frederik Schiller, and co‐workers explore a novel approach to nanopatterning a material with practical technological impact, namely growing hexagonal boron nitride (hBN) mono‐layers on vicinal surfaces. hBN forms a continuous atomically‐thin carpet on a curved rhodium (Rh) crystal, revealing a transformation from 2D to 1D electronic band structure at the Rh(337) orientation through electron scattering at N‐step‐Rh interface bonding points. [Image: see text]

Monolayer hexagonal boron nitride (hBN) is attracting considerable attention because of its potential applications in areas such as nano- and opto-electronics, quantum optics and nanomagnetism. However, the implementation of such functional hBN demands precise lateral nanostructuration and integration with other two-dimensional materials, and hence, novel routes of synthesis beyond exfoliation. Here, a disruptive approach is demonstrated, namely, imprinting the lateral pattern of an atomically stepped one-dimensional template into a hBN monolayer. Specifically, hBN is epitaxially grown on vicinal Rhodium (Rh) surfaces using a Rh curved crystal for a systematic exploration, which produces a periodically textured, nanostriped hBN carpet that coats Rh(111)-oriented terraces and lattice-matched Rh(337) facets with tunable width. The electronic structure reveals a nanoscale periodic modulation of the hBN atomic potential that leads to an effective lateral semiconductor multi-stripe. The potential of such atomically thin hBN heterostructure for future applications is discussed., The authors acknowledge financial support from the Spanish Ministry of Science and Innovation (Grants MAT-2017-88374-P, PID2019-107338RB-C63, MAT2017-88492-R, and Severo Ochoa CEX2019-000910-S), the CSIC (Grant 2020AEP178), the Basque Government (Grant IT-1255-19), the Marie Sklodowska-Curie European Union's Horizon 2020 program (grant MagicFACE 797109), the European Research Council (Advanced Grant 789104-eNANO), and Elettra Sincrotrone Trieste for providing access to its synchrotron radiation facilities. I.P. and F.B. acknowledge funding from EUROFEL, and D.U. from the Ministry of Science and Higher Education of the Russian Federation [Grant No. 075-15-2020-797 (13.1902.21.0024)]. A.A.M. acknowledges the German Ministry for Education and Research (Grant 05K19KER).

Typically, topological superconductivity is reachable via proximity effect by a direct deposition of superconductor (S) on top of a topological insulator (TI) surface. Here we observed and analyzed the double critical current in the Josephson junctions based on the topological insulator in the fabricated planar Superconducting Quantum Interference Device. By measuring critical currents as a function of temperature and magnetic field, we show that the second critical current stems from the intrinsic superconductivity of the S/TI interface, which is supported by the modified Resistively Shunted Junction model and Transmission Electron Microscopy studies. This complex structure of the interface should be taken into account when technological process involves Ar-plasma cleaning.

The development of materials that are non-magnetic in the bulk but exhibit two-dimensional (2D) magnetism at the surface is at the core of spintronics applications. Here, we present the valence-fluctuating material EuIrSi, where in contrast to its non-magnetic bulk, the Si-terminated surface reveals controllable 2D ferromagnetism. Close to the surface the Eu ions prefer a magnetic divalent configuration and their large 4f moments order below 48 K. The emerging exchange interaction modifies the spin polarization of the 2D surface electrons originally induced by the strong Rashba effect. The temperature-dependent mixed valence of the bulk allows to tune the energy and momentum size of the projected band gaps to which the 2D electrons are confined. This gives an additional degree of freedom to handle spin-polarized electrons at the surface. Our findings disclose valence-fluctuating rare-earth based materials as a very promising basis for the development of systems with controllable 2D magnetic properties which is of interest both for fundamental science and applications., This work was supported by the German Research Foundation (DFG) through Grants No. KR3831/5-1, No. LA655/20-1 and Fermi-NEst. Support was provided by the Spanish Ministry of Science, Innovation and Universities (Project No. FIS2016-76617-P and No. FIS2016-75862-P). We acknowledge financial support from the Spanish Ministry of Economy (MAT-2017-88374-P). The authors also acknowledge support by Saint Petersburg State University (Grant No. 15.61.202.2015) and Tomsk State University Academic D. I. Mendeleev Fund Program (Research Grant No. 8.1.01.2018). We acknowledge Diamond Light Source for access to beamline I05 (proposals no. SI18844-1 and SI17761-1) that contributed to the results presented here.

In the novel stoichiometric iron-based material ${\mathrm{RbEuFe}}_{4}{\mathrm{As}}_{4}$, superconductivity coexists with a peculiar long-range magnetic order of Eu 4f states. Using angle-resolved photoemission spectroscopy, we reveal a complex three-dimensional electronic structure and compare it with density functional theory calculations. Multiple superconducting gaps were measured on various sheets of the Fermi surface. High-resolution resonant photoemission spectroscopy reveals magnetic order of the Eu 4f states deep into the superconducting phase. Both the absolute values and the anisotropy of the superconducting gaps are remarkably similar to the sibling compound without Eu, indicating that Eu magnetism does not affect the pairing of electrons. A complete decoupling between Fe- and Eu-derived states was established from their evolution with temperature, thus unambiguously demonstrating that superconducting and a long-range magnetic orders exist independently from each other. The established electronic structure of ${\mathrm{RbEuFe}}_{4}{\mathrm{As}}_{4}$ opens opportunities for the future studies of the highly unorthodox electron pairing and phase competition in this family of iron-based superconductors with doping.

In a Kondo lattice, the Luttinger theorem requires the $f$ electron degree of freedom to enter the Fermi volume in the strong-coupling regime, while the $f$ electron remains nearly localized. A common hypothesis assumes that the Fermi volume shrinks with increasing temperature when the $f$ electron decouples from the Fermi surface with the breakdown of the Kondo lattice effect. However, experimental evidence for this phenomen is still very scarce. Here, the authors demonstrate the reconstruction of the Fermi surface between 14 and 300 K from $l\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}g\phantom{\rule{0}{0ex}}e$ to $s\phantom{\rule{0}{0ex}}m\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}l$ in the prototypical Kondo lattice YbRh${}_{2}$Si${}_{2}$ by Compton scattering.

We present a combined experimental and theoretical study of the two-dimensional electron states at the iridium-silicide surface of the antiferromagnet GdIr2Si2 above and below the Neel temperature. Using angle-resolved photoemission spectroscopy (ARPES) we find a significant spin-orbit splitting of the surface states in the paramagnetic phase. By means of ab initio density-functional-theory (DFT) calculations we establish that the surface electron states that reside in the projected band gap around the M¯ point exhibit very different spin structures which are governed by the conventional and the cubic Rashba effect. The latter is reflected in a triple spin winding, i.e., the surface electron spin reveals three complete rotations upon moving once around the constant energy contours. Below the Neel temperature, our ARPES measurements show an intricate photoemission intensity picture characteristic of a complex magnetic domain structure. The orientation of the domains, however, can be clarified from a comparative analysis of the ARPES data and their DFT modeling. To characterize a single magnetic domain picture, we resort to the calculations and scrutinize the interplay of the Rashba spin-orbit coupling field with the in-plane exchange field, provided by the ferromagnetically ordered 4f moments of the near-surface Gd layer. (Less)

Graphene growth and doping are well studied on flat surfaces of various materials. To further advance the technological implementation of graphene-based systems, fundamental studies need more appropriate model templates, whose surfaces would mimic substrates with non-trivial topography. Here, using electron and photoelectron diffraction and photoemission spectroscopy as well, we demonstrate how a curved tungsten crystal covered by a thin nickel film can properly be used as such platform, allowing the fabrication and comprehensive characterization of nitrogen-doped graphene. We show the way in which nitrogen impurities prefer to embed into the graphene matrix at different areas of the curved metallic surface with variable density of atomic steps. In particular, at atomically flat regions with a strong graphene-metal interaction, pyridinic configuration is the most abundant form of dopants, while graphitic nitrogen strongly dominates in places with a weak coupling of graphene to the substrate, i.e., in the vicinity of the surface irregularities. We recognize single crystals with curvilinear surfaces as versatile platforms for the studies of not only low-dimensional materials, but also molecular adsorption, chemical reactions and catalysis on surfaces with complex structure., The authors acknowledge RFBR for research Grants No. 18-29-19178 and No. 19-32-90013, and SPbU Grant No. 73028629. A. M. acknowledges BMBF Grant No. 05K19KER. F. S., D. V. V. and J. E. O. acknowledge the Spanish Ministry of Science and Innovation (Grants MAT-2017-88374-P), Consejo Superior de Investigaciones Cientificas (Grant 2020AEP178) and the Basque Government (Grant IT-1255-19). The authors thank the Helmholtz-Zentrum Berlin für Materialien und Energie for support within the bilateral Russian-German Laboratory program. This work was supported by the German-Russian Interdisciplinary Science Center (G-RISC: M-2019b-13_r) funded by the German Federal Foreign Office via the German Academic Exchange Service (DAAD).

The design of new composite materials using extreme biomimetics is of crucial importance for bioinspired materials science. Further progress in research and application of these new materials is impossible without understanding the mechanisms of formation, as well as structural features at the molecular and nano-level. It presents a challenge to obtain a holistic understanding of the mechanisms underlying the interaction of organic and inorganic phases under conditions of harsh chemical reactions for biopolymers. Yet, an understanding of these mechanisms can lead to the development of unusual—but functional—hybrid materials. In this work, a key way of designing centimeter-scale macroporous 3D composites, using renewable marine biopolymer spongin and a model industrial solution that simulates the highly toxic copper-containing waste generated in the production of printed circuit boards worldwide, is proposed. A new spongin–atacamite composite material is developed and its structure is confirmed using neutron diffraction, X-ray diffraction, high-resolution transmission electron microscopy/selected-area electron diffraction, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and electron paramagnetic resonance spectroscopy. The formation mechanism for this material is also proposed. This study provides experimental evidence suggesting multifunctional applicability of the designed composite in the development of 3D constructed sensors, catalysts, and antibacterial filter systems.

Quantum materials having Dirac fermions in conjunction with superconductivity is believed to be the candidate material to realize exotic physics as well as advanced technology. Angle-resolved photoemission spectroscopy (ARPES), a direct probe of the electronic structure, has been extensively used to study these materials. However, experiments often exhibit conflicting results on dimensionality and momentum of the Dirac fermions (e.g., Dirac states in BiPd, a novel noncentrosymmetric superconductor), which is crucial for the determination of the symmetry, time-reversal invariant momenta, and other emerging properties. Employing high-resolution ARPES at varied conditions, we demonstrated a methodology to identify the location of the Dirac node accurately and discover that the deviation from two dimensionality of the Dirac states in BiPd proposed earlier is not a material property. These results helped to reveal the topology of the anisotropy of the Dirac states accurately. We have constructed a model Hamiltonian considering higher-order spin-orbit terms and demonstrate that this model provides an excellent description of the observed anisotropy. Intriguing features of the Dirac states in a noncentrosymmetric superconductor revealed in this study are expected to have significant implications regarding the properties of topological superconductors.

We present and discuss the methodology for modeling $4f$ photoemission spectra, $4f$ photoelectron diffraction (PED) patterns, and magnetic dichroism effects for rare-earth-based materials. Using PED and magnetic dichroism in photoemission, we explore the electronic and magnetic properties of the near-surface region of the valence-fluctuating material ${\mathrm{EuIr}}_{2}{\mathrm{Si}}_{2}$. For the Eu-terminated surface, we found that the topmost Eu layer is divalent and exhibits a ferromagnetic order below 10 K. The valency of the next Eu layer, that is the fifth atomic layer, is about 2.8 at low temperature that is close to the valency in the bulk. The properties of the Si-terminated surface are drastically different. The first subsurface Eu layer (fourth atomic layer below the surface) behaves divalently and orders ferromagnetically below 48 K. Experimental data indicate, however, that there is an admixture of trivalent Eu in this layer, resulting in its valency of about 2.1. The next deeper lying Eu layer (eighth atomic layer below the surface) behaves mixed valently, but the estimated valency of 2.4 is notably lower than the value in the bulk. The presented approach and obtained results create a background for further studies of exotic surface properties of $4f$-based materials, and allow us to derive information related to valency and magnetism of individual rare-earth layers in a rather extended area near the surface.

In pnictide RbEuFe

Antiferromagnets may hold potential as spintronic devices due to their robustness to external magnetic fields, if a suitable control method is realised. Here, a transient rotation of the global spin arrangement of GdRh(2)Si(2)is demonstrated via femtosecond optical excitation. A central prospect of antiferromagnetic spintronics is to exploit magnetic properties that are unavailable with ferromagnets. However, this poses the challenge of accessing such properties for readout and control. To this end, light-induced manipulation of the transient ground state, e.g. by changing the magnetic anisotropy potential, opens promising pathways towards ultrafast deterministic control of antiferromagnetism. Here, we use this approach to trigger a coherent rotation of the entire long-range antiferromagnetic spin arrangement about a crystalline axis in GdRh(2)Si(2)and demonstrate deterministic control of this rotation. Our observations can be explained by a laser-induced shift of the direction of the Gd spins' local magnetic anisotropy, and allow for a quantitative description of the transient magnetic anisotropy potential.

Spin-orbit interaction and structure inversion asymmetry in combination with magnetic ordering is a promising route to novel materials with highly mobile spin-polarized carriers at the surface. Spin-resolved measurements of the photoemission current from the Si-terminated surface of the antiferromagnet TbRh2Si2 and their analysis within an ab initio one-step theory unveil an unusual triple winding of the electron spin along the fourfold-symmetric constant energy contours of the surface states. A two-band k⋅p model is presented that yields the triple winding as a cubic Rashba effect. The curious in-plane spin-momentum locking is remarkably robust and remains intact across a paramagnetic-antiferromagnetic transition in spite of spin-orbit interaction on Rh atoms being considerably weaker than the out-of-plane exchange field due to the Tb 4f moments., This work was supported by the German Research Foundation (Grants No. KR-3831/5-1, No. LA655/20-1, GRK1621, Fermi-NESt No. ANR-16-CE92-0018, and SFB1143, project-id 247310070) and the Spanish Ministry of Science, Innovation, and Universities (Grant Nos. FIS2016-76617-P and MAT-2017-88374-P). We also acknowledge funding from the Department of Education of the Basque government (Grant No. IT1164-19), St. Petersburg State University (Project ID 51126254), and the Russian Foundation for Basic Research (Grant No. 20-32-70127). The SR-ARPES experiments at HiSOR were performed with the approval of the Proposal Assessing Committee of the Hiroshima Synchrotron Radiation Center (Proposal No. 18BG023). We also acknowledge the Impuls-und Vernetzungsfonds der Helmholtz Gemeinschaft (Grant No. HRSF-0067)

The emergence of ferromagnetism in Rashba systems, where the evolving exchange interaction enters into competition with spin-orbit coupling, leads to a nontrivial spin-polarized electronic landscape with an intricate momentum-dependent spin structure, which is challenging to unveil. Here, we show a way to disentangle the contributions from the effective spin-orbit and exchange fields and thus to gain knowledge of the spin structure in ferromagnetic Rashba materials, which is required for spintronic applications. Our approach is based exclusively on spin-integrated photoemission measurements combined with a two-band modeling. As an example, we consider the mixed-valent material EuIr2Si2 which, while being nonmagnetic in the bulk, reveals strong ferromagnetism at the iridium-silicide surface where both spin-orbit and exchange magnetic interactions coexist. The combined effect of these interactions causes a complex band dispersion of the surface state which can be observed in photoemission experiments. Our method allows us to comprehensively unravel the surface-state spin structure driven by spin-orbit coupling at the ferromagnetic surface. This approach opens up opportunities to characterize the spin structure of ferromagnetic Rashba materials, especially where dedicated spin-resolved measurements remain challenging., This work was supported by Saint Petersburg State University (Grant No. ID 51126254) and the Russian Foundation for Basic Research (Grant No. 20-32-70127). We acknowledge financial support from the Spanish Ministry of Economy (No. MAT-2017-88374-P) and the German Research Foundation (DFG) through Grants No. LA655/20-1, No. KR3831/5-1, and Fermi-NEst. We acknowledge Diamond Light Source for access to beamline I05 (Proposals No. SI18844-1 and No. SI17761-1).

Titanium carbide attracts growing interest as a substrate for graphene growth and as a component of the composite carbon materials for supercapacitors, an electrode material for metal-air batteries. For all these applications, the surface chemistry of titanium carbide is highly relevant and being, however, insufficiently explored especially at atomic level is a subject of our studies. Applying X-ray photoelectron spectroscopy (XPS) to clean (111) and (755) surfaces of TiC, we were able to obtain the detailed spectroscopic pattern containing information on the plasmon structure, shake up satellite, the peak asymmetry and, finally, surface core level shift (SCLS) in C 1s spectra. The latter is essential for further precise studies of chemical reactions. Later on, we studied interface between TiC (111) and (755) and graphene and found the SCLS variation due to strong chemical interaction between graphene and substrate. This interaction is also reflected in the peculiar band structure of graphene probed by angle-resolved photoelectron spectroscopy (ARPES). Based on LEED data the structure is close to (7√3 × 7√3)R30°, with graphene being slightly corrugated. We found that similarly to the graphene on metals, the chemical interaction between graphene and TiC can be weakened by means of intercalation of oxygen atoms underneath graphene., We thank Helmholtz-Zentrum Berlin (HZB) for the allocation of synchrotron radiation beamtimes at the Russian-German and UE112-PGM2 beamlines. The work was financially supported by the Russian Science Foundation (project 16-42-01093). DFT calculations were performed at “Lomonosov” MSU supercomputer.

A new method for synthesis of graphene-protected iron silicides has been tested, which consists in formation of graphene on Ni(111) followed by two-step intercalation of the system with Fe and Si. Characterization of the samples was performed in situ by low-energy electron diffraction, angular-resolved photoelectron spectroscopy, core-level photoelectron spectroscopy with synchrotron radiation and magnetic linear dichroism in photoemission of Fe 3p electrons. It is shown, that at 400 °C the intercalation of graphene/Ni(111) with iron occurs in a range up to 14 ML. The graphene layer strongly interacts with the topmost Fe atoms and stabilizes the fcc structure of the film. The in-plane ferromagnetic ordering of the film has a threshold nature and arises after the intercalation of 5 ML Fe due to the thickness-driven spin reorientation transition. Subsequent intercalation of graphene/Fe/Ni(111) with Si leads to the formation of the inhomogeneous system consisted of intercalated and nonintercalated areas. The intercalated islands coalesce at 2 ML Si when a Fe-Si solid solution covered with the Fe3Si surface silicide is formed. The Fe3Si silicide is ferromagnetic and has an ordered (√3 × √3)R30° structure. The graphene layer is weakly electronically coupled to the silicide phase keeping its remarkable properties ready for use.

We present a first-principles study of the ${\mathrm{GdRh}}_{2}{\mathrm{Si}}_{2}$(001) surface electronic structure. Two surfaces, Si- and Gd-terminated, are considered. The origin of the two-dimensional (2D) electronic states at both terminations is investigated by tracing the band structure evolution by going from individual Si, Rh, and Gd atomic layers to (non)stoichiometric ultrathin films and, finally, to thicker ${\mathrm{GdRh}}_{2}{\mathrm{Si}}_{2}$ slabs. We find the conic-like (Dirac-like) resonance state located in the vicinity of the $\overline{\mathrm{\ensuremath{\Gamma}}}$ point at the Si termination to form via the Tamm mechanism and explain the reasons for the differences in dispersion and energy position of the resonance states at the Si and Gd terminations. Then, we show how the butterfly-like dispersion of the Shockley state, residing in the bulk projected band gap near the $\overline{\mathrm{M}}$ point, appears due to the interaction of the bands localized in the surface and subsurface Gd-Si-Rh-Si blocks of the Si termination. Also, a giant sign-alternating atomic relaxation near both the Si- and Gd-terminated surfaces is revealed and its effect on the dispersion and energy position of the 2D states is discussed. In this way we shed light on the origin of the 2D states and explain their dispersion seen in angle-resolved photoemission spectroscopy experiments.

Angle-resolved secondary electron emission spectra were analyzed for studying the electron transmission properties of graphene when it is tightly bound to a metallic substrate and when it is decoupled from the latter. As respective model systems, graphene/Ni(111) and graphene/Au/Ni(111) were considered. We discovered two types of spectral structures linked with the transmission properties of graphene: bands related to scattering resonances and to umklapp reflection. These findings are interpreted based on an ab initio theory of the scattering of the outgoing electrons by the graphene overlayers. The experimental secondary electron emission maps are in good agreement with the calculations, indicating that such approach can be successfully applied for studying the electron transmission properties of a variety of two-dimensional materials.

Application of the Luttinger theorem to the Kondo lattice YbRh2Si2 suggests that its large 4f-derived Fermi surface (FS) in the paramagnetic (PM) regime should be similar in shape and volume to that of the divalent local-moment antiferromagnet (AFM) EuRh2Si2 in its PM regime. Here we show by angle-resolved photoemission spectroscopy that paramagnetic EuRh2Si2 has a large FS essentially similar to the one seen in YbRh2Si2 down to 1 K. In EuRh2Si2 the onset of AFM order below 24.5 K induces an extensive fragmentation of the FS due to Brillouin zone folding, intersection and resulting hybridization of the Fermi-surface sheets. Our results on EuRh2Si2 indicate that the formation of the AFM state in YbRh2Si2 is very likely also connected with similar changes in the FS, which have to be taken into account in the controversial analysis and discussion of anomalies observed at the quantum critical point in this system., This work was supported by the German Research Foundation (DFG) (through grant Nos. GE 602/4-1, KR3831/5-1 and Fermi-NEst; GRK1621 and SFB1143), SaintPetersburg State University under Research Grant 15.61.202.2015, Spanish Ministry of Science and Innovation (Grant No. FIS2016-75862-P), and Tomsk State University Academic D.I. Mendeleev Fund Program (Grant No.8.1.01.2017). The SX-ARPES experiment was performed under Proposal Numbers 2016A3810 and 2018B3811 at SPring-8 BL23SU. The present work was financially supported by JSPS KAKENHI Grant Numbers 16H01084 (J-Physics) and 18K03553.

We study the effect of thermal oxygen exposure on a monolayer of h-BN grown on vicinal Ni surfaces by scanning tunneling microscopy, X-ray absorption, and photoemission spectroscopies. Using a curved Ni crystal, we carry out a systematic exploration of the h-BN monolayer interfacing a full variety of vicinal orientations around the (111) high-symmetry direction. We demonstrate the occurrence of two processes upon oxygen exposure: oxygen intercalation underneath the h-BN layer, which leads to decoupling of the h-BN from the substrate, and oxidation of h-BN itself, which proceeds via substitution of nitrogen atoms. Oxygen intercalation appears to be substrate orientation dependent, while oxidation of h-BN is rather uniform over the different vicinal planes. These findings will be of importance for future applications of BN-based devices and materials under ambient conditions., We are grateful to the Interdisciplinary Resource Center for Nanotechnology of the Research Park of Saint Petersburg State University for performing SEM measurements. A.A.M., C.L., and D.A.S. acknowledge DFG (Grant No. LA655-19/1) and BMBF (Grant No. 05K12OD2). L.F. and A.F. acknowledge financial support within the joint project of the Russian Science Foundation (Project 16-42-01093) and DFG (Grant LA655-17/1). K.A.B. and D.Yu.U. acknowledge Saint Petersburg State University for research Grant 11.65.42.2017 and RFBR (Grant 17-02-00427). We acknowledge financial support from the Spanish Ministry of Economy (Grants MAT-2016-78293-C6 and MAT-2017-88374-P) and Basque Government (Grant IT-1255-19). We acknowledge Helmholtz-Zentrum Berlin für Materialien und Energie for support within the bilateral Russian–German Laboratory program.

The implementation of future graphene-based electronics is essentially restricted by the absence of a band gap in the electronic structure of graphene. Options of how to create a band gap in a reproducible and processing compatible manner are very limited at the moment. A promising approach for the graphene band gap engineering is to introduce a large-scale sublattice asymmetry. Using photoelectron diffraction and spectroscopy we have demonstrated a selective incorporation of boron impurities into only one of the two graphene sublattices. We have shown that in the well-oriented graphene on the Co(0001) surface the carbon atoms occupy two nonequivalent positions with respect to the Co lattice, namely top and hollow sites. Boron impurities embedded into the graphene lattice preferably occupy the hollow sites due to a site-specific interaction with the Co pattern. Our theoretical calculations predict that such boron-doped graphene possesses a band gap that can be precisely controlled by the dopant concentration. B-graphene with doping asymmetry is, thus, a novel material, which is worth considering as a good candidate for electronic applications.

Ultrathin (∼2 nm) films of Co 2 FeSi ferromagnetic alloy were formed on silicon by solid-phase epitaxy and studied in situ . Experiments were carried out in an ultrahigh vacuum (UHV) using substrates of Si(1 1 1) single crystals covered with a 5 nm thick CaF 2 barrier layer. The elemental and phase composition as well as the magnetic properties of the synthesized films were analyzed by photoelectron spectroscopy using synchrotron radiation and by magnetic linear dichroism in photoemission of Fe 3 p and Co 3 p electrons. The study shows that the synthesis of the Co 2 FeSi ferromagnetic alloy occurs in the temperature range of 200–400 °C. At higher temperatures, the films become island-like and lose their ferromagnetic properties, as the CaF 2 barrier layer is unable to prevent a mass transfer between the film and the Si substrate, which violates the stoichiometry of the alloy.

Graphene-like nanostructures, solely or in combination with redox active compounds, are an important component of battery electrodes. Design of effective electrode materials requires a deep understanding of electrochemical reactions occurring at graphene surfaces. The methods of X-ray photoelectron spectroscopy (XPS) are very helpful in such research, providing the composition of studied samples and electronic state of individual elements. In this chapter, we demonstrate advantages of XPS for monitoring of chemical vapor deposition graphene growth and lithium penetration under graphene layers, disclosing of interactions with metals and interface states.

The magnetic properties of rare earth compounds are usually well captured by assuming a fully localized $f$ shell and only considering the Hund's rule ground state multiplet split by a crystal electric field (CEF). Currently, the standard technique for probing CEF excitations in lanthanides is inelastic neutron scattering. Here we show that with the recent leap in energy resolution, resonant inelastic soft x-ray scattering (RIXS) has become an attractive alternative for looking at CEF excitations. This has been used for studying the CEF scheme in ${\mathrm{CeRh}}_{2}{\mathrm{Si}}_{2}$, a system that has been investigated intensely for more than two decades now but for which no consensus has been reached yet as to its CEF scheme. Using high energy resolution of about 30 meV as well as polarization analysis in the scattered beam, both features that have become available only very recently in RIXS, allowed us to find a unique CEF description for ${\mathrm{CeRh}}_{2}{\mathrm{Si}}_{2}$. The result agrees well with previous inelastic neutron scattering and magnetic susceptibility studies. Due to its strong resonant character, RIXS is applicable to very small samples, presents very high cross sections for all lanthanides, and further benefits from the very weak coupling to phonon excitations. The foreseeable further progress in energy resolution will make this technique increasingly attractive for the investigation of the CEF scheme in lanthanides.

Using photoelectron diffraction and spectroscopy, we explore the structural and electronic properties of the hexagonal boron nitride (h-BN) monolayer epitaxially grown on the Co(0001) surface. Perfect matching of the lattice parameters allows formation of a well-defined interface where the B atoms occupy the hollow sites while the N atoms are located above the Co atoms. The corrugation of the h-BN monolayer and its distance from the substrate were determined by means of R-factor analysis. The obtained results are in perfect agreement with the density functional theory (DFT) predictions. The electronic structure of the interface is characterized by a significant mixing of the h-BN and Co states. Such hybridized states appear in the h-BN band gap. This allows to obtain atomically resolved scanning tunneling microscopy (STM) images from the formally insulating 2D material being in contact with ferromagnetic metal. The STM images reveal mainly the nitrogen sublattice due to a dominating contribution of nitrogen orbitals to the electronic states at the Fermi level. We believe that the high quality, well-defined structure and interesting electronic properties make the h-BN/Co(0001) interface suitable for spintronic applications., L.V.Ya. acknowledges the RSF (Grant No. 16-42-01093). A.V.T., V.O.S., K.A.B., O.Yu.V., and D.Yu.U. acknowledge St. Petersburg State University for research Grant No. 11.65.42.2017. M.V.K. and I.I.O. acknowledge the RFBR (Grant No. 16-29-06410). C.L. acknowledges the DFG (Grant Nos. LA655-17/1 and LA655-19/1).

The structural and electronic properties of hexagonal boron nitride (hBN) grown on stepped Ni surfaces are systematically investigated using a cylindrical Ni crystal as a tunable substrate. Our experiments reveal homogeneous hBN monolayer coating of the entire Ni curved surface, which in turn undergoes an overall faceting. The faceted system is defined by step-free hBN/Ni(1 1 1) terraces alternating with strongly tilted hBN/Ni(1 1 5) or hBN/Ni(1 1 0) nanostripes, depending on whether we have A-type or B-type vicinal surfaces, respectively. Such deep substrate self-organization is explained by both the rigidity of the hBN lattice and the lack of registry with Ni crystal planes in the vicinity of the (1 1 1) surface. The analysis of the electronic properties by photoemission and absorption spectroscopies reveal a weaker hBN/Ni interaction in (1 1 0)- and (1 1 5)-oriented facets, as well as an upward shift of the valence band with respect to the band position at the hBN/Ni(1 1 1) terrace., We acknowledge financial support from the Deutsches Forschungsgemein chaft DFG (Grants LA655-17/1 and LA655-19/1), the Spanish Ministry of Economy (Grants MAT-2016-78293-C6, MAT-2017-88374-P), the Basque Government (Grant IT-1255-19), the Helmholtz-Zentrum Berlin für Materialien und Energie for support within the bilateral RussianGerman Laboratory program as well as from the joint project of the Russian Science Foundation (project 16-42-01093) and DFG (Grant No. LA655-17/1). DYuU acknowledges St. Petersburg State University for research Grant No. 11.65.42.2017 and Russian Foundation for Basic Research RFBR (Project No. 17-02-00427).

Photoelectron diffraction (XPD) and holography (XPH) are powerful spectroscopic methods that allow comprehensive exploration and characterization of certain structural properties of materials, in particular those of 2D systems and interfaces. Recent developments in XPD and XPH are especially impressive when they are applied to partially disordered systems such as intercalation compounds, doped graphene, buffer layers or adsorbates and imperfectly ordered germanene and phoshporene. In our brief review, we sum up the advances in XPD and XPH studies of 2D materials and discuss the unique opportunities granted by these two interrelated methods., The authors acknowledge financial support of the Russian Foundation for Basic Research (Grant No. 16-29-06410). L.V.Ya. and D.Yu.U. acknowledge RSF (Grant No. 16-42-01093). C.L. acknowledges DFG (Grant Nos. LA655-17=1 and LA655-19=1). D.Yu.U. and D.V.V. acknowledge Saint Petersburg State University for research Grant No. 11.65.42.2017.

Recrystallization of bulk materials is a well-known phenomenon, which is widely used in commercial manufacturing. However, for low-dimensional materials like graphene, this process still remains an unresolved puzzle. Thus, the understanding of the underlying mechanisms and the required conditions for recrystallization in low dimensions is essential for the elaboration of routes towards the inexpensive and reliable production of high-quality nanomaterials. Here, we unveil the details of the efficient recrystallization of one-atom-thick pure and boron-doped polycrystalline graphene layers on a Co(0001) surface. By applying photoemission and electron diffraction, we show how more than 90% of the initially misoriented graphene grains can be reconstructed into a well-oriented and single-crystalline layer. The obtained recrystallized graphene/Co interface exhibits high structural quality with a pronounced sublattice asymmetry, which is important for achieving an unbalanced sublattice doping of graphene. By exploring the kinetics of recrystallization for native and B-doped graphene on Co, we were able to estimate the activation energy and propose a mechanism of this process., L. V. Ya. and D. Yu. U. acknowledge the RSF (Grant No. 16-42-01093). V. O. S., K. A. B., O. Yu. V., D. Yu. U. and A. V. F. acknowledge Saint Petersburg State University for research Grant No. 11.65.42.2017. C. L. acknowledges the DFG (Grant No. LA655-17/1 and LA655-19/1). E. R. acknowledges financial support by the BMBF (Grant No. 05K12KE1). The authors thank the Helmholtz-Zentrum Berlin für Materialien und Energie for support within the bilateral Russian–German Laboratory program.

Using angle-resolved photoemission spectroscopy (ARPES), we study the electronic structure and electron-phonon coupling in a Li-doped graphene monolayer decoupled from the Co(0001) substrate by intercalation of silicon. Based on the photoelectron diffraction measurements, we disclose the structural properties of the Si/Co interface. Our density functional theory calculations demonstrate that in the studied Li/graphene/Si/Co system the magnetism of Co substrate induces notable magnetic moments on Li and Si atoms. At the same time graphene remains almost nonmagnetic and clamped between two magnetically active atomic layers with antiparallel magnetizations. ARPES maps of the graphene Fermi surface reveal strong electron doping, which may lead to superconductivity mediated by electron-phonon coupling (EPC). Analysis of the spectral function of photoelectrons reveals apparent anisotropy of EPC in the k space. These properties make the studied system tempting for studying the relation between superconductivity and magnetism in two-dimensional materials., D.Yu.U., D.V.V., and A.V.F. acknowledge SPbU for research Grant No. 11.65.42.2017 and RFBR (Grant No. 17-02-00427). D.Yu.U., I.I.O., and M.V.K. acknowledge RFBR (Grant No. 16-29-06410). C.L. acknowledges DFG (Grant No. LA655-17/1). A.G. and A.V.F. acknowledge ERC Grant No. 648589 “SUPER-2D” and funding from DFG project CRC 1238 (project A1) and DFG project GR 3708/2-1. We acknowledge Helmholtz-Zentrum Berlin für Materialien und Energie for support within the bilateral Russian-German Laboratory program.