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Growth of lithium whiskers or dendrites is the major obstacle towards safe and stable utilization of lithium metal anodes in rechargeable batteries. In this study, we look deeper into the mechanism of lithium electrodeposition. We find that before lithium whisker or dendrite nucleation occurs, lithium is deposited into the grain boundaries of the metal electrode, which we directly observed in the focused ion beam cross-sections of the lithium electrode. The structure of grain boundaries near the surface predetermines the capacity for smooth deposition, which is proportional to the surface area of such boundaries. We then demonstrate that by reducing the metal grain average size we can extend whisker- and dendrite-free deposition of lithium. With a eutectic Ga-Li alloy containing only 2.5 atomic percent of gallium we observed morphologically stable lithium deposition for 10 hours. The results demonstrate deep interconnections between the metal microstructure and the whisker growth.

Magnetic topological insulators (MTIs) have recently become a subject of poignant interest; among them, Z 2 topological insulators with magnetic moment ordering caused by embedded magnetic atoms attract special attention. In such systems, the case of magnetic anisotropy perpendicular to the surface that holds a topologically nontrivial surface state is the most intriguing one. Such materials demonstrate the quantum anomalous Hall effect, which manifests itself as chiral edge conduction channels that can be manipulated by switching the polarization of magnetic domains. In the present paper, we uncover the atomic structure of the bulk and the surface of Mn 0.06 Sb 1.22 Bi 0.78 Te 3.06 in conjunction with its electronic and magnetic properties; this material is characterized by naturally formed ferromagnetic layers inside the insulating matrix, where the Fermi level is tuned to the bulk band gap. We found that in such mixed crystals septuple layers (SLs) of Mn(Bi,Sb) 2 Te 4 form structures that feature three SLs, each of which is separated by two or three (Bi,Sb) 2 Te 3 quintuple layers (QLs); such a structure possesses ferromagnetic properties. The surface obtained by cleavage includes terraces with different terminations. Manganese atoms preferentially occupy the central positions in the SLs and in a very small proportion can appear in the QLs, as indirectly indicated by a reshaped Dirac cone.

Sodium cation solvation Gibbs free energies (Δ G solv (Na + )) have been obtained in water, dimethylformamide, dimethyl sulfoxide, ethanol, acetone, acetonitrile, and methanol through the "monomer cycle" cluster-continuum approach where a solvent reference state is described by infinitely separated molecules. The following steps are vital for obtaining reliable Δ G solv (Na + ) values: (a) a meticulous conformational search involving dispersion corrected density functional theory (DFT-D) and the continuum solvation model (CSM); (b) gas-phase DFT-D geometry optimization followed by single-point (SP) domain-based local pair natural orbital coupled clusters including single, double, and partly triple excitation (DLPNO-CCSD(T)) calculations in conjunction with the complete basis set extrapolation; (c) advanced statistical thermodynamic treatment of the low harmonic frequencies (<100 cm -1 ) to obtain the robust gas-phase Gibbs free energy correction; (d) gas-phase and dielectric continuum SP with non-electrostatic contributions included in the CSM; (e) an evaluation of the relative thermodynamic stability of the Na + (S) n clusters to identify the number of explicit solvent molecules n to be considered. Our refined computational protocol is promising with a Pearson correlation coefficient between the predicted and experimental data, ρ , of 0.82, and the mean signed and mean unsigned errors of 0.3 and 1.4 kcal mol -1 , respectively.

As a semiconductor ferroelectric, GeTe has become a focus of renewed attention due to the recent discovery of giant Rashba splitting. It already has a wide range of applications, from thermoelectricity to data storage. Its stability in ambient air, as well as the structure and properties of an oxide layer, define the processing media for device production and operation. Here, we studied a reaction between the GeTe (111) surface and molecular oxygen for crystals having solely inversion domains. We evaluated the reaction kinetics both ex situ and in situ using NAP XPS. The structure of the oxide layer is extensively discussed, where, according to HAADF-STEM and STEM-EDX, nanoscale phase separation of GeO 2 and Te is observed, which is unusual for semiconductors. We believe that such behaviour is closely related to the ferroelectric properties and the domain structure of GeTe.

Gibbs free energies for Li+ solvation in water, methanol, acetonitrile, DMSO, dimethylacetamide, dimethoxyethane, dimethylformamide, gamma-butyrolactone, pyridine, and sulfolane have been calculated using the cluster-continuum quasichemical theory. With n independent solvent molecules S initial state forming the "monomer" thermodynamic cycle, Li+ solvation free energies are found to be on average 14 kcal mol-1 more positive compared to those from the "cluster" thermodynamic cycle where the initial state is the cluster Sn. We ascribe the inconsistency between the "monomer" and "cluster" cycles mainly to the incorrectly predicted solvation free energies of solvent clusters Sn from the SMD and CPCM continuum solvation models, which is in line with the earlier study of Bryantsev et al., J. Phys. Chem. B, 2008, 112, 9709-9719. When experimental-based solvation free energies of individual solvent molecules and solvent clusters are employed, the "monomer" and "cluster" cycles result in identical numbers. The best overall agreement with experimental-based "bulk" scale lithium cation solvation free energies was obtained for the "monomer" scale, and we recommend this set of values. We expect that further progress in the field is possible if (i) consensus on the accuracy of experimental reference values is achieved; (ii) the most recent continuum solvation models are properly parameterized for all solute-solvent combinations and become widely accessible for testing.

Renewed interest in the ferroelectric semiconductor germanium telluride was recently triggered by the direct observation of a giant Rashba effect and a 30-year-old dream about a functional spin field-effect transistor. In this respect, all-electrical control of the spin texture in this material in combination with ferroelectric properties at the nanoscale would create advanced functionalities in spintronics and data information processing. Here, we investigate the atomic and electronic properties of GeTe bulk single crystals and their (111) surfaces. We succeeded in growing crystals possessing solely inversion domains of ∼10 nm thickness parallel to each other. Using HAADF-TEM we observe two types of domain boundaries, one of them being similar in structure to the van der Waals gap in layered materials. This structure is responsible for the formation of surface domains with preferential Te-termination (∼68%) as we determined using photoelectron diffraction and XPS. The lateral dimensions of the surface domains are in the range of ∼10-100 nm, and both Ge- and Te-terminations reveal no reconstruction. Using spin-ARPES we establish an intrinsic quantitative relationship between the spin polarization of pure bulk states and the relative contribution of different terminations, a result that is consistent with a reversal of the spin texture of the bulk Rashba bands for opposite configurations of the ferroelectric polarization within individual nanodomains. Our findings are important for potential applications of ferroelectric Rashba semiconductors in nonvolatile spintronic devices with advanced memory and computing capabilities at the nanoscale.

Lithium plating-one of the critical processes in the desired high-energy lithium metal batteries-is accompanied by lithium whisker growth, which causes several problems that prevent the employment of metallic lithium anodes in rechargeable systems. They include low coulombic efficiency, electrolyte consumption, and the risk of short circuits, which can lead to thermal runaway of the battery. In recent years several strategies were suggested to mitigate whisker growth. The mechanism of this process, however, still lacks understanding. Here, we reveal the importance of surface diffusion along grain boundaries in solid lithium. We show that, at first, the plating of lithium onto a lithium substrate is possible as bulk crystal growth with a planar crystallization front for the Li grains with oblique (nonperpendicular to the surface) grain boundaries. Further, the developed compressive stress makes lithium diffusion to the grain base unfavorable, and new grains nucleate at the surface. The latter are the cause of the whisker growth from their roots. These findings indicate that the control of grain-boundary diffusion and grain size and structure paves the way to overcome the nonuniform morphology of plated lithium.

The development of high specific energy Li-O 2 batteries faces a problem of poor cycling as a result of passivation of the positive electrode by both the discharge product (Li 2 O 2 ) and side products (Li 2 CO 3 , etc.). The latter are the result of oxidation of the electrode materials or electrolyte components primarily by discharge intermediate superoxide anions (O 2 - ) and, in less degree, by Li 2 O 2 . We report cyclic voltammetry studies of the electrode passivation in different relatively stable solvents. We found that slower passivation is observed for the electrolytes based on high donor number solvents or solvents with high viscosity. Moreover, such behavior is reproduced for three different electrode materials [glassy carbon (GC), TiC, and TiN] that pinpoints the primary role of different oxygen reduction reaction mechanisms (Li 2 O 2 surface deposition or solution growth) influenced by Li + solvation energy and solvent viscosity. The chemistry of interaction between LiO 2 /Li 2 O 2 and the electrode/solvent turns out to be less important. Additionally, we found that, for the electrode made of GC and TiN in all electrolyte solutions, the passivation by side products suppresses oxygen reduction after a certain number of cycles. In contrast, for TiC after several cycles, further passivation does not happen as a result of the formation of a thin and stable TiO 2 layer in high donor number solvents.

The metallic lithium electrode has major concerns such as extremely high reactivity and nonuniform needle-like electrodeposition, limiting its wide application as a negative electrode in secondary batteries. Its reactions with the electrolyte leading to solid electrolyte interphase (SEI) formation play an important role, and controlling its composition and properties can help to overcome both difficulties. Even though solid electrolyte interphase chemistry and properties seem to be well known, many surface chemistry experiments reported are not perfect with respect to the purity needed for Li studies and can be interpreted alternatively. Here, we studied reactions between lithium and propylene carbonate and ethylene carbonate in model reactions realized in an ultra-high vacuum. In addition to the already reported reaction pathway yielding lithium carbonate and semicarbonate, our theoretical (DFT) modeling confirms the preference of alternative routes. Along with the most beneficial final lithium carbonates, dilithium 1,2-dialkoxide (DD) can form barrierlessly as a final product by two-electron transfer. Experimental XPS/NEXAFS studies of gas phase and solid-gas model reactions revealed that in both cases DD is the main reaction product. Understanding of the discovered reaction pathway can also be essential for reactions in liquid electrolytes, although the low electric conductivity of the SEI makes it less probable.

Solid electrolytes are of high interest for the development of advanced electrochemical energy storage devices with all-solid-state architectures. Here, we report the fabrication of the electrolyte membranes based on LiTFSI (LiN(CF 3 SO 2 ) 2 ) and PEO-PVDF blends with improved properties. We show that addition of PVDF enables preparation of free-standing films of the compositions within the so called "crystallinity gap" of the LiTFSI-PEO system known to provide high ion conductivity. We show that optimal PVDF content enables preparation of the films with reasonable elastic modulus and high ionic conductivity of about 0.3 mS cm -1 at 60 °C and about 0.1 mS cm -1 at room-temperature. Combining FTIR spectroscopy, XRD and DSC measurements we show that a noticeable fraction of PVDF remains crystalline and enhances the mechanical properties of the material, and at the same time it additionally promotes LiTFSI dissociation and disordering. Density functional theory calculations showed that the Li + -PEO-PVDF complexation energy magnitude is almost as high as that of Li-PEO complexes, thus the salt dissociation ability can be retained in spite of the introduction of the substantial amounts of PVDF required for mechanical stability., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The development of high-energy lithium-oxygen batteries has significantly slowed by numerous challenges including capacity limitations due to electrode surface passivation by the discharge product Li 2 O 2 . Since the passivation rate and intensity are dependent on the deposit morphology, herein, we focus on the mechanisms governing Li 2 O 2 formation within the porous cathode. We report evidence of homogeneous nucleation of Li 2 O 2 crystallites and their further assembly in bulk of the electrolyte solution in DMSO, which possesses a high donor number. After careful estimation of the superoxide ion concentration distribution within a phenomenological model, it was found that the high stability of superoxide ions formed during the ORR towards disproportionation and sufficient diffusivity of (0.5-1.2) × 10 -6 cm 2 s -1 enabled Li 2 O 2 nucleation and crystallization not only at the surface but also in the electrolyte, and the reaction zone spread throughout the internal space of the porous electrode. High initial supersaturation promoted the homogeneous nucleation of Li 2 O 2 nanoplates, which instantly assembled into mesocrystals also in the solution bulk. These results were supported by operando SAXS/WAXS and morphology observations. Thus, although homogeneous nucleation is not dominant, it is important for achieving a high capacity in Li-O 2 batteries.

Many obstacles impede the development of Li-air batteries for practical applications. In particular, there is lack of understanding of the dynamics of processes occurring in porous air electrodes during discharge, including oxygen transport limitations, pore clogging and electrode passivation by both insulating discharge and parasitic reaction products. Here, using small-angle neutron scattering, which provides information on the whole electrode adequate to electrochemical data, we uncover the mechanisms limiting the Li-O2 porous carbon electrode capacity by analysis of the cathode pore filling in highly and poorly solvating media - dimethyl sulfoxide and acetonitrile. The results obtained allowed us suppose that in both cases the cell death is mainly triggered by blocking of oxygen transport pathways inside carbon black particle agglomerates. Total discharge capacities are, indeed, higher in highly solvating solutions due to a higher discharge intermediate lifetime and longer diffusion distance, which enable Li2O2 formation outside the carbon black agglomerates, which are, as we demonstrated, in fact mesocrystals that are confirmed by the appearance of a diffraction peak in scattering curves.

Embedding foreign atoms in graphene and interchanging the underlying substrate are proved to be efficient methods for manipulating the properties of graphene. Combining ARPES experiments with DFT calculations we show that boron-doped graphene (B-graphene) grown on a Co(0001) substrate by chemical vapor deposition (CVD) becomes hole doped and its Fermi surface near the K-point reveals strongly spin-polarized states. The latter stems from the spin-polarized mini Dirac cone that is an intrinsic two-dimensional feature of the graphene/Co(0001) interface and is formed by a mixture of C 2p z and Co 3d states. Since the CVD method allows the achievement of up to 20 at% of incorporated B atoms, this provides a certain flexibility for handling the spin-polarized properties of the system. We also show that the bonding of the B-graphene layer to the Co(0001) substrate can be released by intercalation of Li into the interface. This allows the exploration of the doping effect in detail. Finally, our ARPES data indicate a gap opening in the Dirac cone as a result of the highly unbalanced boron concentrations in the two graphene sublattices.

Composites of WS 2 nanotubes (NT-WS 2 ) and gold nanoparticles (AuNPs) were prepared using aqueous HAuCl 4 solutions and subjected to surface analysis. The obtained materials were jointly characterized by X-ray photoelectron (XPS), Raman scattering (RSS), and ultraviolet photoelectron (UPS) spectroscopies. Optical extinction spectroscopy and electron energy loss spectroscopy in the scanning transmission electron microscopy regime (STEM-EELS) were also employed to study plasmon features of the nanocomposite. It was found that AuNPs deposition is accompanied by a partial oxidative dissolution of WS 2 , whereas Au-S interfacial species could be responsible for the tight contact of metal nanoparticles and the disulfide. A remarkable sensitivity of n-type resistance of NT-WS 2 and Au-NT-WS 2 to the adsorption of NO 2 gas was also demonstrated at room temperature using periodical illumination by a 530 nm light-emitting diode. Au-NT-WS 2 nanocomposites are found to possess a higher photoresponse and enhanced sensitivity in the 0.25-2.0 ppm range of NO 2 concentration, as compared to the pristine NT-WS 2 . This behaviour is discussed within the physisorption-charge transfer model to explore sensing properties of the nanocomposites., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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.

Helically spin-polarized Dirac fermions (HSDF) in protected topological surface states (TSS) are of high interest as a new state of quantum matter. In three-dimensional (3D) materials with TSS, electronic bulk states often mask the transport properties of HSDF. Recently, the high-field Hall resistance and low-field magnetoresistance indicate that the TSS may coexist with a layered two-dimensional electronic system (2DES). Here, we demonstrate quantum oscillations of the Hall resistance at temperatures up to 50 K in nominally undoped bulk Bi 2 Se 3 with a high electron density n of about 2·10 19 cm -3 . From the angular and temperature dependence of the Hall resistance and the Shubnikov-de Haas oscillations we identify 3D and 2D contributions to transport. Angular resolved photoemission spectroscopy proves the existence of TSS. We present a model for Bi 2 Se 3 and suggest that the coexistence of TSS and 2D layered transport stabilizes the quantum oscillations of the Hall resistance.

To realize spintronic devices based on topological insulators (TIs), well-defined interfaces between magnetic metals and TIs are required. Here, we characterize atomically precisely the interface between the 3d transition metal Fe and the TI Bi 2 Te 3 at different stages of its formation. Using photoelectron diffraction and holography, we show that after deposition of up to 3 monolayers Fe on Bi 2 Te 3 at room temperature, the Fe atoms are ordered at the interface despite the surface disorder revealed by our scanning-tunneling microscopy images. We find that Fe occupies two different sites: a hollow adatom deeply relaxed into the Bi 2 Te 3 quintuple layers and an interstitial atom between the third (Te) and fourth (Bi) atomic layers. For both sites, our core-level photoemission spectra and density-functional theory calculations demonstrate simultaneous chemical bonding of Fe to both Te and Bi atoms. We further show that upon deposition of Fe up to a thickness of 20 nm, the Fe atoms penetrate deeper into the bulk forming a 2-5 nm interface layer containing FeTe. In addition, excessive Bi is pushed down into the bulk of Bi 2 Te 3 leading to the formation of septuple layers of Bi 3 Te 4 within a distance of ∼25 nm from the interface. Controlling the magnetic properties of the complex interface structures revealed by our work will be of critical importance when optimizing the efficiency of spin injection in TI-based devices.

The charge-transfer kinetics of lithium ion intercalation into Li x Mn 2 O 4 cathode materials was examined in dilute and concentrated aqueous and carbonate LiTFSI solutions using electrochemical methods. Distinctive trends in ion intercalation rates were observed between water-based and ethylene carbonate/diethyl carbonate solutions. The influence of the solution concentration on the rate of lithium ion transfer in aqueous media can be tentatively attributed to the process associated with Mn dissolution, whereas in carbonate solutions the rate is influenced by the formation of a concentration-dependent solid electrolyte interface (SEI). Some indications of SEI layer formation at electrode surfaces in carbonate solutions after cycling are detected by X-ray photoelectron spectroscopy. The general consequences related to the application of superconcentrated electrolytes for use in advanced energy storage cathodes are outlined and discussed.

Regardless of the widely accepted opinion that there is no Raman signal from single-layer graphene when it is strongly bonded to a metal surface, we present Raman spectra of a graphene monolayer on Ni(111) and Co(0001) substrates. The high binding energy of carbon to these surfaces allows formation of lattice-matched (1 × 1) structures where graphene is significantly stretched. This is reflected in a record-breaking shift of the Raman G band by more than 100 cm -1 relative to the case of freestanding graphene. Using electron diffraction and photoemission spectroscopy, we explore the aforementioned systems together with polycrystalline graphene on Co and analyze possible intercalation of oxygen at ambient conditions. The results obtained are fully supported by Raman spectroscopy. Performing a theoretical investigation of the phonon dispersions of freestanding graphene and stretched graphene on the strongly interacting Co surface, we explain the main features of the Raman spectra. Our results create a reliable platform for application of Raman spectroscopy in diagnostics of chemisorbed graphene and related materials.

The structural organization of compounds in a confined space of nanometer-scale cavities is of fundamental importance for understanding the basic principles for atomic structure design at the nanolevel. Here, we explore size-dependent structure relations between one-dimensional PbTe nanocrystals and carbon nanotube containers in the diameter range of 2.0-1.25 nm using high-resolution transmission electron microscopy and ab initio calculations. Upon decrease of the confining volume, one-dimensional crystals reveal gradual thinning, with the structure being cut from the bulk in either a <110> or a <100> growth direction until a certain limit of ∼1.3 nm. This corresponds to the situation when a stoichiometric (uncharged) crystal does not fit into the cavity dimensions. As a result of the in-tube charge compensation, one-dimensional superstructures with nanometer-scale atomic density modulations are formed by a periodic addition of peripheral extra atoms to the main motif. Structural changes in the crystallographic configuration of the composites entail the redistribution of charge density on single-walled carbon nanotube walls and the possible appearance of the electron density wave. The variation of the potential attains 0.4 eV, corresponding to charge density fluctuations of 0.14 e/atom.

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.

Low-field magnetotransport measurements of topological insulators such as Bi2Se3 are important for revealing the nature of topological surface states by quantum corrections to the conductivity, such as weak-antilocalization. Recently, a rich variety of high-field magnetotransport properties in the regime of high electron densities (∼10(19) cm(-3)) were reported, which can be related to additional two-dimensional layered conductivity, hampering the identification of the topological surface states. Here, we report that quantum corrections to the electronic conduction are dominated by the surface states for a semiconducting case, which can be analyzed by the Hikami-Larkin-Nagaoka model for two coupled surfaces in the case of strong spin-orbit interaction. However, in the metallic-like case this analysis fails and additional two-dimensional contributions need to be accounted for. Shubnikov-de Haas oscillations and quantized Hall resistance prove as strong indications for the two-dimensional layered metallic behavior. Temperature-dependent magnetotransport properties of high-quality Bi2Se3 single crystalline exfoliated macro and micro flakes are combined with high resolution transmission electron microscopy and energy-dispersive x-ray spectroscopy, confirming the structure and stoichiometry. Angle-resolved photoemission spectroscopy proves a single-Dirac-cone surface state and a well-defined bulk band gap in topological insulating state. Spatially resolved core-level photoelectron microscopy demonstrates the surface stability.

We observed that thermally treated carbon nanowalls serve efficiently as templates governing the formation of quasiperiodic patterns for nanoparticles deposited. Here we report self-assembled quasi-regular structures of diverse nanoparticles on a freestanding multilayer graphene-like material, i.e. carbon nanowalls. Metallic (Ag, Al, Co, Mo, Ni, and Ta) and semiconductor (Si) nanoparticles form coaxial polygonal closed loop structures or parallel equidistant rows, which evolve upon further deposition into bead-like structures and, finally, into nanowires. Weakly bonded nanoparticles decorate atomic steps, wrinkles and other extended defects on the carbon nanowalls as a result of anisotropic diffusion of atoms or clusters along the hexagonal sp(2)-carbon network followed by their aggregation and agglomeration. The decorated carbon nanowalls are found to be promising materials for surface enhanced Raman scattering (SERS) analysis.

Magnetic doping is expected to open a band gap at the Dirac point of topological insulators by breaking time-reversal symmetry and to enable novel topological phases. Epitaxial (Bi(1-x)Mn(x))2Se3 is a prototypical magnetic topological insulator with a pronounced surface band gap of ∼100 meV. We show that this gap is neither due to ferromagnetic order in the bulk or at the surface nor to the local magnetic moment of the Mn, making the system unsuitable for realizing the novel phases. We further show that Mn doping does not affect the inverted bulk band gap and the system remains topologically nontrivial. We suggest that strong resonant scattering processes cause the gap at the Dirac point and support this by the observation of in-gap states using resonant photoemission. Our findings establish a mechanism for gap opening in topological surface states which challenges the currently known conditions for topological protection.

Inorganic clathrate materials are of great fundamental interest and potential practical use for application as thermoelectric materials in freon-free refrigerators, waste-heat converters, direct solar thermal energy converters, and many others. Experimental studies of their electronic structure and bonding have been, however, strongly restricted by (i) the crystal size and (ii) essential difficulties linked with the clean surface preparation. Overcoming these handicaps, we present for the first time a comprehensive picture of the electronic band structure and the chemical bonding for the Sn(24-x-δ)InxAs(22-y)I8 clathrates obtained by means of photoelectron spectroscopy and complementary quantum modeling.

The full exploration of the potential, which graphene offers to nanoelectronics requires its integration into semiconductor technology. So far the real-world applications are limited by the ability to concomitantly achieve large single-crystalline domains on dielectrics and semiconductors and to tailor the interfaces between them. Here we show a new direct bottom-up method for the fabrication of high-quality atomically precise interfaces between 2D materials, like graphene and hexagonal boron nitride (hBN), and classical semiconductor via Ge intercalation. Using angle-resolved photoemission spectroscopy and complementary DFT modelling we observed for the first time that epitaxially grown graphene with the Ge monolayer underneath demonstrates Dirac Fermions unaffected by the substrate as well as an unperturbed electronic band structure of hBN. This approach provides the intrinsic relativistic 2D electron gas towards integration in semiconductor technology. Hence, these new interfaces are a promising path for the integration of graphene and hBN into state-of-the-art semiconductor technology.

Embedding foreign atoms or molecules in graphene has become the key approach in its functionalization and is intensively used for tuning its structural and electronic properties. Here, we present an efficient method based on chemical vapor deposition for large scale growth of boron-doped graphene (B-graphene) on Ni(111) and Co(0001) substrates using carborane molecules as the precursor. It is shown that up to 19 at. % of boron can be embedded in the graphene matrix and that a planar C-B sp(2) network is formed. It is resistant to air exposure and widely retains the electronic structure of graphene on metals. The large-scale and local structure of this material has been explored depending on boron content and substrate. By resolving individual impurities with scanning tunneling microscopy we have demonstrated the possibility for preferential substitution of carbon with boron in one of the graphene sublattices (unbalanced sublattice doping) at low doping level on the Ni(111) substrate. At high boron content the honeycomb lattice of B-graphene is strongly distorted, and therefore, it demonstrates no unballanced sublattice doping.

We suggest a method for detection of highly conductive surface electron states including topological ones. The method is based on measurements of the photoelectromagnetic effect using terahertz laser pulses. In contrast to conventional transport measurements, the method is not sensitive to the bulk conductivity. The method is demonstrated on an example of topological crystalline insulators Pb(1-x)SnxSe. It is shown that highly conductive surface electron states are present in Pb(1-x)SnxSe both in the inverse and direct electron energy spectrum.

The mechanisms of interaction between inorganic matter and biomolecules, as well as properties of resulting hybrids, are receiving growing interest due to the rapidly developing field of bionanotechnology. The majority of potential applications for metal-biohybrid structures require stability of these systems under vacuum conditions, where their chemistry is elusive, and may differ dramatically from the interaction between biomolecules and metal ions in vivo. Here we report for the first time a photoemission and X-ray absorption study of the formation of a hybrid metal-protein system, tracing step-by-step the chemical interactions between the protein and metals (Cu and Fe) in vacuo. Our experiments reveal stabilization of the enol form of peptide bonds as the result of protein-metal interactions for both metals. The resulting complex with copper appears to be rather stable. In contrast, the system with iron decomposes to form inorganic species like oxide, carbide, nitride, and cyanide.

Oxygen reduction reaction (ORR) plays a key role in lithium-air batteries (LABs) that attract great attention thanks to their high theoretical specific energy several times exceeding that of lithium-ion batteries. Because of their high surface area, high electric conductivity, and low specific weight, various carbons are often materials of choice for applications as the LAB cathode. Unfortunately, the possibility of practical application of such batteries is still under question as the sustainable operation of LABs with carbon cathodes is not demonstrated yet and the cyclability is quite poor, which is usually associated with oxygen reduced species side reactions. However, the mechanisms of carbon reactivity toward these species are still unclear. Here, we report a direct in situ X-ray photoelectron spectroscopy study of oxygen reduction by lithiated graphene and graphene-based materials. Although lithium peroxide (Li2O2) and lithium oxide (Li2O) reactions with carbon are thermodynamically favorable, neither of them was found to react even at elevated temperatures. As lithium superoxide is not stable at room temperature, potassium superoxide (KO2) prepared in situ was used instead to test the reactivity of graphene with superoxide species. In contrast to Li2O2 and Li2O, KO2 was demonstrated to be strongly reactive.

In this paper we propose a new and simple method to tune the carbon nanowall microstructure by sharp variation of CH4/H2 plasma conditions. Using theoretical calculations we demonstrated that the sharp variation of gas pressure and discharge current leads to significant variation of plasma radical composition. In some cases such perturbation creates the necessary conditions for the nucleation of smaller secondary nanowalls on the surface of primary ones.

Many propositions have been already put forth for the practical use of N-graphene in various devices, such as batteries, sensors, ultracapacitors, and next generation electronics. However, the chemistry of nitrogen imperfections in this material still remains an enigma. Here we demonstrate a method to handle N-impurities in graphene, which allows efficient conversion of pyridinic N to graphitic N and therefore precise tuning of the charge carrier concentration. By applying photoemission spectroscopy and density functional calculations, we show that the electron doping effect of graphitic N is strongly suppressed by pyridinic N. As the latter is converted into the graphitic configuration, the efficiency of doping rises up to half of electron charge per N atom.

The optical properties of carbon nanowall (CNW) films in the visible range have been studied and reported for the first time. Depending on the film structure, ultra-low total reflectance up to 0.13% can be reached, which makes the CNW films a promising candidate for the black body-like coating, and thus for a wide range of applications as a light absorber. We have estimated important trends in the optical property variation from sample to sample, and identified the presence of edge states and domain boundaries in carbon nanowalls as well as the film mass density variation as the key factors. Also we demonstrated that at much lower film thickness and density than for a carbon nanotube forest the CNWs yield one order higher specific light absorption.

Unfortunately, the practical applications of Li-O2 batteries are impeded by poor rechargeability. Here, for the first time we show that superoxide radicals generated at the cathode during discharge react with carbon that contains activated double bonds or aromatics to form epoxy groups and carbonates, which limits the rechargeability of Li-O2 cells. Carbon materials with a low amount of functional groups and defects demonstrate better stability thus keeping the carbon will-o'-the-wisp lit for lithium-air batteries.

The long-term stability of functional properties of topological insulator materials is crucial for the operation of future topological insulator based devices. Water and oxygen have been reported to be the main sources of surface deterioration by chemical reactions. In the present work, we investigate the behavior of the topological surface states on Bi2X3 (X = Se, Te) by valence-band and core level photoemission in a wide range of water and oxygen pressures both in situ (from 10(-8) to 0.1 mbar) and ex situ (at 1 bar). We find that no chemical reactions occur in pure oxygen and in pure water. Water itself does not chemically react with both Bi2Se3 and Bi2Te3 surfaces and only leads to slight p-doping. In dry air, the oxidation of the Bi2Te3 surface occurs on the time scale of months, in the case of Bi2Se3 surface of cleaved crystal, not even on the time scale of years. The presence of water, however, promotes the oxidation in air, and we suggest the underlying reactions supported by density functional calculations. All in all, the surface reactivity is found to be negligible, which allows expanding the acceptable ranges of conditions for preparation, handling and operation of future Bi2X3-based devices.

The helical Dirac fermions at the surface of topological insulators show a strong circular dichroism which has been explained as being due to either the initial-state spin angular momentum, the initial-state orbital angular momentum, or the handedness of the experimental setup. All of these interpretations conflict with our data from Bi(2)Te(3) which depend on the photon energy and show several sign changes. Our one-step photoemission calculations coupled to ab initio theory confirm the sign change and assign the dichroism to a final-state effect. Instead, the spin polarization of the photoelectrons excited with linearly polarized light remains a reliable probe for the spin in the initial state.

The unique properties of graphene have raised high expectations regarding its application in carbon-based nanoscale devices that could complement or replace traditional silicon technology. This gave rise to the vast amount of researches on how to fabricate high-quality graphene and graphene nanocomposites that is currently going on. Here we show that graphene can be successfully integrated with the established metal-silicide technology. Starting from thin monocrystalline films of nickel, cobalt and iron, we were able to form metal silicides of high quality with a variety of stoichiometries under a Chemical Vapor Deposition grown graphene layer. These graphene-capped silicides are reliably protected against oxidation and can cover a wide range of electronic materials/device applications. Most importantly, the coupling between the graphene layer and the silicides is rather weak and the properties of quasi-freestanding graphene are widely preserved.

We study the effect of Fe impurities deposited on the surface of the topological insulator Bi(2)Se(3) by means of core-level and angle-resolved photoelectron spectroscopy. The topological surface state reveals surface electron doping when the Fe is deposited at room temperature and hole doping with increased linearity when deposited at low temperature (~8 K). We show that in both cases the surface state remains intact and gapless, in contradiction to current belief. Our results suggest that the surface state can very well exist at functional interfaces with ferromagnets in future devices.