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A series of Li3MI6 compounds with M = Lu–Sm were produced by ball milling and solid state synthesis. Cation disorder within the layers largely influences the ionic transport properties, which can be tuned by isovalent and aliovalent substitution.

The self‐assembly of a nickel‐porphyrin derivative (Ni‐DPPyP) containing two pyridyl coordinating sites and two pentyl chains at trans meso positions was studied with scanning tunneling microscopy (STM), X‐ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED) on Au(111). Deposition of Ni‐DPPyP onto Au(111) gave rise to a close‐packed network for coverages smaller or equal to one monolayer as revealed by STM and LEED. The molecular arrangement of this two‐dimensional network is stabilized via hydrogen bonds formed between the pyridyl's nitrogen and hydrogen atoms from the pyrrole groups of neighboring molecules. Subsequent deposition of cobalt atoms onto the close‐packed network and post‐deposition annealing at 423 K led to the formation of a Co‐coordinated hexagonal porous network. As confirmed by XPS measurements, the porous network is stabilized by metal‐ligand interactions between one cobalt atom and three pyridyl ligands, each pyridyl ligand coming from a different Ni‐DPPyP molecule., The structural transformation of a porphyrin‐based two‐dimensional network from its H‐bonded phase to a porous metal‐coordinated phase after the addition of Co‐atoms on Au(111) under ultra‐high vacuum conditions was inverstigated. The networks were characterized by scanning tunneling microscopy, low‐energy electron diffraction and X‐ray photoelectron spectroscopy.

Directed design of new photocatalysts remains a challenging task in materials chemistry. One approach in metal oxides is to engineer the bulk electronic structure to achieve enhanced visible-light ...

High Cu content perovskite-type LaNi1-xCuxO3-δ oxides are evaluated as alternative air electrode materials for Solid Oxide Cells. Auto-combustion synthesis allowed to obtain fine oxide powders up to a Cu content of x = 0.75 under ambient pressure. Investigations of the crystal structure, oxygen deficiency, chemical and thermal stability, as well as transport properties reveal satisfactory characteristics, with high total electrical conductivity and high concentration of oxygen vacancies at elevated temperatures. LaNi1-xCuxO3-δ-based electrode layers show low polarization resistance values in La0.8Sr0.2Ga0.8Mg0.2O3-δ-based symmetrical cells. The lowest values for Cu-rich compositions at 800 °C are 0.056 Ω cm−2 for LaNi 0.5Cu0.5O3-δ and 0.054 Ω cm−2 for LaNi0.25Cu0.75O3-δ with La0.2Ce0.8O3-δ buffer layer. For the reversible cell with LaNi0.5Cu0.5O3-δ air electrode, approx. 870 mW cm−2 power density output at 900 °C is obtained when fueled with wet H2, as well as over 3 A cm−2 current density at 2 V in the electrolysis mode.

Graphene was shown to reveal intriguing properties of its relativistic two-dimensional electron gas; however, its implementation to microelectronic applications is missing to date. In this work, we present a comprehensive study of epitaxial graphene on technologically relevant and in a standard CMOS process achievable Ge(100) epilayers grown on Si(100) substrates. Crystalline graphene monolayer structures were grown by means of chemical vapor deposition (CVD). Using angle-resolved photoemission spectroscopy and in situ surface transport measurements, we demonstrate their metallic character both in momentum and real space. Despite numerous crystalline imperfections, e.g., grain boundaries and strong corrugation, as compared to epitaxial graphene on SiC(0001), charge carrier mobilities of 1 × 104 cm2/Vs were obtained at room temperature, which is a result of the quasi-charge neutrality within the graphene monolayers on germanium and not dependent on the presence of an interface oxide. The interface roughness due to the facet structure of the Ge(100) epilayer, formed during the CVD growth of graphene, can be reduced via subsequent in situ annealing up to 850 °C coming along with an increase in the mobility by 30%. The formation of a Ge(100)-(2 × 1) structure demonstrates the weak interaction and effective delamination of graphene from the Ge/Si(100) substrate.

Realization of all-solid-state batteries combined with metallic Li/Na is still hindered due to the unstable interface between the alkali metal and solid electrolytes, especially for highly promising thiophosphate materials. Artificial and uniform solid-electrolyte interphases (SEIs), serving as thin ion-conducting films, have been considered as a strategy to overcome the issues of such reactive interfaces. Here, we synthesized sulfide-based artificial SEIs (Li

We studied chemical stability of atomic layer deposition-grown Al2O3 artificial solid electrolyte interphases (SEIs) on lithium and sodium upon contact with liquid electrolyte by electrochemical impedance spectroscopy (EIS) and in the case of Li also by x-ray photoelectron spectroscopy. Both methods show that the formed Al2O3 is porous for all nominal thicknesses, and that the natural SEI grows in its pores and cracks. EIS shows that the porosity of the SEI on Na is higher than the one observed on Li, in particular at higher nominal thicknesses of Al2O3. The observed values of activation energies related to the transport through the SEI indicate either a denser natural SEI in the pores of Al2O3 and/or considerable space charge effect between Al2O3 and the SEI phase.

2D metal-organic-framework (MOF) based composites have emerged as promising candidates for electrocatalysis due to their high structural flexibility and fully exposed active sites. Herein, a freestanding metal-organic layer (MOL) with a 2D kgd (kagome dual) lattice was constructed with abundant surface oxygenate groups serving as anchoring sites to immobilize diverse guests. Taking Bi as an example, tetragonal Bi

The carbon nitride poly(heptazine imide), PHI, has recently emerged as a powerful 2D carbon nitride photocatalyst with intriguing charge storing ability. Yet, insights into how morphology, particle size and defects influence its photophysical properties are virtually absent. Here, ultrasonication is used to systematically tune the particle size as well as concentration of surface functional groups and study their impact. Enhanced photocatalytic activity correlates with an optimal amount of those defects that create shallow trap states in the optical band gap, promoting charge percolation, as evidenced by time-resolved photoluminescence spectroscopy, charge transport studies, and quantum-chemical calculations. Excessive amounts of terminal defects can act as recombination centers and hence, decrease the photocatalytic activity for hydrogen evolution. Re-agglomeration of small particles can, however, partially restore the photocatalytic activity. The type and amount of trap states at the surface can also influence the deposition of the co-catalyst Pt, which is used in hydrogen evolution experiments. Optimized conditions entail improved Pt distribution, as well as an enhanced wettability and colloidal stability. A description of the interplay between these effects is provided to obtain a holistic picture of the size–property–activity relationship in nanoparticulate PHI-type carbon nitrides that can likely be generalized to related photocatalytic systems.

We present a comprehensive study on the silver bismuthate ${\mathrm{Ag}}_{2}{\mathrm{BiO}}_{3}$, synthesized under high-pressure, high-temperature conditions, which has been the subject of recent theoretical work on topologically complex electronic states. We present x-ray photoelectron spectroscopy results showing two different bismuth states and x-ray absorption spectroscopy results on the oxygen $K$ edge showing holes in the oxygen bands. These results support a bond disproportionated state with holes on the oxygen atoms for ${\mathrm{Ag}}_{2}{\mathrm{BiO}}_{3}$. We estimate a band gap of $\ensuremath{\sim}1.25$ eV for ${\mathrm{Ag}}_{2}{\mathrm{BiO}}_{3}$ from optical conductivity measurements, which matches the band gap in density functional calculations of the electronic band structure in the nonsymmorphic space group $Pnn2$, which supports two inequivalent Bi sites. In our band structure calculations the disproportionated ${\mathrm{Ag}}_{2}{\mathrm{BiO}}_{3}$ is expected to host Weyl nodal chains, one of which is located $\ensuremath{\sim}0.5$ eV below the Fermi level. Furthermore, we highlight similarities between ${\mathrm{Ag}}_{2}{\mathrm{BiO}}_{3}$ and the well-known disproportionated bismuthate ${\mathrm{BaBiO}}_{3}$, including breathing phonon modes with similar energy. In both compounds, hybridization of Bi $6s$ and O $2p$ atomic orbitals is important in shaping the band structure, but in contrast to the Ba $5p$ bands in ${\mathrm{BaBiO}}_{3}$, the Ag $4d$ bands in ${\mathrm{Ag}}_{2}{\mathrm{BiO}}_{3}$ extend up to the Fermi level.

The formation of a stable solid electrolyte interphase (SEI) is a prerogative for functional lithium metal batteries. Herein, the formation and evolution of such SEI in contact with glyme-based electrolytes is investigated under open circuit voltage and several constant current cycles. An important conclusion of the study is that Lix Sy species are nonbeneficial SEI components, compared to the Li3 N counterpart. In addition, chemical (X-ray photoelectron spectroscopy, XPS) and electrochemical (impedance spectroscopy) evolution of SEI under galvanostatic conditions are comprehensively tracked.

Research on magnesium-sulfur (Mg–S) batteries has gained great attention due to the high theoretical gravimetric and volumetric energy densities (1700 Wh kg−1 and 3200 Wh L−1), as well as because of their economic, ecologic and safety advantages. In this study, we present room-temperature Mg–S batteries with a sulfurized poly(acrylonitrile) composite (SPAN) cathode and a Mg2+/Li+ hybrid electrolyte (magnesium trifluoromethanesulfonate, (CF3SO3)2Mg), lithium trifluoromethanesulfonate, MgCl2 and AlCl3 in 1,2-dimethoxyethane (DME)). These cells deliver high discharge capacities and energy densities of 1100 mAh gs−1 and 700 Wh kgs−1 at 1 C, respectively, with >99.9% Coulombic efficiency. Electrochemical and kinetic measurements as well as post-mortem analysis revealed that utilization of SPAN and a lithium salt in the electrolyte is crucial and beneficial for the prevention of the polysulfide shuttle. It also dramatically reduces the cell resistance and the overpotential via the formation of MgLiSx species. Concomitantly, this system supports the formation of a solid electrolyte interface (SEI) layer, which greatly improves the reaction kinetics of the Mg2+ ions and the cycle performance.

At very high doping levels the van Hove singularity in the $\pi^*$ band of graphene becomes occupied and exotic ground states possibly emerge, driven by many-body interactions. Employing a combination of ytterbium intercalation and potassium adsorption, we $n$ dope epitaxial graphene on silicon carbide past the $\pi^*$ van Hove singularity, up to a charge carrier density of 5.5$\times$10$^{14}$ cm$^{-2}$. This regime marks the unambiguous completion of a Lifshitz transition in which the Fermi surface topology has evolved from two electron pockets into a giant hole pocket. Angle-resolved photoelectron spectroscopy confirms these changes to be driven by electronic structure renormalizations rather than a rigid band shift. Our results open up the previously unreachable beyond-van-Hove regime in the phase diagram of epitaxial graphene, thereby accessing an unexplored landscape of potential exotic phases in this prototype two-dimensional material., Comment: 6 pages, 2 figures

The class of antiperovskite compounds ${A}_{3}B\mathrm{O}$ ($A$ = Ca, Sr, Ba; $B$ = Sn, Pb) has attracted interest as a candidate three-dimensional Dirac system with topological surface states protected by crystal symmetry. A key factor underlying the rich electronic structure of ${A}_{3}B\mathrm{O}$ is the unusual valence state of $B$, i.e., a formal oxidation state of $\ensuremath{-}4$. Practically, it is not obvious whether anionic $B$ can be stabilized in thin films, due to its unusual chemistry, as well as the polar surface of ${A}_{3}B\mathrm{O}$, which may render the growth-front surface unstable. We report x-ray photoelectron spectroscopy measurements of single-crystalline films of ${\mathrm{Sr}}_{3}\mathrm{SnO}$ and ${\mathrm{Sr}}_{3}\mathrm{PbO}$ grown by molecular beam epitaxy. We observe shifts in the core-level binding energies that originate from anionic Sn and Pb, consistent with density functional theory calculations. Near the surface, we observe additional signatures of neutral or cationic Sn and Pb, which may point to an electronic or atomic reconstruction with possible impact on putative topological surface states.

Exotic ordered ground states driven by electronic correlations are expected to be induced in monolayer graphene when doped to the Van Hove singularity. Such doping levels are reached by intercalating Gd in graphene on SiC(0001), resulting in a strong homogeneity and stability. The electronic spectrum now exhibits severe renormalizations. Flat bands develop which are driven by electronic correlations according to our theoretical studies. Due to strong electron-phonon coupling in this regime, polaron replica bands develop. Thus, interesting ordered ground states should be made accessible.

In heavily $n$-doped graphene, when pushing the Fermi level to the vicinity of the Van Hove singularity, exotic electronic ground states are expected to occur driven by many-body interactions. These competing phases, such as chiral superconductivity, charge, or spin density waves, find their stability based on the amount of doping induced in the graphene layer. In this work we present a method for effectively tuning the doping level of graphene near the Van Hove singularity. Epitaxially grown buffer layer graphene on SiC(0001) is decoupled from the SiC substrate and strongly $n$ doped up to its Van Hove singularity via ytterbium intercalation. Upon annealing the Yb/graphene system at increasing temperatures, a topological transition at the Fermi level and a continuous upshift of the Dirac point are observed, indicating a decrease in charge carrier density. The intercalated Yb atoms adopt an ordered pattern while their concentration is reduced with annealing temperature. These variations significantly affect the charge transfer to the graphene layer and allow the systematic control of the doping level in the vicinity of the Van Hove singularity via one single experimental parameter. As such, the Yb intercalation technique can provide a reliable and convenient way of accessing different ordered ground states predicted in highly doped graphene.

A magnesium-sulfur (Mg-S) battery system based on a sulfurized poly(acrylonitrile) (“SPAN”) composite as cathode material is presented. Using magnesium tetrakis(hexafluoroisopropyloxy) borate, Mg[B(hfip)4]2, as conductive salt in the electrolyte, the cycle performance of Mg-S batteries based on SPAN and different types of Mg anodes, i.e. Mg foil and pressed Mg powder, respectively, were compared. A cell composed of Mg foil and SPAN delivered a discharge capacity around 300 mAh/gsulfur at C/30 while a cell based on SPAN and pressed Mg powder delivered ca. 500 mAh/gsulfur (energy density of ca. 422 mWh/gsulfur) at C/30 and also possessed good rate capability. The higher discharge capacities of Mg-S cells based on pressed anodes are attributed to the substantially higher specific surface area of the pressed cells. Post-mortem analysis of aged cells based on SPAN and a pressed Mg anode indicates the formation of MgF2 on both the cathode and the anode along with magnesium polysulfide species.

We present the electronic and structural properties of monolayer ${\mathrm{WSe}}_{2}$ grown by pulsed-laser deposition on monolayer graphene (MLG) on SiC. The spin splitting in the ${\mathrm{WSe}}_{2}$ valence band at $\overline{\mathrm{K}}$ was ${\mathrm{\ensuremath{\Delta}}}_{\mathrm{SO}}=0.469\ifmmode\pm\else\textpm\fi{}0.008$ eV, as determined by angle-resolved photoemission spectroscopy. Synchrotron-based grazing-incidence in-plane x-ray diffraction (XRD) revealed the in-plane lattice constant of monolayer ${\mathrm{WSe}}_{2}$ to be ${a}_{{\mathrm{WSe}}_{2}}=3.2757\ifmmode\pm\else\textpm\fi{}0.0008$ \AA{}. This indicates a lattice compression of $\ensuremath{-}0.19$% relative to bulk ${\mathrm{WSe}}_{2}$. By using the experimentally determined graphene lattice constant (${a}_{\mathrm{MLG}}=2.4575\ifmmode\pm\else\textpm\fi{}0.0007$ \AA{}), we found that a $3\ifmmode\times\else\texttimes\fi{}3$ unit cell of the slightly compressed ${\mathrm{WSe}}_{2}$ is perfectly commensurate with a $4\ifmmode\times\else\texttimes\fi{}4$ graphene lattice with a mismatch below 0.03%, which could explain why the monolayer ${\mathrm{WSe}}_{2}$ is compressed on MLG. From XRD and first-principles calculations, we conclude that the observed size of strain will affect ${\mathrm{\ensuremath{\Delta}}}_{\mathrm{SO}}$ only on the order of a few meV. In addition, angle-resolved, ultraviolet, and x-ray photoelectron spectroscopies shed light on the band alignment between ${\mathrm{WSe}}_{2}$ and MLG/SiC and indicate electron transfer from graphene to the ${\mathrm{WSe}}_{2}$ monolayer. As further revealed by atomic force microscopy, the ${\mathrm{WSe}}_{2}$ island size depends on the number of carbon layers on top of the SiC substrate. This suggests that the epitaxy of ${\mathrm{WSe}}_{2}$ favors the weak van der Waals interactions with graphene, while it is perturbed by the influence of the SiC substrate and its carbon buffer layer.