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The production of high-quality hexagonal boron nitride (h-BN) is essential for the ultimate performance of two-dimensional (2D) materials-based devices, since it is the key 2D encapsulation material. Here, a decisive guideline is reported for fabricating high-quality h-BN on transition metals: It is crucial to exclude carbon from h-BN related process. Otherwise carbon prevails over boron and nitrogen due to its larger binding energy, thereupon forming graphene on metals after high-temperature annealing. We demonstrate the surface reaction-assisted conversion from h-BN to graphene with high-temperature treatments. The pyrolysis temperature Tp is an important quality indicator for h-BN/metals. When the temperature is lower than Tp, the quality of h-BN layer is improved upon annealing. While the annealing temperature is above Tp, in case of carbon-free conditions, the h-BN disintegrates and nitrogen desorbs from the surface more easily than boron, eventually leading to clean metal surfaces. However, once the h-BN layer is exposed to carbon, graphene forms on Pt(111) in the high-temperature regime. This not only provides an indispensable principle (avoid carbon) for fabricating high-quality h-BN materials on transition metals, but also offers a straightforward method for the surface reaction-assisted conversion from h-BN to graphene on Pt(111)., Accepted by SMALL on October 7, 2022

X-ray Absorption Spectroscopy (XAS) is used for measuring monolayer quantities of Ho3N@C80endofullerene molecules on graphene at a low flux bending magnet beamline. The total electron yield is measured with an Everhart- Thornley detector. In comparison to sample current measurements with the same noise level, our approach reduces data acquisition time and radiation dose by a factor of 25. As the first application of this set-up we report temperature- dependent measurements of the Ho M45 edge with per mille accuracy. This documents the advantages and capabilities of an Everhart-Thornely detector for XAS measurements under low x-ray flux.

Realization of stable spin states in surface-supported magnetic molecules is crucial for their applications in molecular spintronics, memory storage or quantum information processing. In this work, we studied the surface magnetism of dimetallo-azafullerene Tb

The substitution of scandium in fullerene single‐molecule magnets (SMMs) DySc2N@C80 and Dy2ScN@C80 by lutetium has been studied to explore the influence of the diamagnetic metal on the SMM performance of dysprosium nitride clusterfullerenes. The use of lutetium led to an improved SMM performance of DyLu2N@C80, which shows a higher blocking temperature of magnetization (TB=9.5 K), longer relaxation times, and broader hysteresis than DySc2N@C80 (TB=6.9 K). At the same time, Dy2LuN@C80 was found to have a similar blocking temperature of magnetization to Dy2ScN@C80 (TB=8 K), but substantially different interactions between the magnetic moments of the dysprosium ions in the Dy2MN clusters. Surprisingly, although the intramolecular dipolar interactions in Dy2LuN@C80 and Dy2ScN@C80 are of similar strength, the exchange interactions in Dy2LuN@C80 are close to zero. Analysis of the low‐frequency molecular and lattice vibrations showed strong mixing of the lattice modes and endohedral cluster librations in k‐space. This mixing simplifies the spin–lattice relaxation by conserving the momentum during the spin flip and helping to distribute the moment and energy further into the lattice.

A key parameter for the low-temperature magnetic coupling of in dinuclear lanthanide single-molecule magnets (SMMs) is the barrier $U_{FA}$ resulting from the exchange and dipole interactions between the two $4f$ moments. Here we extend the pseudospin model previously used to describe the ground state of dinuclear endofullerenes to account for variations in the orientation of the single-ion anisotropy axes and apply it to the two SMMs Dy$_2$ScN@C$_{80}$ and Dy$_2$TiC@C$_{80}$. While x-ray magnetic circular dichroism (XMCD) indicates the same $J_z=15/2$ Dy groundstate in both molecules, the Dy-Dy coupling strength and the stability of magnetization is distinct. We demonstrate that both the magnitude of the barrier $U_{FA}$ and the angle between the two $4f$ moments are determined directly from precise temperature-dependent magnetization data to an accuracy better than $1^{\circ}$. The experimentally found angles between the $4f$ moments are in excellent agreement with calculated angles between the quantisation axes of the two Dy ions. Theory indicates a larger deviation of the orientation of the Dy magnetic moments from the Dy bond axes to the central ion in Dy$_2$TiC@C$_{80}$. This may explain the lower stability of the magnetisation in Dy$_2$TiC@C$_{80}$, although it exhibits a $\sim 49\%$ stronger exchange coupling than in Dy$_2$ScN@C$_{80}$., 4 figures, 6 pages

Inert single-layer boron nitride (h-BN) grown on a catalytic metal may be functionalized with quaternary ammonium compounds (quats) that are widely used as nonreactive electrolytes. We observe that the quat treatment, which facilitates the electrochemical transfer of two-dimensional materials, involves a decomposition of quat ions and leads to covalently bound quat derivatives on top of the 2D layer. Applying tetraoctylammonium and h-BN on rhodium, the reaction product is top-alkylized h-BN as identified with high-resolution X-ray photoelectron spectroscopy. The alkyl chains are homogeneously distributed across the surface, and the properties thereof are well-tunable by the choice of different quats. The functionalization further weakens the 2D material-substrate interaction and promotes easy transfer. Therefore, the functionalization scheme that is presented enables the design of 2D materials with tailored properties and with the freedom to position and orient them as required. The mechanism of this functionalization route is investigated with density functional theory calculations, and we identify the proximity of the catalytic metal substrate to alter the chemical reactivity of otherwise inert h-BN layers.

Engineering intramolecular exchange interactions between magnetic metal atoms is a ubiquitous strategy for designing molecular magnets. For lanthanides, the localized nature of 4f electrons usually results in weak exchange coupling. Mediating magnetic interactions between lanthanide ions via radical bridges is a fruitful strategy towards stronger coupling. In this work we explore the limiting case when the role of a radical bridge is played by a single unpaired electron. We synthesize an array of air-stable Ln2@C80(CH2Ph) dimetallofullerenes (Ln2 = Y2, Gd2, Tb2, Dy2, Ho2, Er2, TbY, TbGd) featuring a covalent lanthanide-lanthanide bond. The lanthanide spins are glued together by very strong exchange interactions between 4f moments and a single electron residing on the metal–metal bonding orbital. Tb2@C80(CH2Ph) shows a gigantic coercivity of 8.2 Tesla at 5 K and a high 100-s blocking temperature of magnetization of 25.2 K. The Ln-Ln bonding orbital in Ln2@C80(CH2Ph) is redox active, enabling electrochemical tuning of the magnetism., Dilanthanide complexes that possess radical bridges exhibit enhanced magnetic exchange coupling, affording molecular magnets with high blocking temperatures. Here, the authors explore a series of dilanthanide-encapsulated fullerenes where the radical bridge is taken to its limit and the role is played by a single unpaired electron.

Single-layer hexagonal boron nitride is produced on 2 inch Pt(111)/sapphire wafers. The growth with borazine vapor deposition at process temperatures between 1000 and 1300 K is in situ investigated by photoelectron yield measurements. The growth kinetics is slower at higher temperatures and follows a tanh2 law which better fits for higher temperatures. The crystal-quality of hexagonal boron nitride (h-BN)/Pt(111) is inferred from scanning low energy electron diffraction (x-y LEED). The data indicate a strong dependence of the epitaxy on the growth temperature. The dominant structure is an aligned coincidence lattice with 10 h-BN on 9 Pt(1 × 1) unit cells and follows the substrate twinning at the millimeter scale.

The production of high-quality two-dimensional (2D) materials is essential for the ultimate performance of single layers and their hybrids. Hexagonal boron nitride (h-BN) is foreseen to become the key 2D hybrid and packaging material since it is insulating, impermeable, flat, transparent, and chemically inert, though it is difficult to attain in ultimate quality. Here, a scheme is reported for producing single layer h-BN that shows higher quality in view of mosaicity and strain variations than material from chemical vapor deposition (CVD). We delaminate CVD h-BN from Rh(111) and transfer it to a clean metal surface. The twisting angle between BN and the second substrate yields metastable moire structures. Annealing above 1000 K leads to 2D distillation, i.e., catalyst-assisted BN sublimation from the edges of the transferred layer and subsequent condensation into superior quality h-BN. This provides a way for 2D material production remote from CVD instrumentation.

Endohedral fullerenes are perfect nanolaboratories for the study of magnetism. The substitution of a diamagnetic scandium atom in Dy2ScN@C80 with gadolinium decreases the stability of a given magnetization and demonstrates Gd to act as a single atom catalyst that accelerates the reaching of thermal equilibrium. X-ray magnetic circular dichroism at the M4,5 edges of Gd and Dy shows that Gd affects the ground state. The Gd magnetic moment follows the sum of the external and the dipolar magnetic field of the two Dy ions and compared to Dy2ScN@C80 a lower exchange barrier is found between the ferromagnetic and the antiferromagnetic Dy configuration. The Arrhenius equilibration barrier as obtained from superconducting quantum interference device magnetometry is more than one order of magnitude larger, though a much smaller prefactor imposes the faster equilibration in Dy2GdN@C80. This sheds light on the importance of angular momentum balance and symmetry in magnetic relaxation.

2D oxide quasicrystals (OQCs) are recently discovered aperiodic, but well-ordered oxide interfaces. In this topical review, an introduction to these new thin-film systems is given. The concept of quasicrystals and their approximants is explained for BaTiO3 - and SrTiO3 - derived OQCs and related periodic structures in these 2D oxides. In situ microscopy unravels the high-temperature formation process of OQCs on Pt(111). The dodecagonal structure is discussed regarding tiling statistics and tiling decoration based on the results of atomically resolved scanning tunneling microscopy and various diffraction techniques. In addition, angle-resolved ultraviolet photoemission spectroscopy and X-ray photoelectron spectroscopy results prove a metallic character of the 2D oxide.

Magnetic hysteresis is a direct manifestation of nonequilibrium physics that has to be understood if a system is to be used for information storage and processing. The dilanthanide endofullerene ${\mathrm{Tb}}_{2}\mathrm{ScN}@{\mathrm{C}}_{80}$ is shown to be a single-molecule magnet with a remanence time on the order of 100 s at 400 mK. Three different temperature-dependent relaxation barriers are discerned. The lowest 1 K barrier is assigned to intermolecular dipole-dipole interaction, the 10 K barrier to intramolecular exchange and dipolar coupling, and the 50 K barrier to molecular vibrations as was observed for ${\mathrm{Dy}}_{2}\mathrm{ScN}@{\mathrm{C}}_{80}$. The 4 orders of magnitude difference in the prefactor between the Tb and the Dy compound in the decay process across the 10 K barrier is assigned to the lack of Kramers protection in ${\mathrm{Tb}}^{3+}$. The sub-Kelvin hysteresis follows changes in the magnetization at level crossings of the four possible ${\mathrm{Tb}}_{2}$ ground-state configurations. Comparison to a hysteresis model, with magnetic relaxation at level crossings only, reveals cooperative action between nearby molecules.

We have investigated emission patterns and energy spectra of electrons from a tungsten nanotip induced by circularly polarized femtosecond laser pulses. Variations of emission patterns were observed for different helicities of circular polarization while the energy spectra remained almost identical. The physics behind this difference in emission patterns is the change in propagation directions of surface electromagnetic waves on the tip apex. The energy spectra showed the same spectroscopic signatures as the linearly polarized laser in a strong-field regime, which are a low-energy peak and a plateau feature. The low-energy peak is due to a delayed electron emission with respect to a prompt emission. The experimental data and plasmonic simulations support our previous conclusion, where the observed delayed emission processes originate from an inelastic rescattering process. This work demonstrates that the use of circular polarization is an easy means to add extra knobs to control the spatial and temporal emission from a nanotip at the nanometer and femtosecond scale. It could find applications as a helicity-driven subcycle optical switch.

The adsorption of molecules on surfaces affects the surface dipole and thus changes in the work function may be expected. The effect in change of work function is particularly strong if charge between substrate and adsorbate is involved. Here we report the deposition of a strong electron acceptor molecule, tetrafluorotetracyanoquinodimethane C$_{12}$F$_4$N$_4$ (F$_{4}$TCNQ) on a monolayer of hexagonal boron nitride nanomesh ($h$-BN on Rh(111)). The work function of the F$_{4}$TCNQ/$h$-BN/Rh system increases upon increasing molecular coverage. The magnitude of the effect indicates electron transfer from the substrate to the F$_{4}$TCNQ molecules. Density functional theory calculations confirm the work function shift and predict doubly charged F$_{4}$TCNQ$^{2-}$ in the nanomesh pores, where the $h$-BN is closest to the Rh substrate, and to have the largest binding energy there. The preferred adsorption in the pores is conjectured from a series of ultraviolet photoelectron spectroscopy data, where the $\sigma$ bands in the pores are first attenuated. Scanning tunneling microscopy measurements indicate that F$_{4}$TCNQ molecules on the nanomesh are mobile at room temperature, as "hopping" between neighboring pores is observed.

We have deposited Sn on corrugated hexagonal boron nitride (h-BN) nanomeshs formed on Rh(111) and found that Sn atoms are intercalated between h-BN and Rh, flattening the h-BN. Our reflection high-energy electron diffraction (RHEED) analysis showed that the average in-plane lattice constant of h-BN increases due to the loss of the corrugation. Furthermore, electronic structure measurements based on angle-resolved photoemission spectroscopy (ARPES) showed that the h-BN π band width increases significantly while the σ band width does not change as much. These behaviors were partly different from previous reports on the intercalation of h-BN/Rh system. Our results offer a novel, simple method to control the electronic structure of h-BN.

A Bussard ramjet is a relativistic spacecraft, fueled by fusion energy of cosmic matter that is collected during the flight. We derive the equation of motion of such a spaceship for a given mass density in space and the fusion mass defect. Two ramjet engine scenarios, where the thrust for propulsion is generated by emission of photons or acceleration of matter, are outlined. As long as not all collected matter is transformed into fusion energy, mass engines are superior to photon engines. If the collected matter is stopped by the spacecraft before fusion it may not reach relativistic terminal velocities. For an ideal ramjet, where no matter is stopped for the generation of energy for propulsion, endless acceleration and relativistic velocities may be obtained such that crossing the universe in a human lifespan would be possible. A journey along one space coordinate and the smallest possible radii of curves were evaluated. The results are compared to the plots in the novel “Tau Zero” by Poul Anderson.

Fused‐pentagons results in an increase of local steric strain according to the isolated pentagon rule (IPR), and for all reported non‐IPR clusterfullerenes multiple (two or three) metals are required to stabilize the strained fused‐pentagons, making it difficult to access the single‐atom properties. Herein, we report the syntheses and isolations of novel non‐IPR mononuclear clusterfullerenes MNC@C76 (M=Tb, Y), in which one pair of strained fused‐pentagon is stabilized by a mononuclear cluster. The molecular structures of MNC@C76 (M=Tb, Y) were determined unambiguously by single‐crystal X‐ray diffraction, featuring a non‐IPR C 2v(19138)‐C76 cage entrapping a nearly linear MNC cluster, which is remarkably different from the triangular MNC cluster within the reported analogous clusterfullerenes based on IPR‐obeying C82 cages. The TbNC@C76 molecule is found to be a field‐induced single‐molecule magnet (SMM).

Endohedral fullerenes, such as Dy2ScN@C80, are single-molecule magnets with long relaxation times of their magnetization. An open and anisotropic 4f electron shell in the lanthanides (here Dy) imposes a magnetic moment that maintains its orientation at liquid-helium temperatures for macroscopic times. If these molecules shall be used as single-bit information storage elements or for quantum operations, the orientation of the endohedral units and the orientation of the magnetic moments has to be controlled. X-ray absorption spectroscopy (XAS) and magnetic circular dichroism (XMCD)—with variation of the angle of x-ray incidence—allows for the detection of these two structural elements. We present XMCD data of Dy2ScN@C80 on an h−BN/Rh(111) nanomesh that display at 2 K a large hysteresis with a coercive field of 0.4 T. The angular dependence of the XAS data at the Dy M5 edge indicates partial ordering of the endohedral units. In order to quantify anisotropic orientation we introduce the “deviation” D as an operational quantity that measures differences between two spectra.

Endohedral fullerenes are perfect nanolaboratories for the study of 4f electron magnetism. The substitution of a diamagnetic scandium atom in Dy2ScN@C80 with magnetically isotropic gadolinium decreases the stability of a given magnetization that is imposed by the Dy2 unit and demonstrates Gd to accelerate the reaching of thermal equilibrium. X-ray magnetic circular dichroism at the M4,5 edges of Gd and Dy shows that Gd also affects the magnetic ground state. The Gd magnetic moment follows the sum of the external and the dipolar magnetic field of the two Dy ions and compared to Dy2ScN@C80 a lower exchange barrier is found between the ferromagnetic and the antiferromagnetic Dy configuration. The Arrhenius equilibration barrier as obtained from superconducting quantum interference device magnetometry is more than one order of magnitude larger, though a much smaller prefactor imposes the faster equilibration in Dy2GdN@C80. This sheds light on the importance of angular momentum balance and symmetry in magnetic relaxation [1]. [1] Gadolinium as a single atom catalyst in a single molecule magnet, Aram Kostanyan, Christin Schlesier, Rasmus Westerstrom, Jan Dreiser, Fabian Fritz, Bernd Buchner, Alexey A. Popov, Cinthia Piamonteze, Thomas Greber, arXiv:2009.12259 September (2020). The figure shows the Dy2GdN@C80 molecule where the two Dy 4f9 and the Gd 4f7 orbitals of the paramagnetic entities are shown in red. Note the orientation of the Jz=15/2 Dy 4f9 orbitals towards the N3- ligand. Picture by Ari P. Seitsonen. Figure 1

In biomineralization, inorganic materials are formed with remarkable control of the shape and morphology. Chirality, as present in the biomolecular world, is therefore also common for biominerals. Biomacromolecules, like proteins and polysaccharides, are in direct contact with the mineral phase and act as modifiers during nucleation and crystal growth. Owing to their homochirality--they exist only as one of two possible mirror-symmetric isomers--their handedness is often transferred into the macroscopic shape of the biomineral crystals, but the way in which handedness is transmitted into achiral materials is not yet understood at the atomic level. By using the submolecular resolution capability of scanning tunnelling microscopy, supported by photoelectron diffraction and density functional theory, we show how the chiral 'buckybowl' hemibuckminsterfullerene arranges copper surface atoms in its vicinity into a chiral morphology. We anticipate that such new insight will find its way into materials synthesis techniques.

Upon a core level excitation by circularly polarized light (CPL), the angular momentum of light, i.e. helicity, is transferred to the emitted photoelectron. This phenomenon can be confirmed by the parallax shift measurement of the forward focusing peak (FFP) direction in a stereograph of the atomic arrangement. The angular momentum of the emitted photoelectron is the sum of CPL helicity and the magnetic quantum number (MQN) of the initial state that define the quantum number of the core hole final state. The core hole may decay via Auger electron emission, where in this two electron process the angular momentum has to be conserved as well. Starting from a given core hole, different Auger decay channels with different final state energies and angular momenta of the emitted Auger electrons may be populated. Here we report the observation and formulation of the angular momentum transfer of light to Auger electrons, instead of photoelectrons. We measured photoelectron and Auger electron intensity angular distributions from Cu(111) and Cu(001) surfaces as a function of photon energy and photoelectron kinetic energy. By combining Auger electron spectroscopy with the FFP shift measurements at absorption threshold, element- and MQN-specific hole states can be generated in the valence band.

In our paper(1) the N 1s core level energy as obtained by Al Kα excited X-ray photoelectron spectroscopy (XPS) of boron nitride on Ru(0001) is not correctly reproduced, it is 398.63 ± 0.15 eV and not 389.63 ± 0.15 eV. Table 1 reproduces the B 1s and N 1s binding energies and work functions for h-BN on Rh(111), Ru(0001), Ni(111), and Pd(111).(2)Figure 1 reproduces the corresponding core level data with the correct energy scale. We are grateful to W. Auwarter for spotting these inconsistencies.

Vertically stacked two-dimensional (2D) heterostructures composed of 2D semiconductors have attracted great attention. Most of these include hexagonal boron nitride (h-BN) as either a substrate, an encapsulant, or a tunnel barrier. However, reliable synthesis of large-area and epitaxial 2D heterostructures incorporating BN remains challenging. Here, we demonstrate the epitaxial growth of nominal monolayer (ML) MoSe

International audience; Ions inside of fullerene molecules are model systems for the study of the electrostatic interaction across a single layer of carbon. For TbSc2N@C80 on h-BN/Ni(111), we observe with high-resolution X-ray photoelectron spectroscopy a splitting of the C 1s core level. The data may be explained quantitatively with density functional theory. The correlation of the C 1s eigenvalues and the Coulomb potential of the inside ions at the corresponding carbon sites indicates incomplete screening of the electric field due to the endohedral ions. The screening comprises anisotropic charge transfer to the carbon atoms and their polarization. This behavior is essential for the ordering of endohedral single-molecule magnets and is expected to occur in any single-layer material.

The valence band dispersion of the graphite $\ensuremath{\pi}$ band along the ${k}_{z}$ axis was measured using a sequence of photon energies between 60 and 230 eV. The interlayer interaction induces the well-known splitting of the $\ensuremath{\pi}$ band into two, a lower binding energy band ${\ensuremath{\pi}}_{\mathrm{L}}$ and a higher binding energy band ${\ensuremath{\pi}}_{\mathrm{H}}$. However, in the photoelectron spectra, the bands ${\ensuremath{\pi}}_{\mathrm{L}}$ and ${\ensuremath{\pi}}_{\mathrm{H}}$ appeared alternatively in the Brillouin zones along the ${k}_{z}$ direction. As a result, a $4\ensuremath{\pi}$-periodic oscillation in the binding energy as a function of photon energy was observed for the $\ensuremath{\pi}$ band dispersion. This is explained by considering the constructive and destructive interference of ${p}_{z}$ orbitals within the unit cell, called the photoelectron structure factor. We derived the analytic expression of the photoelectron structure factor for graphite. The resonance integrals of the ${p}_{z}$ orbitals were determined for the in-plane and interlayer. Furthermore, the inner potential of graphite from the vacuum level was determined to be 17.17 eV.

We report the investigation of the angular momentum transfer of light to photoelectrons and Auger electrons at the Ni ${L}_{3}$ absorption threshold. Upon core-level excitation by circularly polarized light, the angular momentum of light, or helicity, is transferred to the emitted photoelectron. The angular momentum of the emitted photoelectron (${m}_{\mathrm{f}}$) is the sum of the helicity ($\ensuremath{\sigma}$) and the orbital magnetic quantum number of the initial state (${m}_{\mathrm{i}}$). Here the quantization axis was defined as the direction along the incident light. This can be measured by the parallax shift of the forward focusing peak (FFP) direction in the photoelectron intensity angular distribution. At the absorption threshold, the excited core-level electron is promoted to a conduction-band state and the angular momentum of the light is partially transferred to Auger electrons. We measured photoelectron and Auger electron intensity angular distributions from the Ni(111) surface at the ${L}_{3}$ absorption threshold. We observed a significant angular circular dichroism of the $[101]$ FFP for the ${L}_{3}{M}_{4,5}{M}_{4,5}$ Auger electrons. Furthermore, we discovered non-negligible reversal angular circular dichroism contrasts for the triplet components in the case of the ${L}_{3}{M}_{2,3}{M}_{4,5}$ Auger electrons, suggesting that the angular momentum of light was transferred to the emitted electron in the antiparallel way.

Vertically stacked two-dimensional (2D) heterostructures composed of 2D semiconductors have attracted great attention. Most of these include hexagonal boron nitride (h-BN) as either a substrate, an encapsulant, or a tunnel barrier. However, reliable synthesis of large-area and epitaxial 2D heterostructures incorporating BN remains challenging. Here, we demonstrate the epitaxial growth of nominal monolayer (ML) MoSe2 on h-BN/Rh(111) by molecular beam epitaxy, where the MoSe2/h-BN layer system can be transferred from the growth substrate onto SiO2. The valence band structure of ML MoSe2/h-BN/Rh(111) revealed by photoemission electron momentum microscopy (kPEEM) shows that the valence band maximum located at the K point is 1.33 eV below the Fermi level (EF), whereas the energy difference between K and Γ points is determined to be 0.23 eV, demonstrating that the electronic properties, such as the direct band gap and the effective mass of ML MoSe2, are well preserved in MoSe2/h-BN heterostructures., The access was provided by the NFFA-Europe Infrastructure (proposal ID 121) under Horizon 2020 EU Funding Program. We thank N. Gambacorti for coordinating the access to the NFFA-EU program. This work was financially supported by the European Research Council (Grant No. 240076) and has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement Nos. 696656 and 785219 (Graphene Flagship Core 1 and Core 2). M.P. acknowledges support by the Swiss National Science Foundation (Grant No. 200021-162612).

Magnetic properties of endohedral metallofullerenes with nitride clusters DySc(2)N and Dy(2)ScN and different carbon cages are studied by SQUID magnetometry. All molecules behave as single molecule magnets (SMMs) and exhibit magnetic hysteresis. It is found that the blocking temperature of magnetization and relaxation times strongly depend on the fullerene cage, with the C(80)-I(h) isomer offering the best SMM properties.

The use of methane as a reactive gas dramatically increases the selectivity of the arc-discharge synthesis of M-Ti-carbide clusterfullerenes (M=Y, Nd, Gd, Dy, Er, Lu). Optimization of the process parameters allows the synthesis of Dy2TiC@C80-I and its facile isolation in a single chromatographic step. A new type of cluster with an endohedral acetylide unit, M2TiC2@C80, is discovered along with the second isomer of M2TiC@C80. Dy2TiC@C80-(I,II) and Dy2TiC2@C80-I are shown to be single-molecule magnets (SMM), but the presence of the second carbon atom in the cluster Dy2TiC2@C80 leads to substantially poorer SMM properties.

Methan erhoht als reaktives Gas drastisch die Selektivitat der Lichtbogensynthese von M-Ti-Carbidclusterfullerenen (M=Y, Nd, Gd, Dy, Er, Lu). Ferner ermoglicht die Optimierung der Prozessparameter die Synthese von Dy2TiC@C80-I und dessen einfache Isolierung in einem einzigen chromatographischen Schritt. Neben einem zweiten Isomer des M2TiC@C80 wurde auserdem eine neue Clusterart mit endohedraler Acetylidgruppe, M2TiC2@C80, entdeckt. Weiterhin wirken Dy2TiC@C80-(I,II) und Dy2TiC2@C80-I als Einzelmolekulmagenten (SMMs), jedoch verschlechtert das zweite Kohlenstoffatom im Cluster des Dy2TiC2@C80 die SMM-Eigenschaften erheblich.

A method for the selective synthesis of sulfide clusterfullerenes Dy2S@C2n is developed. Addition of methane to the reactive atmosphere reduces the formation of empty fullerenes in the arc-discharge synthesis, whereas the use of Dy2S3 as a source of metal and sulfur affords sulfide clusterfullerenes as the main fullerene products along with smaller amounts of carbide clusterfullerenes. Two isomers of Dy2S@C82 with Cs(6) and C3v(8) cage symmetry, Dy2S@C72-Cs(10528), and a carbide clusterfullerene Dy2C2@C82-Cs(6) were isolated. The molecular structure of both Dy2S@C82 isomers was elucidated by single-crystal X-ray diffraction. SQUID magnetometry demonstrates that all of these clusterfullerenes exhibit hysteresis of magnetization, with Dy2S@C82-C3v(8) being the strongest single molecule magnet in the series. DC- and AC-susceptibility measurements were used to determine magnetization relaxation times in the temperature range from 1.6 K to 70 K. Unprecedented magnetization relaxation dynamics with three consequent Orbach processes and energy barriers of 10.5, 48, and 1232 K are determined for Dy2S@C82-C3v(8). Dy2S@C82-Cs(6) exhibits faster relaxation of magnetization with two barriers of 15.2 and 523 K. Ab initio calculations were used to interpret experimental data and compare the Dy-sulfide clusterfullerenes to other Dy-clusterfullerenes. The smallest and largest barriers are ascribed to the exchange/dipolar barrier and relaxation via crystal-field states, respectively, whereas an intermediate energy barrier of 48 K in Dy2S@C82-C3v(8) is assigned to the local phonon mode, corresponding to the librational motion of the Dy2S cluster inside the carbon cage.

The Photo-Emission and Atomic Resolution Laboratory is a new soft X-ray beamline at the Swiss Light Source for the study of surface structure using photoelectron diffraction and scanning tunneling microscopy., The Photo-Emission and Atomic Resolution Laboratory (PEARL) is a new soft X-ray beamline and surface science laboratory at the Swiss Light Source. PEARL is dedicated to the structural characterization of local bonding geometry at surfaces and interfaces of novel materials, in particular of molecular adsorbates, nanostructured surfaces, and surfaces of complex materials. The main experimental techniques are soft X-ray photoelectron spectroscopy, photoelectron diffraction, and scanning tunneling microscopy (STM). Photoelectron diffraction in angle-scanned mode measures bonding angles of atoms near the emitter atom, and thus allows the orientation of small molecules on a substrate to be determined. In energy scanned mode it measures the distance between the emitter and neighboring atoms; for example, between adsorbate and substrate. STM provides complementary, real-space information, and is particularly useful for comparing the sample quality with reference measurements. In this article, the key features and measured performance data of the beamline and the experimental station are presented. As scientific examples, the adsorbate–substrate distance in hexagonal boron nitride on Ni(111), surface quantum well states in a metal-organic network of dicyano-anthracene on Cu(111), and circular dichroism in the photoelectron diffraction of Cu(111) are discussed.

This chapter summarizes the investigations of the endohedral metallofullerenes (EMFs) with a C80 carbon shell in view of their magnetic properties, where the recently discovered single-molecule magnetism in dysprosium based species are highlighted.

Increasing the temperature at which molecules behave as single-molecule magnets is a serious challenge in molecular magnetism. One of the ways to address this problem is to create the molecules with strongly coupled lanthanide ions. In this work, endohedral metallofullerenes Y2@C80 and Dy2@C80 are obtained in the form of air-stable benzyl monoadducts. Both feature an unpaired electron trapped between metal ions, thus forming a single-electron metal-metal bond. Giant exchange interactions between lanthanide ions and the unpaired electron result in single-molecule magnetism of Dy2@C80(CH2Ph) with a record-high 100 s blocking temperature of 18 K. All magnetic moments in Dy2@C80(CH2Ph) are parallel and couple ferromagnetically to form a single spin unit of 21 μB with a dysprosium-electron exchange constant of 32 cm−1. The barrier of the magnetization reversal of 613 K is assigned to the state in which the spin of one Dy centre is flipped., Single molecule magnets have demonstrated promise for information storage, molecular spintronics and quantum computing, but are limited by their low operational temperatures. Here, Popov and coworkers prepare a SMM with a high blocking temperature of 18 K by trapping two lanthanide ions with a single-electron bond inside a fullerene.

For the endohedral fullerene molecule HoLu_{2}N@C_{80}, it is shown that the endohedral HoLu_{2}N unit may be oriented in a magnetic field. The Ho magnetic moment is fixed in the strong ligand field and aligns along the holmium-nitrogen axis. The torque of a magnetic field on the Ho magnetic moment leads to a hopping bias of the endohedral unit inclining to an orientation parallel to the externally applied field. This endohedral cluster distribution remains frozen below the onset of thermally induced rotation of the endohedral units. We derive an analytical statistical model for the description of the effect that scales below 7 T with the square of the external field strength, and that allows us to resolve the freezing temperature of the endohedral hopping motion. The freezing temperature is around 55 K and depends on the cooling rate, which in turn determines an activation energy for the hopping motion of 185 meV and a prefactor of 1.8×10^{14} s^{-1}. For TbSc_{2}N@C_{80} we find the same behavior with a 3.5% higher freezing temperature.

This chapter summarizes the investigations of the endohedral metallofullerenes (EMFs) with a C80 carbon shell in view of their magnetic properties, where the recently discovered single-molecule magnetism in dysprosium based species are highlighted.

Hyperthermal atoms may be implanted beneath single layers of graphene or hexagonal boron nitride (h-BN) on a substrate. For the case of h-BN on rhodium, which is a corrugated honeycomb superstructure with a periodicity of 3.2 nm, Ar atoms are implanted at distinct interstitial sites within the supercell, where the h-BN is weakly bound to the substrate. These peculiar structures are reminiscent of "nanotents" with an ultimately thin "rainfly". Here we explore the implantation length (i.e., the distance the atoms move before they come to rest as interstitial defects) and the thermal stability of these atomic agglomerates above room temperature. The results are obtained by variable-temperature scanning tunneling microscopy and density functional theory calculations.

The exposure of hexagonal boron nitride single layers to low energy ions leads to the formation of vacancy defects that are mobile at elevated temperatures. For the case of h-BN on rhodium, a superhoneycomb surface with 3 nm lattice constant (nanomesh), a concerted self-assembly of these defects is observed, where the "can-opener" effect leads to the cut-out of 2 nm "lids" and stable voids in the h-BN layer. These clean-cut voids repel each other, which enables the formation of arrays with a nearest neighbor distance down to about 8 nm. The density of voids depends on the Ar ion dose, and can reach 10(12) cm(-2). If the structures are annealed above 1000 K, the voids disappear and pristine h-BN nanomesh with larger holes is recovered. The results are obtained by scanning tunneling microscopy and density functional theory calculations.

A molecule standing on a metal surface has been found to emit electrons in the presence of an applied electric field. The emitted electrons produce an interference pattern reminiscent of a classic physics experiment. A molecule standing on a metal surface has been found to emit electrons in the presence of an applied electric field. The emitted electrons produce an interference pattern reminiscent of a classic physics experiment.

The accurate description of interface characteristics between organic molecules and metal surfaces has long been debated in theoretical studies. A well-founded description of interface geometry and adsorption energy is highly desirable for these hybrid inorganic/organic interfaces. Using first principles calculations with the inclusion of five van der Waals functionals (vdW-DF family), benzene (C6H6) adsorption on seven transition metal surfaces is studied to explore the performance of these vdW functionals under varying surface chemistry. Our results reveal that vdW interactions are crucial for an accurate description of bonding on transition metal substrates. We find that vdW interactions increase adsorption energy on coinage metal surfaces (Au, Ag, Cu) by about 0.7 eV, while they lead to even larger increases in the adsorption energies on the reactive transition metal surfaces (Pd, Pt, Rh, Ni). Our calculations also reveal that changes in adsorption energies stemming from vdW functionals show significa...

The surface segregation profile of an intermetallic compound becomes vertically and laterally modulated upon epitaxial growth of a single-layer hexagonal boron nitride $(h$-BN) nanomesh. $h$-BN on PtRh(111) forms an 11-on-10 superhoneycomb, such as that on Rh(111) [Corso et al., Science 303, 217 (2004)], though with a smaller lattice constant of 2.73 nm. X-ray photoelectron diffraction shows that the $h$-BN layer reduces the Pt enrichment of the first layer by promoting site swapping of about 10 Pt-Rh pairs within the $10\ifmmode\times\else\texttimes\fi{}10$ unit cell between the first and second layers. This segregation profile is confirmed by density-functional-theory-based cluster-expansion calculations. Generally, a strong modulation of the $h$-BN bonding strength and a higher affinity to one of the constituents leads to self-assembly of top layer patches underneath the nanomesh pores.