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The layered salt Bi14Rh3I9 is a weak three-dimensional (3D) topological insulator (TI), that is, a stack of two-dimensional (2D) TIs. It has a wide non-trivial band gap of 210 meV, which is generated by strong spin-orbit coupling, and possesses protected electronic edge-states. In the structure, charged layers of (Formula presented.) (Bi4Rh)3I]2+ honeycombs and (Formula presented.) Bi2I8]2− chains alternate. The non-trivial topology of Bi14Rh3I9 is an inherent property of the 2D intermetallic fragment. Here, the exfoliation of Bi14Rh3I9 was performed using two different chemical approaches: (a) through a reaction with n-butyllithium and poly(vinylpyrrolidone), (b) through a reaction with betaine in dimethylformamide at 55 °C. The former yielded few-layer sheets of the new compound Bi12Rh3I, while the latter led to crystalline sheets of Bi14Rh3I9 with a thickness down to 5 nm and edge-lengths up to several ten microns. X-ray diffraction and electron microscopy proved that the structure of Bi14Rh3I9 remained intact. Thus, it was assumed that the particles are still TIs. Dispersions of these flakes now allow for next steps towards the envisioned applications in nanoelectronics, such as the study of quantum coherence in deposited films, the combination with superconducting particles or films for the generation of Majorana fermions, or studies on their behavior under the influence of magnetic or electric fields or in contact with various materials occurring in devices. The method presented generally allows to exfoliate layers with high specific charges and thus the use of layered starting materials beyond van der Waals crystals. © 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH

International audience; The study of the new forms of magnetic states in magnetic cylinders has recently attracted much attention [1]. However, multi-layered structures in cylindrical geometry, which are basic blocks for spin torque nano-oscillators for example, have been poorly studied up to now. Among others, one of the main challenge for such studies is the experimental observation of magnetic configurations below 100 nm. In this work, we used off-axis electron holography to observe the remnant magnetic states of Co/Cu multi-layered nano-cylinders with a spatial resolution down to 2 nm. Nanocylinders are grown by electrodeposition in commercial polycarbonate membranes. Their diameters range between 70 and 90 nm. In order to study the effect of the aspect ratio and dipolar coupling on the magnetic states, four series of samples with different nominal Co and Cu thicknesses have been realized, namely Co25 nm/Cu15 nm, Co25 nm/Cu45 nm , Co50 nm/Cu50 nm and Co100 nm/Cu100 nm. The magnetic configurations are recovered from direct qualitative and quantitative comparison between the experimental magnetic phase shift image obtained by holography and the one calculated from micromagnetic simulations (OOMMF). These ones are performed including the geometrical properties of each individual layers deduced from EFTEM experiments. With our method, we have observed in the different wires either uniform magnetic states with antiparallel coupling or vortex states with different orientations of the core with respect to the wire axis [2,3]. In addition, different magnetic states can coexist within the same nanowire. Such a wide variety of magnetic configuration arises from the low values of the Co magnetic constants with respect to bulk, typical of electrodeposition process in single bath. To explain our results, we have calculated the phase diagram of the remnant states in a single disc for different orientations of the crystal anisotropy and saturation field. We show that the occurrence of each configuration depends on the aspect ratio of the layers, the direction of magneto crystalline anisotropy, and, in some cases, the interlayer dipolar coupling. In particular case, we will show that information on the preferential orientation of the crystalline anisotropy can be recovered from the statistics of occurrence of each magnetic configurations in the multilayer. Finally, we discuss the interest of 3D holographic vector field electron tomography for nanomagnetism studies. Preliminary results performed on the Co25 nm/Cu15 nm cylinders demonstrates that it allows getting the exact shape of each layer and the 3D components of the magnetic induction in each layer. This avoids geometrical uncertainties in micromagnetic simulations and solves the problem of 2D projection in off-axis electron holography experiments, leading to a much better determination of the magnetic constant of the layers.

This article addresses extraction of physically meaningful information from STEM EELS and EDX spectrum-images using methods of Multivariate Statistical Analysis. The problem is interpreted in terms of data distribution in a multi-dimensional factor space, which allows for a straightforward and intuitively clear comparison of various approaches. A new computationally efficient and robust method for finding physically meaningful endmembers in spectrum-image datasets is presented. The method combines the geometrical approach of Vertex Component Analysis with the statistical approach of Bayesian inference. The algorithm is described in detail at an example of EELS spectrum-imaging of a multi-compound CMOS transistor.

In the last decades, the blossoming of experimental breakthroughs in the domain of electron energy loss spectroscopy (EELS) has triggered a variety of theoretical developments. Those have to deal with completely different situations, from atomically resolved phonon mapping to electron circular dichroism passing by surface plasmon mapping. All of them rely on very different physical approximations and have not yet been reconciled, despite early attempts to do so. As an effort in that direction, we report on the development of a scalar relativistic quantum electrodynamic (QED) approach of the inelastic scattering of fast electrons. This theory can be adapted to describe all modern EELS experiments, and under the relevant approximations, can be reduced to any of the last EELS theories. In that aim, we present in this paper the state of the art and the basics of scalar relativistic QED relevant to the electron inelastic scattering. We then give a clear relation between the two once antagonist descriptions of the EELS, the retarded green Dyadic, usually applied to describe photonic excitations and the quasi-static mixed dynamic form factor (MDFF), more adapted to describe core electronic excitations of material. We then use this theory to establish two important EELS-related equations. The first one relates the spatially resolved EELS to the imaginary part of the photon propagator and the incoming and outgoing electron beam wavefunction, synthesizing the most common theories developed for analyzing spatially resolved EELS experiments. The second one shows that the evolution of the electron beam density matrix is proportional to the mutual coherence tensor, proving that quite universally, the electromagnetic correlations in the target are imprinted in the coherence properties of the probing electron beam., Re-Submission to SciPost. Updated version: minor revisions, SciPost template

An often-overlooked property of transition metal oxide thin films is their microscopic surface structure and its effect on the electronic properties in the ultrathin limit. Contrary to the expected conservation of the perovskite stacking order in the (001) direction, heteroepitaxially grown SrIrO3 films on TiO2-terminated SrTiO3 are found to exhibit a terminating SrO surface layer. The proposed mechanism for the self-organized conversion involves the adsorption of excess oxygen ions at the apical sites of the IrO2-terminated surface and the subsequent decomposition of the IrO6 octahedra into gaseous molecular IrO3 and the remaining SrO-terminated surface. Whereas the ab initio calculated electronic structure of SrO-terminated SrIrO3 in the monolayer limit exhibits a striking similarity to bulk Sr2IrO4, the broken octahedral symmetry at the IrO2-terminated surface would mix the otherwise crystal field split e(g) and t(2g) states, resulting in distinctly different low-energy electronic states. Published under license by AIP Publishing.

The 2D layered honeycomb magnet α-ruthenium(III) chloride (α-RuCl3) is a promising candidate to realize a Kitaev spin model. As alteration of physical properties on the nanoscale is additionally intended, new synthesis approaches to obtain phase pure α-RuCl3 nanocrystals have been audited. Thermodynamic simulations of occurring gas phase equilibria were performed and optimization of synthesis conditions was achieved based on calculation results. Crystal growth succeeded via chemical vapor transport (CVT) in a temperature gradient of 973 K to 773 K on YSZ substrates. Single crystal sheets of high crystallinity with heights ≤30 nm were obtained via pure CVT. The crystal properties were characterized by means of optical and electron microscopy, AFM, SAED, micro-Raman and XPS proving their composition, morphology, crystallinity and phase-purity. A highlight of our study is the successful individualization of nanocrystals and the delamination of nanosheets on YSZ substrates down to the monolayer limit (≤1 nm) which was realized by means of substrate exfoliation and ultrasonication in a very reproducible way.

The nondestructive characterization of nanoscale devices, such as those based on semiconductor nanowires, in terms of functional potentials is crucial for correlating device properties with their morphological/materials features, as well as for precisely tuning and optimizing their growth process. Electron holographic tomography (EHT) has been used in the past to reconstruct the total potential distribution in three-dimension but hitherto lacked a quantitative approach to separate potential variations due to chemical composition changes (mean inner potential, MIP) and space charges. In this Letter, we combine and correlate EHT and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) tomography on an individual ⟨111⟩ oriented GaAs-AlGaAs core-multishell nanowire (NW). We obtain excellent agreement between both methods in terms of the determined Al concentration within the AlGaAs shell, as well as thickness variations of the few nanometer thin GaAs shell acting as quantum well tube. Subtracting the MIP determined from the STEM tomogram, enables us to observe functional potentials at the NW surfaces and at the Au-NW interface, both ascribed to surface/interface pinning of the semiconductor Fermi level.

Within OECD-countries, the public sector is among the largest employers. With an OECD-average of more than 19% of the total labour force being employed in the public sector, and bureaucracy being present in many aspects of everyday life, public administration plays an important role not only as an institution contributing to a functioning social market economy. As one of the main areas of interaction between citizens and “the State”, bureaucracy also considerably influences citizens’ image of the legislative and executive branch. The partly negative image that citizens have of the bureaucracy needs to be improved not only on that account, though. The interaction between citizens and bureaucracy largely impacts the utilisation of government programmes and measures, and therefore, their effectiveness. This text analyses current literature and applies theories from the field of institutional economics to show the influence of information asymmetries on the interaction between citizens and bureaucracy and discusses possible measures to improve the situation. Keywords: information assymetries, citizens, bureaucracy, institutional economics

PtBi$_2$ is a polymorphic system with interesting electronic properties. Here we report optimized crystal growth and structural characterization of pyrite-type and trigonal modification of PtBi$_2$. Selected area electron diffraction, X-ray powder diffraction and further Rietveld refinement confirms that trigonal PtBi$_2$ crystallizes in non-centrosymmetric $P31m$ space group, pyrite-type PtBi$_2$ in $Pa\bar{3}$ space group. Series of Pt$_{1-x}$Rh$_x$Bi$_2$ samples was obtained for $x=0, 0.03, 0.35$ in the trigonal PtBi$_2$ structure. These Pt$_{1-x}$Rh$_x$Bi$_2$ compounds become superconducting where critical temperature increases from $T_c=600$ mK for $x=0$ up to $T_c=2.7$ K for $x=0.35$. Furthermore we calculate the electronic band structure, using the structure parameters obtained. The calculated density of states (DOS) shows a minimum for the stochiometric compound at the Fermi level. These findings warrant further research by broader array of experimental techniques, as well as the effect of the substitution on the non-trivial band structure.

We have investigated the effect of potassium (K) intercalation on $2H$-MoS$_2$ using transmission electron energy-loss spectroscopy. For K concentrations up to approximately 0.4, the crystals appear to be inhomogeneous with a mix of structural phases and irregular potassium distribution. Above this intercalation level, MoS$_2$ exhibits a $2a \times 2a$ superstructure in the $ab$ plane and unit cell parameters of a = 3.20 $\unicode{x212B}$ and c = 8.23 $\unicode{x212B}$ indicating a conversion from the $2H$ to the $1T'$ or $1T''$ polytypes. The diffraction patterns also show a $\sqrt{3}a \times \sqrt{3}a$ and a much weaker $2\sqrt{3}a \times 2\sqrt{3}a$ superstructure that is very likely associated with the ordering of the potassium ions. A semiconductor-to-metal transition occurs signified by the disappearance of the excitonic features from the electron energy-loss spectra and the emergence of a charge carrier plasmon with an unscreened plasmon frequency of 2.78 eV. The plasmon has a positive, quadratic dispersion and appears to be superimposed with an excitation arising from interband transitions. The behavior of the plasmon peak energy positions as a function of potassium concentration shows that potassium stoichiometries of less than $\sim 0.3$ are thermodynamically unstable while higher stoichiometries up to $\sim 0.5$ are thermodynamically stable. Potassium concentrations greater than $\sim 0.5$ lead to the decomposition of MoS$_2$ and the formation of K$_2$S. The real part of the dielectric function and the optical conductivity of K$_{0.41}$MoS$_2$ were derived from the loss spectra via Kramers-Kronig analysis., Comment: 7 Figures, 2 Tables

We report an optimized chemical vapor transport method that enables the growth of FeP single crystals up to 500 mg in mass and $80\phantom{\rule{0.16em}{0ex}}{\mathrm{mm}}^{3}$ in volume. The high quality of the crystals obtained by this method was confirmed by means of energy-dispersive x-ray spectroscopy, high-resolution transmission electron microscopy, low-temperature single-crystal x-ray diffraction, and neutron diffraction experiments. We investigated the transport and magnetic properties of the single crystals, and we calculated the electronic structure of FeP. We show both theoretically and experimentally that the ground state of FeP is metallic. The examination of the magnetic data reveals antiferromagnetic order below ${T}_{\mathrm{N}}=119\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ while transport remains metallic in both the paramagnetic and the antiferromagnetic phase. The analysis of the neutron diffraction data shows an incommensurate magnetic structure with the propagation vector $\mathbf{Q}=(0,0,\ifmmode\pm\else\textpm\fi{}\ensuremath{\delta})$, where \ensuremath{\delta} is close to 0.2. For a full understanding of the magnetic state, further experiments are needed. The successful growth of large high-quality single crystals paves the way for further investigations of itinerant magnets with incommensurate spin structures using a wide range of experimental tools.

The reduced dimensionality in two-dimensional materials leads to a wealth of unusual properties, which are currently explored for both fundamental and applied sciences. In order to study the crystal structure, edge states, the formation of defects and grain boundaries, or the impact of adsorbates, high-resolution microscopy techniques are indispensable. Here we report on the development of an electron holography (EH) transmission electron microscopy (TEM) technique, which facilitates high spatial resolution by an automatic correction of geometric aberrations. Distinguished features of EH beyond conventional TEM imaging are gap-free spatial information signal transfer and higher dose efficiency for certain spatial frequency bands as well as direct access to the projected electrostatic potential of the two-dimensional material. We demonstrate these features with the example of h-BN, for which we measure the electrostatic potential as a function of layer number down to the monolayer limit and obtain evidence for a systematic increase of the potential at the zig-zag edges.

We introduce a three-step seed-mediated synthesis for single crystalline gold nanoparticles (Au NPs) stabilized by hexadecylpyridinium chloride (CPC) in variable sizes with an independently adjustable ratio of the cubic and octahedral facets. The effect of KBr and ascorbic acid (AA) on shape and growth kinetics is systematically investigated. The kinetic data were evaluated using the minimalistic Finke–Watzky autocatalytic two-step mechanism, which allows to estimate the rate constants of the “pseudoelementary” reactions. The proposed surface-mediated mechanism of reduction of gold ions and Au NP growth allows to explain the effect of gradual increase of bromide ion concentration on switching the Au NP morphology from cubic to octahedral. The plasmonic properties of single particles of different facetings and their assemblies are investigated.

Electron holographic tomography was used to obtain three-dimensional reconstructions of the morphology and electrostatic potential gradient of axial GaInP/InP nanowire tunnel diodes. Crystal growth was carried out in two opposite directions: GaInP-Zn/InP-S and InP-Sn/GaInP-Zn, using Zn as the p-type dopant in the GaInP but with changes to the n-type dopant (S or Sn) in the InP. Secondary electron and electron beam-induced current images obtained using scanning electron microscopy indicated the presence of p-n junctions in both cases and current-voltage characteristics measured via lithographic contacts showed the negative differential resistance, characteristic of band-to-band tunneling, for both diodes. Electron holographic tomography measurements confirmed a short depletion width in both cases (21 ± 3 nm) but different built-in potentials, Vbi, of 1.0 V for the p-type (Zn) to n-type (S) transition, and 0.4 V for both were lower than the expected 1.5 V for these junctions if degenerately doped. Charging induced by the electron beam was evident in phase images which showed nonlinearity in the surrounding vacuum, most severe in the case of the nanowire grounded at the p-type Au contact. We attribute their lower Vbi to asymmetric secondary electron emission, beam-induced current biasing, and poor grounding contacts.

Utilizing the Pauli equation based multislice method, introduced in Phys. Rev. Lett. 116, 127203 (2016), we study the atomic resolution differential phase contrast (DPC) imaging on an example of a hard magnet FePt with in-plane magnetization. Simulated center of mass pattern in a scanning transmission electron microscopy (STEM) experiment carries information about both electric and magnetic fields. The momentum transfer remains curl-free, which has consequences for interpretation of the integrated DPC technique. The extracted magnetic component of the pattern is compared to the expected projected microscopic magnetic field as obtained by density functional theory calculation. Qualitative agreement is obtained for low sample thicknesses and a suitable range of collection angles., 9 pages, 8 figures

Rubrene single crystal domains with hundreds of micrometers size fully covering different substrates are achieved by thermal annealing of evaporated amorphous thin films with the help of a thin glassy underlayer. The sufficiently large energy level offset of the underlayer material and rubrene enables high performance staggered bottom gate rubrene crystalline transistors with maximum field-effect linear mobility over 5 cm2V−1s−1 (μAvg = 4.35 ± 0.76 cm2V−1s−1) for short channel devices of 20 μm, comparable to high quality rubrene bulk single crystals. Moreover, since molecular dopants up to several mole percent can be incorporated into the single crystals with a minimal disturbance of the lattice, the contact resistance of the transistors is significantly reduced to around 1 kOhm.cm by contact doping via adlayer epitaxy of p-type doped rubrene. Our results pave the way for novel high-performance organic electronics using crystalline active materials with mass-production compatible deposition techniques.

Off-axis electron holography is a well-established transmission electron microscopy technique, typically employed to investigate electric and magnetic fields in and around nanoscale materials, which modify the phase of the reconstructed electron wave function. Here, we elaborate on a detailed analysis of the two characteristic intensity terms that are completing the electron hologram, the conventional image intensity and the interference fringe intensity. We show how both are related to elastic and inelastic scattering absorption at the sample and how they may be separated to analyze the chemical composition of the sample. Since scattering absorption is aperture dependent, a quantitative determination of the corresponding attenuation coefficients (reciprocal mean free path lengths) requires the use of holographic image modi with well-defined objective aperture stops in the back-focal plane of the objective lens. The proposed method extends quantitative electron holography to a correlated three-in-one characterization of electric and magnetic fields, Z-contrast and dielectric losses in materials.

Chains of metallic nanoparticles sustain strongly confined surface plasmons with relatively low dielectric losses. To exploit these properties in applications, such as waveguides, the fabrication of long chains of low disorder and a thorough understanding of the plasmon-mode properties, such as dispersion relations, are indispensable. Here, we use a wrinkled template for directed self-assembly to assemble chains of gold nanoparticles. With this up-scalable method, chain lengths from two particles (140 nm) to 20 particles (1500 nm) and beyond can be fabricated. Electron energy-loss spectroscopy supported by boundary element simulations, finite-difference time-domain, and a simplified dipole coupling model reveal the evolution of a band of plasmonic waveguide modes from degenerated single-particle modes in detail. In striking difference from plasmonic rod-like structures, the plasmon band is confined in excitation energy, which allows light manipulations below the diffraction limit. The non-degenerated surface plasmon modes show suppressed radiative losses for efficient energy propagation over a distance of 1500 nm. �� 2019 American Chemical Society.

Inspired by chains of ferrimagnetic nanocrystals (NCs) in magnetotactic bacteria (MTB), the synthesis and detailed characterization of ferrimagnetic magnetite NC chain-like assemblies is reported. An easy green synthesis route in a thermoreversible gelatin hydrogel matrix is used. The structure of these magnetite chains prepared with and without gelatin is characterized by means of transmission electron microscopy, including electron tomography (ET). These structures indeed bear resemblance to the magnetite assemblies found in MTB, known for their mechanical flexibility and outstanding magnetic properties and known to crystallographically align their magnetite NCs along the strongest magnetization easy axis. Using electron holography (EH) and angular dependent magnetic measurements, the magnetic interaction between the NCs and the generation of a magnetically anisotropic material can be shown. The electro- and magnetostatic modeling demonstrates that in order to precisely determine the magnetization (by means of EH) inside chain-like NCs assemblies, their exact shape, arrangement and stray-fields have to be considered (ideally obtained using ET). �� 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Chemistry of materials 31(8), 2795 - 2806 (2019). doi:10.1021/acs.chemmater.8b05017, High-quality single crystals of MnBi2Te4 are grown for the first time by slow cooling within a narrow range between the melting points of Bi$_2$Te$_3$ (586 °C) and MnBi$_2$Te$_4$ (600 °C). Single-crystal X-ray diffraction and electron microscopy reveal ubiquitous antisite defects in both cation sites and, possibly, Mn vacancies (Mn$_{0.85(3)}$Bi$_{2.10(3)}$Te$_4$). Thermochemical studies complemented with high-temperature X-ray diffraction establish a limited high-temperature range of phase stability and metastability at room temperature. Nevertheless, the synthesis of MnBi$_2$Te$_4$ can be scaled-up as powders can be obtained at subsolidus temperatures and quenched at room temperature. Bulk samples exhibit long-range antiferromagnetic ordering below 24 K. The Mn(II) out-of-plane magnetic state is confirmed by the magnetization, X-ray photoemission, X-ray absorption, and linear dichroism measurements. The compound shows a metallic type of resistivity in the range 4.5–300 K and is an n-type conductor that reaches a thermoelectric figure of merit up to ZT = 0.17. Angle-resolved photoemission experiments show a surface state forming a gapped Dirac cone, thus strengthening MnBi$_2$Te$_4$ as a promising candidate for the intrinsic magnetic topological insulator, in accordance with theoretical predictions. The developed synthetic protocols enable further experimental studies of a crossover between magnetic ordering and nontrivial topology in bulk MnBi$_2$Te$_4$., Published by American Chemical Society, Washington, DC

In the present work, different synthesis procedures have been demonstrated to fill carbon nanotubes (CNTs) with Fe1-xNix alloy nanoparticles (x = 0.33, 0.5). CNTs act as templates for the encapsulation of magnetic nanoparticles, and provide a protective shield against oxidation as well as prevent nanoparticles agglomeration. By variation of the reaction parameters, the purity of the samples, degree of filling, the composition and size of filling nanoparticles have been tailored and therefore the magnetic properties. The samples were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Bright-field (BF) TEM tomography, X-ray powder diffraction, superconducting quantum interference device (SQUID) and thermogravimetric analysis (TGA). The Fe1-x Nix-filled CNTs show a huge enhancement in the coercive fields compared to the corresponding bulk materials, which make them excellent candidates for several applications such as magnetic storage devices.