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Manipulation of intrinsic electronic structures by electron or hole doping in a controlled manner in van der Waals layered materials is the key to control their electrical and optical properties. Two-dimensional indium selenide (InSe) semiconductor has attracted attention due to its direct band gap and ultrahigh mobility as a promising material for optoelectronic devices. In this work, we manipulate the electronic structure of InSe by in situ surface electron doping and obtain a significant band gap renormalization of ∼120 meV directly observed by high-resolution angle resolved photoemission spectroscopy. This moderate doping level (carrier concentration of 8.1 × 1012 cm-2) can be achieved by electrical gating in field effect transistors, demonstrating the potential to design of broad spectral response devices.

International audience; Low-dimensional materials differ from their bulk counterpart in many respects. In particular, thescreening of the Coulomb interaction is strongly reduced, which can have important consequencessuch as the significant increase of exciton binding energies. In bulk materials the binding energyis used as an indicator in optical spectra to distinguish different kinds of excitons, but this is notpossible in low-dimensional materials, where the binding energy is large and comparable in size forexcitons of very different localization. Here we demonstrate that the exciton band structure, whichcan be accessed experimentally, instead provides a powerful way to identify the exciton character.By comparing the ab initio solution of the many-body Bethe-Salpeter equation for graphane andsingle-layer hexagonal BN, we draw a general picture of the exciton dispersion in two-dimensionalmaterials, highlighting the different role played by the exchange electron-hole interaction and by theelectronic band structure. Our interpretation is substantiated by a prediction for phosphorene.

The simultaneous formation of nanometer sized zinc oxide (ZnO), and acetate zinc hydroxide double salt (Zn-HDS) is described. These phases, obtained using the sol-gel synthesis route based on zinc acetate salt in alcoholic media, were identified by direct characterization of the reaction products in solution using complementary techniques: nephelometry, in situ Small-Angle X-ray Scattering (SAXS), UV-Vis spectroscopy and Extended X-ray Absorption Fine Structures (EXAFS). In particular, the hydrolytic pathway of ethanolic zinc acetate precursor solutions promoted by addition of water with the molar ratio N=[H2O]/[Zn2+] = 0.05 was investigated in this paper. The aim was to understand the formation mechanism of ZnO colloidal suspension and to reveal the factors responsible for the formation of Zn-HDS in the final precipitates. The growth mechanism of ZnO nanoparticles is based on primary particle (radius ≈ 1.5 nm) rotation inside the primary aggregate (radius

The evolution of both oxygen and framework tetrahedral shells around Ni2+ cations in faujasite upon rehydration can be described in real time thanks to in situ dispersive-EXAFS. Such type of analysis permits precise experimental description of the coordination environment of cations in zeolite structures under different hydration conditions.

The RMn 12− x Fe x series of compounds of ThMn 12 structure type exhibit rather complicated and composition sensitive magnetic properties. In a recent past, systematic neutron diffraction and magnetisation experiments allow to relate the main aspects of the magnetic structures to the polarisation state of the d-band. X-ray magnetic circular dichroism (XMCD) analyses have been undertaken on iron rich compounds with R = Y, Er, and Lu, thus probing the L 2,3 edges of Mn and Fe as well as Er, and the M 4,5 edges of Er. These experiments permit to better understand the local magnetic polarisation of the different interacting orbitals versus temperature and applied field as well as to precise the nature of the magnetic couplings acting between the 3d metals (M).

We report here the X-ray magnetic circular dichroism (XMCD) study at the Gd M(4,5)- and L(2,3)-edges of two linear magnetic chains involving Gd(III) cations bridged by nitronyl nitroxide radicals. This spectroscopy directly probes the magnetic moments of the 4f and 5d orbitals of the gadolinium ions. We compare macroscopic magnetic measurements and local XMCD signals. The M(4,5)-edges results are in agreement with the J values extracted from the fits of the SQUID magnetic measurements. The L(2,3)-edges signals show that the electronic density in the Gd 5d orbitals depends on the neighbors of the gadolinium cations. Nevertheless, the 5d orbitals do not seem to play any role in the superexchange pathway between radicals through the metal ion proposed to explain the particular magnetic exchange interactions between the radicals in these chains.

Les deux enantiomeres de l'aimant a precurseur moleculaire bidimensionnel { [N(C 4 H 9 ) 4 ][NiCr(ox) 3 ]} n (ox = C 2 O 4 2-) ont ete etudies. Le dichroisme circulaire magnetique dans le domaine des rayons X a ete mesure a 11 K, en dessous de la temperature de Curie du materiau (16 K). Le signal dichroique est identique pour les deux enantiomeres. Les spectres dichroiques aux seuils K du nickel et du chrome confirment le couplage ferromagnetique entre les deux ions metalliques. Les moments magnetiques remanents portes par les atomes de Ni et de Cr ont ete clairement mis en evidence, analyses et compares a l'aimantation remanente totale mesuree a 11 K par magnetometrie classique. Pour citer cet article : C. Train et al., C. R. Chimie 6 (2003).

International audience; The strong excitonic emission of hexagonal boron nitride (h-BN) makes this material one of the most promising candidate for light emitting devices in the far ultraviolet (UV). However, single excitons occur only in perfect monocrystals that are extremely hard to synthesize, while regular h-BN samples present a complex emission spectrum with several additional peaks. The microscopic origin of these additional emissions has not yet been understood. In this work we address this problem using an experimental and theoretical approach that combines nanometric resolved cathodoluminescence, high resolution transmission electron microscopy and state of the art theoretical spectroscopy methods. We demonstrate that emission spectra are strongly inhomogeneus within individual few layer flakes and that additional excitons occur at structural deformations, such as faceted plane folds, that lead to local changes of the h-BN layers stacking order.

Photo-induced magnetisation has been recently evidenced by Hashimoto et al. in CoFe cyanide[1]. We synthesized a diamagnetic RbFeCo cyanide able to present the same photomagnetic effect. The magnetic properties of the excited state, the electronic structure and the local structure of the ground and the excited states have been investigated. The conditions required to observe the phenomenon and the mechanism of the electron transfer are discussed.

A short review is given of the theoretical fundamentals, applications and limitations of X-ray magnetic circular dichroism (XMCD) at the M 4,5 and L 2,3 edges of rare earth compounds.

The effect of nitrogen insertion on the electronic properties of cerium and iron in has been studied by means of x-ray absorption spectroscopy (XAS) and magnetic circular x-ray dichroism (MCXD). The evolution of the electronic structure of cerium upon nitrogen insertion has been studied. It emerges from this MCXD study at the edges of cerium that the cerium atoms bear a 5d magnetic moment of about that is coupled antiferromagnetically to that of iron. The spin polarized EXAFS signal has been observed; an attempt to evidence the magnetic environment has been made in the light of previous neutron diffraction results. Comparison of EXAFS and spin polarized EXAFS is revealed to be an efficient new tool to distinguish between magnetic and non-magnetic atoms in the environment of the absorber. The analysis of the Fe K edge MCXD spectra shows that insertion of nitrogen induces a trend to strong ferromagnetism with an almost completely filled majority spin subband.

Magnetic circular x-ray dichroism on Co $/$Cu and Fe $/$Cu multilayers at the $K$ edge of copper shows (i) that the $p$ band of copper is significantly spin polarized by the adjacent Co or Fe atoms, (ii) that the spin polarization of the copper layers strongly depends on the adjacent magnetic layer, and (iii) that the magnetic polarization is not restricted to the interface layer, i.e., it departs from a simple ${1/t}_{\mathrm{Cu}}$ dependence.

This paper reports on two new technical developments concerning sample environments for X-ray magnetic circular dichroism (XMCD). The first measurements under high pressures of up to 30 GPa are described. The difficulties of combining the techniques of high pressure and XMCD are commented on. The second development involves the use of a fast-switching magnetic field. A new superconducting device is used to perform XMCD measurements on paramagnetic compounds in magnetic fields of up to 6 T. The small amplitude of the XMCD signal imposes, for a given signal-to-noise ratio, a noise less than a few 10−5. The signal-to-noise ratio is improved by the use of a series of acquisitions, switching the magnetic field between each acquisition. A very fast switching mechanism has been built based on mechanical rotation of a superconducting coil, with the sample kept in place inside the coil. The XMCD signals at the L II,III-edges of paramagnetic rare-earth compounds have been measured at 4.5 K in fields of up to 6 T with a switching time of 11 s.

The RMn 12− x Fe x series of compounds of ThMn 12 structure type exhibit rather complicated and composition sensitive magnetic properties. In the recent past, systematic neutron diffraction and magnetisation experiments allow to relate the main aspects of the magnetic structures to the polarisation state of the d band. X-ray magnetic circular dichroism (XMCD) analyses have been undertaken on iron rich compounds with R=Er, thus probing the L 2,3 edges of Mn and Fe as well as Er, and the M 4,5 edges of Er. These experiments permit to better understand the local magnetic polarisation of the different interacting orbitals versus temperature and applied field as well as to specify the nature of the magnetic couplings acting between the 3d metals.