A material is said to exhibit dichroism if its photon absorption spectrum depends on the polarization of the incident radiation. In the case of X-ray magnetic circular dichroism (XMCD), the absorption cross-section of a ferromagnet or a paramagnet in a magnetic field changes when the helicity of a circularly polarized photon is reversed relative to the magnetization direction. Although similarities between X-ray absorption and electron energy-loss spectroscopy in a transmission electron microscope (TEM) have long been recognized, it has been assumed that extending such equivalence to circular dichroism would require the electron beam in the TEM to be spin-polarized. Recently, it was argued on theoretical grounds that this assumption is probably wrong. Here we report the direct experimental detection of magnetic circular dichroism in a TEM. We compare our measurements of electron energy-loss magnetic chiral dichroism (EMCD) with XMCD spectra obtained from the same specimen that, together with theoretical calculations, show that chiral atomic transitions in a specimen are accessible with inelastic electron scattering under particular scattering conditions. This finding could have important consequences for the study of magnetism on the nanometre and subnanometre scales, as EMCD offers the potential for such spatial resolution down to the nanometre scale while providing depth information--in contrast to X-ray methods, which are mainly surface-sensitive.

Recently it was demonstrated (Schattschneider et al., Nature 441 (2006), 486), that an analogue of the X-ray magnetic circular dichroism (XMCD) experiment can be performed with the transmission electron microscope (TEM). The new phenomenon has been named energy-loss magnetic chiral dichroism (EMCD). In this work we present a detailed ab initio study of the chiral dichroism in the Fe, Co and Ni transition elements. We discuss the methods used for the simulations together with the validity and accuracy of the treatment, which can, in principle, apply to any given crystalline specimen. The dependence of the dichroic signal on the sample thickness, accuracy of the detector position and the size of convergence and collection angles is calculated.

Magnetic circular dichroism ͑MCD͒ is a standard technique for the study of magnetic properties of materials in synchrotron beamlines. We present here a scattering geometry in the transmission electron microscope through which MCD can be observed with unprecedented spatial resolution. A convergent electron beam is used to scan a cross sectional preparation of a Fe/Au multilayer sample. Differences in the energy-loss spectra induced by the magnetic moments of the Fe atoms can be resolved with a resolution of better than 2 nm. This is a breakthrough achievement when compared both to the previous energy-loss MCD resolution ͑200 nm͒ or the best x-ray MCD experiments ͑approximately 20 nm͒.

A method to produce suspensions of graphene sheets by combining solution-based bromine intercalation and mild sonochemical exfoliation is presented. Ultrasonic treatment of graphite in water leads to the formation of suspensions of graphite flakes. The delamination is dramatically improved by intercalation of bromine into the graphite before sonication. The bromine intercalation was verified by Raman spectroscopy as well as by x-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations show an almost ten times lower interlayer binding energy after introducing Br2 into the graphite. Analysis of the suspended material by transmission and scanning electron microscopy (TEM and SEM) revealed a significant content of few-layer graphene with sizes up to 30 µm, corresponding to the grain size of the starting material.

We report the synthesis of injectable in situ forming hybrid hydrogel material and investigate its ability to support the mineralization process under mild conditions. To achieve this, we have prepared a hyaluronic acid (HA) derivative that is dually functionalized with cross-linkable hydrazide groups and bisphosphonate ligands (HA-hy-BP). The hybrid hydrogel can be formed by simple mixing of two solutions: the solution of HA-hy-BP and the Ca2+ ions containing solution of aldehyde-derivatized HA (HA-al). We found that the conjugation of BP, a P–C–P analogue of pyrophosphate, to the hydrogel matrix promotes an efficient and fast mineralization of the matrix. The mineralization is facilitated by the strong interaction between BP residues and Ca2+ ions that serve as nanometer-sized nucleation points for further calcium phosphate deposition within the HA hydrogel. Compared with previously reported hydrogel template-driven mineralization techniques, the present approach is maximally adapted for clinical settings since the formation of the hybrid takes place during quick mixing of the sterilized solutions. Moreover, the hybrid hydrogel is formed from in vivo degradable components of the extracellular matrix and therefore can be remodeled in vivo through concerted HA degradation and calcium phosphate mineralization.