Reciprocal and real space maps for EMCD experiments

Electron magnetic chiral dichroism (EMCD) is an emerging tool for quantitative measurements of magnetic properties using the transmission electron microscope (TEM), with the possibility of nanometer resolution. The geometrical conditions, data treatment and electron gun settings are found to influence the EMCD signal. In this article, particular care is taken to obtain a reliable quantitative measurement of the ratio of orbital to spin magnetic moment using energy filtered diffraction patterns. For this purpose, we describe a method for data treatment, normalization and selection of mirror axis. The experimental results are supported by theoretical simulations based on dynamical diffraction and density functional theory. Special settings of the electron gun, so called telefocus mode, enable a higher intensity of the electron beam, as well as a reduction of the influence from artifacts on the signal. Using these settings, we demonstrate the principle of acquiring real space maps of the EMCD signal. This enables advanced characterization of magnetic materials with superior spatial resolution.     

Intensity analysis of boron and nitrogen K-edge spectra for hexagonal boron nitride by EELS

Boron and nitrogen K-edge spectra for hexagonal boron nitride (h-BN) were measured by electron energy loss spectroscopy (EELS) at orientations of a momentum transfer q parallel and perpendicular to the c-axis in order to investigate anisotropic unoccupied states π* and σ*, separately. Differences between intensity profiles for B_K and N_K spectra are attributed to different transition probabilities at B_K and N_K edges from Is states to the π* and σ* states. The intensity of the first peak at q ∥ c in the B_K spectrum, which is ascribed to the transition from B-1s to the Q^—₂ state in the π* band, is 10 times as large as that in the N_K spectrum. Quantitative calculation of transition probabilities for B_K and N_K spectra at q ∥ c shows that the contribution of B-2p_z orbital to the Q^—₂ state is 1–7 times as large as that of N-2p_z. This value suggests that the enhanced peak in the B_K spectrum is explained by means of single electron excitations, disregarding the electron-electron interactions for the exciton reported by several workers. The contributions of 2p_x and 2p_y orbitals of B and N atoms to σ* states are also estimated by intensity analysis of B_K and N_K spectra at q⊥c .     

Analysis of the calcium distribution in predentine by EELS and of the early crystal formation in dentine by ESI and ESD

Predentine is a collagen-rich extracellular matrix between the odontoblasts and the dentine with a width of about 15–20 μm. Electron energy-loss spectroscopy of rat incisors shows a significantly higher calcium content in the predentine at the predentine-dentine border than in the middle region of the predentine. At the predentine-dentine border in the dentine, the calcium and the phosphate groups combine to form apatite crystallites. Electron spectroscopic diffraction with zero-loss filtering revealed that the earliest crystallites contain only Debye-Scherrer rings of apatite, which are fewer in number and more diffuse than the diffraction rings from the mature crystallites. We therefore conclude that the early crystallites still contain lattice defects, which are annealed out to some degree with crystal growth. Electron spectroscopic imaging with zero-loss filtering also showed that the earliest crystallites are chains of dots (or small islands); they build up strands composed of islands, which rapidly acquire a needle-like character and coalesce laterally to form ribbon- or plate-like crystallites. The parallel strands sometimes appear to reinforce the macroperiod of the collagen microfibrils (67 nm) by tiny holes without any crystal-substance lined up perpendicular to the parallel strands of the crystallites.     

夹片与锚环摩擦阻力损失的分析

预应力张拉施工中夹片、钢绞线和锚环之间存在着很大的摩擦阻力.分析这三者的关系,寻找限位板台阶深度最优值,研究孔道摩擦阻力,分析孔道传感器测试法.