Chromium (Cr), manganese (Mn) and carbon (C) are well known alloying elements used in technologically important alloy steels and advanced high strength steels. It is known that binary Crc(x) and MnCx carbides can be formed in steels, but in this study we reveal for the first time that Cr and Mn were found combined in novel ternary cementite type (Cr, Mn)C carbides. Electron diffraction experiments showed that Cr, Mn and C formed two distinct carbide phases possessing orthorhombic and monoclinic crystal structures. Density functional theory calculations were performed on these phases and excellent agreement was found between calculations and experiments on the lattice parameters and relative atomic positions. The calculations showed that the combination of Mn and Cr resulted in a very high thermodynamic stability of the (Cr, Mn)C carbides, and that local structural relaxations are associated with carbon additions. Possible implications of these ternary carbides for novel applications in steel design and manufacturing are discussed.@en

A method is presented to use an electron microscope in transmission mode to determine the mis-tilt from a zone axis of a crystalline material. The method involves recording a number of additional diffractiion patterns with incident beams tilted over 2 to 3 degrees. It is shown that an accuracy of 0.02 degree can be achieved, which is far better than that of the specimen-stage tilt axes, which is about 0.1 degree for the beta-tilt.@en

In-situ aberration-corrected transmission electron microscopy combined with density functional theory (DFT) calculations are employed to elucidate the electron beam induced dynamics of surface dislocations on ~ 4 nm × 6 nm sized Au (100) terraces located on top of hillock shaped Au at room temperature and 77 K at video rate (20 frames/s). At room temperature, very small terraces (<4 × 5 atoms) sink into the lower terrace forming surface dislocations associated with a (5 × 1) surface reconstruction unit cell. This injection occurs provided that the number of atoms of the terrace fits the number of extra atoms required to form the surface dislocation. The surface dislocation consists of either 5 or 3 (Type I and Type II) hexagonally stacked atom rows. While the surface dislocations tend to reside near terrace edges, in ~ 20% of the video frames, the surface dislocation resides near the center of the terrace. The occurrence of Type I or Type II structures depends on the terrace width. DFT calculations show that Type I surface dislocations are more stable than Type II, for dislocations that do not span the entire terrace width, in agreement with observations. Surface dislocations are observed to flip by 90¿during the experimental observations; the pathway and energy barrier (1.01 eV) for such flips is clarified through DFT calculations. At 77 K, no injections are observed, but surface dislocations do rarely form from an unreconstructed surface. In addition to dislocation flipping, multiple, dynamic dislocation configurations were observed in conjunction with terrace growth along the dislocation direction.@en

Although Fe(2)C and Fe(2)N are technologically important materials, the exact nature of the chemical bonding of C and N atoms and the related impact on the electronic properties are at present unclear. Here, results of first-principles electronic structure calculations for Fe(2)X (X = C, N) phases are presented. The electronic structure calculations show that the roles of N and C in iron nitrides and carbides are comparable, and that the X-X interactions have significant impact on electronic properties. Accurate analysis of the spatially resolved differences in electron densities reveals a subtle distinction between the chemical bonding and charge transfer of N and C ions.@en

The drive for elucidation of important macromolecular structures to high resolution in their 3D native or near-native state places continuously higher demands on the quality of the experimental data. For instance, recording of diffraction patterns good enough for structural studies from cryo-preserved bio-macromolecules at low dose conditions remains challenging and highly desirable. The emergence of hybrid pixel detectors opens up new possibilities for direct electron detection and superior detector performance. Here, we report on the characteristics of the Medipix2 detector in diffraction studies, with a special focus on the reliability of the intensities acquired in very low dose conditions. Diffraction data recorded on a Medipix2 detector were assessed in refinement analysis. R-factors lower than 10% were obtained from data recorded at electron dose of 0.05 el/angstrom(2). The reproducibility of the data was also shown to be high, given the correlation coefficient of the intensities being higher than 0.9970. The contrast that could be achieved at very low dose conditions was at least an order of magnitude better than that of image plates, based on a direct comparison.@en