Papers by Keyword: High Resolution Electron Microscopy (HREM)

Abstract: The geometric phase technique (GPA) for measuring the distortion of crystalline lattices from high-resolution electron microscopy (HRTEM) images will be described. The method is based on the calculation of the “local” Fourier components of the HRTEM image by filtering in Fourier space. The method will be illustrated with a study of an edge dislocation in silicon where displacements have been measured to an accuracy of 3 pm at nanometre resolution as compared with anisotropic elastic theory calculations. The different components of the strain tensor will be mapped out in the vicinity of the dislocation core and compared with theory. The accuracy is of the order of 0.5% for strain and 0.1° for rigid-body rotations. Using bulk elastic constants for silicon, the stress field is determined to 0.5 GPa at nanometre spatial resolution. Accuracy and the spatial resolution of the technique will be discussed.

Abstract: A new procedure is proposed for the exit electron wave reconstruction using a small set of high-resolution electron microscopy (HREM) images. This procedure is similar to that proposed by van Dyck and coworkers, but the relative shifts between different HREM images are obtained via the genetic algorithm instead of the more widely used cross-correlation function (XCF) method. The new procedure is demonstrated using simulated HREM images with added noise, and shown to be able to deal with situation where the scheme based on the method of XCF is not applicable.

Abstract: In situ high-resolution transmission electron microscopy experiments were applied to examine the nano-scale solidification process of boron-doped silicon from the liquid state. Fine particles of the specimen were first heated up to the melting temperature using a TEM heating-holder, and then gradually cooled across the melting temperature. The specimen was observed nearly along [001] direction. The lattice fringe of (220) plane was observed during solidification, and this part combined with the other liquid part to make a twist boundary. The angle between the (220) planes of these two crystal grains was close to the rotation angle of the (001) Σ5 twist boundary.

Abstract: Cast polycrystalline silicon for solar cell contains mostly straight twin boundaries which are thought to have little effect on the electrical activity. There are, however, some complicated grain boundaries in it. One of these boundaries consists of slightly curved and straight parts. The structure of this boundary was analyzed to investigate the difference of these two types of boundaries. The conventional transmission electron microscopy (TEM) found that this slightly curved boundary was the zigzag shaped boundary made by (11 _ ,2) and ( _ ,211) planes. High resolution electron microscopy (HREM) confirmed that (11 _ ,2) plane was the boundary of {112} Σ3 twin boundary which formed a straight grain boundary at the other end of the analyzed grain boundary, and also confirmed that ( _ ,2 11) plane was also the boundary of {112} Σ3 twin boundary which intersected with the former twin boundary at an angle of 120 [deg].

Abstract: It has been well known that Hadfield steel behaviors excellent wear resistance under high impact energy. Up to now there exist many theories to explain the wear mechanism of Hadfield steel. In this research subsurface microstructure evolution process of Hadfield steel was investigated after high energy impact experiments. It was shown from high resolution electron microscope (HRTEM) examination of subsurface microstructure that nanocrystallized austenite grains have been formed in the procedure of the reaction and rearrangement of high density dislocations under the heavy plastic deformation, sub-grains as a transitional structure and, finally, the formation of nano austenite grains. On the other side, the interactions of twins and stack faults or dislocations and stack faults make austenite crystals transform to amorphous solid. With increasing impact cycles the sizes of nano-grains were decreased and the amorphous volumes were increased further. A large amount of nano-sized grains embedded in bulk amorphous matrix were fully developed, which will dominate the wear of the steel. In the subsurface no martensitic transformation was observed.