JECP/SP: a computer program for generating stereographic projections, applicable to specimen orientation adjustment in TEM experiments

Abstract

1. The crystallographic problem Stereographic projection (SP) is an important crystallographic tool in carrying out electron diffraction experiments and in the analysis of crystal structures and defects. There are several commercial or public-domain computer programs available that allow users to draw stereographic projections of direct and reciprocal space. While these programs are often sufficient for regular use, there are always situations when the user will need to perform a certain operation that is not a feature of any of the existing programs. In the present work, a computer program was written for generating stereographic projections and was also extended as an application for specimen orientation adjustment in TEM experiments. Computer-assisted specimen orientation adjustment in TEM experiments would be especially useful under certain circumstances, for example, when (i) a severely stained specimen is observed and the visibility of Kikuchi line pairs is thus poor; (ii) a beam-sensitive specimen is examined, and thus it is essential to shorten the time spent on specimen tilting when the electron beam is illuminating the area of interest; (iii) a smallgrain-size specimen is investigated, for which even a slight orientation adjustment may cause the corresponding diffraction pattern to disappear due to a lateral sample shift; and (iv) a crystalline specimen is used in acquiring electron diffraction intensities of reachable zone-axis patterns for structure determination. In these cases, under the guidance of this software, the microscope can be kept in the image mode when the specimen is tilted. The holder is tilted to the computer-predicted angles and the illuminated area of the specimen is kept in the area of interest or in some neighboring area until the target tilt angles have been obtained, afterwhich it is moved to the area of interest.