Measurement of electron probe beam diameter by digital image processing

Abstract

AbstractThe present report illustrates a computerized method for precise measurement of the diameter of an electron beam. The value of this measurement extends beyond simply providing an accurate estimate of resolution. Other salient areas which will benefit include quantitative X‐ray microanalysis, energy loss spectroscopy, diffraction studies, and electron beam lithography. The biological sciences as well as the material sciences will gain enormously from improved accuracy in measurement (control) of beam diameter. It is anticipated that most or all of the mathematical manipulations outlined in this paper will be incorporated into digital electronic packages which will perform the functions automatically for setting the electron beam diameter to the scientist's choice. The purpose of the present report is to indicate some of the principles involved so that as electron microscopy becomes more computerized and automated, the user will have some understanding of what the electronics are doing rather than simply depressing a button or two and ignoring the power of what resides within the walls of the instrument.The performance of a scanning electron microscope (SEM) and a scanning transmission electron microscope (STEM) is roughly determined by the incident electron probe beam size (diameter) involving a sufficient electron current. In the present paper, the diameter of an ultrafine electron beam is measured indirectly from the information given by the blurring of an edge in a STEM or a SEM image of a crystalline specimen with fine, sharp edges. The obtained data were processed by digital image processing methods which give an accurate value of the beam diameter. For confirming the validity of this method, a suitable simulation based on the convolution theorem was performed. By using this measurement, we could measure the diameter of an ultrafine electron beam down to 2 nm, which could not be measured easily by previous techniques.