Imaging properties and energy aberrations of a double-pass cylindrical-mirror electron energy analyzer

Abstract

The imaging properties and energy aberrations of a commercial double-pass cylindrical-mirror analyzer have been characterized using an extension of the method recently reported by Seah and Mathieu. The electron beam from the coaxial electron gun was rastered across a test surface and the intensity of either elastically scattered electrons or of electrons at other selected energies was stored in a computer as a function of beam position on the specimen and other experimental parameters. The intensity data were later plotted to provide an ‘‘image’’ of the detected intensity. Images of this type are presented for electron energies of 100, 500, and 1000 eV and for the application of small offset voltages (typically between −1 and +5 V) between the analyzer and the gun cathode with the instrument operated in conditions appropriate for XPS or AES. Small offset voltages (<1.5 V) lead to significant changes in image shapes while larger offset voltages (≳5 V) lead to image shapes similar to those for the elastic peak but with 20%–40% increased widths. Deflection of the incident beam by up to 2 mm from the axis caused variations of up to ±0.15 eV in the measured positions of the elastic peak. Our observations can be interpreted qualitatively in terms of the known relationship between detected signal and combinations of position of electron emission from the specimen, angle of emission, and electron energy. The images obtained with elastically and inelastically scattered electrons provide a convenient and quantitative means of assessing instrument performance and of defining the specimen area being analyzed for the particular combination of instrument operating conditions and the energy width of AES or XPS features from the specimen.