A new ESCA instrument with improved surface sensitivity, fast imaging properties and excellent energy resolution

Abstract

Results from the first experiments with a new ESCA instrument with monochromatic X-ray excitation are presented. The measurements were selected to assess the performance of the instrument in terms of energy and spatial resolution, information rate and surface sensitivity, and to probe the new dimension added to XPS analysis with the introduction of an imaging system. Novel design features described in the paper include a high-power monochromatic X-ray source and an electrostatic lens system permitting either large luminosity or high spatial resolution. A new geometry allows excellent access to the sample area and gives maximum surface sensitivity at glancing angles. The best energy resolution achieved so far with the instrument has been evaluated from the Fermi edge of silver to 0.27 eV (FWHM). The FWHM of the Ag 3d 5 2 line at this resolution is 0.44 eV. At an instrument energy resolution of 0.37 eV (FWHM) a peak intensity of the Ag 3d 5 2 line corresponding to a single-channel detector count rate of 1.9*10 6 cps has been measured. At this resolution, high quality spectra from surface elements of 30 μ × 30 μm can be recorded in a few minutes. The spatial resolution (20%–80%) has been measured to 23 μm. The enhanced surface signal at glancing angles is demonstrated in a series of measurements of the angular dependence of the XPS spectrum from a silicon surface. Preliminary experiments using an image integrating system show the potential of the combination of high spatial resolution in XPS with such techniques to give new information on the distribution of chemical properties or electrostatic potential variations over a surface. Future developments are discussed, including parallel recording of spectra from a large number of small spots, advanced handling of information from an imaging XPS system and further improvements of the spatial resolution.