Development of display-type ellipsoidal mesh analyzer: Computational evaluation and experimental validation

Abstract

An advanced measurement system for two-dimensional photoelectron spectroscopy has been developed to overcome the difficulties faced in the display-type spherical-mirror analyzer (DIANA) having been used so far. One difficulty is to realize selected small area analysis and another is to obtain higher energy resolution. The developed system, which we call “display-type ellipsoidal mesh analyzer (DELMA)”, has an ellipsoidal mesh electrode as its key element, which allows a wide acceptance angle (>∼±45°) comparable to that of DIANA. In this paper we provide details of DELMA on its design and performance. For the imaging performance, we evaluated, using ray-tracing, some important factors that can affect the spatial resolution: off-axis aberration, the effect of shape and position errors, the disturbing effect of mesh holes, and chromatic aberration. In test experiments, a spatial resolution of around 20–30μm was obtained. The ray-tracing results suggest that this resolution can be improved to be less than 10μm by decreasing the size of mesh holes and the error of the mesh shape. We also provide computational results for the energy resolution obtained in various conditions. It depends not only on the size of the energy-selecting aperture but also on the size and shape of an irradiation spot. Experimental results for the energy resolution were in good agreement with computational results. An available resolution seems to be as good as in DIANA (∼0.5%). A much better resolution is possible in our system by the combination of DELMA and a high resolution concentric hemispherical analyzer. In test experiments using an angle-measurement device, a wide acceptance angle of around ±45° has been successfully confirmed. As a practical example of the angular analysis by DELMA, a photoelectron diffraction pattern measured for single crystalline graphite is shown.