LATERALLY RESOLVED MEASUREMENTS OF POLYCRYSTALLINE CESIUM IODIDE SURFACES

The aim of this work was to establish the correlation between the loca l chemical composition and morphology of polycrystalline cesium iodide (CsI) and its local quantum efficiency. We used a laterally resolved Electron Spectroscopy for Chemical Analysis (ESCA-300) apparatus and a Scanning Auger Microprobe (SAM) to investigate the lateral inhomogene ity of the CsI surface stoichiometry. The local quantum efficiency (QE ) was determined by measuring the secondary electron emission in Photo emission Electron Microscopy both with a non-monochromatized deuterium lamp and with tunable X-ray synchrotron radiation as the excitation s ource. CsI films on different substrates were studied. We found that t he local QE depends strongly on the morphology, on the local stoichiom etry and on carbon contamination. The results allow for an optimisatio n of the quantum efficiency of large area photocathodes.