Laterally resolved measurements of polycrystalline cesium iodide surfaces

The aim of this work was to establish the correlation between the local 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 inhomogeneity of the CsI surface stoichiometry. The local quantum efficiency (QE) was determined by measuring the secondary electron emission in Photoemission Electron Microscopy both with a non-monochromatized deuterium lamp and with tunable X-ray synchrotron radiation as the excitation source. CsI films on different substrates were studied. We found that the local QE depends strongly on the morphology, on the local stoichiometry and on carbon contamination. The results allow for an optimisation of the quantum efficiency of large area photocathodes.