SPATIALLY-RESOLVED X-RAY SPECTROSCOPY OF CSI DEPOSITS

Using the X-ray spectromicroscopy technique, we studied the primary an d secondary electron photoemission of cesium iodide (CsI) films deposi ted on different substrates, such as copper, aluminum, stainless-steel , and gold-coated quartz. We found an increase of more than a factor o f 2 in the secondary emission after exposing, for a few seconds in ult ra-high-vacuum (3 X 10(-10) mbar), the sample surface to an X-ray dose -rate of about 5 X 10(11) photons/s cm2 at the Al Kalpha photon energy (1486.7 eV). The activation effect, that lasts for about two days, is related to a change in the surface morphology: after the X-ray exposu re the surface presents a single phase with respect to the presence of two phases in the as-deposited or aged samples (lower Quantum Efficie ncy (QE) condition). Furthermore, the 25 mum lateral resolution of our spectromicroscope allowed us to show that the secondary electron phot oemission is strongly inhomogeneous on the plane of the surface, and t hat this inhomogeneity is more closely related to the spatial inhomoge neity of the Cs photoemission yield than to that of 1. Finally, we fou nd a decomposition effect induced by the X-ray exposure. This photoetc hing is less effective for the CsI deposited on the copper substrate, probably due to the presence of Cu-I compounds at the interface with t he substrate, which is revealed by X-ray diffraction measurements.