Substrate studies of cesium-iodide photocathodes

We report on the quantum efficiency (QE) of cesium-iodide (CsI) photocathodes vacuum deposited on various substrates. The substrates, Ni, Au, solder, and Al were vacuum deposited on copper-clad FR4 and ceramic printed circuit boards. The results were obtained in a low-pressure, parallel-plate, pad-chamber with a solid CsI photocathode operated with ethane and isobutane gas. We present QE measurements for each of the different substrates used, the effect of substrate heating, the importance of surface quality, and our experience with ceramic printed circuit boards. Scanning electron microscope images of the photocathode surface are also shown for Cu and Al substrates.