Electron emission processes in photocathodes and dynodes

The Timed Photon Counter ´Tipsy´ detector relies on electron-emitting thin films for generation of primary electrons from a photocathode and the subsequent amplification via SiN dynodes. Both of these films represent materials challenges, and both are being investigated using synchrotrons to optimize their performance. For the dynodes, a program of soft x-ray photoemission spectroscopy (XPS) has been used to measure the performance of the films and to understand film stoichiometry and the effects of surface termination. The secondary electron yield is estimated by measuring the low energy tail of the XPS spectrum and comparing it to the rate of high energy electron emission. For photocathodes, time resolved x-ray analysis during growth has provided insight into the formation chemistry of these materials. This has allowed optimization beyond Quantum Efficiency (QE) to produce cathodes which are far less rough than traditional alkali antimonides, while retaining reasonable QE.