The Characterization Of Secondary Electron Emitters For Use In Large Area Photo-Detectors

The Large-Area Picosecond Photo-Detector Project is focused on the development of large-area systems to measure the time-of-arrival of relativistic particles with, ultimately, 1 pico-second resolution, and for signals typical of Positron-Emission Tomography (PET), a resolution of about 30 pico-seconds. Our contribution to this project is to help with identification and efficient fabrication of novel electron emitting materials with properties optimized for use in such detectors. We have assembled several techniques into a single ultra-high vacuum apparatus in order to enable characterization of both photocathode and secondary electron emission (SEE) materials. This apparatus will examine how photocathode quantum efficiency and SEE material electron yield correlate to surface chemical composition, state, and band structure. The techniques employed in this undertaking are X-ray photoelectron spectroscopy (XPS) for surface chemical composition, ultraviolet photoelectron spectroscopy (UPS) for the determination of band structure and surface work function, as well surface cleaning techniques such as argon-ion sputtering. To determine secondary electron emission yields and quantum efficiencies of detector materials, we use electron optics from a low energy electron diffraction (LEED) system whose set of hemispherical electrodes allows for efficient collection of secondary and photo electrons. As we gain a stronger insight into the details of mechanisms of electron emission from photocathodes and SEE materials, we will be able to lay a foundation for the larger collaborative effort to design the next generation of large-area photo-detectors. We present our preliminary results on the SEE materials from our as-yet completed characterization system.