Fabrication and characterization of silver polycrystalline photocathode

Silver is considered the most noble metal after gold, which makes it a potential candidate for the metallic photocathode. In this article, we report on the fabrication of a polycrystalline silver photocathode by using a physical vapor deposition (PVD) technique. For the first time, silver photocathodes in both the reflection and transmission modes were fabricated on a super quartz (JGS1) substrate and characterized. The polycrystalline nature of the fabricated sample was confirmed by X-ray diffraction (XRD) analysis. The work function of the fabricated photocathode was measured at around 4.73 eV using photoemission yield spectroscopy in the air (PYSA). Photocurrent measurement and quantum efficiency (Q.E.) calculations were performed using a picoammeter and a 250 nm high power ultraviolet (UV) LED source. Silver photocathode yielded a Q.E. of (8.77±0.90)×10⁻⁶ in reflection mode, and (1.20±0.12)×10⁻⁶ in transmission mode. After being exposed to air for up to 72 h, no sign of degradation in its photocurrent/Q.E. was observed. The silver photocathode thickness was estimated to be (138 ± 5) nm for the reflection mode and (35 ± 1) nm for the transmission mode. The developed photocathode will be ultimately used for the study of the proposed novel photodetector concept called silicon photomultiplier tube (SiPMT).