Free‐Standing Bialkali Photocathodes Using Atomically Thin Substrates. Issue 13 (3rd April 2018) - Yamaguchi, Hisato
Abstract: This study reports successful deposition of high quantum efficiency (QE) bialkali antimonide K2 CsSb photocathodes on graphene films. The results pave the way for an ultimate goal of encapsulating technologically relevant photocathodes for accelerator technology with an atomically thin protecting layer to enhance lifetime while minimizing QE losses. A QE of 17% at ≈3.1 eV (405 nm) is the highest value reported so far on graphene substrates and is comparable to that obtained on stainless steel and nickel reference substrates. The spectral responses of the photocathodes on graphene exhibit signature features of K2 CsSb including the characteristic absorption at ≈2.5 eV. Materials characterization based on X‐ray fluorescence and X‐ray diffraction reveals that the composition and crystal quality of these photocathodes deposited on graphene is comparable to those deposited on a reference substrate. Quantitative agreement between optical calculations and QE measurements for the K2 CsSb on free suspended graphene and a graphene‐coated metal substrate further confirms the high‐quality interface between the photocathodes and graphene. Finally, a correlation between the QE and graphene quality as characterized by Raman spectroscopy suggests that a lower density of atomistic defects in the graphene films leads to higher QE of the deposited K2 CsSb photocathodes. Abstract : Enhancing the lifetime of accelerator technology‐relevant photocathodes while maintaining their high quantum efficiency has been a decadal problem. Bialkali antimonide photocathodes are now successfully deposited on free‐standing atomically thin substrates of graphene. This advances an ultimate goal of enhancing the lifetime of photocathodes without sacrificing the high quantum efficiency by using an atomically thin protection layer.