Free‐Standing Bialkali Photocathodes Using Atomically Thin Substrates

Hisato Yamaguchi; Fangze Liu; Jeffrey DeFazio; Mengjia Gaowei; Claudia W. Narvaez Villarrubia; Junqi Xie; John Sinsheimer; Derek Strom; Vitaly Pavlenko; Kevin L. Jensen; John Smedley; Aditya D. Mohite; Nathan A. Moody

Index: 10.1002/admi.201800249

Full Text: HTML

Abstract

This study reports successful deposition of high quantum efficiency (QE) bialkali antimonide K2CsSb 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 K2CsSb 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 K2CsSb 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 K2CsSb photocathodes.