Free-standing bialkali photocathodes using atomically thin substrates

TL;DR

This study demonstrates the successful deposition of high-efficiency bialkali photocathodes on graphene, showing potential for durable, high-performance photocathodes with minimal QE loss using atomically-thin protective layers.

Contribution

It introduces a method for depositing high-QE bialkali photocathodes on graphene, advancing encapsulation techniques for enhanced photocathode longevity.

Findings

Achieved 17% QE at 405 nm on graphene substrates.

Photocathodes on graphene exhibit characteristic spectral features.

Lower defect density in graphene correlates with higher QE.

Abstract

We report successful deposition of high quantum efficiency (QE) bialkali antimonide K2CsSb photocathodes on graphene films. The results pave a pathway towards 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 (XRF) and X-ray diffraction (XRD) 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.