Revealing the (111) surface electronic structure of epitaxially grown Na$_2$KSb photocathode

TL;DR

This study reports the epitaxial growth and electronic structure analysis of Na$_2$KSb photocathode films, revealing surface states and preserving crystalline order post-activation, advancing understanding of alkali antimonide photocathodes.

Contribution

First demonstration of epitaxial Na$_2$KSb film growth and direct ARPES investigation of its surface electronic structure, linking experimental results with DFT calculations.

Findings

Identification of dispersive surface states from different surface terminations.

Crystalline order maintained after Cs and Sb activation.

Potential pathway for improving multialkali photocathodes.

Abstract

A recent study has established the Na$_2$KSb(Cs) photocathode as a highly efficient emitter of spin-polarized electrons. However, the electronic structure of alkali antimonides remains poorly understood. In this work, we report the first crystalline epitaxial growth of Na$_2$KSb films, achieved via chemical vapor deposition (CVD) on a graphene-coated SiC(0001) substrate. The high crystalline quality of these films enabled a direct investigation of the material's electronic structure using angle-resolved photoemission spectroscopy (ARPES). By comparing the experimental results with density functional theory (DFT) calculations, we have identified dispersive surface states originating from different terminations of the Na$_2$KSb(111) surface. Furthermore, we demonstrate that the crystalline order of the film is preserved following its activation via the deposition of Cs and Sb. This finding opens a pathway for investigating the electronic structure of multialkali Na$_2$KSb(Cs) photocathodes and for rationally improving their properties.