On the Properties of Hydrogen Terminated Diamond as a Photocathode

TL;DR

This study investigates hydrogen-terminated boron-doped diamond as a photocathode, revealing a novel Franck-Condon mechanism responsible for negative electron affinity, which could lead to new electron emitter technologies.

Contribution

It uncovers a new Franck-Condon coupling mechanism responsible for NEA in hydrogen-terminated diamond, demonstrated through low-energy laser ARPES.

Findings

Low-energy laser ARPES reveals NEA mechanism

High-energy ARPES shows limitations of the sudden approximation

First identification of Franck-Condon coupling in this context

Abstract

Electron emission from the negative electron affinity (NEA) surface of hydrogen terminated, boron doped diamond in the [100] orientation is investigated using angle resolved photoemission spectroscopy (ARPES). ARPES measurements using 16 eV synchrotron and 6 eV laser light are compared and found to show a catastrophic failure of the sudden approximation. While the high energy photoemission is found to yield little information regarding the NEA, low energy laser ARPES reveals for the first time that the NEA results from a novel Franck-Condon mechanism coupling electrons in the conduction band to the vacuum. The result opens the door to development of a new class of NEA electron emitters based on this effect.