From electronic structure to design principles for photocathodes: Cu-Ba alloys

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Title: From electronic structure to design principles for photocathodes: Cu-Ba alloys
Authors: Napier, IA
Chang, V
Noakes, TCQ
Harrison, NM
Item Type: Journal Article
Abstract: Producing a metal photocathode with a low work function (WF), low emissivity, and high quantum efficiency is a matter of importance in the design of the next generation of free-electron laser facilities. General rules for the design of appropriate materials are currently unclear and difficult to elucidate from observations of structure-composition relationships of known photocathodes. In this work, high-quality density-functional-theory electronic structure calculations and a simple physical model are employed to develop design rules for photocathodes based on metallic alloys. A theoretical study of metal alloys for photocathode applications is presented, in which high WF, stable copper is paired with low WF, unstable barium in two alloys, Cu 13 Ba and Cu Ba . Surfaces terminating in a plane of Ba atoms have a lower computed surface energy than those terminating in Cu atoms due to surface segregation of the larger Ba atoms. This results in a significant surface dipole due to the interatomic charge transfer from the differences in electronegativity of the species. The details of the surface structure determine the direction of the dipole and thus have a strong influence on the computed WF. The computed WF of the Cu 13 Ba Ba -terminated (100) surface is even lower than that of pure Ba , at 1.95 eV. The computed quantum efficiency (QE) of the best-performing pure Cu surface is 5.86 × 10 − 6 , whereas the best-performing Cu 13 Ba surface terminates in a plane of Ba atoms and has a significantly increased QE of 5.09 × 10 − 3 . A surface terminating in two planes of Ba atoms, the (001) surface of Cu Ba , has an even higher computed QE of 1.38 × 10 − 2 .
Issue Date: 26-Jun-2019
Date of Acceptance: 1-Jun-2019
URI: http://hdl.handle.net/10044/1/72093
DOI: https://doi.org/10.1103/PhysRevApplied.11.064061
ISSN: 2331-7019
Publisher: American Physical Society
Start Page: 064061-1
End Page: 064061-13
Journal / Book Title: Physical Review Applied
Volume: 11
Issue: 6
Copyright Statement: © 2019 American Physical Society.
Keywords: Science & Technology
Physical Sciences
Physics, Applied
Physics
ANGLE-RESOLVED PHOTOEMISSION
WORK FUNCTION
MULTILAYER RELAXATION
SURFACE-ENERGY
FCC METALS
COPPER
AU
AG
CRYSTAL
GROWTH
Science & Technology
Physical Sciences
Physics, Applied
Physics
ANGLE-RESOLVED PHOTOEMISSION
WORK FUNCTION
MULTILAYER RELAXATION
SURFACE-ENERGY
FCC METALS
COPPER
AU
AG
CRYSTAL
GROWTH
Publication Status: Published
Article Number: ARTN 064061
Online Publication Date: 2019-06-26
Appears in Collections:Chemistry
Faculty of Natural Sciences



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