Photoemission simulation for photocathode design: theory and application to copper and silver surfaces

Camino, Bruno; Noakes, T. C. Q.; Surman, M.; Seddon, Elaine A.; Harrison, N. M.

doi:10.1016/j.commatsci.2016.05.025

Cited by 19 publications

(10 citation statements)

References 54 publications

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“…where E Slab is the energy required to form the metal oxide thin film relative to the bulk oxide, E Tot is the computed total energy of the system, E Ag(100) is the computed energy of the Ag slab, E MO bulk is the computed energy for the bulk metal oxide per formula unit, and n is the number of formula units of oxide per unit cell of the slab model. A photoemission model [4] is used to study the quantum efficiency and photoemission properties of the metal oxide thin films on metal substrates. This model, which is based on Spicer's three-step model [23], facilitates the decomposition of the quantum efficiency into contributions from each atomic layer in the slab model.…”

Section: Computational Detailsmentioning

confidence: 99%

“…The transport of the photoexcited electrons to the surface is described based on an estimated, energy-dependent, inelastic mean-free path (IMFP). The IMFP for Ag used in this work is obtained by averaging values found in the literature [4,24,25]. In the current work, the IMFP in the oxide film is approximated by that of the metal substrate.…”

Section: Computational Detailsmentioning

confidence: 99%

“…One way to improve the QE of a metal photocathode is through the reduction of the WF. Change of the metal-surface WF can be achieved by the adsorption of atomic species that change the surface dipole [4]. The adsorption of atomic species also has the potential to induce changes in the surface band structure and therefore to change the photoemission properties of the surface [5].…”

Section: Introductionmentioning

confidence: 99%

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Work function and quantum efficiency study of metal oxide thin films on Ag(100)

2018

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Increasing the quantum efficiency (QE) of metal photocathodes is in the design and development of photocathodes for free-electron laser applications. The growth of metal oxide thin films on certain metal surfaces has previously been shown to reduce the work function (WF). Using a photoemission model B. Camino et al. [Comput. Mater. Sci. 122, 331 (2016)] based on the three-step model combined with density functional theory calculations we predict that the growth of a finite number of MgO(100) or BaO(100) layers on the Ag(100) surface increases significantly the QE compared with the clean Ag(100) surface for a photon energy of 4.7 eV. Different mechanisms for affecting the QE are identified for the different metal oxide thin films. The addition of MgO(100) increases the QE due to the reduction of the WF and the direct excitation of electrons from the Ag surface to the MgO conduction band. For BaO(100) thin films, an additional mechanism is in operation as the oxide film also photoemits at this energy. We also note that a significant increase in the QE for photons with an energy of a few eV above the WF is achieved due to an increase in the inelastic mean-free path of the electrons.

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Section: Computational Detailsmentioning

confidence: 99%

Section: Computational Detailsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Work function and quantum efficiency study of metal oxide thin films on Ag(100)

2018

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“…Upon integrating with other band structure and wave function calculation techniques like density functional theory, this methodology can be used to calculate the electron source relevant photoemission properties from any single crystal surface in order to identify ideal electron emitters from first principle calculations 35 . Such a methodology is essential to screen for materials to identify good electron emitters.…”

Section: Discussionmentioning

confidence: 99%

One-step model of photoemission from single-crystal surfaces

et al. 2017

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In this paper, we present a 3-D one step photoemission model that can be used to calculate the quantum efficiency and momentum distributions of electrons photoemitted from ordered single crystal surfaces close to the photoemission threshold. Using Ag (111) as an example, we show that the model can not only calculate the quantum efficiency from the surface state accurately without using any ad hoc parameters, but also provides a theoretical quantitative explanation of the vectorial photoelectric effect. This model in conjunction with other band structure and wave function calculation techniques can be effectively used to screen single crystal photoemitters for use as electron sources for particle accelerator and ultrafast electron diffraction applications.

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“…The photoemission model used to study QE of the metal and alloy surfaces is developed by Camino [12], based on Spicer's three-step model [13]. Camino's model allows the QE to be decomposed into contributions from each atomic layer and assumes electrons are excited to the conduction band and, if the final state is above the vacuum level, an electron can be emitted.…”

Section: Pbesol (This Work) Exptmentioning

confidence: 99%

From Electronic Structure to Design Principles for Photocathodes: Cu - Ba Alloys

et al. 2019

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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 CuBa. 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 CuBa, has an even higher computed QE of 1.38 × 10 −2 .

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Photoemission simulation for photocathode design: theory and application to copper and silver surfaces

Cited by 19 publications

References 54 publications

Work function and quantum efficiency study of metal oxide thin films on Ag(100)

Work function and quantum efficiency study of metal oxide thin films on Ag(100)

One-step model of photoemission from single-crystal surfaces

From Electronic Structure to Design Principles for Photocathodes: Cu - Ba Alloys

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