Nano/Microscale Thin-Film Photocathodes: Materials and Applications

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D:Materials and Processing".

Deadline for manuscript submissions: closed (1 March 2022) | Viewed by 10611

Special Issue Editor

Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, 22607 Hamburg, Germany
Interests: nano/microscale photocathodes; electron sources; free-electron lasers; accelerators; microwave vacuum devices; electromagnetics; numerical modeling and simulation

Special Issue Information

Dear Colleagues,

Thin-film photocathodes in typical nano/microscale form are prevalently utilized to provide electron beams of increasingly stringent requirements for interdisciplinary researches and practical applications. The design capabilities of photocathodes in electron sources/devices have become an enabling technology in diverse fields such as light sources and detectors, electron cooling, ultrafast electron diffraction, novel particle accelerators, radiology and radiation oncology, electron beam lithography, etc.

In recent years, research frameworks centering on various cathode materials have been formed and recognized in worldwide cathode communities. Collective research efforts toward novel materials and applications have been made to intercorrelate photocathode/photoemission models, nanosynthesis methods, surface sciences, and diagnostics with comprehensive studies extending from broad fundamental interests in cathode performance (e.g., quantum efficiency, intrinsic emittance, response time, robustness, lifetime, etc.), narrowing down to required beam qualities for specific applications.

This Special Issue (SI) aims to summarize recent advances in nano/microscale thin-film photocathode materials across (but not limited to) the above-stated application fields with a focus on cathode materials and performances for light sources and detectors, novel particle accelerators, and ultrafast electron diffraction. The SI is organized through research papers and review articles. Topics include both experimental and theoretical contributions.

Dr. Ye Chen
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • nano/microscale
  • photocathode
  • photoemission
  • synthesis methods
  • electron sources
  • light sources and detectors
  • ultrafast electron diffraction
  • particle accelerators
  • surface science

Published Papers (5 papers)

Order results
Result details
Select all
Export citation of selected articles as:

Research

Jump to: Review

18 pages, 3652 KiB  
Article
Development and Characterization of Multi-Alkali Antimonide Photocathodes for High-Brightness RF Photoinjectors
by Sandeep Kumar Mohanty, Mikhail Krasilnikov, Anne Oppelt, Frank Stephan, Daniele Sertore, Laura Monaco, Carlo Pagani and Wolfgang Hillert
Micromachines 2023, 14(6), 1182; https://0-doi-org.brum.beds.ac.uk/10.3390/mi14061182 - 31 May 2023
Cited by 1 | Viewed by 1100
Abstract
Due to their excellent photoemissive properties, especially low thermal emittance and high sensitivity in the green wavelength, multi-alkali antimonide photocathodes, in particular, cesium–potassium–antimonide, emerged as prominent photoemissive materials for the electron sources of high-repetition-rate FEL applications. To explore its feasibility of operating in [...] Read more.
Due to their excellent photoemissive properties, especially low thermal emittance and high sensitivity in the green wavelength, multi-alkali antimonide photocathodes, in particular, cesium–potassium–antimonide, emerged as prominent photoemissive materials for the electron sources of high-repetition-rate FEL applications. To explore its feasibility of operating in a high-gradient RF gun, DESY collaborated with INFN LASA to develop multi-alkali photocathode materials. In this report, we describe the recipe of K-Cs-Sb photocathodes, which were grown on a Mo substrate by varying the foundational Sb layer thickness using sequential deposition techniques. This report also illustrates the information regarding the film thickness, substrate temperature, deposition rate, and its possible effects on the photocathode’s properties. In addition, the influence of temperature on the cathode degradation is also summarized. Furthermore, in the framework of density functional theory (DFT), we investigated the electronic and optical properties of the K2CsSb material. The optical properties, such as dielectric function, reflectivity, refracting index, and extinction coefficient, were evaluated. The correlation between the calculated and measured optical properties, such as reflectivity, provides a better and more efficient strategy to rationalize and understand the photoemissive material’s properties. Full article
(This article belongs to the Special Issue Nano/Microscale Thin-Film Photocathodes: Materials and Applications)
Show Figures

Figure 1

14 pages, 5209 KiB  
Article
Influence of Surface Cleaning on Quantum Efficiency, Lifetime and Surface Morphology of p-GaN:Cs Photocathodes
by Jana Schaber, Rong Xiang, Jochen Teichert, André Arnold, Petr Murcek, Paul Zwartek, Anton Ryzhov, Shuai Ma, Stefan Gatzmaga, Peter Michel and Nikolai Gaponik
Micromachines 2022, 13(6), 849; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13060849 - 29 May 2022
Cited by 5 | Viewed by 1703
Abstract
Accelerator scientists have high demands on photocathodes possessing high quantum efficiency (QE) and long operational lifetime. p-GaN, as a new photocathode type, has recently gained more and more interest because of its ability to form a negative electron affinity (NEA) surface. Being activated [...] Read more.
Accelerator scientists have high demands on photocathodes possessing high quantum efficiency (QE) and long operational lifetime. p-GaN, as a new photocathode type, has recently gained more and more interest because of its ability to form a negative electron affinity (NEA) surface. Being activated with a thin layer of cesium, p-GaN:Cs photocathodes promise higher QE and better stability than the known photocathodes. In our study, p-GaN samples grown on sapphire or silicon were wet chemically cleaned and transferred into an ultra-high vacuum (UHV) chamber, where they underwent a subsequent thermal cleaning. The cleaned p-GaN samples were activated with cesium to obtain p-GaN:Cs photocathodes, and their performance was monitored with respect to their quality, especially their QE and storage lifetime. The surface topography and morphology were examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM) in combination with energy dispersive X-ray (EDX) spectroscopy. We have shown that p-GaN could be efficiently reactivated with cesium several times. This paper systematically compares the influence of wet chemical cleaning as well as thermal cleaning at various temperatures on the QE, storage lifetime and surface morphology of p-GaN. As expected, the cleaning strongly influences the cathodes’ quality. We show that high QE and long storage lifetime are achievable at lower cleaning temperatures in our UHV chamber. Full article
(This article belongs to the Special Issue Nano/Microscale Thin-Film Photocathodes: Materials and Applications)
Show Figures

Figure 1

Review

Jump to: Research

16 pages, 4214 KiB  
Review
Review of Recent Progress on Advanced Photocathodes for Superconducting RF Guns
by Rong Xiang and Jana Schaber
Micromachines 2022, 13(8), 1241; https://0-doi-org.brum.beds.ac.uk/10.3390/mi13081241 - 02 Aug 2022
Cited by 7 | Viewed by 1874
Abstract
As is well known, the quality of the photocathodes is essential for the stability and reliability of photoinjector operations. Especially for superconducting radio frequency photoinjectors (SRF guns), the photocathode represents one of the most critical parts. Benefiting from the fast development of photocathode [...] Read more.
As is well known, the quality of the photocathodes is essential for the stability and reliability of photoinjector operations. Especially for superconducting radio frequency photoinjectors (SRF guns), the photocathode represents one of the most critical parts. Benefiting from the fast development of photocathode technology in recent years, several SRF guns have been successfully operated or tested for beam generation at the kHz–MHz repetition rate. In this paper, we will review the achievements as well as the open questions in the applications of photocathodes for SRF gun operation. Furthermore, we will discuss the possible improvement of photocathodes for future CW electron sources. Full article
(This article belongs to the Special Issue Nano/Microscale Thin-Film Photocathodes: Materials and Applications)
Show Figures

Figure 1

19 pages, 5816 KiB  
Review
Overview of the Semiconductor Photocathode Research in China
by Huamu Xie
Micromachines 2021, 12(11), 1376; https://0-doi-org.brum.beds.ac.uk/10.3390/mi12111376 - 09 Nov 2021
Cited by 2 | Viewed by 2168
Abstract
With the growing demand from scientific projects such as the X-ray free electron laser (XFEL), ultrafast electron diffraction/microscopy (UED/UEM) and electron ion collider (EIC), the semiconductor photocathode, which is a key technique for a high brightness electron source, has been widely studied in [...] Read more.
With the growing demand from scientific projects such as the X-ray free electron laser (XFEL), ultrafast electron diffraction/microscopy (UED/UEM) and electron ion collider (EIC), the semiconductor photocathode, which is a key technique for a high brightness electron source, has been widely studied in China. Several fabrication systems have been designed and constructed in different institutes and the vacuum of most systems is in the low 10−8 Pa level to grow a high QE and long lifetime photocathode. The QE, dark lifetime/bunch lifetime, spectral response and QE map of photocathodes with different kinds of materials, such as bialkali (K2CsSb, K2NaSb, etc.), Cs2Te and GaAs, have been investigated. These photocathodes will be used to deliver electron beams in a high voltage DC gun, a normal conducting RF gun, and an SRF gun. The emission physics of the semiconductor photocathode and intrinsic emittance reduction are also studied. Full article
(This article belongs to the Special Issue Nano/Microscale Thin-Film Photocathodes: Materials and Applications)
Show Figures

Figure 1

21 pages, 4163 KiB  
Review
Ab Initio Quantum-Mechanical Predictions of Semiconducting Photocathode Materials
by Caterina Cocchi and Holger-Dietrich Saßnick
Micromachines 2021, 12(9), 1002; https://0-doi-org.brum.beds.ac.uk/10.3390/mi12091002 - 24 Aug 2021
Cited by 5 | Viewed by 2687
Abstract
Ab initio Quantum-Mechanical methods are well-established tools for material characterization and discovery in many technological areas. Recently, state-of-the-art approaches based on density-functional theory and many-body perturbation theory were successfully applied to semiconducting alkali antimonides and tellurides, which are currently employed as photocathodes in [...] Read more.
Ab initio Quantum-Mechanical methods are well-established tools for material characterization and discovery in many technological areas. Recently, state-of-the-art approaches based on density-functional theory and many-body perturbation theory were successfully applied to semiconducting alkali antimonides and tellurides, which are currently employed as photocathodes in particle accelerator facilities. The results of these studies have unveiled the potential of ab initio methods to complement experimental and technical efforts for the development of new, more efficient materials for vacuum electron sources. Concomitantly, these findings have revealed the need for theory to go beyond the status quo in order to face the challenges of modeling such complex systems and their properties in operando conditions. In this review, we summarize recent progress in the application of ab initio many-body methods to investigate photocathode materials, analyzing the merits and the limitations of the standard approaches with respect to the confronted scientific questions. In particular, we emphasize the necessary trade-off between computational accuracy and feasibility that is intrinsic to these studies, and propose possible routes to optimize it. We finally discuss novel schemes for computationally-aided material discovery that are suitable for the development of ultra-bright electron sources toward the incoming era of artificial intelligence. Full article
(This article belongs to the Special Issue Nano/Microscale Thin-Film Photocathodes: Materials and Applications)
Show Figures

Figure 1

Back to TopTop