- Physical Review Journals
All JournalsPhysics Magazine

Physical Review Materials

Reuse & Permissions

It is not necessary to obtain permission to reuse this article or its components as it is available under the terms of the Creative Commons Attribution 4.0 International license. This license permits unrestricted use, distribution, and reproduction in any medium, provided attribution to the author(s) and the published article's title, journal citation, and DOI are maintained. Please note that some figures may have been included with permission from other third parties. It is your responsibility to obtain the proper permission from the rights holder directly for these figures.

Export citation

Export citation

Choose format for download:

Download Citation
  • Open Access

Quantitative framework for photoemissive materials: From bialkali-antimonide synthesis to performance in superconducting RF electron injectors

Jonas Dube*,‡, Chen Wang†, Emily Jayne Brookes*, Axel Neumann, Guido Klemz, Ezgi Ergenlik, Pablo Echevarria, Andriy Ushakov, Thorsten Kamps* et al.

Julius Kühn§

  • *Also at Institut für Physik, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
  • †Also at Institut für Werkstofftechnik, Universität Siegen, 57076 Siegen, Germany.
  • ‡Contact author: jonas.dube@helmholtz-berlin.de
  • §Contact author: julius.kuehn@helmholtz-berlin.de
PDF

Phys. Rev. Materials 10, 074601 – Published 10 July, 2026

DOI: https://doi.org/10.1103/d2s8-7pt8

Abstract

Photoemissive materials are central to a wide range of technologies, including ultrafast imaging, low-light detection, and accelerator-based light sources, where they determine the fundamental performance limits of these instruments. Despite their importance, establishing quantitative links between material synthesis, electronic structure, intrinsic photoemission properties, and device performance remains a major challenge. Here, we present a comprehensive study that bridges these aspects for Na–K–Sb photocathodes, combining controlled thin-film growth, in situ spectroscopic analysis, photoemission characterization, and investigation of the operational performance. We developed a reproducible synthesis method yielding highly homogeneous films with quantum efficiencies up to 7.5% at 520nm and a stoichiometry close to the predicted optimum. Electronic structure and photoemission properties were analyzed in a dedicated laboratory environment. Furthermore, we demonstrate the successful operation of these photocathodes in a superconducting radio-frequency photoinjector, where the photocathodes are exposed to extreme conditions, forming a particularly stringent test environment. The operational performance was analyzed over several weeks, including detailed investigation of the degradation and recovery mechanisms associated with gas exposure and electron back-bombardment. The photoemissive threshold energy was identified as a bridging parameter connecting electronic structure, photoemissive key parameters, and the degradation state. The approach provides general design principles for the development and integration of photoemissive materials across a broad range of applications. Together, these results establish a quantitative framework linking synthesis, electronic structure, and operational performance in photoemissive materials.

View figure in article

Physics Subject Headings (PhySH)

Article Text

References (50)

  1. G. Zeng, T. A. Pham, S. Vanka, G. Liu, C. Song, J. K. Cooper, Z. Mi, T. Ogitsu, and F. M. Toma, Development of a photoelectrochemically self-improving Si/GaN photocathode for efficient and durable H2 production, Nat. Mater. 20, 1130 (2021).
  2. K. Nakamura, Y. Hamana, Y. Ishigami, and T. Matsui, Latest bialkali photocathode with ultra high sensitivity, Nucl. Instrum. Methods Phys. Res. Sec. A 623, 276 (2010).
  3. R. Marchand, R. Šachl, M. Kalbáč, M. Hof, R. Tromp, M. Amaro, S. J. van der Molen, and T. Juffmann, Optical near-field electron microscopy, Phys. Rev. Appl. 16, 014008 (2021).
  4. V. N. Litvinenko, N. Bachhawat, J. C. Brutus, L. Cultrera, K. Decker, M. Gaowei, P. Inacker, Y. Jing, J. Ma, K. P. Mondal, et al., Towards advanced polarized electron sources, Nat. Phys. 22, 325 (2026).
  5. I. V. Bazarov, B. M. Dunham, and C. K. Sinclair, Maximum achievable beam brightness from photoinjectors, Phys. Rev. Lett. 102, 104801 (2009).
  6. P. Musumeci, J. Giner Navarro, J. B. Rosenzweig, L. Cultrera, I. Bazarov, J. Maxson, S. Karkare, and H. Padmore, Advances in bright electron sources, Nucl. Instrum. Methods Phys. Res. Sec. A 907, 209 (2018).
  7. C. T. Parzyck, C. A. Pennington, W. J. I. DeBenedetti, J. Balajka, E. M. Echeverria, H. Paik, L. Moreschini, B. D. Faeth, C. Hu, J. K. Nangoi, et al., Atomically smooth films of CsSb: A chemically robust visible light photocathode, APL Mater. 11, 101125 (2023).
  8. L. Guo, K. Shiohara, H. Yamaguchi, G. Wang, Y. Okabe, M. Nakatake, S. Takakura, M. Yamamoto, S. Ogawa, and Y. Takashima, Improved robustness of sequentially deposited potassium cesium antimonide photocathodes achieved by increasing the potassium content towards theoretical stoichiometry, Sci. Rep. 15, 2900 (2025).
  9. V. Pavlenko, J. Smedley, A. Scheinker, R. L. Fleming, A. Alexander, M. A. Hoffbauer, and N. A. Moody, Stoichiometry control and automated growth of alkali antimonide photocathode films by molecular beam deposition, Appl. Phys. Lett. 120, 091901 (2022).
  10. C. A. Pennington, M. Gaowei, E. M. Echeverria, K. Evans-Lutterodt, A. Galdi, T. Juffmann, S. Karkare, J. Maxson, S. J. van der Molen, P. Saha, J. Smedley, W. G. Stam, and R. M. Tromp, A structural analysis of ordered Cs3Sb films grown on single crystal graphene and silicon carbide substrates, APL Mater. 13, 011120 (2025).
  11. W. G. Stam, M. Gaowei, E. M. Echeverria, K. Evans-Lutterodt, J. Jordan-Sweet, T. Juffmann, S. Karkare, J. Maxson, S. J. van der Molen, C. Pennington, P. Saha, J. Smedley, and R. M. Tromp, Growth of ultra-flat ultra-thin alkali antimonide photocathode films, APL Mater. 12, 061114 (2024).
  12. P. Emma, R. Akre, J. Arthur, R. Bionta, C. Bostedt, J. Bozek, A. Brachmann, P. Bucksbaum, R. Coffee, F.-J. Decker, et al., First lasing and operation of an ångstrom-wavelength free-electron laser, Nat. Photon. 4, 641 (2010).
  13. R. Xiang, A. Arnold, and J. W. Lewellen, Superconducting radio frequency photoinjectors for CW-XFEL, Front. Phys. 11, 1166179 (2023).
  14. Z. T. Zhao, Z. Wang, C. Feng, S. Chen, and L. Cao, Energy recovery linac based fully coherent light source, Sci. Rep. 11, 23875 (2021).
  15. A. Neumann, B. Alberdi, T. Birke, P. Echevarria, D. Eichel, F. Falkenstern, R. Fleischhauer, A. Frahm, F. Goebel, A. Heugel, et al., bERLinPro becomes SEALab: Status and perspective of the energy recovery linac at HZB, in Proceedings of 13th International Particle Accelerator Conference, Bangkok, Thailand, Jun. 2022 (JACoW Publishing, Geneva, Switzerland, 2022), pp. 1110–1113.
  16. V. Rusetsky, V. Golyashov, S. Eremeev, D. Kustov, I. Rusinov, T. Shamirzaev, A. Mironov, A. Demin, and O. Tereshchenko, New spin-polarized electron source based on alkali antimonide photocathode, Phys. Rev. Lett. 129, 166802 (2022).
  17. J. Schaber, R. Xiang, and N. Gaponik, Review of photocathodes for electron beam sources in particle accelerators, J. Mater. Chem. C 11, 3162 (2023).
  18. D. Filippetto, P. Musumeci, R. Li, B. Siwick, M. Otto, M. Centurion, and J. Nunes, Ultrafast electron diffraction: Visualizing dynamic states of matter, Rev. Mod. Phys. 94, 045004 (2022).
  19. A. H. Zewail, 4D Ultrafast electron diffraction, crystallography, and microscopy, Annu. Rev. Phys. Chem. 57, 65 (2006).
  20. B. Alberdi Esuain, J.-G. Hwang, A. Neumann, and T. Kamps, Novel approach to push the limit of temporal resolution in ultrafast electron diffraction accelerators, Sci. Rep. 12, 13365 (2022).
  21. D. H. Dowell, I. Bazarov, B. Dunham, K. Harkay, C. Hernandez-Garcia, R. Legg, H. Padmore, T. Rao, J. Smedley, and W. Wan, Cathode R&D for future light sources, Nucl. Instrum. Methods Phys. Res. Sec. A 622, 685 (2010).
  22. I. Petrushina, V. Litvinenko, Y. Jing, J. Ma, I. Pinayev, K. Shih, G. Wang, Y. Wu, Z. Altinbas, J. Brutus, et al., High-brightness continuous-wave electron beams from superconducting radio-frequency photoemission gun, Phys. Rev. Lett. 124, 244801 (2020).
  23. R. Xiang and J. Schaber, Review of recent progress on advanced photocathodes for superconducting RF guns, Micromachines 13, 1241 (2022).
  24. J. Maxson, L. Cultrera, C. Gulliford, and I. Bazarov, Measurement of the tradeoff between intrinsic emittance and quantum efficiency from a NaKSb photocathode near threshold, Appl. Phys. Lett. 106, 234102 (2015).
  25. K. Mondal, M. Goawei, L. Cultrera, J. Walsh, R. Bagy, and Y. Yang, Development of sodium potassium antimonide photocathodes for use of coherent electron cooling, in Proceedings of 6th North American Particle Accelerator Conference, Sacramento, CA, 10-15 Aug 2025 (JACoW Publishing, Geneva, Switzerland, 2025).
  26. M. A. Schmeißer, S. Mistry, H. Kirschner, S. Schubert, A. Jankowiak, T. Kamps, and J. Kühn, Towards the operation of Cs-K-Sb photocathodes in superconducting rf photoinjectors, Phys. Rev. Accel. Beams 21, 113401 (2018).
  27. L. Cultrera, H. Lee, and I. Bazarov, Alkali antimonides photocathodes growth using pure metals evaporation from effusion cells, J. Vacuum Sci. Technol. B 34, 011202 (2015).
  28. J. Dube, J. Kühn, C. Wang, S. Mistry, G. Klemz, A. Galdi, and T. Kamps, Triple evaporation growth and photoemission characterization of bialkali antimonide photocathodes, J. Appl. Phys. 138, 045704 (2025).
  29. J. Kühn, J. Borninkhof, M. Bürger, A. Frahm, A. Jankowiak, T. Kamps, M. Schmeißer, M. Schuster, P. Murcek, J. Teichert, and R. Xiang, UHV photocathode plug transfer chain for the bERLinPro SRF-photoinjector, in Proceedings of International Particle Accelerator Conference (IPAC'17), Copenhagen, Denmark, 14–19 May, 2017 (JACoW Publishing, Geneva, Switzerland, 2017).
  30. J. Kühn, N. Al-Saokal, M. Bürger, M. Dirsat, A. Frahm, A. Jankowiak, T. Kamps, G. Klemz, S. Mistry, A. Neumann, and H. Plötz, Thermal load studies on the photocathode insert with exchangeable plug for the bERLinPro SRF-photoinjector, in Proceedings of 19th International Conference on RF Superconductivity, Dresden, Germany (JACoW Publishing, Geneva, Switzerland, 2019).
  31. S. Mistry, J. Dube, T. Kamps, J. Kuehn, and C. Wang, Evaluation of the in-situ photocathode handling for SRF photoinjector of SEALab, in Proceedings of the 13th International Particle Accelerator Conference, IPAC'22 (JACoW Publishing, Geneva, Switzerland, 2023), pp. 4240–4242.
  32. C. Wang, J. Dube, A. Galdi, T. Kamps, and J. Kühn, Triple evaporation growth of sodium-potassium-antimonide thin films as photoemission source for electron accelerators, J. Phys. D: Appl. Phys. 59, 075102 (2026).
  33. G. S. Gevorkyan, S. Karkare, S. Emamian, I. V. Bazarov, and H. A. Padmore, Effects of physical and chemical surface roughness on the brightness of electron beams from photocathodes, Phys. Rev. Accel. Beams 21, 093401 (2018).
  34. L. Cultrera, S. Karkare, B. Lillard, A. Bartnik, I. Bazarov, B. Dunham, W. Schaff, and K. Smolenski, Growth and characterization of rugged sodium potassium antimonide photocathodes for high brilliance photoinjector, Appl. Phys. Lett. 103, 103504 (2013).
  35. C. Pennington, E. Echeverria, A. Flint, N. Gonzalez, T. Wu, T. Arias, K. P. Mondal, K. Evans-Lutterodt, M. Gaowei, J. Smedley, et al., Enhanced quantum efficiency from optical interference in alkali antimonide photocathodes: Modeling and experimental results, J. Appl. Phys. 139, 065305 (2026).
  36. R. Amador, H.-D. Saßnick, and C. Cocchi, Electronic structure and optical properties of Na2KSb and NaK2Sb from first-principles many-body theory, J. Phys.: Condens. Matter 33, 365502 (2021).
  37. R. Follath, M. Hävecker, G. Reichardt, K. Lips, J. Bahrdt, F. Schäfers, and P. Schmid, The energy materials in-situ laboratory Berlin (EMIL) at BESSY II, J. Phys.: Conf. Ser. 425, 212003 (2013).
  38. J. W. Kim and A. Kim, Absolute work function measurement by using photoelectron spectroscopy, Curr. Appl. Phys. 31, 52 (2021).
  39. A. P. Baddorf, Identifying the secondary electron cutoff in ultraviolet photoemission spectra for work function measurements of non-ideal surfaces, Sci. Rep. 13, 13452 (2023).
  40. A. H. A. H. Sommer, Photoemissive Materials: Preparation, Properties, and UIses (Wiley, New York, 1968).
  41. M. C. Divall, E. Prat, S. Bettoni, C. Vicario, A. Trisorio, T. Schietinger, and C. P. Hauri, Intrinsic emittance reduction of copper cathodes by laser wavelength tuning in an rf photoinjector, Phys. Rev. ST Accel. Beams 18, 033401 (2015).
  42. I. Bazarov, L. Cultrera, A. Bartnik, B. Dunham, S. Karkare, Y. Li, X. Liu, J. Maxson, and W. Roussel, Thermal emittance measurements of a cesium potassium antimonide photocathode, Appl. Phys. Lett. 98, 224101 (2011).
  43. M. Abo-Bakr, N. Al-Saokal, W. Anders, Y. Bergmann, K. Bürkmann-Gehrlein, et al., The Berlin Energy Recovery Linac Project BERLinPro - status, plans and future opportunities, in Proceedings of 63th ICFA Advance Beam Dynamics Workshop on Energy Recovery Linacs, Berlin, Germany (JACoW Publishing, Geneva, Switzerland, 2019).
  44. T. Kamps, M. Abo-Bakr, B. Alberdi, T. Birke, P. Echevarria, E. Ergenlik, R. Fleischhauer, A. Frahm, H. Huck, G. Klemz, et al., Accelerator physics experiments at the versatile SRF photoinjector of SEALab, in Proceedings of 14th International Particle Accelerator Conference, Venice, Italy (JACoW Publishing, Geneva, Switzerland, 2023), pp. 2115–2118.
  45. E. Wang, Y. Hao, Y. C. Jing, V. Litvinenko, I. Pinayev, T. Rao, J. Skaritka, G. Wang, and T. Xin, K2CsSb photocathode performance in QWR SRF gun, in Proceedings of North American Particle Accelerator Conference (NAPAC'16), Chicago, IL, USA, October 9–14, 2016 (JACoW Publishing, Geneva, Switzerland, 2017).
  46. V. Pavlenko, F. Liu, M. A. Hoffbauer, N. A. Moody, and E. R. Batista, Kinetics of alkali-based photocathode degradation, AIP Adv. 6, 115008 (2016).
  47. S. K. Mohanty, Development of multi-alkali antimonide photocathodes for high-brightness RF photoinjectors, Ph.D. thesis, Universität Hamburg, 2024.
  48. CST Studio Suite version 2024.05, Dassault Systemes Deutschland GmbH, Vélizy-Villacoublay, France (2024), https://www.3ds.com/products/simulia/cst-studio-suite.
  49. H.-W. Glock, J. Knobloch, A. Neumann, and A. Veléz, Industrial X-ray tomographie as a tool for shape and integrity control of SRF cavities, in Proceedings of 20th International Conference on RF Superconductivity, East Lansing, MI (JACOW Publishing, Geneva, Switzerland, 2022), pp. 725–732.
  50. N. Fairley, V. Fernandez, M. Richard‐Plouet, C. Guillot-Deudon, J. Walton, E. Smith, D. Flahaut, M. Greiner, M. Biesinger, S. Tougaard, D. Morgan, and J. Baltrusaitis, Systematic and collaborative approach to problem solving using X-ray photoelectron spectroscopy, Appl. Surf. Sci. Adv. 5, 100112 (2021).

Outline

Information

Phys. Rev. Materials 10, 074601– Published 10 July, 2026
  • Received 2 April 2026
  • Accepted 23 June 2026
Crossmark - Check for updates button
Creative Commons Logo

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Sign In to Your Journals Account

Filter

Filter

Article Lookup

Enter a citation