Graphene as reusable substrate for bialkali photocathodes

Journal Article · Mon Jun 22 00:00:00 EDT 2020 · Applied Physics Letters

DOI:https://doi.org/10.1063/5.0010816· OSTI ID:1856175

Guo, Lei ^[1]; Yamaguchi, Hisato ^[2]; Yamamoto, Masahiro ^[3]; Matsui, Fumihiko ^[4]; Wang, Gaoxue ^[2]; Liu, Fangze ^[5]; Yang, Ping ^[2]; Batista, Enrique R. ^[2]; Moody, Nathan A. ^[2]; Takashima, Yoshifumi ^[6]; Katoh, Masahiro ^[7]

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1. Nagoya Univ. (Japan). Synchrotron Radiation Research Center (NUSR)
2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
3. High Energy Accelerator Research Organization (KEK), Tsukuba (Japan)
4. National Institute of Natural Sciences (NINS), Okazaki (Japan). Institute of for Molecular Sciences (IMS)
5. Los Alamos National Laboratory (LANL), P.O. Box 1663, Los Alamos, New Mexico 87545, USA
6. Nagoya University Synchrotron Radiation Research Center (NUSR), Furo, Chikusa, Nagoya, Aichi 464-8601, Japan
7. Nagoya Univ. (Japan). Synchrotron Radiation Research Center (NUSR); National Institute of Natural Sciences (NINS), Okazaki (Japan). Institute for Molecular Sciences (IMS); Hiroshima Univ. (Japan). Hiroshima Synchrotron Radiation Center

Bialkali photocathodes, such as cesium potassium antimonide (CsK₂Sb), can generate a high-brightness electron beam using a high-power green laser. These photocathode materials have potential applications in advanced accelerators and electron microscopes. It is known that the quantum efficiency (QE) of these photocathodes is affected severely by their substrates; however, reusability of the substrates is not well known. Here, we use graphene, silicon (Si), and molybdenum (Mo) substrates to evaluate the effects of substrates on the QE of redeposited CsK₂Sb photocathodes after thermal cleanings. We found the QE of CsK₂Sb photocathodes redeposited on a graphene substrate after a thermal cleaning at 500 °C remained largely unchanged. On the other hand, the QE of redeposited photocathodes on Si and Mo substrates after thermal cleaning at the same temperature decreased drastically. We used X-ray photoelectron spectroscopy (XPS) to quantitatively evaluate the residues of photocathodes after thermal cleaning at 400 °C and 500 °C. We found that the Sb, K, and Cs are removed by thermal cleaning at 500 °C for the graphene substrate, but all or the majority of these elements remained on the Si and Mo substrates. The results were consistent with our density functional theory (DFT) calculations for the case of Si, which we investigated. Furthermore, our angle-resolved photoemission spectroscopy (ARPES) on graphene indicated that its intrinsic electronic structure is preserved after photocathode deposition and thermal cleaning at 500 °C. Hence, we attributed the difference in amount of photocathode residue to the unique dangling-bond- free surface of inert graphene. Our results provide a foundation for graphene-based reusable substrates for high-QE semiconductor photocathodes.

• Research Organization: Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: High Energy Accelerator Research Organization (KEK); USDOE; USDOE Office of Science (SC)
• Grant/Contract Number: 89233218CNA000001
• OSTI ID: 1856175
• Alternate ID(s): OSTI ID: 1634855
• Report Number(s): LA-UR-22-20503
• Journal Information: Applied Physics Letters, Journal Name: Applied Physics Letters Journal Issue: 25 Vol. 116; ISSN 0003-6951
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

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