#1Los Alamos NATIONAL LABORATORY October 10, 2021 Towards the use of 2D materials as unique protection layer for bialkali photocathodes Hisato Yamaguchi Los Alamos National Laboratory (LANL) New Mexico, U.S.A. YouTube scientific videos on our findings: https://www.youtube.com/watch?v=S4krKYGUopg&feature=youtu.be https://www.youtube.com/watch?v=rkusTI_4500 NNS Managed by Triad National Security, LLC, for the U.S. Department of Energy's NNSA. 11/8/2021 1#2Addressing decadal R&D priority for cathodes ACCELERATORS FOR AMERICA'S FUTURE Directing Matter and Energy: Five Challenges for Science and the Imagination Decadal Challenges for Predicting and Controlling Materials Performance xtremes NM Whop held December 6-10 2009 Physics OCTOBER 26, 2009 Sponsored by the Office of High Energy Energy's Office of Science by the of the US Depart SYMPOSIUM ashington Harris Wardman Park Hotel 4 Productio pportunities in devrinping accelerators for national needs WASHINGTON DC Exp s and Produc dancecurity es and apport 11gy and Enviament Nation Space is limited. For symposium information and registration www.acceleratorsamerica.org Energy. Office of Science ENERGY Report from the Basic E Basic Energy Sciences 2011 Summary Report Office of ENERGY Sene LCLS/SSRL Users' Meeting and Workshops October 3-6 2012 SLAC National Accelerator Laboratory (http://science.energy.gov/-/media/bes/pdf/reports/files/ngps rpt.pdf), 2009. 2 May 11-12, 2010 Report of the Basic Energy Sciences Workshop on Compact Light Sources SCIENTIFIC ASSESSMENT OF High-power Free-electron Laser Technology [1] Hemminger, J.C., Next Generation Photon Sources for Grand Challenges in Science and and high brightness [2] Barletta, W.A. et al, Compact Light Sources. Department of Energy's Office of Science (http://science.energy.gov/-/media/bes/pdf/reports/files/CLS.pdf), 2010. [3] Henning, W. and C. Shank, Accelerators for America's future. Department of Energy's Office of Science (www.acceleratorsamerica.org/files/Report.pdf), 2010. Los Alamos NATIONAL LABORATORY · Our project aims to address nationally articulated need (DOE commissioned studies) which call for transformative advances in electron source development: long lifetime at high efficiency "Singular risk area1" "One of the highest accelerator R&D priorities for the next decade2" Transformative: enabling discovery science, national security missions 11/8/2021 2#3The problem: Performance-Lifetime limitation Our innovation: Decouple the limitation by 2D materials Current status & problem Quantum Efficiency (%) 20 15 15 Efficiency vs. Effective Lifetime in photoinjector environment Cs2Te (263nm) Cs2Te (270nm) Cal (209 m) Diamond (209mm) Cs2CsSb (527nm) Cs3Sb (527nm) Cs:GaAs (750nm) Bare Metals (268nm) 10 State-of-the-art 0 0 200 Target 400 600 1/e Lifetime (hours) Bridging the technology gap "Cook-and- look" approach Observe and exploit only High risk Technology isolation 800 1 103 ? Technology Gap Compromised performance goals One-off solutions Technology stagnation Our idea N.A.Moody US patent 8,823,259 (2014) hv O2 CO2 CO HO 000 coating layer photocathodes Los Alamos NATIONAL LABORATORY Present approaches do not depart from historical methods G.Wang and N.Moody et al. npj 2D Materials and Applications 17 (2018) 11/8/2021 3#4Why 2D materials & our team expertise Discovered Geometric pore 0.64 A in 2004 2D materials (U.S.) Photocathode on graphene 0.4 mm QE (%) 17.00 16.00 Bialkali (Japan) Evaporation sources Sb 0 K Cs QE (%) hv 000 Theory (U.S.) O CO₂ CO HO 11 guard ring stem electrode original insulator coating layer photocathodes additional insulator Bond length (C-C) 1.42 A van der Waals radius of carbon atom 1.10 A Impermeable to gases • • High material stability • Allows electron transmission 0.4 mm K₂CsSb/Gr in vacuum tube -15.00 -14.00 10mm - 13.00 0 K₂CsSb/Mo in vacuum chamber Bialkali in vacuum tubes (U.S.) Los Alamos NATIONAL LABORATORY cathode anode electron beam laser DC gun (Japan) US-Japan team working together under DOE-KEK funding 11/8/2021 4#5-6 20x10 Quantum efficiency 10 15 ☐ Copper (110) Graphene Copper (110) Experimental demonstration of our concept on metal photocathodes Cu (110) Annealed Cu (110) Graphene (Cu) Annealed Graphene (Cu) Copper (110) Annealing Graphene Copper (110) 0- 3.5 4.0 4.5 Photon energy (eV) Raman الممد 5.0 AFM Intensity (Arb. units) 1500 2000 2500 3000 Raman shift (cm³) Normalized QE 0.8 10-6 Torr 200 torr 1.0- 0.6 0.4 -0- Cu (110) -Graphene (Cu) • Successful electron transmission through graphene • 8 orders of magnitude improvement in operating pressure 0 5 10 15 20 F.Liu et al. Appl. Phys. Lett. (2017) Time (h) 1 μm 7 Height (nm) 1.2. 0.8 0.4- Height profile 0.0 0.0 0.2 0.5 nm тил 0.4 Distance (μm) 0.6 . High crystal quality graphene Uniform & atomically thin graphene 11/8/2021 5#6Normalized intensity 2.0 Milestone #1: Demonstration of material compatibility between 2D materials and bialkali photocathodes 17μm Optical Pre-deposition Post-deposition hv e- Photocathode material Gr substrate Mesh grid 34μm N.A.Moody, H. Yamaguchi et al. US Patent 10,535,486 (2020) 100 um 1 mm 1 mm H. Yamaguchi et al. npj 2D Materials and Applications (2017) XRD K₂CsSb/sapphire K₂CsSb (002) K₂CsSb/hBN (004) 2.5 3.0 3.5 4.0 4.5 5.0 d-spacing (A) Intensity (arb. units) 3 XRF K₂CsSb/hBN Fit K Sb M 4 5 Cs Energy (KeV) • • High crystallinity achieved on 2D material (XRD) Nearly ideal stoichiometry of K1.85 CS1.08 Sb achieved on 2D material (XRF) H.Yamaguchi et al. phys. stat. solidi (a) (2019) 11/8/2021 6#7High spatial resolution maps with high QE and uniformity Vol. 5 No. 13 July 9 2018 www.advmatinterfaces.de *ADVANCED MATERIALS INTERFACES (a) QE - 17.00 16.00 -15.00 - 14.00 (b) - 13.00 0.4 mm (c) QE - 17.00 Cathode/Ni 60- - 16.00 Cathode/Gr Cathode/SS 40- - 15.00 - 14.00 - 13.00 Pixels (Counts) 20- 0 WILEY-VCH Los Alamos NATIONAL LABORATORY 0.4 mm Cathode/Gr (a) 20μm Cathode/Ni (b) 10μm 0.56 (c) 1 1.01 12 13 14 15 16 17 18 19 20 QE (%) Metal/3L-Gr/K2CsSb 3L-Gr/K2CsSb Metal 0.8- Absorption 0.6- 0.4- 0.2- 0.73 0.0+ 2.0 2.5 3.0 3.5 4.0 Spatial resolution: ~500 nm Photon Energy (eV) H. Yamaguchi et al. Advanced Materials Interfaces (2018) 11/8/2021 7#8Recognition of our work: R&D 100 Award in 2019 2019 ■ 2019 R&D 100 ENTRY ■ R&D 100 WINNER Nathan A. Moody, Hisato Yamaguchi, and team SPECIAL RECOGNITION 2019 R&D ATOMIC INNOVATIVE NANOMATERIALS DESIGNED TO PROTECT EXQUISITELY SENSITIVE TECHNOLOGIES WITH A ONE-ATOM-THICK SHIELD ARMOR A diamond-hard, yet flexible, two-dimensional coating Customizable for selective permeability of particles and molecules Nonreactive with extreme environments Extends device lifetimes and can enhance performance Applicable to the most-challenging substrates 100 GOLD Los Alamos NATIONAL LABORATORY Coating of surfaces with macro-scale roughness Coated k K 米糕 Coating of surfaces with micro-scale roughness (e.g. rolled stainless steel) 2D material ALFs LDS 20m Name anaos 1320 5μm Substrate Special recognition Market Disruptor Products 11/8/2021 8#9Milestone #2 (achieved recently): QE maps of K₂CsSb through graphene coating 17μm Quantum efficiency (%) map through graphene 2-layer Gr, 3eV (405 nm) 0.25 Photocathode material hv e- 0000 0.20 0.15 0.10 20 μm 7.5 μm 0.05 Graphene 2-layer Gr, 4.4 eV (280 nm) substrate Mesh grid 3-layer Gr, 3eV (405 nm) 0.6 0.25 0.5 0.20 First ever QE of bialkali photocathodes 0.4 0.15 through graphene 0.3 coating demonstrated 0.10 0.2 500 μm 20 μm 0.1 Los Alamos NATIONAL LABORATORY 0.053/2021 9 Submitted#10Spectral QE of K2CsSb photocathodes through graphene coating QE through graphene coating 2 layers graphene 0.6 3 layers graphene 17μm 0.4 hv 0.2. 7.5 μm Quantum efficiency (%) 20 20 15 10 50 QE without graphene coating 2 layers graphene 3 layers graphene hv e 1 17μm Quantum efficiency (%) 0.0 Los Alamos NATIONAL LABORATORY 3 T 4 Photon energy (eV) LO 5 2 3 4 7.5 μm 5 Photon enregy eV Submitted 11/8/2021 10#11Unexpected finding #1: QE enhancement of bialkali photocathodes by coating metal substrates with graphene 23 2019 pissa www.pss-a.com applications and materials science (c) Photocathode material (d) 1.41 Substrate Atomically thin layer hv e- Photocathode material Atomically thin layer Metal substrate Relative quantum efficiency 1.00 Graphene coating 0.91 0.82 No graphene 0.73 0.64 WILEY-VCH Enhanced mirroring effect Selected as a journal cover 10μm Relative enhancement 1.3- 1.2- Side view 1.1- 1.0- 400 • Model Experiment 500 600 Wavelength (nm) ↑ ↑ QE 1.0 0.8 0.6 0.4 Coated Name: Imags 1320 375nm Los Alamos NATIONAL LABORATORY 405nm 532nm 633nm H. Yamaguchi et al. phys. stat. solidi (a) (2019) 5μm 11#12Unexpected finding #2: Graphene as reusable substrate for bialkli photocathodes Graphene Active material deposition Thermal cleaning at 500 °C Silicon (Si) or molybdenum (Mo) 8 New 7 Used Quantum efficiency QE[%] CO 5 + 3 2 1 New No residue On other substrates On graphene Residue (a) Graphene/Si Silicon (Si) Molybdenum @ 532 nm (Mo) Cs 4d 500°C 400°C 1 New Graphene 4 cm 5 Used Graphene Si Substrates Used 80 Binding Energy (eV) (b) Graphene/Si Si 2p (Oxide) 76 News released (d) Si Cs 4d 500°C 400°C 80 78 76 Binding Energy (eV) (e) Si Si 2p (Oxide) (g) Mo Cs 4d (h) Mo 500°C 82 80 Binding Energy (ev) 78 76 Sb 4p 400°C 500°C 500°C Si 2p (1/2 & 3/2) 400°C Si 2p (1/2 & 3/2) 500°C 400°C ح 400°C 105 102 99 96 93 102 99 93 105 102 99 93 90 Binding Energy (eV) Binding Energy (eV) Binding Energy (eV) (c) Graphene/Si (f) Si (i) Mo C 1s C 1s C 1s 300 K 2p 500°C K 2p 500°C 400°C 400°C 297 294 288 297 291 288 297 294 291 288 285 Binding Energy (eV) Binding Energy (eV) Binding Energy (eV) 500°C 400°C No detectable photocathode residue on graphene by X-ray photoelectron spectroscopy Mo L.Guo et al. Appl. Phys. Lett. (2020) 11/8/2021 12#13Summary • • • • • • Patent granted for our concept in the U.S. (2014) Successful demonstration of our concept on metal photocathodes published in Applied Physics Letters (2017) Successful demonstration of material compatibility between bialkali photocathodes and 2D materials published in nature partner journals 2D Materials and Applications (2017) Successful demonstration of high QE (17 % at its peak) from bialkali photocathodes deposited on 2D materials published in Advanced Materials Interfaces (2018) Our technology won R&D 100 Award (2019) Successful demonstration of 2D materials as QE enhancer for bialkali photocathodes published in physica status solidi (a) (2019) Successful demonstration of 2D materials as reusable substrates for bilalkali photocathodes published in Applied Physics Letters (2020) Successful demonstration of QE from bialkali photocathodes through graphene protection layers submitted (2021) Los Alamos NATIONAL LABORATORY 11/8/2021 13#14Collaborators External Jeff DeFazio (Photonis) Kevin Jensen (NRL) Mengjia Gaowei (BNL) Lei Guo (Nagoya Univ., Japan) Masahiro Yamamoto (KEK, Japan) KEK Funding Internal Nathan Moody Fangze Liu (now in China) Vitaly Pavlenko John Smedley Gaoxue Wang Enrique Batista Ping Yang John Lewellen (now at SLAC) DEPARIMENT OF ENER External U.S. DEPARTMENT OF Office of ENERGY Science TED STATE FAMERI Los Alamos NATIONAL LABORATORY Internal LORD LABORATORY DIRECTED RESEARCH & DEVELOPMENT 11/8/2021 14