Collaborators:Jefferson Lab, Univ. of Arkansas,

Brookhaven Lab, Argonne Lab CNM, Univ. of California Santa Barbara

8 Oct 2020Euclid Techlabs LLC Eric Montgomery, Director of Research

Spin Polarized Cathode Development for EIC at Euclid

Outline of TalkWho is Euclid?CollaboratorsMotivation1: Superlattice Production2: Nanopillar Arrays3: Half-Metal Spin Filters4: Unpolarized Cathode Development5: Future EffortsConclusion

4. Epi Cathode, Encapsulated, UNCD5. Epi-single crystal,Diamondback,Plasmon enhanced, MBE production SL

Who is Euclid?Euclid Techlabs, LLC in Bolingbrook, IL, specializes in linear particle accelerators, ultrafast electron microscopy, and advanced material technologies for energy, defense, and medical applications.20 researchers • engineers • technicians10,000 ft2 research space, and growing

• time-resolved ultra-fast electron microscopy• ultra-compact linear accelerators• electron guns (thermionic, field, or photoemission)• fast tuners for SRF cavities• advanced dielectric materials• HPHT and CVD diamond growth and applications• thin-film applications in accelerator technologies

Current Collaborating Laboratories

R&D 100 Award: Laser-Free Stroboscopic TEM Pulser

Recent Euclid AchievementsCover of RSI, Feb 2020New 100% Polarized Spintronics Candidate

“Chemical substitution induced half-metallicity in CrMnSb(1-x)Px”O’Leary et al., J. Appl. Phys. 128, 113906 (2020)

Science Advances: Ultrafast Imaging of GHz Fields in TEM

“Direct visualization of electromagnetic wave dynamics by laser-free ultrafast electron

microscopy.” Fu et al., Sci. Adv. 6(40), eabc3456 (2020).

M&M 2020 Innovation AwardMicroscopy & Microanalysis Conference

Collaborations with BNL and JLab

UNCD Photocathodes (with ANL) E. Wang

Ultrafast TEM Pulser (with NIST) Y. Zhu

SRF Photogun & Flux Concentrator L. Doom

Encapsulated Photocathodes E. Wang

Nanostructured GaAs SL Cathodes M. Poelker, S. Zhang

Heusler Alloy Spin Filters M. Poelker, S. Zhang

Also long-time work with ATF (M. Palmer), and idea for SRF fast tuners (I. Ben-Zvi)

Motivation

• The preferred state-of-the-art spin-polarized electron source is the GaAs/GaAsP superlattice photocathode (or SL).

• This cathode is not available from any vendor worldwide since SVT exited the market.

• SL stockpile in the US is enough for CEBAF at JLab but not EIC.

• A new commercial vendor offers advantages:

• Fast and responsive development with minimal paperwork

• Longevity of production beyond a single grant or postdoc

• Euclid Techlabs is well suited to take this challenge

Euclid Cathodes To Date (spin polarized)

UNCD diamond field emission cathodes (ANL, BNL) 2015-2018

Nanopillar array GaAs photocathodes (JLab, ANL, GW) 2019

Nanostructured SL photocathodes (JLab, ANL, UArk) 2019

Encapsulated photocathodes (BNL) 2020

Heusler alloy half metal spin filters (Jlab, UCSB) 2020

Epitaxial cesium antimonide (ASU) 2020

PIs: S. Poddar A. Liu E. Montgomery

Spin Polarized Cathode Work

Superlattice and Nanostructured Cathodes

Nishitani 200590 layers

0.001

0.01

0.1

1

0

10

20

30

40

50

60

70

650 670 690 710 730 750 770 790 810

QE

(%)

Pola

rizat

ion

(%)

wavelength (nm)

InGaAs/AlGaAs SSLPolarization (%) QE ( %)

Montgomery et al 201920 layers

MBE at U. of Arkansas (Salamo et al.)Polarimetry at JLab (Stutzman)

Superlattice and Nanostructured Cathodes

Sample ID UArk1 Dosage (µC/cm2) 200Recipe (sccm) Ar: 10 Cl2: 2 BCl3:2ICP (W) 850 HF (Plate) (W) 50Pressure (mTorr) 5Diameter (nm) 130Height (nm) 460

AlGaAs/GaAs SL with Array

Backscattering efficiency (blue), absorption efficiency(orange), and a green line corresponding to a fractionof beam energy absorbed by an infinitely wide slab ofthe same thickness as sphere. (A. Afanasev)GaAs Array (S. Poddar at ANL CNM)

Overview: Half-Metal Spin Filters

Minority spin channel band gapThreshold for photoemission: 3.4eVRequires UV laserUp to 4.4 eV photon energy only one spin can be photoexcited => 100% polarization

fEf

Kamper et al, PRL 59, 2788 (1987)

Mustonen et al, PRB 93, 014405(2016)

Example:

CrO2

Original slide credit L. Cultrera

Spin Injection in Devices – Tunnel Junctions

Original slide credit L. Cultrera

Cu CuEuO

Jutong et al, PRB 86, 205310 (2012)Example: Cu/EuO/Cu tunnel junction

Spin Filtering of Electron Vacuum Emission

Original slide credit L. Cultrera

Muller et al, PRL 29, 1651 (1972)Example: EuS

Below Curie temp (21K)Field emissionW needle coated with EuSPolarization 89±7%

Other materials?What about room temp?How high can P be?

Heusler Alloy Half-Metal Spin FiltersSome Heusler alloys = half metals. Lattice match to GaAs.100% spin polarized: transport filtering possible?With cesiation, visible drive laser photoemission anticipated.NO LITERATURE ON THIS MATERIAL FOR PHOTOEMISSIONEuclid will test at JLab this month (October 2020)

UCSB MBE Heusler alloy growth system (Palmström et al)

JLab Mott polarimeter

Euclid XHV suitcase

Non-Spin Polarized Cathode Work

(N)UNCD Field Emission Cathodes

3 µAà3mA/cm2 @~1 MV/m and 2 KelvinTurn-On 0.7 MV/m

29.7 μA @ 5.5 V/μm 60.3 μA @ 5.9 V/μm100 μA @ 6.1 V/μm

BNL with E. Wang – Cryo UNCD in-gun

Baryshev et al. (2020), https://arxiv.org/abs/2003.09571

Epitaxial | Encapsulated Antimonides

50 nm epitaxial growth of Cs3Sb at Arizona State on Euclid’s lattice-matched substrate: extra MTE from this roughness simulated to be only 0.1 meV!

Credit G. Wang (Euclid/IIT)

RF sputtering/ modeling surface

Euclid PI: A. LiuBNL PI: E. Wang

Lattice-matched substrate

versus Si wafer substrate

±5 nm

±5 nm

Future Work related to EICNovel Damage-Resistant Superlattice (proposal pending)- Addresses cesium loss and lattice damage from ion back-bombardment

and laser heating

- Proposal pending: Small Business Innovation Research Phase I

Diamond Mott Polarimeter (proposal pending)- Goal is to reduce uncertainty in Mott polarimetry <<0.5%

- Proposal pending: Small Business Innovation Research Phase I

Dedicated EIC Superlattice Production Facility (planned)- Proposed to site at Argonne Clean Room as industrial partner

- Effusion Cells: Ga, As, P, Be, Al…

- RHEED capability

- Maintained and operated by Euclid engineers

- Available to users

ConclusionEnvisioned Superlattice Production Facility Timeline (in discussions)

~2020 Lab and industrial partner agreementsCollaboration development

~2021 Funding in place for production facilityInitial SL growth with academic partners

~2022 Procurement, calibration and optimization~2023 Production begins

Collaboration Welcomed! Any Questions?