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All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

IMPROVED LIFETIME OF A HIGH SPIN POLARIZATION SUPERLATTICE PHOTOCATHODE

Highly spin polarized electron beams are required for the operation of a wide range of accelerators and instruments. The production of such electrons requires the use of Negative Electron Affinity (NEA) activated GaAs-based cathodes operated in photoelectron guns. Because of their extreme sensitivity to poor vacuum conditions the degradation of the photoemission process is so strong that NEA activated GaAs-based photocathodes can only survive in the extreme vacuums typical of DC gun. State-of-the-art on photocathode technology for spin polarized beam productions are summarized. Recent results on the use of robust NEA coating based on the Cs-Te and Cs-Sb leading to improved operational lifetime of a high spin polarization photocathode are reviewed.

47 OTHER INSTRUMENTATION↗
DOE OSTI2020

Materials Data on Cs2Te3 by Materials Project

Cs2Te3 crystallizes in the orthorhombic Cmc2_1 space group. The structure is three-dimensional. there are two inequivalent Cs sites. In the first Cs site, Cs is bonded in a 8-coordinate geometry to eight Te atoms. There are a spread of Cs–Te bond distances ranging from 3.90–4.20 Å. In the second Cs site, Cs is bonded in a 7-coordinate geometry to seven Te atoms. There are a spread of Cs–Te bond distances ranging from 3.89–4.04 Å. There are two inequivalent Te sites. In the first Te site, Te is bonded in a 5-coordinate geometry to three Cs and two equivalent Te atoms. Both Te–Te bond lengths are 2.83 Å. In the second Te site, Te is bonded to six Cs and one Te atom to form a mixture of distorted face, edge, and corner-sharing TeCs6Te pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs2Te by Materials Project

Cs2Te is Cotunnite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Cs1+ sites. In the first Cs1+ site, Cs1+ is bonded in a 5-coordinate geometry to five equivalent Te2- atoms. There are a spread of Cs–Te bond distances ranging from 3.95–4.44 Å. In the second Cs1+ site, Cs1+ is bonded to four equivalent Te2- atoms to form a mixture of edge and corner-sharing CsTe4 tetrahedra. There are a spread of Cs–Te bond distances ranging from 3.78–3.87 Å. Te2- is bonded in a 9-coordinate geometry to nine Cs1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CsTe by Materials Project

CsTe crystallizes in the orthorhombic Pbam space group. The structure is three-dimensional. Cs1+ is bonded in a 8-coordinate geometry to eight equivalent Te1- atoms. There are a spread of Cs–Te bond distances ranging from 3.89–4.30 Å. Te1- is bonded in a 9-coordinate geometry to eight equivalent Cs1+ and one Te1- atom. The Te–Te bond length is 2.83 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CsTe4 by Materials Project

CsTe4 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Cs1+ is bonded in a 8-coordinate geometry to eight Te+0.25- atoms. There are a spread of Cs–Te bond distances ranging from 3.94–4.16 Å. There are four inequivalent Te+0.25- sites. In the first Te+0.25- site, Te+0.25- is bonded in a 5-coordinate geometry to three equivalent Cs1+ and two Te+0.25- atoms. There are one shorter (2.83 Å) and one longer (2.96 Å) Te–Te bond lengths. In the second Te+0.25- site, Te+0.25- is bonded in a 5-coordinate geometry to two equivalent Cs1+ and three Te+0.25- atoms. There are a spread of Te–Te bond distances ranging from 2.80–3.37 Å. In the third Te+0.25- site, Te+0.25- is bonded in a 6-coordinate geometry to one Cs1+ and five Te+0.25- atoms. There are one shorter (2.91 Å) and one longer (3.60 Å) Te–Te bond lengths. In the fourth Te+0.25- site, Te+0.25- is bonded in a 4-coordinate geometry to two equivalent Cs1+ and three Te+0.25- atoms.

36 MATERIALS SCIENCE↗