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DOE OSTI2023

Ion-beam-assisted growth of cesium-antimonide photocathodes

We report on the novel use of a Cs+ ion gun for an ion-beam-assisted molecular-beam-epitaxy (IBA-MBE) method to sequentially deposit Cs-Sb cathodes on room temperature substrates as opposed to the standard technique of thermal evaporation on elevated-temperature substrates. The details of the ultrahigh-vacuum chamber, the Cs+ ion source, and the growth technique are elaborated. The final quantum efficiency (QE) is reasonably good for Cs-Sb cathodes grown on two different substrates—Si (100) and strontium titanate—and is comparable to the QE of cathodes grown using thermal sources. This suggests that IBA-MBE could be a viable alternative to grow alkali-antimonides without substrate heating, paving the way for the growth of epitaxial alkali-antimonides in a more reproducible fashion, which may help improve the efficiency of photon detectors and accelerator applications that use alkali-antimonides as electron sources.

Engineering↗

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 Cs3Sb by Materials Project

Cs3Sb is alpha bismuth trifluoride structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. there are two inequivalent Cs1+ sites. In the first Cs1+ site, Cs1+ is bonded to four equivalent Cs1+ and four equivalent Sb3- atoms to form a mixture of distorted corner, edge, and face-sharing CsCs4Sb4 tetrahedra. All Cs–Cs bond lengths are 4.05 Å. All Cs–Sb bond lengths are 4.05 Å. In the second Cs1+ site, Cs1+ is bonded in a body-centered cubic geometry to eight equivalent Cs1+ atoms. Sb3- is bonded in a body-centered cubic geometry to eight equivalent Cs1+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on CsSb by Materials Project

CsSb is Magnesium tetraboride-like structured and crystallizes in the orthorhombic P2_12_12_1 space group. The structure is three-dimensional. there are two inequivalent Cs1+ sites. In the first Cs1+ site, Cs1+ is bonded in a 6-coordinate geometry to six Sb1- atoms. There are a spread of Cs–Sb bond distances ranging from 3.86–4.18 Å. In the second Cs1+ site, Cs1+ is bonded in a 5-coordinate geometry to five Sb1- atoms. There are a spread of Cs–Sb bond distances ranging from 3.84–4.05 Å. There are two inequivalent Sb1- sites. In the first Sb1- site, Sb1- is bonded in a 7-coordinate geometry to five Cs1+ and two equivalent Sb1- atoms. There are one shorter (2.90 Å) and one longer (2.92 Å) Sb–Sb bond lengths. In the second Sb1- site, Sb1- is bonded in a 8-coordinate geometry to six Cs1+ and two equivalent Sb1- atoms.

36 MATERIALS SCIENCE↗