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The Center for Bright Beams, A National Science Foundation Science and Technology Center

Computational Screening for Low Emittance Photocathodes

A chart depicting the electronic band structure of PbTe. More details in teh caption.

A graph showing the electronic band structure of PbTe. The letters on the x-axis represent high symmetry points within reciprocal space. One can see high curvatures in the bands at L points, indicating a low MTE due to transverse momentum of the electron.

The electronic band structure of PbTe. Each letter represents a high symmetry point within reciprocal space. One can see high curvatures in the bands at L points, in-dicating a low MTE due to transverse momentum of the electron.
 

J. T. Paul, R. G. Hennig, A. Galdi, I. V. Bazarov, S. Karkare, H. Padmore

In order to improve beam brightness, we look for currently unused materials that can emit more clustered electrons

Using the MaterialsProject database, we searched over 69,000 materials to identify potential photocathodes. Initial screening criteria reduced this number to approximately 38,000. We then estimated me of these materials using the band structures from MaterialsProject and our calculations, finding a higher density mesh was needed to obtain an accurate estimate.

Summary of the screening process. This shows that the screening by our criteria of radioactivity, stability, and bandgap reduces the number of materials from 69,640 to 38,019.

Screening

Number of Materials

Material Project Database 69,640
No Radioactive Elements 66,119
ΔEhull≤ 50 meV/atom 43,087

0 eV < Egap ≤ 4 eV

38,019
20 k-points: m* ≤ .2m0 517
200 k-points: m* ≤ .2m0 In Progress
High Quantum Efficiency In Progress
Low MTE In Progress
 

This project enhances the Center for Bright Beam's objective of striving towards ultralow emittance photocathodes. Particle Accelerators around the world would benefit through improved beam brightness.

 

Link to full publication:
http://accelconf.web.cern.ch/AccelConf/ipac2018/papers/thpml053.pdf