  We have computationally explored workfunction values of Cs2Te5, an existing
crystalline phase of the Cs-Te system and a small bandgap semiconductor, in
order to search for reduced workfunction alternatives of Cs2Te that preserve
the exceptionally high quantum efficiency of the Cs2Te seasoned photoemissive
material. We have found that the Cs2Te5(010) surface exhibits a workfunction
value of ~ 1.9 eV when it is covered by Cs atoms. Cs2Te5 is analogous to our
recently proposed low-workfunction materials, Cs2TeC2 and other ternary
acetylides [J. Z. Terdik, et al., Phys. Rev. B 86, 035142 (2012)], in as much
as it also contains quasi one-dimensional substructures embedded in a
Cs-matrix, forming the foundation for anomalous workfunction anisotropy, and
low workfunction values. The one-dimensional substructures in Cs2Te5 are
polytelluride ions in a tetragonal rod packing. Cs2Te5 has the advantage of
simpler composition and availability as compared to Cs2TeC2, however its low
workfunction surface is less energetically favored to the other surfaces than
in Cs2TeC2.
