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Searching for low-workfunction phases in the Cs-Te system: The case of Cs2Te5
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Image of FIG. 1.
FIG. 1.

A near top down view of a 3 × 3 × 3 supercell of the rectangular unit cell of CsTe. Cell data are from Ref. . Bronze spheres denote Te, blue ones are Cs. Notice the quasi 1D [ ] polytelluride ions embedded in Cs matrix in the form of 4 Å wide wavy Te-ribbons, showed in detail in Fig. 2 .

Image of FIG. 2.
FIG. 2.

An isolated Te-ribbon of the 3 × 3 × 3 supercell of CsTe. In the wavy Te-ribbons, six-membered rings of Te in chair-conformation are connected via common vortices into quasi 1D chains.

Image of FIG. 3.
FIG. 3.

Panels (A) and (B) show the (bc) and (ba) plane views of a 3 × 3 × 3 supercell of the CsTe crystal, respectively, where a, b, and c denote the crystallographic axes. Only those crystal surfaces have been considered that do not cleave polytelluride ions and have small Miller indices. These are (110), (010)-C1, and (010)-C2. The (010)-C1 surface slab leaves some Te atoms directly exposed on both of its surfaces, while the (010)-C2 one has one fully Cs covered surface and one partially Cs covered one.

Image of FIG. 4.
FIG. 4.

Band structure of CsTe. Energy levels are relative to the top of the valence band. The band gap is 0.19 eV. The selection of the special k-points is based on the orthorhombic symmetry of the cell and is identical with that used for CsTe in Ref. , as both CsTe (space group: Pnma) and CsTe (space group: Cmcm) crystallize in the orthorhombic system.

Image of FIG. 5.
FIG. 5.

Optical absorption spectra in terms of the macroscopic dielectric constant for CsTe as compared to that of CsTe and CsTeC. The energy of the incident photons is denoted by ω, while the polarization of the photons is indicated by the coordinate directions in the curve-keys with being parallel with the main crystallographic axis. The calculations predict that CsTe would have a significantly higher absorption probability at lower photon energies, also at 1.9 eV which is the workfunction value of the Cs-covered CsTe(010) surface.


Generic image for table
Table I.

Calculated properties of CsTe surfaces: workfunctions ( ), bandgaps at the Γ-point , and surface energies (σ). For the CsTe(010)-C2 cleavage, data refer to the fully Cs-covered surface. The workfunction of this surface has been calculated both from the asymmetrically cesiated CsTe(010)-C2 slab ( ) and from the symmetrized (with additional Cs) and relaxed version of it ( ). The average surface energy of the asymmetrically cesiated CsTe(010)-C2 slab was 22.6 meV/Å, and the contribution of the Cs-rich side is estimated to be close to the CsTe(010)-C1 value ( ).


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Searching for low-workfunction phases in the Cs-Te system: The case of Cs2Te5