Anomalous work function anisotropy in ternary acetylides

Abstract

Anomalous anisotropy of workfunction values in ternary alkali metal transition metal acetylides is reported. Workfunction values of some characteristic surfaces in these emerging semiconducting materials may differ by more than ≈ 2 eV as predicted by Density Functional Theory calculations. This large anisotropy is a consequence of the relative orientation of rod-like [MC2]∞ negatively charged polymeric subunits and the surfaces, with M being a transition metal or metalloid element and C2 refers to the acetylide ion C 2− 2 , with the rods embedded into an alkali cation matrix. It is shown that the conversion of the seasoned Cs2Te photo-emissive material to ternary acetylide Cs2TeC2 results in substantial reduction of its ≈ 3 eV workfunction down to 1.71-2.44 eV on the Cs2TeC2(010) surface while its high quantum yield is preserved. Similar low workfunction values are predicted for other ternary acetylides as well, allowing for a broad range of applications from improved electron-and light-sources to solar cells, field emission displays, detectors and scanners.

AISeC2H (AI=K, Rb, Cs): Crystalline Compounds with the Elusive −Se‐C≡C‐H Anion

“…The latter are semiconductors with small indirect band gaps, whose sizes depend on the nature of the respective alkali metal ion A + . Very recently, these compounds have attracted some attention, as based on DFT calculations it was concluded that they should exhibit an anomalous anisotropy of workfunction values making them interesting candidates for possible applications as photocathodes and novel intercalation electrode materials for batteries . Even better workfunction values were calculated for a potential Cs 2 TeC 2 compound, which was assumed to crystallize in the Na 2 PdC 2 structure type with linear ⋅⋅⋅Te‐C≡C‐Te⋅⋅⋅ chains in these calculations .…”

“…Very recently, these compounds have attracted some attention, as based on DFT calculations it was concluded that they should exhibit an anomalous anisotropy of workfunction values making them interesting candidates for possible applications as photocathodes and novel intercalation electrode materials for batteries . Even better workfunction values were calculated for a potential Cs 2 TeC 2 compound, which was assumed to crystallize in the Na 2 PdC 2 structure type with linear ⋅⋅⋅Te‐C≡C‐Te⋅⋅⋅ chains in these calculations . Although the assumption of Te 0 with a linear coordination is not in agreement with the expected coordination geometry, it was the same group that claimed in a recent work the successful synthesis and structural elucidation of Li 2 TeC 2 crystallizing in the Na 2 PdC 2 structure type as well as Na 2 TeC 2 , crystallizing in a different structure, but also exhibiting linear ⋅⋅⋅Te‐C≡C‐Te⋅⋅⋅ chains .…”

Ultrahigh energy density Li-ion batteries based on cathodes of 1D metals with –Li–N–B–N– repeating units in α-LixBN2 (1 ⩽ x ⩽ 3)

“…However, due to its explosivity when heated to 240 o C, or due to mechanical impact or electrical ark 12 its application is rendered unsafe in batteries. Conjugated 1D polymers occur in many other materials, especially in coordination polymers, such as CuCN, AgCN, AuCN or ternary acetylides 13,14 .…”

Materials design by quantum‐chemical and other theoretical/computational means: Applications to energy storage and photoemissive materials

“…Ultrathin oxide monolayers over metal surfaces change the electrostatic boundary conditions on the surface and thus they may significantly decrease or increase the workfunctions and the shape and occupation of surface bands which leads to drastic changes in the properties of the emitted electrons . In the second example, we have pointed out that the workfunction of the seasoned, high quantum efficiency Cs 2 Te photoemissive material can be lowered from ≈3 eV to about 2.4 eV by acetylation resulting in Cs 2 TeC 2 , whereas its quantum efficiency is preserved . Analogous compounds Cs 2 PdC 2 and Cs 2 PtC 2 exist and we have managed to synthesize Li 2 TeC 2 (X‐ray diffraction confirms theoretically predicted structure; K. Németh et al, to be published) as the first member of ternary acetylides with Te.…”