Interrelation of Work Function and Surface Stability: The Case of BaAl₄

Abstract

The relationship between the work function (Φ) and the surface stability of compounds is, to our knowledge, unknown, but very important for applications such as organic light-emitting diodes. This relation is studied using first-principles calculations on various surfaces of BaAl4. The most stable surface [Ba terminated (001)] has the lowest Φ (1.95 eV), which is lower than that of any elemental metal including Ba. Adding barium to this surface neither increases its stability nor lowers its work function. BaAl4 is also strongly bound. These results run counter to the common perception that stability and a low Φ are incompatible. Furthermore, a large anisotropy and a stable low-work-function surface are predicted for intermetallic compounds with polar surfaces.

Generalised coexistence of a low work function and a stable surface: CaAl4 and BaAuIn3

“…In contrast, previous work [7] showed that the surface with the lowest work function is also the most stable one, at least for BaAl 4 . From analysis of the results we predicted that this should be a more general feature of complex metals, more specifically of intermetallic compounds with polar unit cells.…”

“…The method to calculate the work function of a specific surface is described in Ref. [7]. A bulk calculation provides an accurate E F .…”

“…How c is calculated is described in Ref. [7]. It is the difference between the energy of a slab and the equivalent bulk, normalised to unit area.…”

Work function anisotropy and surface stability of half-metallicCrO2

“…The most stable surfaces also had the lowest work functions. [3][4][5] In the case of BaAl 4 , this model correctly predicts a Ba terminated surface that also has the lowest work function; the more electropositive element, i.e., Ba, prefers to reside at the surface and, hence, also induces a dipole moment that tends to lower the work function. The other intermetallics studied, CaAl 4 , LaB 6 , Ca 2 N, and BaAuIn 3 , exhibited similar behavior.…”

“…This was first demonstrated in a computational study for BaAl 4 . 3 The barium terminated ͑001͒ surface has a work function of 1.95 eV, which is lower than that of elemental barium ͑2.32 eV͒. It is even lower than that of any element, which is clearly in contradiction with the alloy effect.…”