Effect of the surface structure and atomic termination on the surface dipole and work function of La3Te4

Abstract

The work function is a key surface property that plays a prominent role in electronic transport and the thermoelectric (TE) properties of a TE material. For TE nanocomposite materials, the jump in the work function at the interface of the constituent materials can impact the figure of merit (ZT) of the system. The work function in turn is sensitive to the interfacial surface structure. In this work, the effects of the surface structure and atomic termination on the surface dipole and work function of various La₃Te₄ slab structures were investigated using first-principles electronic structure calculations. The computed surface dipole and work function of La₃Te₄ slabs are found to depend not only on the atomic surface structure, growth direction, and termination, but also on the composition of each surface component (Te-rich or La-rich). We also discovered that while the surface electron density can explain the trends in the work function with modifications of La-rich surfaces, it fails to do so in the case of Te-rich surfaces. On the other hand, changes in the work function can be explained by the electronic dipole density at the surface. We also propose a new way to estimate the surface dipole using first principles calculations, and the relationship between the work function and ZT of the two nanocomposite systems La₃Te₄–Ni and La₃Te₄–Ca is discussed.