Determination of the surface atomic geometry of PbTe(100) by dynamical low-energy electron-diffraction intensity analysis

Contrary to expectations based on results for other cubic binary semiconductors, an analysis of surface Pb core-level shifts from rocksalt structure PbS(100) suggests large top-layer contractions for group-IV A element chalcogenides. To examine this possibility, we performed a surface-structure analysis for PbTe(100) using eight beams of low-energy electrons diffracted from PbTe(100) at 50 K. A dynamical analysis of the intensities of these beams, based on relativistic potentials shown to be accurate for fifth-row elements, leads to the conclusion that the Pb sublattice in the outer layer is relaxed into the bulk by 0.22 (7%) relative to the outer-layer Te sublattice. The average spacing between the first and second layers is 4% smaller than the bulk interlayer spacing, while the average second-to-third-layer spacing is expanded 2% relative to the bulk spacing. Our results are analogous to those found for the (100) surfaces of other cubic materials. A covariance analysis of parameter estimation error indicates that the relaxation detected by the normal-incidence low-energy electron-diffraction experiment is statistically significant, i.e., the deviations of the three surface-structure parameters from the corresponding bulk-structure values are many times larger than the parameter estimation error levels associated with errors in the measured intensities. Moreover, deviations from the bulk structure of the top two layers alone suffice to describe the measurements. Surface-structure optimization that allowed two additional structural parameters (second-layer rumple and third-to-fourth interlayer spacing) to vary yielded a structure insignificantly different from that produced by the three-variable-parameter optimization.