He and Ne diffraction from W(100): Two views of the c(2 × 2) phase transition

Helium and neon diffraction have been used to follow the phase transition of the W(100) surface, which reconstructs to a c(2 × 2) structure on cooling below room temperature. For the case of He, we find that the reconstruction-induced half order peaks broaden and shift towards the specular peak on heating through this transition, in agreement with the observations of others. However, the corresponding Ne diffraction peaks show no appreciable shift or broadening under identical conditions, indicating, that thermal He and Ne atoms probe surface structures with different periodicities. © 1989.