W (100) studied by He diffraction

Abstract

C(2×2) reconstruction of clean W(100) is observed by low energy helium scattering. In the transition region we observe that half-order peaks disappear while being angularly broadened and shifted towards the specular position. This is explainable by a strong in-plane thermal expansion of reconstructed areas separated by dense walls. In the high temperature phase only the specular intensity is observable and the low reflectivity of the surface is evidence for atomic-scale disorder. We conclude that the reconstruction transition is an order-disorder one with incommensurability in the critical region.