Structure of Kcn Monolayer Films Vapor-Deposited onto Cleaved KBr(001) by Helium Atom Diffraction

Abstract

AbstractAngular distribution measurements of the helium atom scattering intensity from monolayer films of KCN/KBr(001) for several azimuths over a temperature range of approximately 40–200 K reveal that above ˜95 K the KCN monolayer forms a (1×1) overlayer structure with respect to the KBr substrate. (The lattice spacing of bulk KCN in the rocksalt-structure phase differs from that of KBr by only ˜ 1%.) Below this temperature the overlayer appears to be (2×1), and “missing” diffraction spots in the <110> high symmetry direction suggest the existence of a glide plane. The inferred structure for this low temperature phase consists of K+ ions fixed in their rocksaltstructure positions relative to the substrate and the CN− ions oriented so that their dipoles are aligned antiferroelectrically within the new unit cell.