Phonons in Iron Monolayers

The systematic investigation of the lattice dynamics from bulk to a single atomic layer of material was a great experimental challenge until now. Recently, nuclear inelastic scattering has been introduced as a unique technique capable of determining the density of phonon states of nanoscale materials in-situ with a depth resolution of one atomic layer. This became possible by setting up a dedicated ultrahigh vacuum system for samples growth and characterization directly at the nuclear resonance beamline ID18 of the ESRF. The new instrument allowed for systematic investigation of the evolution of the density of phonon states of iron from the bulk to a single atomic layer. The isotopic selectivity of the nuclear resonance absorption was employed to experimentally determine the atomic vibrations at and near the Fe(110) surface with a monolayer sensitivity. The experimental achievements stimulated a rapid progress of the ab-initio calculations of surface phonons.