Invited Lecture
Probing microscopic motion without a microscope; matter-wave interferometry experiments of ultra-fast motion on solid surfaces

Studying the complex diffusive motion of atoms and molecules on the surface of a solid material is a basic step in understanding a wide range of phenomena, examples include thin film growth, heterogeneous catalysis, associative desorption and many others. With the exception of ultra-cold surfaces, or very strongly bound systems, atoms and molecule travel from one adsorption site to another on a time scale that is many orders of magnitude too fast for applying conventional microscopy approaches. This severe technical limitation has resulted in a surprisingly limited experimental data base for atomic-scale surface diffusion of adsorbates.

In this talk, I will describe the helium-spin-echo experiment, which is a matter-wave interferometry experiment capable of studying atomic-scale motion taking place on a pico-nano second time scale. I will briefly explain the method and the apparatus and show examples where the technique was used to study hopping diffusion of atoms and molecules, correlated motion of adsorbates, tunneling diffusion, nano-scale friction of adsorbates and the Schwoebel energy barrier of a single atomic step.