Surface Reactions Following Ultra Fast Substrate Excitation: A Path Towards Atomic Scale Resolution of High-temperature Reactions at Metal Surfaces.

摘要

This project aims at elucidating the dynamics of small molecules at metal surfaces at the atomic scale in a high-temperature environment. Scanning tunneling microscopy (STM) is used to image the location and chemical identity of molecular species at a copper surface. Because STM has an image acquisition time on the seconds to minutes scale, the sample generally needs to be cooled down to keep molecular adsorbates in place during imaging. A slight increase in temperature then allows the study of diffusion, but the adsorbates generally diffuse so fast that they cannot be studied anymore before other surface processes get into play. This leaves only molecular diffusion to be studied and it does not allow a realistic vista on what may occur at surfaces at elevated temperatures. To circumvent this obstacle, we use energetic femtosecond laser pulses to heat the top atomic layers of the substrate, thereby creating temperature transients with hundreds of Kelvin amplitude but only picoseconds duration. We also use pores in adsorbate films to confine reactants.