Electronic structure and electron dynamics at molecule–metal interfaces: implications for molecule-based electronics

It is now generally recognized that the contact between a metal electrode and a single, a small group, or a thin film of molecules can play a critical, if not dominant, role in the performance of molecule-based electronics. The central issue is: how does an electron cross a metal–molecule interface? From a theoretical perspective, a quantitative answer to this question consists of three components: energetic alignment, electronic coupling, and dynamic localization due to polarization in nuclear coordinates. These three concepts are not unique to molecular electronics but have long been at the center of chemisorption studies. This account takes an experimentalistʹs view and discusses concepts of electron transfer/transport at metal–molecule interfaces and their intimate relationships to adsorption and non-adiabatic surface dynamics. Particular attention will be paid to photoemission measurements, including time-resolved two-photon photoemission, in probing energetic alignment, electronic coupling, and dynamic localization at molecule–metal interfaces.