Melamine Self-assembly and Dehydrogenation on Ag(111) Studied by Tip-enhanced Raman Spectroscopy

Abstract

The adsorption and self-assembly structures of melamine molecules on an Ag(111) surface are studied by low temperature scanning tunneling microscopy (STM) combined with tip-enhanced Raman spectroscopy (TERS). Two ordered self-assembly phases of melamine molecules on Ag(111) were studied by STM and TERS, combining with first-principles simulations. The $α$-phase consists of flat-lying melamine molecules, while the $β$-phase consists of mixed up-standing/tilted melamine molecules. Moreover, dehydrogenation of melamine can be controlled by annealing the sample as well as by a tip-enhanced photo-catalytic effect. Our work demonstrates TERS as a powerful tool not only for investigating the configuration and vibration properties of molecules on a metal surface with high spatial resolution but also for manipulating the chemical reactions with tip and photo-induced effects.