Dehydrogenation Induced Formation of Chiral Core-Shell Arrays of Melamine on Ag（111）

The structural evolution of supramolecular phases of melamine on Ag（111） surface as a function of annealing temperature is investigated by employing low-temper at ure scanning tunneling microscopy/spectroscopy（LTSTM/STS）.It is found that partial deprotonation of the melamine molecules leads to formation of distinct types of ordered supramolecular arrangements.Apart from two previously reported phases（α and β）,a new phase comprising arrays of close-packed hexagonal core-shell-type clusters is identified for the first time.Based on high-resolution STM images as well as structural modeling,we show that the new phase presents a two-level hierarchical order and chirality is expressed at both levels.Using STS characterization,we further reveal that the chiral arrangement of the clusters confines surface electrons into a honeycomb pathway with handedness,which could give rise to novel interfacial electronic properties such as Dirac fermions as well as flat band.