Atomic Bromine Layer as a Hole-Doping Decoupling Adlayer for Molecular Spin Modulation

Controlling surface-confined molecular spin is a central challenge for molecule-based nanotechnologies where molecular devices are frequently fabricated by functional molecules in contact with solid surfaces. Herein, combined scanning tunneling microscopy/spectroscopy and density functional theory studies demonstrate the crucial role of an atomic bromine monolayer on Au(111) in modulating the spin configurations of the adsorbed 3d metal phthalocyanines (MPcs, M = Fe and Co). The Br layer exhibits a large band gap that can efficiently decouple the MPc molecules from their underlying Au substrate and enable experimental detections of the intramolecular spin excitations. Moreover, the Br layer can significantly increase surface work function that induces hole doping of the adsorbed MPcs and consequently modulates their magnetic moments. These results indicate that the atomic Br layer can well serve as a dual-functional ultrathin film for both decoupling and hole doping and hence offer a versatile platform for probing and harnessing magnetic molecules in the fields of molecular spintronics and devices.