Synthesis and properties of a new bilayer borophene

Research on borophene has predominantly focused on its monolayer forms due to the challenges associated with synthesizing multilayer boron sheets, despite the exotic properties predicted theoretically. In this study, we present the successful synthesis of a new bilayer borophene structure on an Ir(111) substrate, which demonstrates a distinct morphology compared to previously reported bilayer phases. Using scanning tunneling microscopy and spectroscopy, we observe a significantly reduced local work function (LWF) in this bilayer configuration compared to single-layer borophene on iridium. Specifically, the bilayer islands show clear shifts in the peak positions of field emission resonance spectroscopy, a finding that is further supported by density functional theory (DFT) calculations and simulations. The ultra-low LWF of this bilayer borophene provides new opportunities for the nanoengineering of novel borophene structures and suggests potential applications in electronic devices.