Probing the weak interaction between silver and boron

Understanding the boron-coinage-metal interactions is critical for understanding the nucleation and growth mechanisms of borophene on coinage-metal substrates. Binary metal-boron clusters provide ideal models for obtaining atomic-level information about the metal-boron interactions. Here we report an investigation of the structure and bonding of the AgB₈ ^- cluster as a model system to gain insight into the interaction of boron with silver, the most inert substrate to grow borophene. Photoelectron spectroscopy reveals that the spectra of AgB₈ ^- resemble those of bare B₈ ^-, suggesting extremely weak chemical interactions between Ag and boron. Quantum calculations show that AgB₈ ^- (C _s, ¹A') consists of a B₈ borozene weakly interacting with a Ag atom on its edge. Chemical bonding analyses find that the Ag atom interacts with the B₈ motif primarily through its 5s orbital with little perturbation to the structure and bonding of the B₈ borozene. Compared to CuB₈ ^- and AuB₈ ^-, Ag is found to have the weakest interaction with B₈, consistent with the fact that silver substrates are the most inert for borophene syntheses.