Hydrogen adsorption and properties of goldene: a first-principles study.

Abstract

Goldene, a single-atom Au monolayer with a hexagonal lattice in the P6/mmm space group, exhibits interesting hyrdrogen absorption properties, as revealed using density functional theory calculations. This study focuses on H-adsorbed goldene at different coverage ratios, and provides insights into the energetic and electronic properties of this system, distinguishing it from the well-studied pristine goldene. Hydrogen adsorption on goldene, while energetically comparable to bulk gold, shows a slight reduction in energetic favorability and introduces specific scanning tunneling microscopy images, reported here for the first time. Raman spectra of H-adsorbed goldene at a 1/9 coverage ratio are also first reported here, along with a vibrational mode analysis, highlighting distinct atomic displacement patterns. Finally, for completeness, previously reported results on the dynamical and mechanical stability of pristine goldene are reported, with a special emphasis on the quadratic flexural mode characteristic of 2D materials. New insights into the thermodynamic properties of goldene compared to bulk gold are also discussed. Although bulk gold remains thermodynamically more stable at all temperatures, the vibrational contributions to the Helmholtz free energy favor goldene above 175 K, narrowing the stability gap with temperature. Overall, this study validates goldene's robustness and expands its potential for experimental and theoretical exploration in the context of hydrogen adsorption and functionalized 2D materials more broadly.