Synthesis of goldene comprising single-atom layer gold

The synthesis of monolayer gold has so far been limited to free-standing several-atoms-thick layers, or monolayers confined on or inside templates. Here we report the exfoliation of single-atom-thick gold achieved through wet-chemically etching away Ti3C2 from nanolaminated Ti3AuC2, initially formed by substituting Si in Ti3SiC2 with Au. Ti3SiC2 is a renown MAX phase, where M is a transition metal, A is a group A element, and X is C or N. Our developed synthetic route is by a facile, scalable and hydrofluoric acid-free method. The two-dimensional layers are termed goldene. Goldene layers with roughly 9% lattice contraction compared to bulk gold are observed by electron microscopy. While ab initio molecular dynamics simulations show that two-dimensional goldene is inherently stable, experiments show some curling and agglomeration, which can be mitigated by surfactants. X-ray photoelectron spectroscopy reveals an Au 4f binding energy increase of 0.88 eV. Prospects for preparing goldene from other non-van der Waals Au-intercalated phases, including developing etching schemes, are presented.

The discovery of graphene created great interest in two-dimensional (2D) materials1, but it is tricky to synthesize 2D materials comprised solely of metals. Gold nanoparticles are of interest due to their application in electronics, catalysis, photonics, sensing and biomedicine2. Recent advances have demonstrated that gold nanoparticle catalysts can turn plastic waste and biomass into value-added chemicals3, and photocatalytically drive overall water splitting and hydrogen peroxide production4. Anisotropic gold structures are a growing area of research with various low-symmetry allotrope structures that show unique properties compared to their bulk counterparts5. Plasmonic properties of gold nanoparticles vary depending on geometrical properties. Cluster Au5–13− anions6 form planar molecules due to strong relativistic effects7 that stabilize the outer 6s shell and destabilize the 5d shell. The planarity is attributed to the unique hybridization of the half-filled 6s orbital with the fully occupied \(5{{d}}_{{{z}}^{2}}\) orbital8,9. Atomically thin 2D Au sheets are therefore expected to offer unusual plasmonic and electronic properties and to be potentially beneficial to photonic and medical applications such as solar energy harvesting and plasmonic photothermal therapies for cancer treatment10,11. Furthermore, the high surface-area-to-volume ratio and abundance of unsaturated atoms exposed on the surface, originating from its atomically thin 2D nature, would also contribute to enhanced catalytic properties and enrich design variation for various applications12. Additionally, the overall use of Au resources would be minimized due to the increase in surface-area-to-volume ratio for atomic sheets.

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