Goldene

Goldene is a single-layer allotrope of gold. The thinnest commercial gold leaf is some 400 times thicker than goldene. It features 9% lattice contraction compared to bulk gold.

History
Goldene was first synthesized as a free-standing material in 2024 by a team at Linköping University in Sweden. A 2022 claim by a team at New York University Abu Dhabi has been disputed as actually containing multiple layers.

Synthesis
The team used a material containing silicene between layers of titanium carbide. Gold layered on top of this combination diffused into the structure and replaced the silicon. Etching away the titanium carbide released free-standing goldene sheets that were up to 100 nanometres wide. The etching was performed using Murukami's reagent, in a 100-year-old technique used to decorate ironwork by Japanese blacksmiths. Surfactant molecules formed a barrier between goldene and the surrounding liquid — to stop the sheets from adhering.

The team is exploring the potential for preparing goldene from other non-van der Waals Au-intercalated phases, including developing etching schemes.

Graphene comparison
Forming 2D allotropes of metals such as gold has been difficult because metal atoms tend to cluster together and form nanoparticles instead of nanosheets.

Properties
The material displayed Au 4f binding energy increase of 0.88 eV. The material is a semiconductor, with the valence band maximum 50 meV below the Fermi level.

Applications
Potential applications included sensing and catalysis.