New Wonder Material Goldene

10 September 2024

Scientists in Sweden Have Created the World’s Thinnest Gold Leaf

The Development of ‘Goldene’ Marks an Important Milestone in the Field of Materials Science

Earlier this year a team of scientists at Sweden’s Linköping University made a significant breakthrough in the field of nanotechnology by successfully isolating goldene for the first time. Goldene is a single-layer allotrope of gold – meaning that it consists of a single layer of gold atoms. Even the thinnest commercial gold leaf is several hundred times thicker than this new groundbreaking substance.

Materials like graphene and hexagonal boron nitride have unique properties due to their thin, sheet-like structure.

2D Materials: Flat – But far from Boring

Single-layer materials, also known as 2D materials, are crystalline solids that are just one atom thick. Due to their large surface area-to-volume ratio, these ultra-thin materials have characteristics that differ significantly from those of chemically identical bulk solids. They have extraordinary optical, electronic and catalytic properties, making them a significant focus of research and potential applications. Single-layer materials that have been discovered or developed recently include borophene, germanene, silicene and of course graphene, which is known for its exceptional strength, electrical conductivity, and thermal properties. These materials can be produced using techniques like exfoliation (peeling layers from bulk materials) or bottom-up synthesis (building layers atom by atom).

Overcoming Material Challenges

Goldene is the first free-standing 2D metal. Its discovery could redefine the boundaries of what’s possible with elemental materials. However, creating stable monolayer sheets of pure metals such as gold is a complex and delicate process, due to the nature of metallic bonding. In metals, electrons are not bound to individual atoms but are instead shared across a lattice of atoms. This delocalized bonding causes metal atoms to naturally bond with each other, leading to the formation of clusters or nanoparticles rather than nanosheets. Single-atom layers are less stable and more prone to defects compared to their bulk counterparts. This inherent instability can cause the layers to curl up or collapse, making it hard to maintain a flat, single-atom structure. Several teams have previously produced gold sheets sandwiched between other materials, such as graphene-coated silicon carbide. But even when single-atom layers are embedded within other materials, extracting them without causing the atoms to agglomerate is extremely difficult. To overcome these obstacles the researchers in Sweden first created a three-dimensional structure of titanium, silicon and carbon. They then applied a surface layer of gold, allowing the gold particles to diffuse into the material.

This process replaced the silicon atoms with gold, resulting in a goldene sheet embedded within the matrix. The team employed a century-old technique used by Japanese iron smiths in order to exfoliate single gold layers from the initial composite structure. With a potassium-based solution called Murakami's reagent, they etched away the titanium carbide base material, leaving the goldene sheet intact. To refine their method, the team tested various reaction conditions and etching solution concentrations. In doing so, they discovered that cetrimonium bromide (CTAB) or cysteine help stabilize the isolated sheets and force the gold atoms to remain spread out in a single layer rather than forming clusters. Both act as a surfactant (a substance that reduces the surface tension between two liquids, a liquid and a gas, or a liquid and a solid).

A New Golden(e) Era

Monolayer gold is a groundbreaking material with unique properties that differ significantly from bulk gold:

Semiconducting Properties: In contrast to bulk gold, which is an excellent conductor, goldene behaves as a semiconductor. This creates many new possibilities for its use in powerful electronic devices.
Catalysis: Goldene holds promising potential in environmental applications. Its enhanced chemical reactivity with an abundance of unsaturated atoms exposed on the surface means that it is a highly effective catalyst and could play a key role in carbon dioxide conversion as well as hydrogen generation.
Light-Sensing Capabilities: Due to its ability to capture light efficiently, goldene could be used in advanced light-sensing and photovoltaic devices.

Goldene’s enhanced chemical reactivity could transform CO2 conversion and enable more efficient hydrogen production

2D Gold Synthesis Unlocks New Horizons in Science and Technology

With their successful synthesis of gold in a two-dimensional form researchers have paved the way for exciting new developments in various fields of science and technology. The scalable method could be used to prepare other elemental 2D materials (often referred to as ‘metallenes’). Stable single-atom layers also open up new opportunities to explore quantum effects and the fundamental properties of materials at the atomic level, potentially driving progress in physics and chemistry.