2D Metals: The New Frontier of Atomically Thin Materials

By Nayan Jha, Physics Teacher

Introduction

Imagine taking an ordinary piece of metal and reducing its thickness until it is only a few atoms thick. Sounds impossible, right?

For a long time, scientists thought that producing a truly two-dimensional (2D) sheet of metal would be extremely difficult. Unlike materials such as graphene, metal atoms are strongly bonded to their neighbouring atoms in all directions.

However, researchers Guangyu Zhang, Luojun Du and colleagues at the Institute of Physics of the Chinese Academy of Sciences have demonstrated a method for producing atomically thin sheets of several metals.

This development could open a new area of research in condensed-matter physics and materials science.

Step 1: What is a 2D material?

A 2D material is a material whose thickness is extremely small—often just one or a few atomic layers.

A famous example is graphene, which consists of a single layer of carbon atoms arranged in a honeycomb structure.

Since graphene was discovered in 2004, scientists have produced and studied hundreds of other two-dimensional materials.

Many of these materials naturally consist of layers. The atoms within each layer are strongly connected by chemical bonds, while neighbouring layers are held together by relatively weak van der Waals (vdW) interactions.

Because these interactions are weak, scientists can sometimes separate—or “shave off”—individual layers.

Step 2: Why are 2D metals so difficult to make?

Metals are different.

In a conventional metal, each atom interacts strongly with many surrounding atoms. These bonds are not restricted to a simple stack of weakly connected layers.

Therefore, scientists could not simply peel a metal apart in the same way that graphene or some other layered materials can be exfoliated.

This raised an important question:

Can a metal actually exist as an atomically thin, two-dimensional sheet?

The work of Zhang, Du and their colleagues provides an important answer: yes, under suitable conditions.

Step 3: The researchers’ new technique

The researchers developed a technique involving what can be described as “van der Waals squeezing.”

The basic setup used:

• Pure metal powder
• Two monolayers of MoS₂ (molybdenum disulfide)
• Sapphire substrates
• High temperature
• High pressure

The MoS₂/sapphire structures acted as extremely thin van der Waals anvils around the metal.

Step 4: Melting the metal

First, the researchers placed the metal powder between the two MoS₂/sapphire structures.

The system was then heated.

As the temperature increased sufficiently, the metal powder melted and formed a tiny liquid metal droplet.

At this stage, the material was no longer a collection of individual powder particles but a molten metal region.

Step 5: Applying pressure

The researchers then applied a pressure of approximately 200 MPa.

For comparison, atmospheric pressure at Earth’s surface is about 0.1 MPa, so 200 MPa represents a very large pressure.

The MoS₂ layers helped confine and squeeze the molten metal.

This process is referred to as van der Waals squeezing.

Step 6: Cooling the material

The pressure was maintained while the opposite sides of the anvils cooled toward room temperature.

During this process, the molten metal was confined into an extremely thin region.

Eventually, the material solidified into an atomically thin metal sheet.

This is remarkable because the researchers were able to create metal layers only a few angstroms thick.

Step 7: Which metals were produced?

The research team successfully produced five atomically thin metals:

1. Bismuth (Bi)
2. Tin (Sn)
3. Lead (Pb)
4. Indium (In)
5. Gallium (Ga)

The thinnest sheets were approximately 6.3 Å (angstroms) thick.

Since

1 Å = 10⁻¹⁰ metre,

6.3 Å is only:

6.3 × 10⁻¹⁰ metre

That gives us an idea of just how extraordinarily thin these materials are.

Step 8: Why is this discovery important?

Creating a metal in two dimensions gives physicists a new system in which to investigate the behaviour of electrons and atoms.

When a material becomes extremely thin, its physical properties can change significantly.

Scientists can investigate questions such as:

• How do electrons behave when confined to nearly two dimensions?
• Do metals exhibit unusual electrical properties at atomic thickness?
• How do their optical and magnetic properties change?
• Can quantum effects become particularly important?
• Could these materials be useful in future electronic or nanoscale devices?

These questions make 2D metals an exciting area of fundamental physics research.

Step 9: From graphene to 2D metals

The discovery of graphene demonstrated that materials could behave very differently when reduced to a single atomic layer.

The development of atomically thin metals expands this concept further.

Instead of studying only semiconducting or insulating 2D materials, researchers can now investigate metallic systems at extreme thickness scales.

This could help scientists understand how the properties of matter change as we move from the three-dimensional world toward the two-dimensional limit.

A simple analogy

Think of a thick metal sheet like a large block of clay.

Trying to peel a metal into a single atomic layer is not like peeling the pages of a book, because the atoms inside the metal are strongly connected in many directions.

The researchers instead used another strategy:

Melt → Confine → Squeeze → Cool → Form an ultrathin metal sheet

This simple sequence captures the basic idea behind the technique.

The bigger picture

The researchers describe their work as just the “tip of the iceberg.”

The five metals produced in this study may be only the beginning. The technique could potentially provide scientists with opportunities to investigate other metals and unusual low-dimensional structures.

For physics, this is particularly interesting because reducing dimensionality can reveal phenomena that are difficult to observe in bulk materials.

Conclusion

The production of atomically thin sheets of bismuth, tin, lead, indium and gallium represents an important development in the study of two-dimensional materials.

The key idea is not simply making a metal thinner. It is about exploring how the fundamental properties of matter change when a material is confined to an almost two-dimensional form.

From graphene to 2D metals, scientists are continuing to discover that when matter is reduced to the nanoscale, familiar materials can display entirely new possibilities.

Physics teaches us that changing the dimensions of matter can change the physics itself.

— Nayan Jha
Physics Teacher