2D Materials: An Introduction to Two-Dimensional Materials
Materials at the Nanoscale
The foundation of technology is the understanding of material systems. Specific material properties are required depending on the application. For example, the electrical conductivity of copper is exploited to build circuits, the compressive strength of concrete is needed to create skyscrapers, and the durability and pliability of vulcanised rubber is important for car tyres. The more we understand about the properties of a material, the further we can push technology.
When we think about the properties of a material, we often think that they are based solely on what the material is made of. Metal conducts electricity because its atoms are held together with metallic bonds – which leave electrons free to drift through the material when an electric field is applied. Concrete is strong because it contains cement that rigidly locks incompressible pieces of sand and gravel together. Vulcanised rubber is pliable, but still durable, because it is made of flexible polymer chains that are firmly linked together.
|Metals conduct electricity because some electrons free themselves from their orbits and can flow through the material.
However, there is something else that can affect how a material behaves: its size. This is especially true of some materials when their dimensions are reduced to the nanoscale (i.e. their size can reasonably be expressed in nanometers – generally smaller than a few hundred nanometers and down to less than a nanometer). Electrical conductivity, chemical reactivity, mechanical properties, and even how a material interacts with light can all change at the nanoscale.
As our ability to create and study nanomaterials has progressed, fascinating and unexpected new properties are being discovered. This has opened up completely new avenues for future technologies that rely on the size of a material as well as its bulk properties. We are truly entering the age of nanotechnology.
What are 2D materials?
Nanomaterials can be broadly classified by the total number of their nanoscopic dimensions:
- If all three dimensions of a material are nano-sized, it would be called a 0D (zero-dimensional) material, more commonly known as a nanoparticle.
- If two dimensions of a material are nano-sized, with the other dimension much larger (much like a piece of string shrunk down to a tiny size), then this is a 1D material or ‘nanotube/nanowire’.
- If only one dimension is nano-sized, it would be a 2D material – resembling a large, but very thin sheet (like a piece of paper).
- Finally, if a material does not have any dimensions that are small enough to be considered nano-sized, then it is not a nanomaterial. Instead, it should be referred to as a ‘bulk’ material, and it is this class that we deal with in our everyday lives.
The table below gives a simplified explanation.
|Number of Nanoscopic Dimensions
|Anything you can see by eye
|1D (nanotube or nanowire)
With 2D materials, it is often possible to reduce the thickness of the material down to a single atom. This is the case for the most well-known 2D material – graphene – and is where the most interesting properties occur.