Pieces of a graphene lattice made from patchy particles. Image: Swinkels et al.
Pieces of a graphene lattice made from patchy particles. Image: Swinkels et al.

Not only is graphene the strongest of all materials, but it is also exceptionally good at conducting heat and electrical currents, making it one of the most versatile materials known. For all these reasons, the discovery of graphene was awarded the Nobel Prize in Physics in 2010.

Yet, many properties of the material and its cousins are still poorly understood – for the simple reason that the atoms they are made up of are very difficult to observe. A team of researchers from the University of Amsterdam in the Netherlands and New York University have now found a surprising way to resolve this issue.

Two-dimensional (2D) materials like graphene, which consist of a single layer of atoms or molecules, have attracted a lot of attention recently. This is mainly due to their unusual properties, which are very different from their three-dimensional ‘bulk’ counterparts.

Perhaps surprisingly, crucial to the special properties of these materials are defects, locations where their crystal structure is not perfect. At these locations, the ordered arrangement of the layer of atoms or molecules is disturbed and the coordination changes locally.

Despite the fact that defects have been shown to be crucial for a material’s properties, and are almost always either present or added on purpose, not much is known about how these defects form and evolve over time. The reason for this is simple: atoms are just too small and move too fast to directly follow them.

In an effort to make the defects in graphene-like materials observable, the team of researchers found a way to build micrometer-size models of atomic graphene. To do this, they used so-called 'patchy particles’. These particles, which are large enough to be easily visible in a microscope but small enough to reproduce many of the properties of actual atoms, can interact with the same coordination as the atoms in graphene, and form the same structures.

Using such patchy particles, the researchers built a model system and used it to obtain insight into the defects in 2D materials, including their formation and evolution over time. Their researchers report their findings in a paper in Nature Communications.

Graphene is made up of carbon atoms that each have three neighbours arranged in a ‘honeycomb’ structure. It is this special structure that gives graphene its unique mechanical and electronic properties.

To achieve the same structure with their model, the researchers used tiny particles of polystyrene, decorated with three even tinier patches of a material known as 3-(trimethoxysilyl)propyl (TPM). The configuration of the TPM patches mimicked the coordination of carbon atoms in the graphene lattice. The researchers then made these patches attractive so that the particles could form bonds with each other, again in analogy with the carbon atoms in graphene.

After being left alone for a few hours, microscope observations revealed that the ‘mock carbon’ particles did indeed arrange themselves into a honeycomb lattice. The researchers then looked in more detail at defects in this model graphene lattice, finding that they showed characteristic defect motifs known from atomic graphene. Unlike with real graphene, however, the researchers were able to follow these defects from the very start of their formation, up to their integration into the lattice.

This new look at the growth of graphene-like materials immediately led to new knowledge about these 2D structures. Unexpectedly, the researchers found that the most common type of defect forms in the very initial stages of growth, before the lattice is properly established. They also observed how the lattice mismatch is then ‘repaired’ by another defect, leading to a stable defect configuration, which either remains or only very slowly heals to form a more perfect lattice.

The model system thus not only offers the ability to replicate the graphene lattice on a larger scale for all sorts of applications, but also allows direct observations that provide insights into atomic dynamics in this class of materials. As defects are central to the properties of all atomically thin materials, these direct observations could prove useful for engineering their atomic counterparts, such as for applications in ultra-lightweight materials and optical and electronic devices.

This story is adapted from material from the University of Amsterdam, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.