This 'wonder material' can be bent in unprecedented ways

Physicists at the University of Vienna, in collaboration with a team from the Vienna University of Technology, have found a way to make graphene – a material known for its extreme strength and superior electrical conductivity – much more stretchable. The method involves 'filling' the material with tiny imperfections, creating wavy patterns that resemble the folds of an accordion. The discovery could help develop flexible technologies such as wearable electronics and rollable products, among other applications.

 

Technically, graphene is just one atom thick and is very stiff. While this stiffness has many advantages, it also limits the material's ability to bend and stretch. Since graphene was discovered in 2004, scientists have repeatedly tried to adjust the stiffness of the material by removing atoms, but the results have been inconsistent – some studies have shown a slight decrease in stiffness, while others have shown the opposite.

 

To clarify this difference, the team at the University of Vienna conducted a series of experiments in a special environment, keeping the graphene completely pure, unaffected by air or dust. 'The unique system we developed at the University of Vienna allows us to study 2D materials without interference,' said Dr. Jani Kotakoski, who led the research team. In addition, this is the first time an experiment has been performed where the graphene has been completely isolated from the surrounding air and 'foreign' particles. Without this isolation, particles would quickly stick to the surface and distort the experimental procedure and measurement results.

The team created defects in graphene by using low-energy argon (Ar) ions (below 200 eV) to remove atoms in a controlled manner. These missing atoms are called 'vacancies.' They then used advanced microscopy and image analysis technology to study the atomic structure, and measured the material's response to pressure using nanoindentation on an atomic force microscope (AFM).

 

Before the addition of defects, graphene had a two-dimensional elastic modulus (E²D) of 286 N/m. After the addition of atomic gaps, this dropped to 158 N/m – a huge change that far exceeded the predictions of most previous theories, and helps explain why previous experiments had produced inconsistent results. Simulations suggest that this softening is mainly due to ripples forming around regions with two or more missing atoms. Single gaps have little effect.

'Think of it like an accordion. When you pull it out, these ripples flatten out, and that requires much less force than stretching a flat sheet of material – so it becomes more stretchable,' Joudi explains. Other recent simulations have also supported this hypothesis, showing both the ripple formation and the increased stretchability.

The team also found that if the graphene surface was not cleaned before adding the defects, the opposite effect occurred: the material became stiffer. This is because dirt or foreign particles on the surface prevented the ridges from forming. This shows the importance of the measurement environment when working with 2D materials. The results open up a way to tune the stiffness of graphene and pave the way for potential future applications.