Mechanical strength

Partners of the European Project 'Graphene Flagship' at the University of Strasbourg and CNRS (France), along with an international team of collaborators, created new 'switches' that respond to light. The team combined light-sensitive molecules with layers of graphene and other 2D materials to create new devices that could be used in sensors, optoelectronics and flexible devices.

The researchers designed a molecule that can reversibly undergo chemical transformations when illuminated with ultraviolet and visible light. This molecule (a photoswitchable spiropyran) can be then attached to the surface of materials like graphene or molybdenum disulfide, thus generating an atomically precise hybrid macroscopic superlattice. When illuminated, the whole supramolecular structure experiences a collective structural rearrangement, which could be directly visualized with a sub-nanometer resolution by scanning tunneling microscopy.

Researchers at the Institute for Basic Science (IBS) have measured the tensile strength of centimeter-scale monolayer graphene films, using camphor - a chemical that easily volatilizes at room temperature - as a temporary support layer. The mechanical properties of monolayer graphene pieces bigger than a few micrometers have never been tested, simply because moving such an ultrathin film to a standard testing apparatus has not been possible.

In this study, camphor is used as a transient support, and what differentiates it from conventional methods is that it is sublimed away in air at room temperature naturally, or at higher temperatures for faster processing. Thanks to this method, ultrathin films with an area larger than 1 cm x 1 cm are transferred without damage, then the camphor layer disappears in the air without leaving traces. In this way, tensile measurements were made on centimeter-scale 300 nm-thick graphene oxide film specimens, almost ten times thinner than previously reported. It was also possible to work with a graphene oxide film that was only 35 nm thick, and suspend it over a 1 cm x 1 cm hole.