New Process Enables Fabrication of Ultrathin Carbon Nanomembranes

Bielefeld University researchers have developed a new nano-fabrication process to make a variety of carbon nanomembranes (CNM), by employing self-assembled monolayers (SAMs). The CNMs consist of just one layer of molecules, with a thickness of ∼0.5 to ∼3 nanometers — much thinner than conventional membranes.

In the future, CNMs could be used to filter out very fine materials and for example enable separating gases from one another, which would filtering toxins from the air.

More than ten years ago, Professor Gölzhäuser and his team created the groundwork for the current development, producing a carbon nanomembrane from biphenyl molecules. In the new study, the process was altered so as to allow the use of other starting materials. The prerequisite is that these molecules are also equipped with several so-called phenyl rings.

For their new method, the researchers use the starting material in powder form. They dissolve the powder to pure alcohol and immerse very thin metal layer in this solution. After a short time the dissolved molecules settle themselves on the metal layer to form a monolayer of molecules. After being exposed to electron irradiation, the monolayer becomes a cross-linked nanomembrane. Subsequently the researchers ensure that the metal layer disintegrates, leaving only the nanomembrane remaining. ‘Up until now, we have produced small samples which are are a few centimetres square’, says Gölzhäuser. ‘However, with this process it is possible to make nanomembranes that are as big as square metres.’

This new method is so special because the researchers can produce made-to-measure nanomembranes. “Every starting material has a different property, from thickness or transparency to elasticity,” said Gölzhäuser. “By using our process, these characteristics are transferred onto the nanomembrane. In this way, carbon nanomembranes can be produced to address many different needs. That was not possible before now.” For example, the process can produce ultrathin films with or without nanopores.

The process also allows for making graphene from nanomembranes by heating them in a vacuum at a temperature of about 700 degrees Celsius.

Gölzhäuser’s team is working on the project with physicists from Ulm University, Frankfurt University, and the Max Planck Institute for Polymer Research.

The study has been funded by Germany's Federal Ministry of Education and Research (BMBF) and the German Research Foundation (DFG). -- Bielefeld University