Feb 28, 2007
Super-thin membrane breaks record
Physicists in the UK and Germany have created a new kind of structurally stable membrane that is just one atom thick. The membrane, which is made of graphene, could be used in a variety of applications, including gas sieves, ultrafast electronic switches and imaging individual molecules.
In 2004, Andre Geim and co-workers at Manchester University in the UK and the Institute for Microelectronics Technology in Chernogolovka, Russia, showed how to make graphene – two-dimensional sheets of carbon that are just one atom thick – from graphite, the form of carbon that is found in pencils. This material has since become one of the hottest topics in physics because of its interesting electronic properties. These include the fact that electrons in graphene behave like relativistic particles that have no rest mass and travel at about 106 m/s. Although this is a factor of 300 slower than the speed of light in vacuum, it is still much faster than the speed of electrons in an ordinary conductor.
Graphene can be used to make new types of ultrafast microelectronics devices and circuits, but researchers are unsure as to whether the material can exist in its free state, without being placed on top of other materials. Now, an international team, led by Geim and Jannik Meyer of the Max Planck Institute in Germany has succeeded in making free-hanging graphene for the first time.
To achieve this, the researchers began by placing a metallic scaffold on top of a sheet of pre-prepared graphene on a silicon chip. Next, they dissolved the chip in acids, to leave behind the graphene hanging in air or a vacuum from the scaffold. The resulting membranes are the thinnest material possible.
The UK-Germany team also say they now know why such atomically-thin materials, which were previously believed to be impossible, are stable. They found that the graphene is not perfectly flat, as expected, but "wavy", or crumpled out of plane. This helps stabilize otherwise intrinsically unstable ultrathin matter.
Meyer and co-workers say the membranes could be used as sieves to filter light gases, or to make miniature electromechanical switches. The structures could also find use as a non-obscuring support for electron microscopy to study individual molecules. "This is a completely new type of technology – even nanotechnology is not the right word to describe these membranes," says Geim.
"We have made proof-of-concept devices and believe the technology transfer to other areas should be straightforward," he adds. "However, the real challenge is to make such membranes cheap and readily available for large-scale applications."
The researchers reported their work in Nature.