For the first time researchers have shown that freestanding metal membranes consisting of a single layer of atoms can be stable under ambient conditions. This result of an international research team from Germany, Poland and Korea is published in Science on March 14, 2014.
The success and promise of atomically thin carbon, in which carbon atoms are arranged in a honeycomb lattice, also known as graphene has triggered enormous enthusiasm for other two dimensional materials, for example, hexagonal boron nitride and molybdenum sulphide. These materials share a common structural aspect, namely, they are layered materials that one can think of as individual atomic planes that can be pulled away from their bulk 3D structure. This is because the layers are held together through so called van der Waals interactions which are relatively weak forces as compared to other bonding configurations such as covalent bonds. Once isolated these atomically thin layers maintain mechanical integrity (i.e. they are stable) under ambient conditions.
In the case of bulk metals, their crystalline structure is three dimensional, and is thus not a layered structure and moreover metallic atom bonds are relatively strong. These structural aspects of metals would seem to imply the existence of metal atoms as a freestanding 2D material is unlikely. The formation of 2D atomically thin metallic layers over other surfaces has previously been demonstrated, however in this case the metal atoms interact with the underlying substrate. On the other hand, metallic bonding is non-directional and this fact along with the excellent plasticity of metals at the nanoscale suggest atomically thin 2D freestanding membranes composed of metal atoms might just be possible. Indeed, this is what an international group of researchers based in Germany, Poland and South Korea have now demonstrated is possible using iron atoms. Aside from the demonstration that metal atoms can form freestanding 2D membranes there is significant interest in the potential of such 2D metal materials as they are expected to have exotic properties.
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