Stacked graphene layers respond differently to heating

The upper layer of graphene in a bilayer assembly behaves differently upon heating to the lower layer as revealed by Raman spectroscopy. By growing samples in which the lower layer was uniquely made up of ¹²C graphene and the upper layer was ¹³C graphene, Martin Kalbac and colleagues from the Institute of Physical Chemistry in Prague could distinguish between the behaviours of the two layers as the temperature was raised from 298 to 1073 K. There experiments are described in Chemistry - A European Journal.

The bottom layer, which was in direct contact with the silica-silicon substrate, suffered strong mechanical stress-induced changes. However, there was no AB stacking between the two graphene layers, so the interaction between them was weak and the stress on the upper layer was minimal. This layer was more relaxed and behaved like a freely moving graphene layer, which was reflected in the Raman spectra.