Nanoscale fluorination opens the door to tunable bandgap graphene and new moiré structures

The ability to draw electronic nanopatterns on the two-dimensional graphene can lead to important applications. Li et al. showcased a method to do this using electron beam activated fluorination in graphene, a reversible process that can modify its transport properties.

The bandgap of fluorographene increases with higher fluorine content. For instance, a two-dimensional C₂F structure is insulating with a bandgap equivalent to that of a diamond, while C₄F has a smaller bandgap and is semiconducting.

Using a precursor gas containing fluorine and an electron beam to control the reaction, the researchers were able to tune the bandgap in an area of graphene. They tested the method by creating insulating and semiconducting strips onto graphene with a high resolution of 9 – 15 nm.

“Graphically, when we add fluorine atoms to graphene, the electron beam acts like a paint brush,” said author Hu Li. “We can directly write any electronic patterns on our pristine graphene.”

The bilayer C₂F/graphene structure also allows for the observation of unique rectangular moiré patterns, which are periodic potentials between neighboring layers of graphene. Typically, similar triangular moiré patterns are observed, but the authors note this may be the first experimental observation of rectangular patterns.

“What we believe is that new electronic properties will come out of these moiré patterns,” said author Klaus Leifer.

Another key benefit to this process is its reversibility – the pattern can be erased simply by applying the electron beam without the gas supply. These unique nanoscale properties make this technique promising in future electronic applications.

Source: “Direct writing of lateral fluorographene nanopatterns with tunable bandgaps and its application in new generation of moiré superlattice,” by Hu Li, Tianbo Duan, Soumyajyoti Haldar, Biplab Sanyal, Olle Eriksson, Hassan Jafri, Samar Hajjar-Garreau, Laurent Simon, and Klaus Leifer, Applied Physics Reviews (2020). The article can be accessed at https://doi.org/10.1063/1.5129948 .