The drawback of graphene is that has no gap. Therefore, it is not possible to use it as a usual transistor (it is never off). The idea of using nanoribons is to induce a gap in graphene by quantum confinement and therefore recover the transistor behaviour. However this is very difficult to achieve in a controlled way (the precise size and type of edge, zigzag or armchair has to be controlled). In general, fuctionalization modifies graphene chemical potential and can be used as a tool to control the device's response. Therefore, the purpose of functionalization depends on the application. If you want to do a chemical sensor, molecules with different oxidation state will act as a gate chemically controlled.

For conventional electronics applications, functionalization could be used to set the chemical potential to a predefined value near which the device works most efficiently.

Thank you very much Vincent. A few methods are now known to precisely design GNRs. What kind of response of the device is affected by functionalisation of GNRs? Is it the ON/OFF ratio or the carrier mobility?

In addition to chemical potential I would guess that functionalization reduces the mobility and as a consequence the ON/OFF ratio (it reduces the ON current). But it could be used to place the device close to threshold so that a small additional signal would switch the device.

Thank you vincent. Do you have any reference for this? If yes, plz suggest or send the file.

You also functionalize to help bind stuff to a substrate and also conversely to unbind or disperse.

There is an excellent paper about the tailoring the electronic band gap properties of graphene. I'm attaching the paper in pdf from Nature NPG.

oops, I forgot to attach the pdf

Thank you Souraya