Graphene, silicene, stanene, and others. In the future we'll probably see a combination of stuff used in a circuit. It all depends on whether they can process these in stacks, be stable, and have the properties they desire. Apparently to work around some of the issues with these materials they can use other materials along with it. In any case, this tech if it does eventuate won't be in the near future, and will probably be the next thing on from the next thing on from silicon. There is already the technology to charge a smartphone in 30 seconds... except you only get 20 seconds talk time! Having an example of the usage limitations currently would have been good! In other words, I was messing around with the 30 seconds talk time, but if they got 10 hours talk time it's better than 1 hour talk time.