Electron energy loss spectroscopy ( EELS ) fingerprints of p‐ and n‐type doping in graphene

Abstract

Doping is a great way to make nanomaterials suitable for use in nanoscale devices and electronics. Dopant atoms supply mobile charge carriers in the form of electrons (n‐type) or holes (p‐type) whilst leaving the material neutral, and the physical interface between p‐ and n‐type materials ‐ the pn junction diode ‐ is a fundamental building block of electronic circuits. There is a general consensus that moving beyond the (mainly) Si‐, Ge‐ and GaAs‐based technology of the last seventy years is highly desirable, so there is currently lots of interest in finding superior replacements for next‐generation electronics. Graphene's discovery [1] lies at the root of this renewed interest, and it now seems likely that graphene, or nanomaterials inspired by graphene, will find their way into consumer and industrial electronics in some significant form quite soon. To make progress, we need information about the electronic structure of the material of interest, and how doping affects that electronic structure. Atomic‐resolution electron energy loss spectroscopy (EELS) is a great way to achieve this because it can reveal the bonding around an individual dopant atom. This insight can then be directly compared with theoretical electronic structure calculations in the form of density functional theory (DFT) to yield a detailed understanding of the electronic structure and the potential implications for use in nanoscale devices. In this talk I shall present atomic‐resolution K ‐edge EEL spectra for the case of substitutional B and N dopants in graphene synthesised using low‐energy ion implantation, and I shall explain how a careful comparison with theoretical DFT calculations indicates that the EELS data is in fact the first direct experimental evidence of p‐ and n‐type doping in graphene. [2] This approach demonstrates how potentially very lucrative information can be extracted from joint studies of experimental and theoretical EELS, and it could be readily extended to other nanomaterials.