XPS evidence for molecular charge-transfer doping of graphene

TL;DR

This study uses XPS to demonstrate charge-transfer doping in graphene with molecular acceptors and donors, quantifies the charge transfer, and explains related Raman and conductivity phenomena, clarifying differences from electrochemical doping.

Contribution

It provides direct XPS evidence for molecular charge-transfer doping in graphene and quantifies the extent of charge transfer, revealing the origins of Raman shifts and conductivity behavior.

Findings

Charge-transfer doping occurs in graphene with TCNE and TTF molecules.

Quantitative estimates of charge transfer were obtained.

Differences between charge-transfer and electrochemical doping are explained.

Abstract

By employing x-ray photoelectron spectroscopy (XPS), we have been able to establish the occurrence of charge-transfer doping in few-layer graphene covered with electron acceptor (TCNE) and donor (TTF) molecules. We have performed quantitative estimates of the extent of charge transfer in these complexes and elucidated the origin of unusual shifts of their Raman G bands and explained the differences in the dependence of conductivity on n- and p-doping. The study unravels the cause of the apparent difference between the charge-transfer doping and electrochemical doping.