Molecular Doping of Graphene

TL;DR

This paper combines experimental and theoretical approaches to understand how different adsorbates, especially NO2, chemically dope graphene by affecting its electronic properties, with implications for sensors and electronics.

Contribution

It provides the first joint experimental-theoretical analysis of adsorbates on graphene, revealing the relation between magnetic moment and doping strength, and explaining sensor capabilities.

Findings

NO2 is a strong acceptor due to its paramagnetism

N2O4 causes weak doping as a diamagnetic molecule

Graphene's density of states enables detailed doping studies

Abstract

Graphene, a one-atom thick zero gap semiconductor [1, 2], has been attracting an increasing interest due to its remarkable physical properties ranging from an electron spectrum resembling relativistic dynamics [3-12] to ballistic transport under ambient conditions [1-4]. The latter makes graphene a promising material for future electronics and the recently demonstrated possibility of chemical doping without significant change in mobility has improved graphene's prospects further [13]. However, to find optimal dopants and, more generally, to progress towards graphene-based electronics requires understanding the physical mechanism behind the chemical doping, which has been lacking so far. Here, we present the first joint experimental and theoretical investigation of adsorbates on graphene. We elucidate a general relation between the doping strength and whether or not adsorbates have a magnetic moment: The paramagnetic single NO2 molecule is found to be a strong acceptor, whereas its diamagnetic dimer N2O4 causes only weak doping. This effect is related to the peculiar density of states of graphene, which provides an ideal situation for model studies of doping effects in semiconductors. Furthermore, we explain recent results on its "chemical sensor" properties, in particular, the possibility to detect a single NO2 molecule [13].